commit 7b5aa6fcc99f16ef5019daf2376ae5575120fd0e
Author: Bruno Charest <bruno.charest@gmail.com>
Date:   Fri Sep 18 18:01:07 2026 -0400

    Add initial llm-bridge project

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..d699ecb
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,98 @@
+name: CI
+
+# The gates this repository relies on: formatting, lints and the 190-odd tests
+# that need neither a browser nor a network. The browser end-to-end suite is a
+# separate, opt-in job: it drives a real Chromium against a local fixture, and a
+# runner without a browser should not make the whole pipeline red.
+
+on:
+  # A push to the default branch, and every pull request. Add the branch name
+  # here if this repository defaults to something else.
+  push:
+    branches: [main, master]
+  pull_request:
+  workflow_dispatch:
+  schedule:
+    # Every night at 04:17 UTC, so the browser suite still runs on its own.
+    - cron: "17 4 * * *"
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  CARGO_TERM_COLOR: always
+  RUST_BACKTRACE: 1
+
+jobs:
+  check:
+    name: fmt, clippy and tests (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install the Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+
+      - name: Cache the build
+        uses: Swatinem/rust-cache@v2
+
+      - name: Check formatting
+        run: cargo fmt --all --check
+
+      - name: Lint every target
+        run: cargo clippy --all-targets --locked -- -D warnings
+
+      # Unit tests, binary tests, HTTP integration tests against the mock
+      # backend, and doc tests. Everything here runs without Chrome.
+      - name: Run the test suite
+        run: cargo test --locked --all-targets
+
+      - name: Run the doc tests
+        run: cargo test --locked --doc
+
+      - name: Build the release binary
+        run: cargo build --locked --release
+
+  browser-e2e:
+    name: browser end-to-end (Chromium + fixture)
+    runs-on: ubuntu-latest
+    # On demand, or with the nightly run: these tests need a browser and are the
+    # ones most sensitive to the runner image.
+    if: github.event_name == 'workflow_dispatch' || github.event_name == 'schedule'
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install the Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache the build
+        uses: Swatinem/rust-cache@v2
+
+      # The runner image ships Chrome; the tests find it through CHROME, which
+      # is the same override a user can set on a machine with an unusual layout.
+      - name: Locate a Chromium-based browser
+        run: |
+          for path in /usr/bin/google-chrome /usr/bin/google-chrome-stable /usr/bin/chromium /usr/bin/chromium-browser; do
+            if [ -x "$path" ]; then
+              "$path" --version
+              echo "CHROME=$path" >> "$GITHUB_ENV"
+              exit 0
+            fi
+          done
+          echo "no Chromium-based browser found on this runner" >&2
+          exit 1
+
+      # The suite is #[ignore]d by default so that "cargo test" stays usable on
+      # a machine without a browser.
+      - name: Run the browser suite
+        run: cargo test --locked --test e2e_browser -- --ignored --test-threads=1 --nocapture
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..24dd03c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/target
+*.log
+.demo-state/
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..a39cce4
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diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..890960b
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,57 @@
+[package]
+name = "llm-bridge"
+version = "0.1.0"
+edition = "2021"
+description = "OpenAI-compatible local API gateway that drives a real authenticated browser to talk to LLM web UIs"
+license = "MIT"
+default-run = "llm-gateway"
+rust-version = "1.85"
+
+[[bin]]
+name = "llm-gateway"
+path = "src/main.rs"
+
+[lib]
+name = "llm_bridge"
+path = "src/lib.rs"
+
+[dependencies]
+tokio = { version = "1", features = ["full"] }
+axum = "0.8"
+tower = "0.5"
+tower-http = { version = "0.6", features = ["cors", "trace"] }
+hyper = "1"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+chromiumoxide = "0.9"
+futures = "0.3"
+async-trait = "0.1"
+tokio-stream = "0.1"
+async-stream = "0.3"
+clap = { version = "4", features = ["derive", "env", "wrap_help"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter", "json"] }
+tracing-appender = "0.2"
+anyhow = "1"
+thiserror = "2"
+toml = "0.8"
+uuid = { version = "1", features = ["v4", "v7", "serde"] }
+notify = "8"
+arc-swap = "1"
+dirs = "6"
+base64 = "0.22"
+regex = "1"
+sha2 = "0.10"
+mime_guess = "2"
+tempfile = "3"
+reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }
+tiktoken-rs = "0.6"
+
+[dev-dependencies]
+tower = { version = "0.5", features = ["util"] }
+http-body-util = "0.1"
+
+[profile.release]
+opt-level = 3
+lto = "thin"
+strip = true
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..9bbe936
--- /dev/null
+++ b/README.md
@@ -0,0 +1,498 @@
+# llm-bridge — llm-gateway
+
+A local, OpenAI-compatible HTTP API that answers by driving a **real, signed-in
+browser session** on an LLM web UI instead of a paid API key.
+
+```
+OpenAI SDK / curl / Continue / Cursor
+                |
+                |  POST /v1/chat/completions   (OpenAI format)
+                v
+        llm-gateway (Axum, Rust)
+                |
+                |  Chrome DevTools Protocol
+                v
+     Chrome/Chromium, dedicated profile, signed in once
+                |
+                v
+        chatgpt.com (or any configured chat web UI)
+```
+
+The client never knows a browser is involved: it sends OpenAI requests and
+receives OpenAI responses, including SSE streaming.
+
+## What it does
+
+- `POST /v1/chat/completions` and `POST /v1/completions` (legacy), with `stream: true`.
+- `GET /v1/models`, `GET /health`, `GET /v1/providers/{provider}/status`,
+  `POST /v1/providers/{provider}/validate`, `POST /v1/admin/reload`. Both
+  provider routes accept the `provider@account` spelling, so one account of a
+  provider can be checked on its own.
+- Multi-turn continuity: each OpenAI conversation is mapped to a web
+  conversation, so only the newest message is sent once the thread exists.
+- **Markdown fidelity**: once the answer has settled the gateway clicks the
+  provider's own copy button and reads the clipboard over CDP, so tables, code
+  fences and lists arrive intact instead of being flattened by `innerText`.
+- **Several providers**: ChatGPT, Claude and DeepSeek ship as configuration
+  files; adding another one is a TOML file, not a code change.
+- **Several accounts per provider**: each declared account gets its own browser
+  profile, session and tab pool, and is selected with `model = "chatgpt@perso"`.
+- **Several completions per request**: `n > 1` is honoured, and the variants run
+  in parallel when the account has more than one tab (`max_tabs`).
+- Optional local dashboard on `/dashboard` with live logs and manual tests.
+- Every selector lives in `~/.llm-gateway/providers/<provider>.toml`, reloaded
+  live: adapting to a UI change is a configuration edit, not a rebuild.
+
+## Requirements
+
+- Rust 1.85 or newer (tested with 1.98).
+- Chrome, Chromium, Edge or Brave. Firefox is **not** supported: it does not
+  speak CDP.
+
+## Install and first run
+
+```bash
+cargo build --release
+./target/release/llm-gateway config init      # creates ~/.llm-gateway
+./target/release/llm-gateway login chatgpt    # sign in once, in the window that opens
+./target/release/llm-gateway test chatgpt     # send one prompt and print the answer
+./target/release/llm-gateway serve            # starts the API on 127.0.0.1:8080
+```
+
+Three providers are installed on the first run: `chatgpt`, `claude` and
+`deepseek`. Each needs its own sign-in:
+
+```bash
+./target/release/llm-gateway login claude
+./target/release/llm-gateway selftest claude   # do the selectors still match?
+```
+
+The Claude and DeepSeek selectors were collected from public sources and have not
+been validated against a signed-in session here: run the selftest first, and see
+`providers/selectors.md` for which key to fix if the UI moved.
+
+Then, with any OpenAI client:
+
+```bash
+# bash / zsh
+curl -s http://127.0.0.1:8080/v1/chat/completions \
+  -H 'content-type: application/json' \
+  -d '{"model": "chatgpt", "messages": [{"role": "user", "content": "Bonjour"}]}'
+```
+
+```powershell
+# PowerShell: single quotes are literal, so do NOT escape the double quotes.
+# Writing '{\"model\":...}' sends the backslashes and the body is rejected with
+# "Failed to parse the request body as JSON".
+curl.exe -s http://127.0.0.1:8080/v1/chat/completions -H "content-type: application/json" `
+  -d '{"model":"chatgpt","messages":[{"role":"user","content":"Bonjour"}]}'
+
+# Or, without any quoting puzzle at all:
+$body = @{ model = "chatgpt"; messages = @(@{ role = "user"; content = "Bonjour" }) } |
+        ConvertTo-Json -Depth 5
+Invoke-RestMethod -Uri http://127.0.0.1:8080/v1/chat/completions -Method Post `
+  -Body $body -ContentType application/json
+
+# ./demo.ps1 walks through the whole API (health, models, streaming, status,
+# validation, reload) so you do not have to type any of this by hand.
+```
+
+```python
+from openai import OpenAI
+
+client = OpenAI(base_url="http://127.0.0.1:8080/v1", api_key="unused")
+print(client.chat.completions.create(
+    model="chatgpt",
+    messages=[{"role": "user", "content": "Bonjour"}],
+).choices[0].message.content)
+```
+
+Streaming works the same way with `stream=True`.
+
+## Command line
+
+```
+llm-gateway [GLOBAL OPTIONS] [COMMAND]
+
+serve [--backend browser|mock]   start the API server (default command)
+test <provider[@account]>|--all [--prompt TEXT] [--json]
+selftest <provider[@account]>|--all [--json]
+list [--json]
+login <provider[@account]> [--account ID]   open a window to sign in once
+logout <provider[@account]> [--account ID] [--all]   delete the stored profile(s)
+conversations list|clear [--provider NAME[@ACCOUNT]] [--account ID]
+reload                           ask a running server to reload its configuration
+config path|init|show
+```
+
+Global options: `--host`, `--port`, `--browser <chrome|chromium|edge|brave>`,
+`--browser-path`, `--profile-dir`, `--provider`, `--headless`, `--log-level`,
+`--log-format pretty|json`, `--config`, `--debug`, `--max-tabs`, `--api-key`,
+`--markdown auto|clipboard|dom|text`, `--yes`.
+
+Exit codes: `0` success, `1` runtime error, `2` selftest failure.
+
+## Model names
+
+`model` selects the provider:
+
+| Value | Meaning |
+|---|---|
+| `chatgpt` | the provider, its default model |
+| `chatgpt/gpt-4o` | the provider and a model name recorded in the response |
+| `gpt-4o` | accepted when exactly one provider is configured |
+
+The model is **echoed back** but the web UI keeps whatever model it has
+selected; a warning is added to `x_gateway_warnings` when you ask for another
+one. Driving the UI model picker is not implemented yet.
+
+When a provider declares several accounts, the account is part of the same
+string, between the provider and the model name:
+
+| Value | Meaning |
+|---|---|
+| `chatgpt` | the provider, its default account |
+| `chatgpt@perso` | the account whose id (or label) is `perso` |
+| `chatgpt@bruno.charest@gmail.com` | the account with that address |
+| `chatgpt@perso/gpt-4o` | that account, and a model name |
+
+`GET /v1/models` lists one entry per provider and per declared account, so a
+client that only reads that endpoint still discovers them.
+
+The same spelling works outside `model`, wherever a provider is named:
+
+| Command | Effect |
+|---|---|
+| `test chatgpt@perso` / `selftest chatgpt@perso` | checks that one account |
+| `test --all` / `selftest --all` | checks **every account** of every provider |
+| `GET /v1/providers/chatgpt@perso/status` | the state of that account |
+| `POST /v1/providers/chatgpt@pro/validate` | a full report for that account |
+
+A bare provider name means its default account, and the answer says which one was
+actually probed (`"provider": "chatgpt@perso"`), so two accounts of the same
+provider are never confused in a report or in the logs.
+
+## Multi-turn conversations
+
+A client that resends the whole history (every OpenAI SDK does) is mapped to one
+web conversation:
+
+1. The conversation id comes from the `X-Conversation-Id` request header when
+   present, otherwise from a fingerprint of the system prompt and the first user
+   message (`conversation.id_source = "fingerprint"` in the config).
+2. The first turn replays the whole history into the page.
+3. Later turns reopen the stored web conversation and send **only the newest
+   message**.
+4. The response always carries `X-Conversation-Id`, so a client can pin a
+   thread explicitly.
+5. If the web conversation is gone, the turn automatically falls back to
+   replaying the history in a new one.
+
+`~/.llm-gateway/conversations.json` is plain JSON you can read and edit:
+
+```json
+{
+  "version": 1,
+  "threads": {
+    "fp-3f1a...": {
+      "provider": "chatgpt",
+      "account": "perso",
+      "web_url": "https://chatgpt.com/c/68f0...",
+      "web_id": "68f0...",
+      "created_at": 1760000000,
+      "last_used_at": 1760000100,
+      "turns": 3,
+      "messages_sent": 7,
+      "state": "ready"
+    }
+  }
+}
+```
+
+`llm-gateway conversations list` and `clear` inspect and prune it. The listing
+shows the account that served each thread, and both commands accept
+`--provider chatgpt@perso` or `--account perso` to narrow the selection;
+`--account default` selects the threads of a provider that declares no account.
+A thread is marked `incomplete` when a client disconnects mid-generation; the
+next turn then replays the history instead of trusting a half-written thread.
+
+## OpenAI parameter support
+
+| Parameter | Behaviour |
+|---|---|
+| `model` | selects the provider (see above) |
+| `messages` | string content or an array of `text` / `image_url` parts |
+| `stream` | SSE chunks, `data: [DONE]` termination |
+| `stream_options.include_usage` | adds a final usage chunk |
+| `temperature`, `top_p`, `max_tokens`, `stop`, `response_format`, `seed`, `user`, penalties, `logprobs` | ignored, logged, and listed in `x_gateway_warnings` |
+| `tools`, `functions`, `tool_choice` | **not supported**: HTTP 400 `unsupported_parameter` |
+| `n > 1` | supported: `n` completions, each in its own web conversation. Clamped to `capture.max_variants` (4 by default) with a warning. Variants run in parallel when the account allows more than one tab |
+
+`usage` is estimated with `tiktoken` when its vocabulary can be loaded, and with
+a characters/4 heuristic otherwise (offline machines).
+
+`/v1/completions` accepts a string or an array prompt and answers with the
+legacy `text_completion` shape. Streaming is not available on that endpoint.
+
+## Signing in with Google (or any OAuth provider that blocks automation)
+
+Symptom: after `llm-gateway login chatgpt`, the Google window answers
+"**This browser or app may not be secure**".
+
+Why it happens: Google refuses to sign a browser it identifies as automated or
+outdated. Two things mattered here, and the first one was a bug in this project:
+
+1. The stealth helper used to advertise an **outdated Chrome user agent**
+   (`Chrome/107` in 2026). That alone reads as "old browser = insecure", which is
+   exactly what the message means. It is fixed: the default is now
+   `[browser] stealth = "off"` and the user agent is never spoofed.
+2. Google can also refuse a browser it knows is being driven over CDP. That part
+   cannot be argued with, so the gateway offers a sign-in path where no
+   automation is involved at all.
+
+### Recommended: sign in from a browser you start yourself
+
+```bash
+llm-gateway login chatgpt --manual      # prints the exact command, or add --launch
+```
+
+It tells you to run something like:
+
+```
+"C:\Program Files\Google\Chrome\Application\chrome.exe" \
+  --user-data-dir="C:\Users\you\.llm-gateway\profiles\chatgpt\user-data-dir" \
+  --no-first-run --no-default-browser-check https://chatgpt.com/
+```
+
+Sign in with Google in that window: it is an ordinary Chrome launched by you,
+with no automation switch and no debugging port. Then close it and press Enter.
+The gateway relaunches that same profile for later requests, so the session is
+already there.
+
+### Alternative: keep that window and let the gateway drive it
+
+Start the same command with `--remote-debugging-port=9222` (the `--manual` output
+prints it) and keep it open, then:
+
+```bash
+llm-gateway serve --attach --debug-port 9222
+```
+
+The gateway attaches to your browser, reuses a tab it can see (otherwise it opens
+one in that same browser, with your session), and **never closes your browser**
+when it shuts down. If Google still refuses the sign-in with the debugging port
+open, use the recommended path above.
+
+### Also worth knowing
+
+- Email + password sign-in on the provider site is not blocked by any of this;
+  only Google's OAuth screen applies these checks.
+- `--stealth minimal` adds a `navigator.webdriver` patch on top of the default;
+  `--stealth aggressive` restores the old user-agent spoofing and is documented
+  as harmful for sign-in.
+- When a request hits a signed-out page, the API answers with
+  `401 requires_login` and the message now mentions the `--manual` path.
+
+## Configuration
+
+`~/.llm-gateway/config.toml` (created on first run, see
+`config.toml.example` for the annotated version). Precedence:
+**CLI flags > `LLM_GATEWAY_*` environment variables > the file > defaults**.
+
+The settings that matter most:
+
+```toml
+[browser]
+executable = ""      # empty: auto-detect Chrome, Edge or Brave
+headless = false     # keep it false so you can sign in and solve captchas
+max_tabs = 1         # concurrent turns per provider *account*, i.e. tabs kept open
+busy_wait_s = 30     # how long a request waits for a free tab before a 429
+
+[conversation]
+strategy = "auto"    # auto | reuse | replay
+id_source = "fingerprint"  # fingerprint | header | uuid
+
+[capture]
+poll_interval_ms = 400   # DOM polling while waiting for the answer
+quiet_ms = 1500          # silence after which the answer is considered final
+response_timeout_s = 180 # hard budget for one answer
+markdown = "auto"        # auto | clipboard | dom | text (see below)
+max_variants = 4         # upper bound accepted for the "n" parameter
+```
+
+`max_tabs` is the setting that turns the gateway from a queue into a pool: with
+`max_tabs = 2` an account can answer two requests (or two variants of one `n = 2`
+request) at the same time, in two tabs of the same browser.
+
+`capture.markdown` decides where the answer text comes from:
+
+| Value | Behaviour |
+|---|---|
+| `auto` | the provider's copy button (Markdown through the clipboard) when it has one, the DOM conversion otherwise |
+| `clipboard` | always the copy button; falls back to the DOM when the clipboard cannot be read |
+| `dom` | always convert the answer HTML to Markdown |
+| `text` | the visible text only, formatting flattened (the historical behaviour) |
+
+A provider may override it in its own `[input]` section. Streamed deltas always
+stay plain text: only the settled answer is re-read with full fidelity.
+
+Provider files (`~/.llm-gateway/providers/*.toml`) hold the URLs, the CSS
+selectors, the timeouts and the capabilities of each web UI. They are watched:
+editing one reloads it within a second, without restarting the server or the
+browser. See `providers/selectors.md`.
+
+They are **copies** created on the first run, so upgrading the binary does not
+change them. Refresh them after an upgrade with
+`llm-gateway config init --force` (the previous file is kept next to it as
+`<provider>.toml.bak`).
+
+`llm-gateway --version` prints the compilation date
+(`0.1.0 (built 2026-09-18T17:26:11Z)`): if it does not match your sources, run
+`cargo build --release` again.
+
+## Error mapping
+
+Errors use the OpenAI error shape and stable codes:
+
+| Situation | HTTP | code |
+|---|---|---|
+| Unknown model | 404 | `model_not_found` |
+| Unknown account in the model string | 404 | `account_not_found` (the message lists the known ones) |
+| Bad request, ignored-but-unsupported parameter | 400 | `invalid_request`, `unsupported_parameter` |
+| Images sent to a provider without upload support | 400 | `unsupported_content_type` |
+| Missing or wrong API key | 401 | `invalid_api_key` |
+| Signed out | 401 | `requires_login` |
+| Captcha challenge | 403 | `captcha_required` |
+| Browser profile locked by another instance | 409 | `browser_profile_locked` |
+| Tab busy (30 s wait) or upstream throttling | 429 | `provider_busy`, `upstream_rate_limit` |
+| Selector gone, upstream error | 500 | `selector_missing`, `upstream_error` |
+| Browser missing, provider misconfigured | 503 | `browser_unavailable`, `provider_misconfigured` |
+| No answer in time | 504 | `upstream_timeout` |
+
+On a failure the server saves a screenshot and the full DOM in
+`~/.llm-gateway/debug/`, plus one line per failure in `debug/index.jsonl`
+(`--debug` does it for every request).
+
+## Dashboard
+
+`http://127.0.0.1:8080/dashboard` shows the providers, their live state, the
+recent logs (SSE) and lets you send a prompt by hand. If an API key is
+configured, paste it in the header field.
+
+## Development
+
+```bash
+cargo fmt --all --check
+cargo clippy --all-targets -- -D warnings
+cargo test                                    # no browser, no network
+./scripts/e2e.ps1                             # real Chrome, local fixture page
+
+./scripts/ci.ps1                              # all of the above, in one go
+./scripts/ci.ps1 -E2e                         # ... plus the browser suite
+```
+
+`.github/workflows/ci.yml` runs the same gates on Linux and Windows for every
+push and pull request, and builds the release binary. The browser suite needs a
+real Chromium, so it is a separate job that runs on demand (or nightly) instead
+of blocking a machine that has no browser.
+
+- `tests/api_integration.rs` drives the whole HTTP surface through a mock backend,
+  including multi-account routing and `n > 1`.
+- `tests/e2e_browser.rs` drives a real Chrome against
+  `tests/fixtures/chatgpt_mock.html`, a static fake of the ChatGPT DOM with
+  login, captcha, rate-limit, error, timeout, rewrite and attachment modes. That
+  fixture is what makes the capture loop regression-testable without a network
+  or an account.
+- `demo.ps1` / `demo.sh` run a full cycle; add `-Mock` (or `--mock`) to run
+  without a browser or a login.
+
+## Limits and honest caveats
+
+- **Streamed deltas are best effort.** The final answer written into a
+  non-streaming response is always the exact captured text. If the web UI
+  rewrites text it has already shown (React re-render, code block highlighting),
+  a streaming client may have received text that the final answer no longer
+  contains. A warning is logged when that happens.
+- **Markdown fidelity depends on the provider.** The clipboard path is exact,
+  because the provider copies what it rendered; the DOM conversion is a faithful
+  approximation that covers the constructs a chat UI actually produces. A page
+  that refuses the clipboard read (or a provider with no copy button) silently
+  falls back to it. Only the settled answer is re-read: streamed deltas stay
+  plain text.
+- **One turn at a time per provider account** by default: a second request waits
+  up to `browser.busy_wait_s` (30 s) and then gets a 429. Raise `max_tabs` to
+  let an account answer several requests at once, in several tabs.
+- **Only one tab per browser is rendered** by Chrome. On the other tabs the
+  prompt is submitted with in-page events rather than a synthetic mouse click,
+  which every chat UI tested here accepts, and the clipboard read still works
+  because the permission is granted over CDP.
+- **Selectors are the fragile part.** The fixture page covers regressions in our
+  capture loop; it cannot predict a change on the real site. Run
+  `llm-gateway selftest` after a UI update. The Claude and DeepSeek files are
+  starting points collected from public sources, not validated against a
+  signed-in session.
+- **No tool calling, no model switching.**
+- Latency is browser latency: a fresh conversation takes a few seconds to start
+  generating, plus the page load.
+
+## Security and terms of use
+
+- The API binds to `127.0.0.1` by default. If you expose it on a network,
+  configure `server.api_key` (or `--api-key`) and put it behind TLS.
+- Browser profiles contain live session cookies: they live in
+  `~/.llm-gateway/profiles/<provider>` and are never encrypted by this tool.
+  Use disk encryption and `llm-gateway logout --all` when you are done.
+- The tool only uses **your own** signed-in subscriptions. It does not bypass
+  paywalls, quotas or captchas: when a challenge appears it stops and tells you.
+- You remain responsible for complying with each provider's terms of service.
+  Automating a web UI may be restricted by them; check before you rely on it.
+
+## Layout of the state directory
+
+```
+~/.llm-gateway/
+  config.toml                  global configuration
+  providers/                   one TOML per provider (selectors, URLs, timeouts)
+  profiles/<provider>/user-data-dir/            persistent Chrome profile
+  profiles/<provider>/accounts/<account>/user-data-dir/   one per declared account
+  conversations.json           client conversation -> web conversation mapping
+  debug/                       screenshots, DOM dumps, index.jsonl
+  logs/llm-gateway.log         JSON logs
+```
+
+## Providers and accounts
+
+| Provider | File | Models | Notes |
+|---|---|---|---|
+| OpenAI ChatGPT | `providers/chatgpt.toml` | `gpt-4o`, `gpt-4o-mini`, `gpt-4.1` | `#prompt-textarea`, per-answer copy button |
+| Anthropic Claude | `providers/claude.toml` | `claude-sonnet-4`, `claude-opus-4`, `claude-haiku-4` | ProseMirror editor; selectors from public sources |
+| DeepSeek | `providers/deepseek.toml` | `deepseek-chat`, `deepseek-reasoner` | `textarea#chat-input`, `.ds-markdown` answers |
+
+An account is a browser profile: declaring two ChatGPT accounts gives two
+independent sessions, each with its own tab pool, driven side by side.
+
+```toml
+[[accounts]]
+id = "perso"
+email = "bruno.charest@gmail.com"
+default = true
+
+[[accounts]]
+id = "pro"
+email = "brunocharest.bc@gmail.com"
+```
+
+```bash
+llm-gateway login chatgpt --account perso
+llm-gateway login chatgpt@pro
+llm-gateway list                 # shows every account and its profile
+llm-gateway logout chatgpt@pro   # forget one account
+```
+
+The model string then carries the account:
+`{"model": "chatgpt@pro"}`, or `{"model": "chatgpt@brunocharest.bc@gmail.com"}`,
+or `{"model": "chatgpt@pro/gpt-4o"}`. Each account keeps its own thread store
+entries, so the same prompt sent to two accounts never shares one web
+conversation. Adding accounts to a provider that was already signed in changes
+its profile layout (`profiles/<provider>/accounts/<id>/…`), so sign that
+provider in again once.
diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000..30c5ae1
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,44 @@
+//! Build stamp: lets `llm-gateway --version` tell you when the binary was built.
+//!
+//! Without it, a stale release binary looks exactly like a fresh one, which has
+//! already caused a confusing "unknown argument" report.
+
+use std::time::{SystemTime, UNIX_EPOCH};
+
+fn main() {
+    let seconds = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|elapsed| elapsed.as_secs())
+        .unwrap_or(0);
+    println!(
+        "cargo:rustc-env=LLM_GATEWAY_BUILD_TIME={}",
+        format_utc(seconds)
+    );
+}
+
+/// `YYYY-MM-DDTHH:MM:SSZ`, without pulling a date crate into the build script.
+fn format_utc(seconds: u64) -> String {
+    let days = (seconds / 86_400) as i64;
+    let rem = seconds % 86_400;
+
+    // Howard Hinnant's civil-from-days algorithm.
+    let z = days + 719_468;
+    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
+    let doe = z - era * 146_097;
+    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
+    let mut year = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let day = doy - (153 * mp + 2) / 5 + 1;
+    let month = if mp < 10 { mp + 3 } else { mp - 9 };
+    if month <= 2 {
+        year += 1;
+    }
+
+    format!(
+        "{year:04}-{month:02}-{day:02}T{:02}:{:02}:{:02}Z",
+        rem / 3600,
+        (rem % 3600) / 60,
+        rem % 60
+    )
+}
diff --git a/config.toml.example b/config.toml.example
new file mode 100644
index 0000000..f1df0a6
--- /dev/null
+++ b/config.toml.example
@@ -0,0 +1,109 @@
+# llm-gateway global configuration.
+# Copied to ~/.llm-gateway/config.toml on first run; edits there win.
+# Precedence: CLI flags > LLM_GATEWAY_* environment variables > this file > defaults.
+
+[server]
+# Bind address. Keep it on the loopback interface unless you set an api_key.
+host = "127.0.0.1"
+port = 8080
+# Optional bearer token required from clients. Empty disables authentication.
+api_key = ""
+# Adds an "x_gateway_warnings" array to responses describing ignored parameters.
+include_warnings = true
+# Maximum accepted request body, in bytes.
+request_body_limit = 33554432
+
+[browser]
+# Path to the Chrome/Chromium/Edge/Brave executable. Empty = auto-detect
+# (honours the CHROME environment variable, then well-known install paths).
+executable = ""
+# Headless hides the window; keep it false so you can log in and solve captchas.
+headless = false
+# Root of the persistent browser profiles. Empty = <state dir>/profiles.
+profile_dir = ""
+# Concurrent turns allowed per provider account, i.e. how many tabs stay open.
+# 1 serialises the turns of an account; a larger value lets several requests
+# (or the variants of one "n": 4 request) run in parallel.
+max_tabs = 1
+# How long a request waits for a free tab before it is refused with 429.
+busy_wait_s = 30
+launch_timeout_s = 60
+request_timeout_s = 60
+# Extra Chromium command line switches.
+extra_args = [
+  "--disable-blink-features=AutomationControlled",
+  "--no-first-run",
+  "--no-default-browser-check",
+]
+
+# How much the browser hides that it is automated:
+#   off         leave the page alone (default). The switch above already hides
+#               navigator.webdriver and the user agent stays genuine, which is
+#               what sign-in pages expect.
+#   minimal     additionally patch navigator.webdriver from an injected script.
+#   aggressive  full stealth, including a spoofed user agent. Warning: it
+#               advertises an outdated Chrome version, which some sign-in
+#               providers reject as an insecure browser.
+stealth = "off"
+
+# Attach to a browser you started instead of launching one. Use it when a
+# sign-in provider refuses a browser the gateway launched: start Chrome
+# yourself with a debugging port (llm-gateway login <provider> --manual prints
+# the exact command), keep it open, and set attach = true.
+attach = false
+debug_port = 9222
+
+[conversation]
+# Thread store file. Empty = <state dir>/conversations.json.
+store = ""
+# auto   = reuse the web conversation when possible, otherwise replay the history
+# reuse  = always reuse (fails if the web conversation is gone)
+# replay = always send the full history into a new conversation
+strategy = "auto"
+# fingerprint = derive an id from the opening messages (works with header-less clients)
+# header      = only trust the X-Conversation-Id header (else a fresh uuid per request)
+# uuid        = never reuse a conversation unless the header is supplied
+id_source = "fingerprint"
+
+[capture]
+# DOM polling interval while waiting for the answer.
+poll_interval_ms = 400
+# The answer is considered finished after this much silence and no streaming indicator.
+quiet_ms = 1500
+# Hard budget for one generated answer.
+response_timeout_s = 180
+# auto | insert_text | exec_command | type_str
+inject_method = "auto"
+# Fidelity of the captured answer:
+#   auto       the provider's copy button (Markdown through the clipboard) when
+#              it has one, the DOM conversion otherwise. Default.
+#   clipboard  always the copy button; falls back to the DOM when the clipboard
+#              cannot be read.
+#   dom        always convert the answer HTML to Markdown.
+#   text       the visible text only, formatting flattened (historical behaviour).
+markdown = "auto"
+# How long the clipboard read is given before the DOM conversion wins.
+clipboard_timeout_ms = 1500
+# Upper bound accepted for the OpenAI "n" parameter. Values above it are clamped
+# and reported in x_gateway_warnings.
+max_variants = 4
+
+[tokens]
+# tiktoken encoding used for the estimated usage block.
+encoding = "o200k_base"
+# Fall back to a characters/4 heuristic when the encoding cannot be loaded.
+fallback_heuristic = true
+
+[debug]
+# never | on_error | always
+screenshots = "on_error"
+# Empty = <state dir>/debug.
+dir = ""
+
+[logging]
+# trace | debug | info | warn | error
+level = "info"
+# pretty | json
+format = "pretty"
+# Additional JSON log file. Empty = <state dir>/logs/llm-gateway.log
+file = ""
diff --git a/demo.ps1 b/demo.ps1
new file mode 100644
index 0000000..fe54b23
--- /dev/null
+++ b/demo.ps1
@@ -0,0 +1,140 @@
+<#
+.SYNOPSIS
+  End to end demonstration of llm-gateway.
+
+.DESCRIPTION
+  Starts the API server on a spare port, runs a full cycle against it
+  (health, models, non-streaming completion, streaming completion, provider
+  status, validation, configuration reload) and stops the server.
+
+  Without -Mock the server talks to a real browser: log in first with
+  "llm-gateway login chatgpt" and make sure the provider is configured.
+  With -Mock everything runs in memory, no browser and no login needed.
+
+.EXAMPLE
+  ./demo.ps1 -Mock
+  ./demo.ps1 -Port 8099
+#>
+param(
+    [switch]$Mock,
+    [int]$Port = 8099,
+    [string]$Provider = 'chatgpt'
+)
+
+$ErrorActionPreference = 'Stop'
+$root = Split-Path -Parent $MyInvocation.MyCommand.Path
+Push-Location $root
+
+$stateDir = Join-Path $root '.demo-state'
+New-Item -ItemType Directory -Force -Path $stateDir | Out-Null
+$env:LLM_GATEWAY_HOME = $stateDir
+
+$backend = if ($Mock) { 'mock' } else { 'browser' }
+$base = "http://127.0.0.1:$Port"
+
+Write-Host "== building ==" -ForegroundColor Cyan
+cargo build --quiet
+if ($LASTEXITCODE -ne 0) { throw 'cargo build failed' }
+$exe = Join-Path $root 'target/debug/llm-gateway.exe'
+
+Write-Host "== starting llm-gateway (backend: $backend, port: $Port) ==" -ForegroundColor Cyan
+$server = Start-Process -FilePath $exe -ArgumentList @('serve', '--port', "$Port", '--backend', $backend) -PassThru -NoNewWindow
+
+try {
+    $health = $null
+    foreach ($attempt in 1..60) {
+        try {
+            $health = Invoke-RestMethod -Uri "$base/health" -TimeoutSec 2
+            break
+        } catch {
+            Start-Sleep -Milliseconds 500
+        }
+    }
+    if (-not $health) { throw "the server did not become healthy on $base" }
+
+    Write-Host "
+== /health ==" -ForegroundColor Green
+    $health | ConvertTo-Json -Depth 6
+
+    Write-Host "
+== /v1/models ==" -ForegroundColor Green
+    (Invoke-RestMethod -Uri "$base/v1/models").data | ForEach-Object { "  " + $_.id }
+
+    $payload = @{
+        model    = $Provider
+        messages = @(@{ role = 'user'; content = 'Say ok and nothing else.' })
+    } | ConvertTo-Json -Depth 5
+
+    Write-Host "
+== POST /v1/chat/completions (non-streaming) ==" -ForegroundColor Green
+    $answer = Invoke-RestMethod -Uri "$base/v1/chat/completions" -Method Post -Body $payload -ContentType 'application/json'
+    "  id      : " + $answer.id
+    "  model   : " + $answer.model
+    "  answer  : " + $answer.choices[0].message.content
+    "  usage   : prompt " + $answer.usage.prompt_tokens + ", completion " + $answer.usage.completion_tokens
+
+    Write-Host "
+== POST /v1/chat/completions (two completions) ==" -ForegroundColor Green
+    $variantsPayload = @{
+        model    = $Provider
+        n        = 2
+        messages = @(@{ role = 'user'; content = 'Answer with one word.' })
+    } | ConvertTo-Json -Depth 5
+    $variants = Invoke-RestMethod -Uri "$base/v1/chat/completions" -Method Post -Body $variantsPayload -ContentType 'application/json'
+    "  choices : " + $variants.choices.Count
+    $variants.choices | ForEach-Object { "  [" + $_.index + "] " + $_.message.content }
+    if ($variants.x_gateway_warnings) { "  warning : " + $variants.x_gateway_warnings[0] }
+
+    $accounts = ($health.providers | Where-Object { $_.name -eq $Provider }).accounts
+    if ($accounts) {
+        Write-Host "
+== accounts of $Provider ==" -ForegroundColor Green
+        $accounts | ForEach-Object {
+            "  " + $_.id + "  " + $_.email + $(if ($_.default) { "  (default)" } else { "" })
+        }
+        $account = $accounts[0].id
+        $accountPayload = @{
+            model    = "$Provider@$account"
+            messages = @(@{ role = 'user'; content = 'Say ok and nothing else.' })
+        } | ConvertTo-Json -Depth 5
+        $accounted = Invoke-RestMethod -Uri "$base/v1/chat/completions" -Method Post -Body $accountPayload -ContentType 'application/json'
+        "  model $Provider@$account answered: " + $accounted.choices[0].message.content
+    }
+
+    Write-Host "
+== POST /v1/chat/completions (streaming) ==" -ForegroundColor Green
+    $streamPayload = @{
+        model    = $Provider
+        stream   = $true
+        messages = @(@{ role = 'user'; content = 'Count from one to five.' })
+    } | ConvertTo-Json -Depth 5
+    $streamed = Invoke-WebRequest -Uri "$base/v1/chat/completions" -Method Post -Body $streamPayload -ContentType 'application/json'
+    $streamed.Content -split "`n" | Select-Object -First 12 | ForEach-Object { "  " + $_ }
+    "  ... ($((($streamed.Content -split "`n") | Measure-Object).Count) lines of SSE)"
+
+    Write-Host "
+== GET /v1/providers/$Provider/status ==" -ForegroundColor Green
+    Invoke-RestMethod -Uri "$base/v1/providers/$Provider/status" | ConvertTo-Json -Depth 5
+
+    Write-Host "
+== POST /v1/providers/$Provider/validate ==" -ForegroundColor Green
+    Invoke-RestMethod -Uri "$base/v1/providers/$Provider/validate" -Method Post | ConvertTo-Json -Depth 5
+
+    Write-Host "
+== POST /v1/admin/reload ==" -ForegroundColor Green
+    Invoke-RestMethod -Uri "$base/v1/admin/reload" -Method Post | ConvertTo-Json -Depth 5
+
+    Write-Host "
+== dashboard ==" -ForegroundColor Green
+    "  $base/dashboard"
+    "  state directory: $stateDir"
+}
+finally {
+    Write-Host "
+== stopping the server ==" -ForegroundColor Cyan
+    if ($server -and -not $server.HasExited) {
+        Stop-Process -Id $server.Id -Force
+        $server.WaitForExit(5000) | Out-Null
+    }
+    Pop-Location
+}
diff --git a/demo.sh b/demo.sh
new file mode 100644
index 0000000..a869099
--- /dev/null
+++ b/demo.sh
@@ -0,0 +1,91 @@
+#!/usr/bin/env bash
+# End to end demonstration of llm-gateway (bash / curl equivalent of demo.ps1).
+#
+#   ./demo.sh --mock
+#   ./demo.sh --port 8099 --provider chatgpt
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$ROOT"
+
+PORT=8099
+PROVIDER=chatgpt
+MOCK=0
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --mock) MOCK=1; shift ;;
+    --port) PORT="$2"; shift 2 ;;
+    --provider) PROVIDER="$2"; shift 2 ;;
+    *) echo "unknown option: $1" >&2; exit 1 ;;
+  esac
+done
+
+BACKEND="browser"
+[[ "$MOCK" == "1" ]] && BACKEND="mock"
+BASE="http://127.0.0.1:$PORT"
+STATE="$ROOT/.demo-state"
+mkdir -p "$STATE"
+# shellcheck disable=SC2030
+export LLM_GATEWAY_HOME="$STATE"
+
+echo "== building =="
+cargo build --quiet
+EXE="$ROOT/target/debug/llm-gateway"
+
+echo "== starting llm-gateway (backend: $BACKEND, port: $PORT) =="
+"$EXE" serve --port "$PORT" --backend "$BACKEND" &
+SERVER_PID=$!
+trap 'echo; echo "== stopping the server =="; kill "$SERVER_PID" 2>/dev/null || true' EXIT
+
+for _ in $(seq 1 60); do
+  if curl -sf "$BASE/health" >/dev/null 2>&1; then break; fi
+  sleep 0.5
+done
+
+echo
+echo "== /health =="
+curl -s "$BASE/health" | python3 -m json.tool 2>/dev/null || curl -s "$BASE/health"
+
+echo
+echo "== /v1/models =="
+curl -s "$BASE/v1/models"
+
+echo
+echo "== POST /v1/chat/completions (non-streaming) =="
+curl -s "$BASE/v1/chat/completions" \
+  -H 'content-type: application/json' \
+  -d "{\"model\":\"$PROVIDER\",\"messages\":[{\"role\":\"user\",\"content\":\"Say ok and nothing else.\"}]}"
+
+echo
+echo "== POST /v1/chat/completions (two completions) =="
+curl -s "$BASE/v1/chat/completions" \
+  -H 'content-type: application/json' \
+  -d "{\"model\":\"$PROVIDER\",\"n\":2,\"messages\":[{\"role\":\"user\",\"content\":\"Answer with one word.\"}]}"
+
+echo
+echo "== accounts of $PROVIDER (when the provider file declares some) =="
+curl -s "$BASE/health" | grep -o '"accounts":\[[^]]*\]' || echo "  none declared"
+
+echo
+echo "== POST /v1/chat/completions (streaming, first lines) =="
+curl -sN "$BASE/v1/chat/completions" \
+  -H 'content-type: application/json' \
+  -d "{\"model\":\"$PROVIDER\",\"stream\":true,\"messages\":[{\"role\":\"user\",\"content\":\"Count from one to five.\"}]}" | head -n 12 || true
+
+echo
+echo "== GET /v1/providers/$PROVIDER/status =="
+curl -s "$BASE/v1/providers/$PROVIDER/status"
+
+echo
+echo "== POST /v1/providers/$PROVIDER/validate =="
+curl -s -X POST "$BASE/v1/providers/$PROVIDER/validate"
+
+echo
+echo "== POST /v1/admin/reload =="
+curl -s -X POST "$BASE/v1/admin/reload"
+
+echo
+echo "== dashboard =="
+echo "  $BASE/dashboard"
+echo "  state directory: $STATE"
diff --git a/providers/chatgpt.toml b/providers/chatgpt.toml
new file mode 100644
index 0000000..f3a55d3
--- /dev/null
+++ b/providers/chatgpt.toml
@@ -0,0 +1,86 @@
+# ChatGPT provider configuration, driven entirely by this file.
+# Selectors change when the web UI is updated: edit them here (reloaded live),
+# never in the Rust source. Validate with: llm-gateway selftest chatgpt
+
+[provider]
+name = "chatgpt"
+display_name = "OpenAI ChatGPT"
+web_url = "https://chatgpt.com/"
+new_conversation_url = "https://chatgpt.com/"
+# Captures the web conversation id from the current URL (one capture group).
+conversation_url_pattern = "^https://chatgpt\\.com/c/([0-9a-zA-Z-]{8,})"
+default_models = ["gpt-4o", "gpt-4o-mini", "gpt-4.1"]
+enabled = true
+
+[selectors]
+input_field = "div#prompt-textarea, div.ProseMirror[contenteditable='true']"
+# The id and the data-testid are language independent; the aria-label fallbacks
+# only match an English UI (see providers/selectors.md, "Localised user
+# interfaces").
+send_button = "button[data-testid='send-button'], button#composer-submit-button, button[aria-label='Send prompt'], button[aria-label='Envoyer la requête']"
+response_container = "div[data-message-author-role='assistant']"
+streaming_indicator = "button[data-testid='stop-button']"
+file_input = "input[type='file']"
+new_chat_button = "a[data-testid='create-new-chat-button']"
+# Clicked once the answer has settled, to read the provider's own Markdown
+# through the clipboard. Looked up inside the answer node, so it must be
+# relative to it. Leave empty to always convert the DOM instead.
+copy_button = "button[data-testid='copy-turn-action-button'], button[aria-label='Copy'], button[aria-label='Copier']"
+login_page_indicator = "button[data-testid='login'], form[action*='login'], a[href*='auth/login'], a[href*='auth/0']"
+captcha_indicator = "iframe[src*='captcha'], iframe[src*='challenges.cloudflare.com'], div#challenge-form"
+error_banner = "[data-testid='error-message'], div[role='alert']"
+
+[login]
+url_patterns = ["/auth/login", "/login", "accounts.google.com", "/auth/0"]
+# The page a signed-out visitor lands on (title "ChatGPT: Chat, Work, Create &
+# Code with AI") has no prompt field and shows these call to action buttons.
+# The text patterns are only used when that field is missing, so a signed-in
+# conversation is never mistaken for a sign-in screen.
+text_patterns = ["log in", "sign up", "create an account"]
+
+[rate_limit]
+text_patterns = [
+  "too many requests",
+  "rate limit",
+  "trop de requêtes",
+  "réessayez plus tard",
+  "you've reached",
+]
+
+[timeouts]
+page_load = 30
+response_generation = 120
+response_timeout = 180
+
+[input]
+poll_interval_ms = 400
+quiet_ms = 1500
+inject_method = "auto"
+
+[options]
+supports_images = true
+supports_streaming = true
+supports_new_chat = true
+
+# Multi-account. A ChatGPT account is a browser profile, so declaring two
+# accounts gives two independent sessions, each with its own tab pool, driven
+# side by side. Address them with the model string:
+#
+#   {"model": "chatgpt"}                              -> the default account
+#   {"model": "chatgpt@perso"}                        -> by account id
+#   {"model": "chatgpt@brunocharest.bc@gmail.com"}     -> by address
+#   {"model": "chatgpt@perso/gpt-4o"}                 -> account and model
+#
+# Sign each one in once:  llm-gateway login chatgpt --account perso
+# Their profiles live in profiles/chatgpt/accounts/<account>/user-data-dir.
+#
+# [[accounts]]
+# id = "perso"
+# email = "bruno.charest@gmail.com"
+# label = "Personal"
+# default = true
+#
+# [[accounts]]
+# id = "pro"
+# email = "brunocharest.bc@gmail.com"
+# label = "Work"
diff --git a/providers/claude.toml b/providers/claude.toml
new file mode 100644
index 0000000..2e9cea1
--- /dev/null
+++ b/providers/claude.toml
@@ -0,0 +1,79 @@
+# Claude (claude.ai) provider configuration, driven entirely by this file.
+# Selectors change when the web UI is updated: edit them here (reloaded live),
+# never in the Rust source. Validate with: llm-gateway selftest claude
+#
+# The values below come from the public claude.ai DOM observed in 2026 and from
+# published selector lists (May 2026). They are a starting point, not a
+# guarantee: run 'llm-gateway selftest claude' before relying on them.
+
+[provider]
+name = "claude"
+display_name = "Anthropic Claude"
+web_url = "https://claude.ai/new"
+new_conversation_url = "https://claude.ai/new"
+# Captures the web conversation id from the current URL (one capture group).
+conversation_url_pattern = '^https://claude\.ai/chat/([0-9a-zA-Z-]{8,})'
+default_models = ["claude-sonnet-4", "claude-opus-4", "claude-haiku-4"]
+enabled = true
+
+[selectors]
+# Claude uses ProseMirror, so the editor is a contenteditable div rather than a
+# textarea. The fallbacks cover the composer variants seen behind A/B tests.
+input_field = "div.ProseMirror[contenteditable='true'], div[contenteditable='true'][data-placeholder], [data-testid='composer-input']"
+send_button = "button[aria-label='Send Message'], button[aria-label='Send message'], button[data-testid='send-button'], button[type='submit']"
+# One node per assistant answer, in document order.
+response_container = "div.font-claude-response, div[data-is-streaming], div.font-claude-message"
+streaming_indicator = "button[aria-label='Stop response'], button[aria-label='Stop Response']"
+file_input = "input[type='file']"
+new_chat_button = "a[href='/new'], button[aria-label='New chat']"
+login_page_indicator = "a[href*='/login'], button[data-testid='login-button'], form[action*='login']"
+captcha_indicator = "iframe[src*='challenges.cloudflare.com'], iframe[title*='challenge'], div#challenge-form"
+error_banner = "[role='alert'], div[data-testid='error']"
+# Relative to the answer node: the hover toolbar button that copies the answer
+# as Markdown.
+copy_button = "button[aria-label='Copy'], button[data-testid='copy-button']"
+
+[login]
+url_patterns = ["/login", "/magic-link", "accounts.google.com"]
+# Only consulted when the prompt field is missing, so a chat page that happens
+# to mention "log in" is never misclassified.
+text_patterns = ["sign in", "log in", "continue with google"]
+
+[rate_limit]
+text_patterns = [
+  "message limit",
+  "rate limit",
+  "too many requests",
+  "you've reached",
+  "limite de messages",
+  "trop de requêtes",
+  "réessayez plus tard",
+]
+
+[timeouts]
+page_load = 30
+response_generation = 120
+response_timeout = 180
+
+[input]
+poll_interval_ms = 400
+quiet_ms = 1500
+inject_method = "auto"
+
+[options]
+supports_images = true
+supports_streaming = true
+supports_new_chat = true
+
+# Multi-account: each account is a separate browser profile, so several
+# subscriptions can be driven side by side. Declare them like this and address
+# them with model = "claude@work".
+#
+# [[accounts]]
+# id = "perso"
+# email = "bruno.charest@gmail.com"
+# default = true
+#
+# [[accounts]]
+# id = "work"
+# email = "brunocharest.bc@gmail.com"
diff --git a/providers/deepseek.toml b/providers/deepseek.toml
new file mode 100644
index 0000000..6dc7542
--- /dev/null
+++ b/providers/deepseek.toml
@@ -0,0 +1,73 @@
+# DeepSeek (chat.deepseek.com) provider configuration, driven entirely by this
+# file. Selectors change when the web UI is updated: edit them here (reloaded
+# live), never in the Rust source. Validate with: llm-gateway selftest deepseek
+#
+# The values below combine the public chat.deepseek.com DOM with published
+# selector lists (May 2026). They are a starting point, not a guarantee: run
+# 'llm-gateway selftest deepseek' before relying on them.
+
+[provider]
+name = "deepseek"
+display_name = "DeepSeek"
+web_url = "https://chat.deepseek.com/"
+new_conversation_url = "https://chat.deepseek.com/"
+# Captures the web conversation id from the current URL (one capture group).
+conversation_url_pattern = '^https://chat\.deepseek\.com/a/chat/s/([0-9a-zA-Z-]{8,})'
+default_models = ["deepseek-chat", "deepseek-reasoner"]
+enabled = true
+
+[selectors]
+# The composer is a plain <textarea>. DeepSeek localises its placeholder and the
+# id seen in older builds is gone, so the wording observed on the live page comes
+# first and the older guesses are kept as fallbacks.
+input_field = "textarea#chat-input, textarea[placeholder*='Message DeepSeek'], textarea[placeholder*='Envoyer'], textarea[placeholder*='Send a message'], textarea[placeholder*='message']"
+send_button = "div[role='button'][aria-label='Send'], button[aria-label='Send message'], button[data-testid='send-button']"
+# The answer body is rendered by the "ds-markdown" component; the attribute
+# first variant mirrors the ChatGPT markup.
+response_container = "div[data-message-author-role='assistant'], div.ds-markdown, div[class*='markdown-body']"
+streaming_indicator = "div[role='button'][aria-label*='Stop'], button[aria-label*='Stop'], div[class*='_stop']"
+file_input = "input[type='file']"
+new_chat_button = "a[href='/'], div[class*='new-chat'], button[aria-label='New chat']"
+login_page_indicator = "div[class*='ds-modal'], a[href*='sign_in'], button[data-testid='login-button']"
+captcha_indicator = "iframe[src*='captcha'], div[class*='captcha'], div#challenge-form"
+error_banner = "[role='alert'], div[class*='ds-toast'], div[class*='error']"
+# Relative to the answer node: the toolbar button that copies the answer.
+copy_button = "[aria-label='Copy'], [data-testid='copy-button'], div[class*='ds-icon-button'][role='button']"
+
+[login]
+url_patterns = ["/sign_in", "/login", "account.deepseek.com"]
+text_patterns = ["log in", "sign in", "log in with google", "se connecter"]
+
+[rate_limit]
+text_patterns = [
+  "too many requests",
+  "rate limit",
+  "please try again later",
+  "请求过于频繁",
+  "服务器繁忙",
+  "trop de requêtes",
+]
+
+[timeouts]
+page_load = 30
+response_generation = 120
+# DeepSeek R1 reasons for a long time before answering: keep a generous budget.
+response_timeout = 300
+
+[input]
+poll_interval_ms = 400
+quiet_ms = 1500
+inject_method = "auto"
+
+[options]
+supports_images = true
+supports_streaming = true
+supports_new_chat = true
+
+# Multi-account: each account is a separate browser profile. Address them with
+# model = "deepseek@perso".
+#
+# [[accounts]]
+# id = "perso"
+# email = "bruno.charest@gmail.com"
+# default = true
diff --git a/providers/selectors.md b/providers/selectors.md
new file mode 100644
index 0000000..6e5499a
--- /dev/null
+++ b/providers/selectors.md
@@ -0,0 +1,169 @@
+# Provider selectors
+
+Every selector lives in a provider configuration file
+(`~/.llm-gateway/providers/<provider>.toml`), never in the Rust source. When a
+web UI changes, edit the TOML: the server picks the change up within a second
+(no restart, no browser relaunch). `llm-gateway selftest <provider>` tells you
+whether the current selectors still work.
+
+## Why this file exists
+
+Web UIs change without notice. The three failure modes we care about are:
+
+| Symptom | Reported as | What to do |
+|---|---|---|
+| The prompt field disappeared | HTTP 500, code `selector_missing` | Update `selectors.input_field` |
+| The send button disappeared | HTTP 500, code `selector_missing` | Update `selectors.send_button` |
+| The answer container moved | empty answer or HTTP 500 | Update `selectors.response_container` |
+| The streaming indicator is wrong | answers truncated or 504 | Update `selectors.streaming_indicator` |
+| The session expired | HTTP 401, code `requires_login` | Run `llm-gateway login <provider>` |
+
+A failing capture always leaves a screenshot and a DOM dump in
+`~/.llm-gateway/debug/`, plus one line per failure in `debug/index.jsonl`.
+
+## How to update a selector
+
+1. Open the provider page in a normal browser, signed in.
+2. Open the developer tools, inspect the element you need.
+3. Prefer stable hooks in this order: `data-testid` > `id` > semantic attributes
+   (`aria-label`, `role`, `type`) > a CSS class. Avoid generated class names such
+   as `.css-1x2y3z`: they change on every deploy.
+4. Put a comma separated list in the TOML when a UI has several variants
+   (`div#prompt-textarea, div.ProseMirror[contenteditable='true']`): the first
+   match wins and the fallbacks keep you running through a partial rollout.
+5. Run `llm-gateway selftest <provider>` and keep the TOML only when it reports
+   `ok`.
+
+## Required and optional selectors
+
+| Key | Required | Used for |
+|---|---|---|
+| `input_field` | yes | focusing the editor, verifying the injected text, detecting an empty editor after submit |
+| `send_button` | yes | submitting the prompt (Enter is the fallback) |
+| `response_container` | yes | one node per assistant answer, in document order; the driver reads the n-th node. It must select the **answer text**, not the whole exchange: a container that also holds the action toolbar would capture the word "Copy" as part of the answer |
+| `copy_button` | no | the per-answer "copy" control, which gives the answer as Markdown through the clipboard. It may be inside the answer node or a sibling of it: the driver looks for it there and never elsewhere on the page, so the copy button of a previous answer is never clicked |
+| `streaming_indicator` | recommended | element that only exists while the answer is generated (a stop button) |
+| `file_input` | for images | hidden input fed through `DOM.setFileInputFiles` |
+| `attachment_indicator` | optional | chip shown once an upload has been ingested |
+| `new_chat_button` | optional | starting a brand new conversation without reloading |
+| `login_page_indicator` | recommended | detecting a sign-in page even when the URL does not say so. On chatgpt.com the signed-out landing page exposes `button[data-testid='login']` |
+| `[login] text_patterns` | recommended | lowercase substrings of the visible text that reveal a signed-out page; only consulted when the prompt field is missing, so a chat page that mentions "log in" is never misclassified |
+| `captcha_indicator` | recommended | detecting a bot challenge |
+| `error_banner` | recommended | surfacing the upstream error message to the API client |
+| `model_selector` | reserved | not driven yet: the gateway never changes the model in the UI |
+
+## Answer fidelity (Markdown)
+
+A web UI renders its answer as rich HTML and `innerText` flattens it: a table
+collapses into loose lines and a code block loses its fences. Once the answer has
+settled the driver therefore reads it a second time, in this order:
+
+1. **the clipboard** — it clicks the provider's own copy button and reads the
+   clipboard over CDP (`Browser.setPermission` then
+   `navigator.clipboard.readText()`). The provider copies exactly the Markdown it
+   rendered, so nothing is guessed. Requires `selectors.copy_button`.
+2. **the DOM** — it converts the answer node's `innerHTML` to Markdown
+   (headings, lists, quotes, links, images, fenced code, GitHub tables).
+3. **the visible text** — the historical behaviour, used when both fail.
+
+`[capture] markdown` chooses between them and a provider may override it in its
+own `[input]` section. Streamed deltas always come from the DOM, so they stay
+plain text; the final answer — the one a non-streaming client receives — is the
+converted one, and the source used is logged as `fidelity`.
+
+## Current status
+
+| Provider | File | Last validated | Status |
+|---|---|---|---|
+| OpenAI ChatGPT | `providers/chatgpt.toml` | 2026-09-18, signed-in session | `selftest` ok; `fidelity = "clipboard"` |
+| Anthropic Claude | `providers/claude.toml` | 2026-09-18, signed-in session | `selftest` ok; `fidelity = "clipboard"` |
+| DeepSeek | `providers/deepseek.toml` | 2026-09-18, signed-in session | `selftest` ok; **`fidelity = "dom"`**: the copy button has not been observed yet |
+| Local fixture (tests only) | generated by `tests/e2e_browser.rs` | 2026-09-18 | validated: full pipeline, streaming, login, captcha, rate limit, error banner, timeout, missing selector, rewrite, attachment, Markdown fidelity |
+
+The Claude and DeepSeek selectors were collected from public sources rather than
+observed on a signed-in session. Treat them as a starting point: the first run of
+`llm-gateway selftest <provider>` tells you whether they still match, and the
+failure modes above tell you which key to fix.
+
+The ChatGPT selectors shipped in this repository are the ones observed on the
+public web UI in September 2026. They are a starting point, not a guarantee:
+run the selftest before relying on them.
+
+## Upgrading the installed files
+
+The provider files under `~/.llm-gateway/providers/` are **copies** made on the
+first run: editing the ones in this repository does not change them. After
+upgrading the binary, refresh them with:
+
+```bash
+llm-gateway config init --force     # keeps the previous file as <provider>.toml.bak
+```
+
+## Localised user interfaces
+
+A provider translates its own UI, and the browser locale of the machine does not
+change that: the same ChatGPT account serves a French page under `lang="fr-CA"`
+and an English one under `lang="en-US"`. Every `aria-label` fallback therefore
+only matches one language, which is why the stable hooks come first:
+
+| Observed (French UI, September 2026) | Selector to prefer |
+|---|---|
+| `<button type="submit" id="composer-submit-button" aria-label="Envoyer la requête" data-testid="send-button">` | `button[data-testid='send-button']`, `button#composer-submit-button` |
+| the answer toolbar copy control | `button[data-testid='copy-turn-action-button']` |
+| `<textarea placeholder="Message DeepSeek" name="search" rows="2">` | `textarea[placeholder*='Message DeepSeek']` - the English placeholder and the `#chat-input` id of older builds are gone |
+
+The `[login] text_patterns` follow the same rule: they are lowercase substrings of
+the page text, so a French sign-in page needs French patterns
+(`"se connecter"`, `"s'inscrire"`) next to the English ones. A page that is not
+recognised as a sign-in page is reported as a missing prompt field instead, which
+is a confusing way to learn that the session expired.
+
+## Several accounts of one provider
+
+A signed-in account is a browser profile, so driving two ChatGPT accounts means
+two profiles, two sessions and two tab pools. Declare them in the provider file:
+
+```toml
+[[accounts]]
+id = "perso"                          # the short name used in the model string
+email = "bruno.charest@gmail.com"     # also accepted as the account key
+label = "Personal"                    # free-form, shown by 'llm-gateway list'
+default = true                        # used by {"model": "chatgpt"}
+
+[[accounts]]
+id = "pro"
+email = "brunocharest.bc@gmail.com"
+```
+
+Then sign each one in once and address it in the model string:
+
+```bash
+llm-gateway login chatgpt --account perso
+llm-gateway login chatgpt@pro                  # the same thing
+```
+
+```jsonc
+{"model": "chatgpt"}                                  // the default account
+{"model": "chatgpt@pro"}                              // by id
+{"model": "chatgpt@brunocharest.bc@gmail.com"}         // by address
+{"model": "chatgpt@pro/gpt-4o"}                       // account and model
+```
+
+Their profiles live in `profiles/<provider>/accounts/<account>/user-data-dir`.
+A provider that declares no account keeps the historical
+`profiles/<provider>/user-data-dir`, so adding accounts later means signing in
+again for the first one. Each account has its own tab pool, so `max_tabs`
+applies per account.
+
+## Adding a new provider
+
+1. Copy `providers/chatgpt.toml` to `~/.llm-gateway/providers/<name>.toml`.
+2. Set `provider.name`, `provider.web_url`, `provider.new_conversation_url` and
+   `provider.conversation_url_pattern` (one capture group, the web conversation
+   id extracted from the page URL).
+3. Fill in the selectors, then `llm-gateway selftest <name>`.
+4. `llm-gateway login <name>` once, and the provider is usable as a model:
+   `{"model": "<name>"}` or `{"model": "<name>/<model>"}`.
+
+Nothing else is provider specific: the capture loop, the error mapping, the
+conversation store and the API are shared.
diff --git a/scripts/ci.ps1 b/scripts/ci.ps1
new file mode 100644
index 0000000..1643f2f
--- /dev/null
+++ b/scripts/ci.ps1
@@ -0,0 +1,76 @@
+<#
+.SYNOPSIS
+  Run the same gates as the CI workflow, on this machine.
+
+.DESCRIPTION
+  Mirrors .github/workflows/ci.yml so a change can be checked before pushing:
+  formatting, clippy with warnings as errors, the unit and integration tests
+  (no browser, no network), the doc tests and a release build.
+
+  The browser end-to-end suite needs a real Chromium and is opt-in: pass -E2e
+  to add it after the other gates.
+
+.EXAMPLE
+  ./scripts/ci.ps1
+  ./scripts/ci.ps1 -E2e
+  ./scripts/ci.ps1 -SkipRelease
+#>
+param(
+    [switch]$E2e,
+    [switch]$SkipRelease
+)
+
+$ErrorActionPreference = 'Stop'
+$root = Split-Path -Parent (Split-Path -Parent $MyInvocation.MyCommand.Path)
+Push-Location $root
+
+$script:failed = @()
+
+function Invoke-Gate {
+    param([string]$Name, [string[]]$Arguments)
+    Write-Host "== $Name" -ForegroundColor Cyan
+    Write-Host "   cargo $($Arguments -join ' ')" -ForegroundColor DarkGray
+    & cargo @Arguments
+    if ($LASTEXITCODE -ne 0) {
+        Write-Host "   FAILED ($LASTEXITCODE)" -ForegroundColor Red
+        $script:failed += $Name
+    } else {
+        Write-Host "   ok" -ForegroundColor Green
+    }
+}
+
+Invoke-Gate 'formatting'     @('fmt', '--all', '--check')
+Invoke-Gate 'clippy'         @('clippy', '--all-targets', '--locked', '--', '-D', 'warnings')
+Invoke-Gate 'tests'          @('test', '--locked', '--all-targets')
+Invoke-Gate 'doc tests'      @('test', '--locked', '--doc')
+if (-not $SkipRelease) {
+    Invoke-Gate 'release build' @('build', '--locked', '--release')
+}
+
+if ($E2e) {
+    # The browser suite is #[ignore]d by default and needs a real browser.
+    $chrome = @(
+        "$env:ProgramFiles\Google\Chrome\Application\chrome.exe",
+        "$env:LOCALAPPDATA\Google\Chrome\Application\chrome.exe",
+        "$env:ProgramFiles\Microsoft\Edge\Application\msedge.exe",
+        "$env:LOCALAPPDATA\BraveSoftware\Brave-Browser\Application\brave.exe"
+    ) | Where-Object { Test-Path $_ } | Select-Object -First 1
+
+    if (-not $chrome) {
+        Write-Warning 'no Chromium-based browser found: skipping the browser suite'
+    } else {
+        $env:CHROME = $chrome
+        Invoke-Gate 'browser e2e' @('test', '--test', 'e2e_browser', '--', '--ignored', '--test-threads=1')
+    }
+}
+
+Pop-Location
+
+if ($script:failed.Count -gt 0) {
+    Write-Host ''
+    Write-Host "failed gates: $($script:failed -join ', ')" -ForegroundColor Red
+    exit 1
+}
+Write-Host ''
+Write-Host 'all gates passed' -ForegroundColor Green
+exit 0
diff --git a/scripts/e2e.ps1 b/scripts/e2e.ps1
new file mode 100644
index 0000000..2d1686c
--- /dev/null
+++ b/scripts/e2e.ps1
@@ -0,0 +1,45 @@
+<#
+.SYNOPSIS
+  Run the browser end-to-end suite against the local fixture page.
+
+.DESCRIPTION
+  The suite needs a real Chromium-based browser; it is ignored by default so
+  that "cargo test" stays usable without a browser. It drives a local static
+  fake of the ChatGPT page (tests/fixtures/chatgpt_mock.html): full pipeline,
+  streaming, conversation reuse, login, captcha, rate limit, error banner,
+  first-token timeout, missing selector, mid-stream rewrite and attachments.
+
+.EXAMPLE
+  ./scripts/e2e.ps1
+  ./scripts/e2e.ps1 -Test fixture_full_pipeline
+#>
+param(
+    [string]$Test = ''
+)
+
+$ErrorActionPreference = 'Stop'
+$root = Split-Path -Parent (Split-Path -Parent $MyInvocation.MyCommand.Path)
+Push-Location $root
+
+$chrome = @(
+    "$env:ProgramFiles\Google\Chrome\Application\chrome.exe",
+    "$env:LOCALAPPDATA\Google\Chrome\Application\chrome.exe",
+    "$env:ProgramFiles\Microsoft\Edge\Application\msedge.exe",
+    "$env:LOCALAPPDATA\BraveSoftware\Brave-Browser\Application\brave.exe"
+) | Where-Object { Test-Path $_ } | Select-Object -First 1
+
+if (-not $chrome) {
+    Write-Warning 'no Chromium-based browser found: the browser suite cannot run'
+    Pop-Location
+    exit 2
+}
+Write-Host "using $chrome" -ForegroundColor Cyan
+
+$arguments = @('test', '--test', 'e2e_browser')
+if ($Test) { $arguments += $Test }
+$arguments += @('--', '--ignored', '--test-threads=1', '--nocapture')
+
+& cargo @arguments
+$code = $LASTEXITCODE
+Pop-Location
+exit $code
diff --git a/src/browser/cdp.rs b/src/browser/cdp.rs
new file mode 100644
index 0000000..42a25ff
--- /dev/null
+++ b/src/browser/cdp.rs
@@ -0,0 +1,748 @@
+//! Chromium implementation of the browser engine, driven over CDP.
+
+use std::path::{Path, PathBuf};
+use std::time::{Duration, Instant};
+
+use async_trait::async_trait;
+use chromiumoxide::browser::{Browser, BrowserConfig};
+use chromiumoxide::cdp::browser_protocol::browser::{
+    PermissionDescriptor, PermissionSetting, SetPermissionParams,
+};
+use chromiumoxide::error::CdpError;
+use chromiumoxide::{Element, Page};
+use futures::StreamExt;
+use tokio::sync::Mutex;
+use tokio::task::JoinHandle;
+
+use crate::config::StealthMode;
+use crate::error::{GatewayError, Result};
+
+use super::engine::{BrowserEngine, BrowserSettings, TabStats};
+use super::pool::{TabLease, TabPool};
+
+/// Script installed in every new document when stealth is set to "minimal".
+///
+/// It only hides the automation marker; the user agent is left untouched so the
+/// browser still looks like the real Chrome it is. Spoofing an outdated user
+/// agent (see StealthMode::Aggressive) is what makes OAuth providers such as
+/// Google answer "this browser or app may not be secure".
+const MINIMAL_STEALTH_SCRIPT: &str = r#"
+Object.defineProperty(Object.getPrototypeOf(navigator), 'webdriver', { get: () => false });
+if (!window.chrome) { window.chrome = { runtime: {} }; }
+"#;
+
+/// Permissions granted before reading the clipboard over CDP.
+const CLIPBOARD_PERMISSIONS: [&str; 2] = ["clipboard-read", "clipboard-write"];
+
+/// How long a real mouse click is given before the scripted fallback runs.
+const CLICK_TIMEOUT: Duration = Duration::from_secs(2);
+
+/// Click and focus from inside the page.
+///
+/// Used when the mouse click cannot complete: it also moves the focus, which a
+/// scripted `click()` alone does not do, so the editor accepts the text.
+const SCRIPTED_CLICK: &str =
+    "function() { if (this.focus) { this.focus(); } this.click(); return true; }";
+
+struct Running {
+    browser: Browser,
+    handler: JoinHandle<()>,
+    /// One entry per tab slot of the pool; `None` until that slot is used.
+    pages: Vec<Option<Page>>,
+    /// False when the browser belongs to the user (attach mode): it must not be
+    /// closed when the gateway shuts down.
+    owned: bool,
+}
+
+/// Launches and owns one browser process, or attaches to a running one.
+pub struct CdpEngine {
+    settings: BrowserSettings,
+    state: Mutex<Option<Running>>,
+    pool: TabPool,
+    /// Serialises mouse, key and text input across the tabs of this browser.
+    input_lock: Mutex<()>,
+}
+
+impl CdpEngine {
+    pub fn new(settings: BrowserSettings) -> Self {
+        let owner = match &settings.account {
+            Some(account) => format!("{}@{}", settings.provider, account),
+            None => settings.provider.clone(),
+        };
+        let pool = TabPool::new(owner, settings.max_tabs, settings.busy_wait);
+        Self {
+            settings,
+            state: Mutex::new(None),
+            pool,
+            input_lock: Mutex::new(()),
+        }
+    }
+
+    /// Endpoint of the browser we attach to.
+    pub fn attach_endpoint(&self) -> String {
+        format!("http://127.0.0.1:{}", self.settings.debug_port)
+    }
+
+    /// Page of one tab slot, launching the browser and opening the tab when
+    /// that slot is used for the first time.
+    async fn ensure_page(&self, slot: usize) -> Result<Page> {
+        let mut guard = self.state.lock().await;
+
+        let stale = guard
+            .as_ref()
+            .is_some_and(|running| running.handler.is_finished());
+        if stale {
+            if let Some(mut dead) = guard.take() {
+                let _ = dead.browser.close().await;
+                dead.handler.abort();
+            }
+            tracing::warn!(
+                provider = %self.settings.provider,
+                "the browser went away, starting a new one"
+            );
+        }
+
+        if guard.is_none() {
+            let running = if self.settings.attach {
+                self.attach().await?
+            } else {
+                self.launch().await?
+            };
+            *guard = Some(running);
+        }
+
+        let running = guard.as_mut().expect("the browser was just started");
+        if let Some(page) = running.pages.get(slot).and_then(|page| page.clone()) {
+            return Ok(page);
+        }
+
+        let page = running
+            .browser
+            .new_page("about:blank")
+            .await
+            .map_err(|err| self.classify(err))?;
+        self.apply_stealth(&page).await;
+        if running.pages.len() <= slot {
+            running.pages.resize(slot + 1, None);
+        }
+        running.pages[slot] = Some(page.clone());
+        tracing::debug!(
+            provider = %self.settings.provider,
+            slot,
+            "opened a new tab"
+        );
+        Ok(page)
+    }
+
+    /// Start our own browser process.
+    async fn launch(&self) -> Result<Running> {
+        std::fs::create_dir_all(&self.settings.profile_dir).map_err(|e| {
+            GatewayError::BrowserUnavailable(format!(
+                "cannot create the profile directory {}: {e}",
+                self.settings.profile_dir.display()
+            ))
+        })?;
+
+        let mut builder = BrowserConfig::builder().user_data_dir(self.settings.profile_dir.clone());
+        builder = if self.settings.headless {
+            builder.new_headless_mode()
+        } else {
+            builder.with_head()
+        };
+        if let Some(executable) = &self.settings.executable {
+            builder = builder.chrome_executable(executable.clone());
+        }
+        for arg in &self.settings.extra_args {
+            builder = builder.arg(arg.as_str());
+        }
+
+        let config = builder
+            .launch_timeout(self.settings.launch_timeout)
+            .request_timeout(self.settings.request_timeout)
+            .build()
+            .map_err(|e| GatewayError::BrowserUnavailable(e.to_string()))?;
+
+        tracing::debug!(
+            provider = %self.settings.provider,
+            account = self.settings.account.as_deref().unwrap_or("-"),
+            profile = %self.settings.profile_dir.display(),
+            headless = self.settings.headless,
+            stealth = ?self.settings.stealth,
+            launch_timeout_s = self.settings.launch_timeout.as_secs(),
+            "launching the browser"
+        );
+
+        let (browser, mut handler) = match Browser::launch(config).await {
+            Ok(pair) => pair,
+            Err(err) => return Err(self.classify(err)),
+        };
+
+        // The handler drives the websocket: without polling it the connection
+        // stalls after a few messages.
+        let handle = tokio::spawn(async move {
+            while let Some(event) = handler.next().await {
+                if event.is_err() {
+                    break;
+                }
+            }
+        });
+
+        Ok(Running {
+            browser,
+            handler: handle,
+            pages: Vec::new(),
+            owned: true,
+        })
+    }
+
+    /// Attach to a browser the user started, and reuse one of its tabs.
+    async fn attach(&self) -> Result<Running> {
+        let endpoint = self.attach_endpoint();
+        tracing::info!(endpoint = %endpoint, "attaching to the running browser");
+
+        let (mut browser, mut handler) = match Browser::connect(endpoint.clone()).await {
+            Ok(pair) => pair,
+            Err(err) => {
+                return Err(GatewayError::BrowserUnavailable(format!(
+                    "cannot attach to the browser on {endpoint}: {err}\n\
+                     Start one first, for example:\n  {}",
+                    external_launch(
+                        self.settings.executable.as_ref(),
+                        &self.settings.profile_dir,
+                        "about:blank",
+                        Some(self.settings.debug_port),
+                    )
+                    .command_line()
+                )))
+            }
+        };
+
+        let handle = tokio::spawn(async move {
+            while let Some(event) = handler.next().await {
+                if event.is_err() {
+                    break;
+                }
+            }
+        });
+
+        let page = self.pick_page(&mut browser).await?;
+        self.apply_stealth(&page).await;
+
+        Ok(Running {
+            browser,
+            handler: handle,
+            // The tab the user already had open takes the first slot.
+            pages: vec![Some(page)],
+            owned: false,
+        })
+    }
+
+    /// Reuse an already open tab so the user keeps their window and session.
+    ///
+    /// The tabs of a browser we did not launch are only visible through the
+    /// target list, not through the page registry of the handler.
+    async fn pick_page(&self, browser: &mut Browser) -> Result<Page> {
+        // The handler learns about the tabs of a browser it did not launch
+        // through Target.targetCreated events, which arrive just after the
+        // connection: retry briefly instead of giving up on the first miss.
+        let deadline = Instant::now() + Duration::from_secs(5);
+        let mut last_error = None;
+        loop {
+            match browser.fetch_targets().await {
+                Ok(targets) => {
+                    let reusable: Vec<_> = targets
+                        .into_iter()
+                        .filter(|target| target.r#type.as_str() == "page")
+                        .filter(|target| {
+                            !target.url.is_empty()
+                                && target.url != "about:blank"
+                                && !target.url.starts_with("devtools://")
+                        })
+                        .collect();
+
+                    for target in reusable {
+                        match browser.get_page(target.target_id.clone()).await {
+                            Ok(page) => {
+                                // A browser that is still starting up hands out
+                                // sessions for tabs it then replaces: the handle
+                                // exists but every command fails with "session
+                                // with given id not found". Prove the tab answers
+                                // before adopting it.
+                                if self.page_answers(&page).await {
+                                    tracing::info!(
+                                        url = %target.url,
+                                        "reusing the tab already open in the browser"
+                                    );
+                                    return Ok(page);
+                                }
+                                tracing::debug!(
+                                    url = %target.url,
+                                    "the tab is not answering yet, looking for another one"
+                                );
+                            }
+                            Err(err) => last_error = Some(err),
+                        }
+                    }
+                }
+                Err(err) => last_error = Some(err),
+            }
+
+            if Instant::now() >= deadline {
+                break;
+            }
+            tokio::time::sleep(Duration::from_millis(150)).await;
+        }
+
+        if let Some(err) = last_error {
+            tracing::debug!(error = %err, "no reusable tab found in the running browser");
+        }
+        tracing::info!("no tab of yours could be reused, opening one in your browser instead");
+        browser
+            .new_page("about:blank")
+            .await
+            .map_err(|err| self.classify(err))
+    }
+
+    /// True when Chrome is rendering that tab.
+    ///
+    /// A hidden tab never delivers the IntersectionObserver callback that
+    /// chromiumoxide's mouse click waits for, so the click would hang forever.
+    async fn page_is_visible(&self, page: &Page) -> bool {
+        match page
+            .evaluate_expression("document.visibilityState === 'visible'")
+            .await
+        {
+            Ok(result) => result.into_value::<bool>().unwrap_or(false),
+            Err(_) => false,
+        }
+    }
+
+    /// True when the tab answers a trivial CDP command.
+    ///
+    /// Attaching to a browser the user just started races with Chrome creating
+    /// its first tabs: the target list already advertises them while their
+    /// session is still being replaced.
+    async fn page_answers(&self, page: &Page) -> bool {
+        matches!(
+            tokio::time::timeout(Duration::from_secs(3), page.evaluate_expression("1")).await,
+            Ok(Ok(_))
+        )
+    }
+
+    async fn apply_stealth(&self, page: &Page) {
+        match self.settings.stealth {
+            StealthMode::Off => {}
+            StealthMode::Minimal => {
+                if let Err(err) = page.evaluate_on_new_document(MINIMAL_STEALTH_SCRIPT).await {
+                    tracing::debug!(error = %err, "cannot install the stealth script");
+                }
+            }
+            StealthMode::Aggressive => {
+                tracing::warn!(
+                    "aggressive stealth advertises an outdated user agent, which some sign-in pages reject as insecure"
+                );
+                if let Err(err) = page.enable_stealth_mode().await {
+                    tracing::debug!(error = %err, "stealth mode unavailable on this browser build");
+                }
+            }
+        }
+    }
+
+    fn classify(&self, err: CdpError) -> GatewayError {
+        let text = err.to_string();
+        let lower = text.to_lowercase();
+        if lower.contains("already in use")
+            || lower.contains("singletonlock")
+            || lower.contains("processsingleton")
+            || lower.contains("cannot create a file when that file already exists")
+        {
+            return GatewayError::BrowserProfileLocked {
+                path: self.settings.profile_dir.clone(),
+            };
+        }
+        if lower.contains("no such file")
+            || lower.contains("cannot find")
+            || lower.contains("failed to spawn")
+            || lower.contains("os error 2")
+        {
+            return GatewayError::BrowserUnavailable(format!(
+                "cannot start the browser executable: {text}"
+            ));
+        }
+        GatewayError::BrowserUnavailable(text)
+    }
+}
+
+#[async_trait]
+impl BrowserEngine for CdpEngine {
+    fn kind(&self) -> &'static str {
+        "chromium-cdp"
+    }
+
+    fn settings(&self) -> &BrowserSettings {
+        &self.settings
+    }
+
+    async fn start(&self) -> Result<()> {
+        self.ensure_page(0).await.map(|_| ())
+    }
+
+    async fn acquire_page(&self, wait: Duration) -> Result<TabLease> {
+        self.acquire_within(wait).await
+    }
+
+    async fn is_running(&self) -> bool {
+        let guard = self.state.lock().await;
+        guard
+            .as_ref()
+            .is_some_and(|running| !running.handler.is_finished())
+    }
+
+    fn stats(&self) -> TabStats {
+        TabStats {
+            max_tabs: self.pool.max_tabs(),
+            busy: self.pool.busy(),
+        }
+    }
+
+    async fn grant_permission(&self, name: &str) -> Result<()> {
+        let guard = self.state.lock().await;
+        let Some(running) = guard.as_ref() else {
+            return Ok(());
+        };
+        let params =
+            SetPermissionParams::new(PermissionDescriptor::new(name), PermissionSetting::Granted);
+        running
+            .browser
+            .execute(params)
+            .await
+            .map(|_| ())
+            .map_err(|err| GatewayError::BrowserUnavailable(err.to_string()))
+    }
+
+    async fn click(&self, page: &Page, element: &Element) -> Result<()> {
+        if self.page_is_visible(page).await {
+            let _guard = self.input_lock.lock().await;
+            match tokio::time::timeout(CLICK_TIMEOUT, element.click()).await {
+                Ok(Ok(_)) => return Ok(()),
+                Ok(Err(err)) => return Err(dom_error(err)),
+                Err(_) => tracing::debug!(
+                    "the mouse click did not complete, clicking from the page instead"
+                ),
+            }
+        } else {
+            tracing::debug!("the tab is not rendered, clicking from the page");
+        }
+        element
+            .call_js_fn(SCRIPTED_CLICK, false)
+            .await
+            .map(|_| ())
+            .map_err(dom_error)
+    }
+
+    async fn press_key(&self, element: &Element, key: &str) -> Result<()> {
+        let _guard = self.input_lock.lock().await;
+        element.press_key(key).await.map(|_| ()).map_err(dom_error)
+    }
+
+    async fn type_text(&self, element: &Element, text: &str) -> Result<()> {
+        let _guard = self.input_lock.lock().await;
+        element.type_str(text).await.map(|_| ()).map_err(dom_error)
+    }
+
+    async fn shutdown(&self) -> Result<()> {
+        let running = self.state.lock().await.take();
+        if let Some(mut running) = running {
+            if running.owned {
+                if let Err(err) = running.browser.close().await {
+                    tracing::debug!(error = %err, "closing the browser reported an error");
+                }
+            } else {
+                tracing::info!("detaching: the browser you started keeps running");
+            }
+            running.handler.abort();
+        }
+        Ok(())
+    }
+}
+
+impl CdpEngine {
+    /// Lease a tab, waiting at most `wait` for one to be free.
+    async fn acquire_within(&self, wait: Duration) -> Result<TabLease> {
+        let reservation = self.pool.reserve_within(wait).await?;
+        match self.ensure_page(reservation.slot()).await {
+            Ok(page) => Ok(reservation.into_lease(page)),
+            Err(err) => {
+                // The reservation gives its slot back on drop.
+                drop(reservation);
+                Err(err)
+            }
+        }
+    }
+
+    /// Grant every permission the clipboard read needs. Best effort.
+    pub async fn grant_clipboard_permissions(&self) -> Result<()> {
+        for name in CLIPBOARD_PERMISSIONS {
+            if let Err(err) = self.grant_permission(name).await {
+                tracing::debug!(permission = name, error = %err, "cannot grant a clipboard permission");
+            }
+        }
+        Ok(())
+    }
+}
+
+/// A browser the user starts themselves, described as a command line.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ExternalLaunch {
+    pub program: String,
+    pub args: Vec<String>,
+}
+
+impl ExternalLaunch {
+    /// Command line to paste in a shell.
+    pub fn command_line(&self) -> String {
+        let mut out = quote(&self.program);
+        for arg in &self.args {
+            out.push(' ');
+            out.push_str(&quote_argument(arg));
+        }
+        out
+    }
+
+    /// Start it, detached from the gateway.
+    pub fn spawn(&self) -> std::io::Result<std::process::Child> {
+        std::process::Command::new(&self.program)
+            .args(&self.args)
+            .spawn()
+    }
+}
+
+/// Command line that opens a browser the user owns, on the gateway profile.
+///
+/// With a debug port the gateway can attach to that window; without one the
+/// sign-in happens in a completely normal browser, which is what OAuth
+/// providers that block automation require.
+pub fn external_launch(
+    executable: Option<&PathBuf>,
+    profile_dir: &Path,
+    url: &str,
+    debug_port: Option<u16>,
+) -> ExternalLaunch {
+    let program = executable
+        .map(|path| path.to_string_lossy().to_string())
+        .unwrap_or_else(|| "chrome".to_string());
+    let mut args = vec![
+        format!("--user-data-dir={}", profile_dir.display()),
+        "--no-first-run".to_string(),
+        "--no-default-browser-check".to_string(),
+    ];
+    if let Some(port) = debug_port {
+        args.push(format!("--remote-debugging-port={port}"));
+    }
+    args.push(url.to_string());
+    ExternalLaunch { program, args }
+}
+
+/// Quote only the value of a --key=value switch, which reads better.
+fn quote_argument(arg: &str) -> String {
+    match arg.split_once('=') {
+        Some((key, value)) if key.starts_with("--") => format!("{key}={}", quote(value)),
+        _ => quote(arg),
+    }
+}
+
+fn quote(value: &str) -> String {
+    if value.contains(' ') || value.contains('\t') {
+        format!("\"{value}\"")
+    } else {
+        value.to_string()
+    }
+}
+
+/// Resolve the browser executable: explicit path, environment, then well-known
+/// installation directories.
+pub fn resolve_executable(explicit: Option<&PathBuf>, env_var: Option<String>) -> Option<PathBuf> {
+    if let Some(path) = explicit {
+        if path.is_file() {
+            return Some(path.clone());
+        }
+        tracing::warn!(path = %path.display(), "configured browser executable does not exist");
+    }
+    if let Some(candidate) = env_var {
+        let path = PathBuf::from(candidate);
+        if path.is_file() {
+            return Some(path);
+        }
+    }
+    candidate_executables()
+        .into_iter()
+        .find(|path| path.is_file())
+}
+
+/// Well-known installation paths of Chromium-based browsers.
+pub fn candidate_executables() -> Vec<PathBuf> {
+    let mut candidates: Vec<PathBuf> = Vec::new();
+    #[cfg(windows)]
+    {
+        for base in ["ProgramFiles", "ProgramFiles(x86)", "LOCALAPPDATA"] {
+            if let Some(root) = std::env::var_os(base) {
+                let root = PathBuf::from(root);
+                candidates.push(
+                    root.join("Google")
+                        .join("Chrome")
+                        .join("Application")
+                        .join("chrome.exe"),
+                );
+                candidates.push(root.join("Chromium").join("Application").join("chrome.exe"));
+                candidates.push(
+                    root.join("Microsoft")
+                        .join("Edge")
+                        .join("Application")
+                        .join("msedge.exe"),
+                );
+                candidates.push(
+                    root.join("BraveSoftware")
+                        .join("Brave-Browser")
+                        .join("Application")
+                        .join("brave.exe"),
+                );
+                candidates.push(
+                    root.join("BraveSoftware")
+                        .join("Brave-Browser-Beta")
+                        .join("Application")
+                        .join("brave.exe"),
+                );
+            }
+        }
+    }
+    #[cfg(not(windows))]
+    {
+        for path in [
+            "/usr/bin/google-chrome",
+            "/usr/bin/google-chrome-stable",
+            "/usr/bin/chromium",
+            "/usr/bin/chromium-browser",
+            "/opt/google/chrome/chrome",
+            "/snap/bin/chromium",
+            "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
+        ] {
+            candidates.push(PathBuf::from(path));
+        }
+    }
+    candidates
+}
+
+/// Map the browser family flag onto a concrete executable.
+pub fn executable_hint(name: &str) -> Result<Option<PathBuf>> {
+    let needle = match name.trim().to_lowercase().as_str() {
+        "" | "auto" | "chrome" | "chromium" => return Ok(None),
+        "edge" | "msedge" => "msedge",
+        "brave" => "brave",
+        other => return Err(GatewayError::UnsupportedBrowser(other.to_string())),
+    };
+    Ok(candidate_executables().into_iter().find(|path| {
+        path.is_file()
+            && path
+                .file_name()
+                .is_some_and(|file| file.to_string_lossy().to_lowercase().contains(needle))
+    }))
+}
+
+/// Map a CDP failure onto a gateway error, as `browser::dom` does.
+fn dom_error(err: CdpError) -> GatewayError {
+    crate::browser::dom::cdp_error(err)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn unsupported_browsers_are_rejected_explicitly() {
+        let err = executable_hint("firefox").unwrap_err();
+        assert_eq!(err.code(), "unsupported_browser");
+        assert!(executable_hint("chrome").unwrap().is_none());
+        assert!(executable_hint("auto").unwrap().is_none());
+        assert!(executable_hint("").unwrap().is_none());
+    }
+
+    #[test]
+    fn browser_families_match_their_executable_name() {
+        if let Some(path) = executable_hint("edge").unwrap() {
+            assert!(path.to_string_lossy().to_lowercase().contains("msedge"));
+        }
+        if let Some(path) = executable_hint("brave").unwrap() {
+            assert!(path.to_string_lossy().to_lowercase().contains("brave"));
+        }
+    }
+
+    #[test]
+    fn the_external_launch_command_has_no_automation_flags() {
+        let profile = PathBuf::from("/home/me/.llm-gateway/profiles/chatgpt/user-data-dir");
+        let launch = external_launch(
+            Some(&PathBuf::from("/usr/bin/google-chrome")),
+            &profile,
+            "https://chatgpt.com/",
+            None,
+        );
+        let line = launch.command_line();
+        assert!(line.starts_with("/usr/bin/google-chrome"));
+        assert!(
+            line.contains("--user-data-dir=/home/me/.llm-gateway/profiles/chatgpt/user-data-dir")
+        );
+        assert!(line.ends_with("https://chatgpt.com/"));
+        assert!(!line.contains("enable-automation"));
+        assert!(!line.contains("remote-debugging-port"));
+
+        let attach = external_launch(None, &profile, "https://chatgpt.com/", Some(9222));
+        assert!(attach
+            .command_line()
+            .contains("--remote-debugging-port=9222"));
+        assert_eq!(attach.command_line().split(' ').next(), Some("chrome"));
+    }
+
+    #[test]
+    fn paths_with_spaces_are_quoted() {
+        let profile = PathBuf::from("C:/Program Files/profile");
+        let launch = external_launch(
+            Some(&PathBuf::from("C:/Program Files/Google/Chrome/chrome.exe")),
+            &profile,
+            "https://chatgpt.com/",
+            Some(9222),
+        );
+        assert!(launch
+            .command_line()
+            .starts_with("\"C:/Program Files/Google/Chrome/chrome.exe\""));
+        assert!(launch
+            .command_line()
+            .contains("--user-data-dir=\"C:/Program Files/profile\""));
+    }
+
+    #[test]
+    fn the_minimal_stealth_script_does_not_touch_the_user_agent() {
+        assert!(MINIMAL_STEALTH_SCRIPT.contains("webdriver"));
+        assert!(!MINIMAL_STEALTH_SCRIPT.contains("userAgent"));
+        assert!(!MINIMAL_STEALTH_SCRIPT.contains("Chrome/1"));
+    }
+
+    #[test]
+    fn an_engine_names_its_owner_and_its_pool() {
+        let settings = BrowserSettings {
+            provider: "chatgpt".to_string(),
+            account: Some("perso".to_string()),
+            max_tabs: 3,
+            ..BrowserSettings::default()
+        };
+        let engine = CdpEngine::new(settings);
+        assert_eq!(engine.kind(), "chromium-cdp");
+        assert_eq!(engine.settings().max_tabs, 3);
+        assert_eq!(engine.stats().max_tabs, 3);
+        assert_eq!(engine.stats().busy, 0);
+        assert!(!engine.stats().is_saturated());
+    }
+
+    #[test]
+    fn the_clipboard_permissions_are_the_ones_the_browser_expects() {
+        assert_eq!(CLIPBOARD_PERMISSIONS, ["clipboard-read", "clipboard-write"]);
+    }
+}
diff --git a/src/browser/debug.rs b/src/browser/debug.rs
new file mode 100644
index 0000000..8e7eb7d
--- /dev/null
+++ b/src/browser/debug.rs
@@ -0,0 +1,140 @@
+//! Debug artifacts written when a capture fails.
+
+use std::path::{Path, PathBuf};
+
+use chromiumoxide::Page;
+
+use crate::config::ScreenshotMode;
+use crate::util;
+
+use super::dom;
+
+/// Screenshot and DOM dump of a failed capture.
+#[derive(Debug, Clone, Default)]
+pub struct CapturedArtifacts {
+    pub screenshot: Option<PathBuf>,
+    pub html: Option<PathBuf>,
+}
+
+impl CapturedArtifacts {
+    pub fn is_empty(&self) -> bool {
+        self.screenshot.is_none() && self.html.is_none()
+    }
+}
+
+/// Writes screenshots and DOM dumps next to the state directory.
+#[derive(Debug, Clone)]
+pub struct DebugRecorder {
+    dir: PathBuf,
+    mode: ScreenshotMode,
+}
+
+impl DebugRecorder {
+    pub fn new(dir: PathBuf, mode: ScreenshotMode) -> Self {
+        Self { dir, mode }
+    }
+
+    pub fn dir(&self) -> &Path {
+        &self.dir
+    }
+
+    pub fn mode(&self) -> ScreenshotMode {
+        self.mode
+    }
+
+    /// Whether a capture should happen for this outcome.
+    pub fn should_capture(&self, on_error: bool) -> bool {
+        match self.mode {
+            ScreenshotMode::Never => false,
+            ScreenshotMode::OnError => on_error,
+            ScreenshotMode::Always => true,
+        }
+    }
+
+    /// Save a screenshot and the current DOM. Failures are logged, never returned:
+    /// debugging must not mask the original error.
+    pub async fn capture(
+        &self,
+        provider: &str,
+        trace_id: &str,
+        page: &Page,
+        reason: &str,
+    ) -> CapturedArtifacts {
+        let mut artifacts = CapturedArtifacts::default();
+        if let Err(err) = std::fs::create_dir_all(&self.dir) {
+            tracing::warn!(error = %err, dir = %self.dir.display(), "cannot create the debug directory");
+            return artifacts;
+        }
+
+        let stamp = util::format_compact_utc(util::now_secs());
+        let safe_trace: String = trace_id
+            .chars()
+            .filter(|c| c.is_ascii_alphanumeric())
+            .collect();
+        let base = format!("{provider}_{safe_trace}_{stamp}");
+
+        match dom::screenshot_png(page).await {
+            Ok(bytes) => {
+                let path = self.dir.join(format!("{base}.png"));
+                match std::fs::write(&path, bytes) {
+                    Ok(()) => artifacts.screenshot = Some(path),
+                    Err(err) => tracing::warn!(error = %err, "cannot write the screenshot"),
+                }
+            }
+            Err(err) => tracing::warn!(error = %err, "cannot take a screenshot"),
+        }
+
+        match dom::page_html(page).await {
+            Ok(html) => {
+                let path = self.dir.join(format!("{base}.html"));
+                match std::fs::write(&path, html) {
+                    Ok(()) => artifacts.html = Some(path),
+                    Err(err) => tracing::warn!(error = %err, "cannot write the DOM dump"),
+                }
+            }
+            Err(err) => tracing::warn!(error = %err, "cannot read the page DOM"),
+        }
+
+        let index_line = format!(
+            "{{\"ts\":{},\"provider\":\"{provider}\",\"trace_id\":\"{trace_id}\",\"reason\":{},\"screenshot\":{},\"html\":{}}}\n",
+            util::now_secs(),
+            serde_json::to_string(reason).unwrap_or_else(|_| "\"\"".into()),
+            serde_json::to_string(&artifacts.screenshot.as_ref().map(|p| p.display().to_string()))
+                .unwrap_or_else(|_| "null".into()),
+            serde_json::to_string(&artifacts.html.as_ref().map(|p| p.display().to_string()))
+                .unwrap_or_else(|_| "null".into()),
+        );
+        let index = self.dir.join("index.jsonl");
+        if let Err(err) = std::fs::OpenOptions::new()
+            .create(true)
+            .append(true)
+            .open(&index)
+            .and_then(|mut file| {
+                use std::io::Write;
+                file.write_all(index_line.as_bytes())
+            })
+        {
+            tracing::warn!(error = %err, "cannot append to the debug index");
+        }
+
+        artifacts
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn capture_policy_follows_the_mode() {
+        let recorder = DebugRecorder::new(PathBuf::from("/tmp"), ScreenshotMode::OnError);
+        assert!(!recorder.should_capture(false));
+        assert!(recorder.should_capture(true));
+
+        let always = DebugRecorder::new(PathBuf::from("/tmp"), ScreenshotMode::Always);
+        assert!(always.should_capture(false));
+
+        let never = DebugRecorder::new(PathBuf::from("/tmp"), ScreenshotMode::Never);
+        assert!(!never.should_capture(true));
+    }
+}
diff --git a/src/browser/dom.rs b/src/browser/dom.rs
new file mode 100644
index 0000000..db95a07
--- /dev/null
+++ b/src/browser/dom.rs
@@ -0,0 +1,193 @@
+//! Thin, error-mapped helpers around a Chromium page handle.
+
+use std::path::PathBuf;
+use std::time::{Duration, Instant};
+
+use chromiumoxide::cdp::browser_protocol::dom::SetFileInputFilesParams;
+use chromiumoxide::error::CdpError;
+use chromiumoxide::page::ScreenshotParams;
+use chromiumoxide::{Element, Page};
+use serde::de::DeserializeOwned;
+
+use crate::error::{GatewayError, Result};
+
+/// Map a CDP failure onto a gateway error.
+pub fn cdp_error(err: CdpError) -> GatewayError {
+    let text = err.to_string();
+    let lower = text.to_lowercase();
+    if lower.contains("already in use")
+        || lower.contains("singletonlock")
+        || lower.contains("processsingleton")
+    {
+        return GatewayError::BrowserProfileLocked {
+            path: PathBuf::new(),
+        };
+    }
+    GatewayError::BrowserUnavailable(text)
+}
+
+/// Evaluate a JavaScript expression and decode the returned JSON value.
+pub async fn evaluate_json<T: DeserializeOwned>(page: &Page, script: &str) -> Result<T> {
+    let result = page.evaluate_expression(script).await.map_err(cdp_error)?;
+    result
+        .into_value::<T>()
+        .map_err(|e| GatewayError::Internal(format!("decoding the page result: {e}")))
+}
+
+/// Evaluate JavaScript, ignoring a decoding failure.
+pub async fn evaluate_ok(page: &Page, script: &str) -> Result<()> {
+    page.evaluate_expression(script).await.map_err(cdp_error)?;
+    Ok(())
+}
+
+/// Navigate to a URL with a hard timeout.
+///
+/// Navigating to a URL that only differs by its fragment is a same-document
+/// navigation: Chrome never fires the load event the CDP helper waits for, so
+/// the fragment is set directly instead of hanging.
+pub async fn goto(page: &Page, url: &str, timeout: Duration) -> Result<()> {
+    let current = page.url().await.ok().flatten().unwrap_or_default();
+    if !current.is_empty() && strip_fragment(&current) == strip_fragment(url) {
+        let current_fragment = fragment(&current);
+        let wanted = fragment(url);
+        if current_fragment != wanted {
+            let value = if wanted.is_empty() {
+                String::new()
+            } else {
+                format!("#{wanted}")
+            };
+            let script = format!("location.hash = {}", crate::browser::js::js_string(&value));
+            evaluate_ok(page, &script).await?;
+        }
+        tracing::debug!(url, "already on the requested page, navigation skipped");
+        return Ok(());
+    }
+
+    match tokio::time::timeout(timeout, page.goto(url)).await {
+        Ok(Ok(_)) => Ok(()),
+        Ok(Err(err)) => Err(cdp_error(err)),
+        Err(_) => Err(GatewayError::CaptureTimeout {
+            stage: format!("loading {url}"),
+            timeout_s: timeout.as_secs(),
+        }),
+    }
+}
+
+/// URL without its fragment.
+fn strip_fragment(url: &str) -> &str {
+    url.split('#').next().unwrap_or(url)
+}
+
+/// Fragment of a URL, without the leading hash.
+fn fragment(url: &str) -> &str {
+    match url.split_once('#') {
+        Some((_, fragment)) => fragment,
+        None => "",
+    }
+}
+
+/// Poll for a selector until it appears.
+pub async fn wait_for_selector(
+    page: &Page,
+    selector: &str,
+    step: &str,
+    timeout: Duration,
+) -> Result<Element> {
+    if selector.trim().is_empty() {
+        return Err(GatewayError::SelectorMissing {
+            selector: selector.to_string(),
+            step: format!("{step}: no selector configured"),
+        });
+    }
+    let started = Instant::now();
+    loop {
+        match page.find_element(selector).await {
+            Ok(element) => return Ok(element),
+            Err(_) => {
+                if started.elapsed() >= timeout {
+                    break;
+                }
+                tokio::time::sleep(Duration::from_millis(250)).await;
+            }
+        }
+    }
+    tracing::debug!(
+        selector,
+        timeout_s = timeout.as_secs(),
+        "selector never appeared"
+    );
+    Err(GatewayError::SelectorMissing {
+        selector: selector.to_string(),
+        step: step.to_string(),
+    })
+}
+
+/// True when the selector currently matches at least one node.
+pub async fn selector_exists(page: &Page, selector: &str) -> bool {
+    if selector.trim().is_empty() {
+        return false;
+    }
+    page.find_element(selector).await.is_ok()
+}
+
+/// Attach files to a hidden file input (images, PDFs).
+pub async fn set_file_input_files(page: &Page, selector: &str, files: &[PathBuf]) -> Result<()> {
+    if files.is_empty() {
+        return Ok(());
+    }
+    let element = wait_for_selector(
+        page,
+        selector,
+        "uploading an attachment",
+        Duration::from_secs(15),
+    )
+    .await?;
+    let params = SetFileInputFilesParams {
+        files: files
+            .iter()
+            .map(|path| path.to_string_lossy().to_string())
+            .collect(),
+        node_id: Some(element.node_id),
+        backend_node_id: None,
+        object_id: None,
+    };
+    page.execute(params).await.map_err(cdp_error)?;
+    Ok(())
+}
+
+/// Current URL of the page.
+pub async fn page_url(page: &Page) -> Result<String> {
+    Ok(page.url().await.map_err(cdp_error)?.unwrap_or_default())
+}
+
+/// Full HTML of the page.
+pub async fn page_html(page: &Page) -> Result<String> {
+    page.content().await.map_err(cdp_error)
+}
+
+/// PNG screenshot of the current viewport.
+pub async fn screenshot_png(page: &Page) -> Result<Vec<u8>> {
+    page.screenshot(ScreenshotParams::default())
+        .await
+        .map_err(cdp_error)
+}
+
+/// Bring the page to the front, best effort.
+pub async fn focus_page(page: &Page) {
+    if let Err(err) = page.bring_to_front().await {
+        tracing::trace!(error = %err, "cannot bring the page to the front");
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn fragments_are_split_off_the_url() {
+        assert_eq!(strip_fragment("https://x/c/1#c=abc"), "https://x/c/1");
+        assert_eq!(fragment("https://x/c/1#c=abc"), "c=abc");
+        assert_eq!(fragment("https://x/c/1"), "");
+        assert_eq!(strip_fragment("https://x/c/1"), "https://x/c/1");
+    }
+}
diff --git a/src/browser/engine.rs b/src/browser/engine.rs
new file mode 100644
index 0000000..ad38e8d
--- /dev/null
+++ b/src/browser/engine.rs
@@ -0,0 +1,126 @@
+//! Browser engine abstraction.
+//!
+//! The trait isolates process lifecycle (launch, reuse, shutdown) and tab
+//! admission so the business logic never talks to Chrome directly. DOM
+//! interaction goes through the helpers of `browser::dom`, which take a page
+//! handle; a future WebDriver backend would add a page-ops trait there without
+//! touching the providers.
+
+use std::path::PathBuf;
+use std::time::Duration;
+
+use async_trait::async_trait;
+use chromiumoxide::{Element, Page};
+use serde::Serialize;
+
+use crate::config::StealthMode;
+use crate::error::Result;
+
+use super::pool::TabLease;
+
+/// Everything needed to spawn one browser process.
+///
+/// One instance describes one provider *account*: the account owns its browser
+/// profile, its tab pool and therefore its signed-in session.
+#[derive(Debug, Clone)]
+pub struct BrowserSettings {
+    /// Provider this browser belongs to, for logs and errors.
+    pub provider: String,
+    /// Account id, when the provider declares several.
+    pub account: Option<String>,
+    pub executable: Option<PathBuf>,
+    pub headless: bool,
+    pub profile_dir: PathBuf,
+    /// Concurrent turns allowed on this account, i.e. tabs kept open.
+    pub max_tabs: usize,
+    /// How long a request waits for a free tab before it gets a 429.
+    pub busy_wait: Duration,
+    pub launch_timeout: Duration,
+    pub request_timeout: Duration,
+    pub extra_args: Vec<String>,
+    pub stealth: StealthMode,
+    /// Attach to a browser the user started instead of launching our own.
+    pub attach: bool,
+    pub debug_port: u16,
+}
+
+impl Default for BrowserSettings {
+    fn default() -> Self {
+        Self {
+            provider: "provider".to_string(),
+            account: None,
+            executable: None,
+            headless: false,
+            profile_dir: PathBuf::new(),
+            max_tabs: 1,
+            busy_wait: Duration::from_secs(30),
+            launch_timeout: Duration::from_secs(60),
+            request_timeout: Duration::from_secs(60),
+            extra_args: Vec::new(),
+            stealth: StealthMode::Off,
+            attach: false,
+            debug_port: 9222,
+        }
+    }
+}
+
+/// Occupancy of a provider account's tab pool.
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize)]
+pub struct TabStats {
+    pub max_tabs: usize,
+    pub busy: usize,
+}
+
+impl TabStats {
+    pub fn is_saturated(&self) -> bool {
+        self.busy >= self.max_tabs
+    }
+}
+
+/// Lifecycle of the browser backing one provider account.
+#[async_trait]
+pub trait BrowserEngine: Send + Sync {
+    /// Backend name, for logs and status reports.
+    fn kind(&self) -> &'static str;
+
+    fn settings(&self) -> &BrowserSettings;
+
+    /// Launch the browser if needed. Idempotent.
+    async fn start(&self) -> Result<()>;
+
+    /// Lease one tab for a turn.
+    ///
+    /// Returns `provider_busy` when every tab stays busy for longer than
+    /// `wait`; the caller chooses the budget so that a status probe does not
+    /// wait as long as a real turn.
+    async fn acquire_page(&self, wait: Duration) -> Result<TabLease>;
+
+    async fn is_running(&self) -> bool;
+
+    /// Current tab occupancy.
+    fn stats(&self) -> TabStats;
+
+    /// Grant a CDP permission to every origin, best effort.
+    ///
+    /// Used for the clipboard: reading it is what gives the gateway the
+    /// provider's own Markdown instead of the flattened visible text.
+    async fn grant_permission(&self, name: &str) -> Result<()>;
+
+    /// Click an element.
+    ///
+    /// A real mouse event is preferred, because web UIs trust it. It is only
+    /// usable on a tab Chrome actually renders, so a hidden tab (the second tab
+    /// of a `max_tabs > 1` account) is clicked from the page instead: waiting
+    /// for a mouse event there hangs forever. Real mouse events are serialised
+    /// browser wide, which costs milliseconds while a generation costs seconds.
+    async fn click(&self, page: &Page, element: &Element) -> Result<()>;
+
+    /// Type a key into an element, with real key events.
+    async fn press_key(&self, element: &Element, key: &str) -> Result<()>;
+
+    /// Type text into an element, character by character.
+    async fn type_text(&self, element: &Element, text: &str) -> Result<()>;
+
+    /// Close the browser process started by this engine.
+    async fn shutdown(&self) -> Result<()>;
+}
diff --git a/src/browser/js.rs b/src/browser/js.rs
new file mode 100644
index 0000000..d1c783a
--- /dev/null
+++ b/src/browser/js.rs
@@ -0,0 +1,406 @@
+//! JavaScript snippets injected into the provider page.
+//!
+//! Every selector comes from the provider TOML configuration: this module only
+//! builds strings, it never hardcodes a site specific selector.
+
+use serde::{Deserialize, Serialize};
+
+use crate::providers::config::Selectors;
+
+/// Helpers shared by every snippet. All selector lookups are guarded so an
+/// invalid or stale selector degrades into a missing element instead of an
+/// exception.
+const HELPERS: &str = r#"
+  const q = (s) => { if (!s) return null; try { return document.querySelector(s); } catch (e) { return null; } };
+  const qa = (s) => { if (!s) return []; try { return Array.prototype.slice.call(document.querySelectorAll(s)); } catch (e) { return []; } };
+  const txt = (el) => { if (!el) return ''; const t = el.innerText; if (typeof t === 'string' && t.length) return t; const c = el.textContent; return typeof c === 'string' ? c : ''; };
+  const val = (s) => { const el = q(s); return el ? txt(el).trim().slice(0, 500) : null; };
+"#;
+
+/// Encode a Rust string as a JavaScript string literal.
+pub fn js_string(raw: &str) -> String {
+    serde_json::to_string(raw).unwrap_or_else(|_| "\"\"".to_string())
+}
+
+/// State of the page before a prompt is sent.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct ProbeResult {
+    pub url: String,
+    pub title: String,
+    pub ready_state: String,
+    pub has_input: bool,
+    pub input_len: usize,
+    pub has_send: bool,
+    pub send_disabled: bool,
+    pub has_login: bool,
+    pub has_captcha: bool,
+    pub response_count: usize,
+    pub streaming: bool,
+    pub error_text: Option<String>,
+    pub body_text: String,
+}
+
+/// State of the answer container while polling.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct ReadResponseResult {
+    pub count: usize,
+    pub text: String,
+    pub streaming: bool,
+    pub error_text: Option<String>,
+    pub has_login: bool,
+    pub has_captcha: bool,
+}
+
+/// Outcome of a text injection attempt.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct InjectionResult {
+    pub ok: bool,
+    pub len: usize,
+    pub reason: Option<String>,
+}
+
+/// Rich content of a settled answer node.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct AnswerHtml {
+    /// `innerHTML` of the answer node: the input of the Markdown conversion.
+    pub html: String,
+    /// `innerText` of the same node, the historical fallback.
+    pub text: String,
+    /// True when the node itself was found.
+    pub found: bool,
+}
+
+/// Outcome of clicking the provider copy button and reading the clipboard.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct ClipboardResult {
+    /// True when a copy button was found and clicked.
+    pub clicked: bool,
+    /// Markdown the provider itself wrote to the clipboard.
+    pub clipboard: Option<String>,
+    /// Why the clipboard could not be read, when it could not.
+    pub error: Option<String>,
+}
+
+/// Probe the page: presence of the input, the send button, the answer container
+/// and any login/captcha/error banner.
+pub fn probe_script(sel: &Selectors) -> String {
+    let mut s = String::with_capacity(2048);
+    s.push_str("(() => {\n");
+    s.push_str(HELPERS);
+    s.push_str(&format!(
+        "  const input = q({});\n",
+        js_string(&sel.input_field)
+    ));
+    s.push_str(&format!(
+        "  const send = q({});\n",
+        js_string(&sel.send_button)
+    ));
+    s.push_str(&format!(
+        "  const login = q({});\n",
+        js_string(&sel.login_page_indicator)
+    ));
+    s.push_str(&format!(
+        "  const captcha = q({});\n",
+        js_string(&sel.captcha_indicator)
+    ));
+    s.push_str(&format!(
+        "  const banner = q({});\n",
+        js_string(&sel.error_banner)
+    ));
+    s.push_str(&format!(
+        "  const stop = q({});\n",
+        js_string(&sel.streaming_indicator)
+    ));
+    s.push_str("  return {\n");
+    s.push_str("    url: String(location.href),\n");
+    s.push_str("    title: String(document.title || ''),\n");
+    s.push_str("    ready_state: String(document.readyState || ''),\n");
+    s.push_str("    has_input: !!input,\n");
+    s.push_str("    input_len: txt(input).trim().length,\n");
+    s.push_str("    has_send: !!send,\n");
+    s.push_str("    send_disabled: send ? (send.disabled === true || send.getAttribute('aria-disabled') === 'true') : false,\n");
+    s.push_str("    has_login: !!login,\n");
+    s.push_str("    has_captcha: !!captcha,\n");
+    s.push_str(&format!(
+        "    response_count: qa({}).length,\n",
+        js_string(&sel.response_container)
+    ));
+    s.push_str("    streaming: !!stop,\n");
+    s.push_str(&format!(
+        "    error_text: val({}),\n",
+        js_string(&sel.error_banner)
+    ));
+    s.push_str(&format!(
+        "    body_text: (document.body ? txt(document.body) : '').slice(0, {}).toLowerCase()\n",
+        BODY_SAMPLE_CHARS
+    ));
+    s.push_str("  };\n})()");
+    s
+}
+
+/// Read the n-th answer container of the page.
+pub fn read_response_script(sel: &Selectors, index: usize) -> String {
+    let mut s = String::with_capacity(1024);
+    s.push_str("(() => {\n");
+    s.push_str(HELPERS);
+    s.push_str(&format!(
+        "  const nodes = qa({});\n",
+        js_string(&sel.response_container)
+    ));
+    s.push_str("  const node = (nodes.length > ");
+    s.push_str(&index.to_string());
+    s.push_str(") ? nodes[");
+    s.push_str(&index.to_string());
+    s.push_str("] : null;\n");
+    s.push_str("  return {\n");
+    s.push_str("    count: nodes.length,\n");
+    s.push_str("    text: txt(node),\n");
+    s.push_str(&format!(
+        "    streaming: !!(q({})),\n",
+        js_string(&sel.streaming_indicator)
+    ));
+    s.push_str(&format!(
+        "    error_text: val({}),\n",
+        js_string(&sel.error_banner)
+    ));
+    s.push_str(&format!(
+        "    has_login: !!(q({})),\n",
+        js_string(&sel.login_page_indicator)
+    ));
+    s.push_str(&format!(
+        "    has_captcha: !!(q({}))\n",
+        js_string(&sel.captcha_indicator)
+    ));
+    s.push_str("  };\n})()");
+    s
+}
+
+/// Read the HTML and the visible text of the n-th answer node.
+///
+/// Used once, after the answer has settled: the HTML is what makes tables and
+/// code fences survive, and it is too big to fetch on every poll.
+pub fn read_answer_html_script(sel: &Selectors, index: usize) -> String {
+    let mut s = String::with_capacity(768);
+    s.push_str("(() => {\n");
+    s.push_str(HELPERS);
+    s.push_str(&format!(
+        "  const nodes = qa({});\n",
+        js_string(&sel.response_container)
+    ));
+    s.push_str("  const node = (nodes.length > ");
+    s.push_str(&index.to_string());
+    s.push_str(") ? nodes[");
+    s.push_str(&index.to_string());
+    s.push_str("] : null;\n");
+    s.push_str("  if (!node) return { html: '', text: '', found: false };\n");
+    s.push_str("  return { html: String(node.innerHTML || ''), text: txt(node), found: true };\n");
+    s.push_str("})()");
+    s
+}
+
+/// Click the provider copy button of the n-th answer node and read the
+/// clipboard.
+///
+/// This is the highest fidelity source available: the web UI copies exactly the
+/// Markdown it rendered, so tables, code fences and lists arrive intact. The
+/// expression is asynchronous, and Chromium is asked to await its promise.
+pub fn copy_answer_script(sel: &Selectors, index: usize, timeout_ms: u64) -> String {
+    let mut s = String::with_capacity(1280);
+    s.push_str("(async () => {\n");
+    s.push_str(HELPERS);
+    s.push_str(&format!(
+        "  const nodes = qa({});\n",
+        js_string(&sel.response_container)
+    ));
+    s.push_str("  const node = (nodes.length > ");
+    s.push_str(&index.to_string());
+    s.push_str(") ? nodes[");
+    s.push_str(&index.to_string());
+    s.push_str("] : null;\n");
+    s.push_str("  if (!node) return { clicked: false, clipboard: null, error: 'the answer node is gone' };\n");
+    // Toolbars of several web UIs only exist once the message has been hovered.
+    s.push_str("  try {\n");
+    s.push_str("    node.dispatchEvent(new MouseEvent('mouseover', { bubbles: true }));\n");
+    s.push_str("    node.dispatchEvent(new MouseEvent('mouseenter', { bubbles: true }));\n");
+    s.push_str("  } catch (e) {}\n");
+    s.push_str("  await new Promise((resolve) => setTimeout(resolve, 60));\n");
+    // The toolbar of a real web UI sits next to the answer text rather than
+    // inside it, so the button is searched from the answer node outwards: a
+    // descendant first, then the nearest button that follows it in document
+    // order within a few levels. Searching the whole page would click the copy
+    // button of a previous answer.
+    s.push_str(&format!(
+        "  const candidates = qa({});\n",
+        js_string(&sel.copy_button)
+    ));
+    s.push_str("  let button = null;\n");
+    s.push_str("  for (const candidate of candidates) {\n");
+    s.push_str("    if (node.contains(candidate)) { button = candidate; break; }\n");
+    s.push_str("    if (!(node.compareDocumentPosition(candidate) & 4)) continue;\n");
+    s.push_str("    let scope = candidate.parentElement;\n");
+    s.push_str("    let depth = 1;\n");
+    s.push_str("    while (scope && !scope.contains(node) && depth < 5) { scope = scope.parentElement; depth += 1; }\n");
+    s.push_str("    if (scope && depth <= 4) { button = candidate; break; }\n");
+    s.push_str("  }\n");
+    s.push_str(
+        "  if (!button) return { clicked: false, clipboard: null, error: 'no copy button' };\n",
+    );
+    s.push_str("  try { button.click(); } catch (e) { return { clicked: false, clipboard: null, error: String(e) }; }\n");
+    s.push_str("  await new Promise((resolve) => setTimeout(resolve, 80));\n");
+    s.push_str("  if (!navigator.clipboard || !navigator.clipboard.readText) {\n");
+    s.push_str("    return { clicked: true, clipboard: null, error: 'navigator.clipboard is unavailable on this page' };\n");
+    s.push_str("  }\n");
+    s.push_str("  try {\n");
+    s.push_str("    const text = await Promise.race([\n");
+    s.push_str("      navigator.clipboard.readText(),\n");
+    s.push_str(&format!(
+        "      new Promise((_, reject) => setTimeout(() => reject(new Error('the clipboard read timed out')), {timeout_ms}))\n"
+    ));
+    s.push_str("    ]);\n");
+    s.push_str("    return { clicked: true, clipboard: typeof text === 'string' ? text : null, error: null };\n");
+    s.push_str("  } catch (e) {\n");
+    s.push_str("    return { clicked: true, clipboard: null, error: String(e && e.message ? e.message : e) };\n");
+    s.push_str("  }\n");
+    s.push_str("})()");
+    s
+}
+
+/// Insert text into the focused element using the DOM editing command.
+pub fn exec_command_insert_script(text: &str) -> String {
+    let mut s = String::with_capacity(512);
+    s.push_str("(() => {\n");
+    s.push_str(HELPERS);
+    s.push_str(&format!("  const value = {};\n", js_string(text)));
+    s.push_str("  const el = document.activeElement;\n");
+    s.push_str("  if (!el) return { ok: false, len: 0, reason: 'no active element' };\n");
+    s.push_str("  try { document.execCommand('insertText', false, value); } catch (e) { return { ok: false, len: 0, reason: String(e) }; }\n");
+    s.push_str("  return { ok: true, len: txt(el).trim().length, reason: null };\n");
+    s.push_str("})()");
+    s
+}
+
+/// Check that the editor really contains the text we tried to inject.
+pub fn verify_input_script(sel: &Selectors, expected_len: usize) -> String {
+    let mut s = String::with_capacity(512);
+    s.push_str("(() => {\n");
+    s.push_str(HELPERS);
+    s.push_str(&format!(
+        "  const el = q({});\n",
+        js_string(&sel.input_field)
+    ));
+    s.push_str("  if (!el) return { ok: false, len: 0, reason: 'input field missing' };\n");
+    s.push_str(
+        "  const text = (typeof el.value === 'string' && el.value.length) ? el.value : txt(el);\n",
+    );
+    s.push_str("  const len = text.trim().length;\n");
+    s.push_str(&format!(
+        "  return {{ ok: len >= {}, len: len, reason: len === 0 ? 'editor is empty' : null }};\n",
+        expected_len.min(8)
+    ));
+    s.push_str("})()");
+    s
+}
+
+/// Remove whatever is already in the editor before injecting the prompt.
+pub fn clear_input_script(sel: &Selectors) -> String {
+    let mut s = String::with_capacity(512);
+    s.push_str("(() => {\n");
+    s.push_str(HELPERS);
+    s.push_str(&format!(
+        "  const el = q({});\n",
+        js_string(&sel.input_field)
+    ));
+    s.push_str("  if (!el) return { ok: false, len: 0, reason: 'input field missing' };\n");
+    s.push_str("  el.focus();\n");
+    s.push_str("  try { document.execCommand('selectAll', false, null); document.execCommand('delete', false, null); } catch (e) { return { ok: false, len: 0, reason: String(e) }; }\n");
+    s.push_str("  const len = (typeof el.value === 'string' && el.value.length) ? el.value.length : txt(el).trim().length;\n");
+    s.push_str("  return { ok: true, len: len, reason: null };\n");
+    s.push_str("})()");
+    s
+}
+
+/// Number of body characters sampled for rate-limit detection.
+pub const BODY_SAMPLE_CHARS: usize = 40_000;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn selectors() -> Selectors {
+        Selectors {
+            input_field: "div#prompt-textarea".into(),
+            send_button: "button[data-testid='send-button']".into(),
+            response_container: "div[data-message-author-role='assistant']".into(),
+            streaming_indicator: "button[data-testid='stop-button']".into(),
+            file_input: "input[type='file']".into(),
+            new_chat_button: String::new(),
+            login_page_indicator: "form[action*='login']".into(),
+            captcha_indicator: "iframe[src*='captcha']".into(),
+            error_banner: "[role='alert']".into(),
+            model_selector: String::new(),
+            attachment_indicator: String::new(),
+            copy_button: String::new(),
+        }
+    }
+
+    #[test]
+    fn scripts_embed_selectors_and_are_syntactically_closed() {
+        let sel = selectors();
+        let probe = probe_script(&sel);
+        assert!(probe.contains("div#prompt-textarea"));
+        assert!(probe.contains("button[data-testid='send-button']"));
+        assert!(probe.starts_with("(() => {"));
+        assert!(probe.trim_end().ends_with("})()"));
+        assert!(!probe.contains("{input}"));
+
+        let read = read_response_script(&sel, 2);
+        assert!(read.contains("nodes[2]"));
+        assert!(read.trim_end().ends_with("})()"));
+    }
+
+    #[test]
+    fn text_is_escaped_not_interpolated() {
+        let script = exec_command_insert_script("a \" b\nline 'quote' </script>");
+        assert!(script.contains(r#""a \" b\nline 'quote' </script>""#));
+        assert!(script.trim_end().ends_with("})()"));
+    }
+
+    #[test]
+    fn the_copy_script_awaits_the_clipboard_and_has_a_deadline() {
+        let mut sel = selectors();
+        sel.copy_button = "button[aria-label='Copy']".into();
+        let script = copy_answer_script(&sel, 1, 2000);
+        assert!(script.starts_with("(async () => {"));
+        assert!(script.trim_end().ends_with("})()"));
+        assert!(script.contains("nodes[1]"));
+        assert!(script.contains("navigator.clipboard.readText()"));
+        assert!(script.contains("setTimeout"));
+        assert!(script.contains("2000"));
+        assert!(script.contains("button[aria-label='Copy']"));
+        // The toolbar of several web UIs only exists after a hover.
+        assert!(script.contains("mouseover"));
+        // The button is searched from the answer node outwards, never from the
+        // whole page, so a previous answer's button is never clicked.
+        assert!(script.contains("node.compareDocumentPosition"));
+        assert!(script.contains("node.contains(candidate)"));
+    }
+
+    #[test]
+    fn the_html_script_returns_the_node_markup() {
+        let script = read_answer_html_script(&selectors(), 0);
+        assert!(script.contains("innerHTML"));
+        assert!(script.contains("nodes[0]"));
+        assert!(script.trim_end().ends_with("})()"));
+    }
+
+    #[test]
+    fn verification_uses_a_small_threshold() {
+        let script = verify_input_script(&selectors(), 400);
+        assert!(script.contains("len >= 8"));
+    }
+}
diff --git a/src/browser/mod.rs b/src/browser/mod.rs
new file mode 100644
index 0000000..7ee641f
--- /dev/null
+++ b/src/browser/mod.rs
@@ -0,0 +1,15 @@
+//! Browser automation: engine lifecycle, DOM helpers and session state.
+
+pub mod cdp;
+pub mod debug;
+pub mod dom;
+pub mod engine;
+pub mod js;
+pub mod pool;
+pub mod session;
+
+pub use cdp::{executable_hint, external_launch, resolve_executable, CdpEngine, ExternalLaunch};
+pub use debug::{CapturedArtifacts, DebugRecorder};
+pub use engine::{BrowserEngine, BrowserSettings, TabStats};
+pub use pool::{TabLease, TabPool};
+pub use session::{Session, SessionState, SessionStatus};
diff --git a/src/browser/pool.rs b/src/browser/pool.rs
new file mode 100644
index 0000000..fba2470
--- /dev/null
+++ b/src/browser/pool.rs
@@ -0,0 +1,237 @@
+//! Tab admission control.
+//!
+//! One provider account can run up to `max_tabs` turns at the same time. A turn
+//! leases a tab for its whole duration: the lease is returned to the pool when
+//! it is dropped, which is also what happens when a turn fails or its client
+//! disappears mid-generation. A request that cannot get a tab within the
+//! configured budget is rejected with 429 instead of queueing forever.
+
+use std::sync::{Arc, Mutex};
+use std::time::{Duration, Instant};
+
+use chromiumoxide::Page;
+use tokio::sync::{OwnedSemaphorePermit, Semaphore};
+
+use crate::error::{GatewayError, Result};
+
+/// Slots of one pool, shared with the leases handed out from it.
+#[derive(Debug)]
+struct Slots {
+    idle: Mutex<Vec<usize>>,
+}
+
+/// Bounded pool of browser tabs belonging to one provider account.
+#[derive(Debug, Clone)]
+pub struct TabPool {
+    owner: Arc<str>,
+    max_tabs: usize,
+    wait: Duration,
+    permits: Arc<Semaphore>,
+    slots: Arc<Slots>,
+}
+
+impl TabPool {
+    pub fn new(owner: impl Into<String>, max_tabs: usize, wait: Duration) -> Self {
+        let max_tabs = max_tabs.max(1);
+        Self {
+            owner: Arc::from(owner.into().as_str()),
+            max_tabs,
+            wait,
+            permits: Arc::new(Semaphore::new(max_tabs)),
+            slots: Arc::new(Slots {
+                idle: Mutex::new((0..max_tabs).collect()),
+            }),
+        }
+    }
+
+    pub fn max_tabs(&self) -> usize {
+        self.max_tabs
+    }
+
+    /// Number of tabs currently leased.
+    pub fn busy(&self) -> usize {
+        self.max_tabs - self.permits.available_permits()
+    }
+
+    /// Reserve a slot, waiting at most the configured budget.
+    pub async fn reserve(&self) -> Result<Reservation> {
+        self.reserve_within(self.wait).await
+    }
+
+    /// Reserve a slot, waiting at most `wait`.
+    ///
+    /// A status probe uses a much shorter budget than a turn: it must answer
+    /// quickly rather than queue behind a generation in progress.
+    pub async fn reserve_within(&self, wait: Duration) -> Result<Reservation> {
+        let started = Instant::now();
+        let permit = match tokio::time::timeout(wait, self.permits.clone().acquire_owned()).await {
+            Ok(Ok(permit)) => permit,
+            Ok(Err(_)) => return Err(GatewayError::internal("the tab pool is closed")),
+            Err(_) => {
+                return Err(GatewayError::ProviderBusy {
+                    provider: self.owner.to_string(),
+                    waited_ms: started.elapsed().as_millis() as u64,
+                })
+            }
+        };
+
+        // Holding a permit guarantees that a slot is free: a slot is out of the
+        // idle list exactly while its permit is held.
+        let slot = self
+            .slots
+            .idle
+            .lock()
+            .map_err(|_| GatewayError::internal("the tab pool is poisoned"))?
+            .pop()
+            .ok_or_else(|| GatewayError::internal("the tab pool lost a slot"))?;
+
+        Ok(Reservation {
+            slot,
+            pool: self.clone(),
+            permit: Some(permit),
+        })
+    }
+
+    fn return_slot(&self, slot: usize) {
+        match self.slots.idle.lock() {
+            Ok(mut idle) => idle.push(slot),
+            Err(err) => tracing::warn!(error = %err, "cannot return a tab slot to the pool"),
+        }
+    }
+}
+
+/// A reserved slot, not bound to a page yet.
+///
+/// Creating the page can fail, so an unconsumed reservation gives its slot back
+/// on drop rather than leaking it for the life of the process.
+#[derive(Debug)]
+pub struct Reservation {
+    slot: usize,
+    pool: TabPool,
+    permit: Option<OwnedSemaphorePermit>,
+}
+
+impl Reservation {
+    pub fn slot(&self) -> usize {
+        self.slot
+    }
+
+    /// Bind the reservation to the page created for it.
+    pub fn into_lease(mut self, page: Page) -> TabLease {
+        let permit = self
+            .permit
+            .take()
+            .expect("a reservation is consumed at most once");
+        TabLease {
+            page,
+            slot: self.slot,
+            pool: self.pool.clone(),
+            _permit: permit,
+        }
+    }
+}
+
+impl Drop for Reservation {
+    fn drop(&mut self) {
+        // Only when the reservation was never turned into a lease: the permit
+        // is released after the slot is back in the list.
+        if self.permit.is_some() {
+            self.pool.return_slot(self.slot);
+        }
+    }
+}
+
+/// One browser tab, leased for the duration of a turn.
+pub struct TabLease {
+    page: Page,
+    slot: usize,
+    pool: TabPool,
+    _permit: OwnedSemaphorePermit,
+}
+
+impl TabLease {
+    pub fn page(&self) -> &Page {
+        &self.page
+    }
+
+    pub fn slot(&self) -> usize {
+        self.slot
+    }
+}
+
+impl std::fmt::Debug for TabLease {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("TabLease")
+            .field("slot", &self.slot)
+            .field("max_tabs", &self.pool.max_tabs())
+            .finish()
+    }
+}
+
+impl Drop for TabLease {
+    fn drop(&mut self) {
+        // The slot goes back before the permit is released, so a waiter that
+        // grabs the permit always finds a slot in the idle list.
+        self.pool.return_slot(self.slot);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn a_second_request_waits_then_times_out() {
+        let pool = TabPool::new("chatgpt", 1, Duration::from_millis(120));
+        let held = pool.reserve().await.unwrap();
+        assert_eq!(pool.busy(), 1);
+
+        let err = pool.reserve().await.unwrap_err();
+        assert_eq!(err.http_status(), 429);
+        assert_eq!(err.code(), "provider_busy");
+
+        drop(held);
+        assert_eq!(pool.busy(), 0);
+        assert!(pool.reserve().await.is_ok());
+    }
+
+    #[tokio::test]
+    async fn parallel_tabs_are_allowed_up_to_the_limit() {
+        let pool = TabPool::new("chatgpt", 3, Duration::from_millis(50));
+        let a = pool.reserve().await.unwrap();
+        let b = pool.reserve().await.unwrap();
+        let c = pool.reserve().await.unwrap();
+        assert_eq!(pool.busy(), 3);
+        assert!(pool.reserve().await.is_err());
+
+        // Every reservation got a distinct slot.
+        let mut slots = vec![a.slot(), b.slot(), c.slot()];
+        slots.sort_unstable();
+        assert_eq!(slots, vec![0, 1, 2]);
+
+        drop(b);
+        assert_eq!(pool.busy(), 2);
+        let d = pool.reserve().await.unwrap();
+        assert_eq!(d.slot(), 1);
+    }
+
+    #[tokio::test]
+    async fn a_dropped_reservation_returns_its_slot() {
+        let pool = TabPool::new("chatgpt", 2, Duration::from_millis(10));
+        {
+            let _reserved = pool.reserve().await.unwrap();
+            assert_eq!(pool.busy(), 1);
+        }
+        // Creating the page failed: the slot must not be lost forever.
+        assert_eq!(pool.busy(), 0);
+        let a = pool.reserve().await.unwrap();
+        let b = pool.reserve().await.unwrap();
+        assert_ne!(a.slot(), b.slot());
+    }
+
+    #[test]
+    fn a_zero_tab_pool_still_serves_one_request() {
+        let pool = TabPool::new("chatgpt", 0, Duration::from_millis(10));
+        assert_eq!(pool.max_tabs(), 1);
+    }
+}
diff --git a/src/browser/session.rs b/src/browser/session.rs
new file mode 100644
index 0000000..7980834
--- /dev/null
+++ b/src/browser/session.rs
@@ -0,0 +1,453 @@
+//! A provider browser session: the reusable tab plus its observed state.
+
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use chromiumoxide::Page;
+use serde::{Deserialize, Serialize};
+use tokio::sync::RwLock;
+
+use crate::error::{GatewayError, Result};
+use crate::providers::config::ProviderConfig;
+use crate::util;
+
+use super::dom;
+use super::engine::BrowserEngine;
+use super::js::{self, ProbeResult};
+use super::pool::TabLease;
+
+/// Coarse state of a provider session.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum SessionState {
+    Available,
+    RequiresLogin,
+    Captcha,
+    Busy,
+    Misconfigured,
+    Error,
+}
+
+impl SessionState {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Available => "available",
+            Self::RequiresLogin => "requires_login",
+            Self::Captcha => "captcha",
+            Self::Busy => "busy",
+            Self::Misconfigured => "misconfigured",
+            Self::Error => "error",
+        }
+    }
+}
+
+/// Detailed status returned by the status and validate endpoints.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SessionStatus {
+    pub provider: String,
+    pub state: SessionState,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub detail: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub url: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub browser: Option<String>,
+    pub checked_at: u64,
+}
+
+impl SessionStatus {
+    fn build(
+        provider: &str,
+        state: SessionState,
+        detail: Option<String>,
+        url: Option<String>,
+    ) -> Self {
+        Self {
+            provider: provider.to_string(),
+            state,
+            detail,
+            url,
+            browser: None,
+            checked_at: util::now_secs(),
+        }
+    }
+
+    pub fn available(provider: &str, url: Option<String>) -> Self {
+        Self::build(provider, SessionState::Available, None, url)
+    }
+
+    pub fn requires_login(provider: &str, detail: impl Into<String>, url: Option<String>) -> Self {
+        Self::build(
+            provider,
+            SessionState::RequiresLogin,
+            Some(detail.into()),
+            url,
+        )
+    }
+
+    pub fn captcha(provider: &str, url: Option<String>) -> Self {
+        Self::build(
+            provider,
+            SessionState::Captcha,
+            Some("captcha challenge displayed".into()),
+            url,
+        )
+    }
+
+    pub fn error(provider: &str, detail: impl Into<String>) -> Self {
+        Self::build(provider, SessionState::Error, Some(detail.into()), None)
+    }
+
+    pub fn misconfigured(provider: &str, detail: impl Into<String>) -> Self {
+        Self::build(
+            provider,
+            SessionState::Misconfigured,
+            Some(detail.into()),
+            None,
+        )
+    }
+
+    pub fn busy(provider: &str) -> Self {
+        Self::build(provider, SessionState::Busy, None, None)
+    }
+
+    pub fn with_browser(mut self, browser: &str) -> Self {
+        self.browser = Some(browser.to_string());
+        self
+    }
+
+    pub fn is_available(&self) -> bool {
+        self.state == SessionState::Available
+    }
+
+    /// Translate the status into the error a client should receive.
+    pub fn as_error(&self) -> GatewayError {
+        match self.state {
+            SessionState::Available => GatewayError::internal("session is available"),
+            SessionState::RequiresLogin => GatewayError::RequiresLogin {
+                provider: self.provider.clone(),
+            },
+            SessionState::Captcha => GatewayError::Captcha {
+                provider: self.provider.clone(),
+            },
+            SessionState::Busy => GatewayError::ProviderBusy {
+                provider: self.provider.clone(),
+                waited_ms: 0,
+            },
+            SessionState::Misconfigured => GatewayError::ProviderMisconfigured {
+                provider: self.provider.clone(),
+                detail: self.detail.clone().unwrap_or_default(),
+            },
+            SessionState::Error => GatewayError::UpstreamError {
+                provider: self.provider.clone(),
+                message: self
+                    .detail
+                    .clone()
+                    .unwrap_or_else(|| "unknown error".into()),
+            },
+        }
+    }
+}
+
+/// A live page bound to one provider account. Cheap to clone: every field is
+/// shared, and the tab is released only when the last clone goes away.
+#[derive(Clone)]
+pub struct Session {
+    provider: Arc<str>,
+    account: Option<Arc<str>>,
+    browser: Arc<str>,
+    engine: Arc<dyn BrowserEngine>,
+    lease: Arc<TabLease>,
+    web_url: Arc<RwLock<Option<String>>>,
+}
+
+impl std::fmt::Debug for Session {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Session")
+            .field("provider", &self.provider)
+            .field("account", &self.account)
+            .field("browser", &self.browser)
+            .field("tab_slot", &self.lease.slot())
+            .finish()
+    }
+}
+
+impl Session {
+    /// Bind a leased tab to its provider account.
+    pub fn new(
+        provider: impl Into<String>,
+        browser: impl Into<String>,
+        engine: Arc<dyn BrowserEngine>,
+        lease: TabLease,
+    ) -> Self {
+        let account = engine
+            .settings()
+            .account
+            .as_deref()
+            .filter(|value| !value.is_empty())
+            .map(Arc::<str>::from);
+        Self {
+            provider: Arc::from(provider.into().as_str()),
+            account,
+            browser: Arc::from(browser.into().as_str()),
+            engine,
+            lease: Arc::new(lease),
+            web_url: Arc::new(RwLock::new(None)),
+        }
+    }
+
+    /// Shared page handle, for spawning a turn into its own task.
+    pub fn page_handle(&self) -> Arc<Page> {
+        Arc::new(self.lease.page().clone())
+    }
+
+    pub fn provider(&self) -> &str {
+        &self.provider
+    }
+
+    /// Account of this session, when the provider declares several.
+    pub fn account(&self) -> Option<&str> {
+        self.account.as_deref()
+    }
+
+    /// Provider and account, as used in logs and error messages.
+    pub fn owner(&self) -> String {
+        match self.account() {
+            Some(account) => format!("{}@{account}", self.provider),
+            None => self.provider.to_string(),
+        }
+    }
+
+    pub fn browser(&self) -> &str {
+        &self.browser
+    }
+
+    pub fn page(&self) -> &Page {
+        self.lease.page()
+    }
+
+    /// Slot of the tab pool this session holds, for diagnostics.
+    pub fn tab_slot(&self) -> usize {
+        self.lease.slot()
+    }
+
+    /// Engine that owns the browser of this session.
+    pub fn engine(&self) -> &Arc<dyn BrowserEngine> {
+        &self.engine
+    }
+
+    /// Allow the page to read and write the clipboard.
+    ///
+    /// The gateway reads the provider's own Markdown through the clipboard, and
+    /// Chrome only allows that when the permission was granted over CDP (the
+    /// page cannot show a permission prompt during automation).
+    pub async fn grant_clipboard_access(&self) -> Result<()> {
+        for name in ["clipboard-read", "clipboard-write"] {
+            if let Err(err) = self.engine.grant_permission(name).await {
+                tracing::debug!(permission = name, error = %err, "cannot grant a clipboard permission");
+            }
+        }
+        Ok(())
+    }
+
+    /// URL of the web conversation currently bound to this session.
+    pub async fn web_url(&self) -> Option<String> {
+        self.web_url.read().await.clone()
+    }
+
+    pub async fn set_web_url(&self, url: Option<String>) {
+        let mut guard = self.web_url.write().await;
+        *guard = url;
+    }
+
+    /// Read the page state with a bounded timeout.
+    pub async fn probe(&self, cfg: &ProviderConfig, timeout: Duration) -> Result<ProbeResult> {
+        let script = js::probe_script(cfg.selectors());
+        match tokio::time::timeout(
+            timeout,
+            dom::evaluate_json::<ProbeResult>(self.page(), &script),
+        )
+        .await
+        {
+            Ok(result) => result,
+            Err(_) => Err(GatewayError::CaptureTimeout {
+                stage: "probing the provider page".into(),
+                timeout_s: timeout.as_secs(),
+            }),
+        }
+    }
+
+    /// Probe the page until it shows something meaningful, or the budget runs out.
+    ///
+    /// A page that is still hydrating looks empty, and classifying it too early
+    /// reports a missing selector on a perfectly healthy provider.
+    pub async fn settled_probe(
+        &self,
+        cfg: &ProviderConfig,
+        budget: Duration,
+    ) -> Result<ProbeResult> {
+        let deadline = Instant::now() + budget;
+        let mut probe = self.probe(cfg, budget).await?;
+        while Instant::now() < deadline {
+            if page_is_meaningful(cfg, &probe) {
+                break;
+            }
+            tokio::time::sleep(Duration::from_millis(250)).await;
+            probe = self.probe(cfg, budget).await?;
+        }
+        Ok(probe)
+    }
+
+    /// Classify the current page into a status.
+    pub async fn status(&self, cfg: &ProviderConfig, timeout: Duration) -> SessionStatus {
+        if !cfg.is_usable() {
+            return SessionStatus::misconfigured(cfg.name(), cfg.problems.join("; "))
+                .with_browser(&self.browser);
+        }
+        match self.settled_probe(cfg, timeout).await {
+            Ok(probe) => classify(cfg, &probe, &self.browser),
+            Err(err) => {
+                SessionStatus::error(cfg.name(), err.to_string()).with_browser(&self.browser)
+            }
+        }
+    }
+}
+
+/// True when the probe says something usable about the page: the chat editor,
+/// a challenge, or a sign-in screen. An empty shell means "still loading".
+pub fn page_is_meaningful(cfg: &ProviderConfig, probe: &ProbeResult) -> bool {
+    probe.has_input
+        || probe.has_captcha
+        || cfg.is_signed_out_page(
+            &probe.url,
+            &probe.body_text,
+            probe.has_login,
+            probe.has_input,
+        )
+}
+
+/// Turn a page probe into a status.
+pub fn classify(cfg: &ProviderConfig, probe: &ProbeResult, browser: &str) -> SessionStatus {
+    let provider = cfg.name();
+    let url = if probe.url.is_empty() {
+        None
+    } else {
+        Some(probe.url.clone())
+    };
+
+    let status = if !cfg.is_usable() {
+        SessionStatus::misconfigured(provider, cfg.problems.join("; "))
+    } else if probe.has_captcha {
+        SessionStatus::captcha(provider, url.clone())
+    } else if cfg.is_signed_out_page(
+        &probe.url,
+        &probe.body_text,
+        probe.has_login,
+        probe.has_input,
+    ) {
+        SessionStatus::requires_login(
+            provider,
+            format!(
+                "not signed in: run 'llm-gateway login {provider} --manual', sign in inside the \
+                 window it opens, then close that window"
+            ),
+            url.clone(),
+        )
+    } else if !probe.has_input {
+        SessionStatus::error(
+            provider,
+            format!(
+                "prompt field not found on {} (selectors.input_field = {})",
+                if probe.url.is_empty() {
+                    "an unknown page"
+                } else {
+                    probe.url.as_str()
+                },
+                cfg.selectors().input_field
+            ),
+        )
+    } else {
+        SessionStatus::available(provider, url.clone())
+    };
+
+    status.with_browser(browser)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::providers::config::ProviderConfig;
+
+    const CHATGPT: &str = include_str!("../../providers/chatgpt.toml");
+
+    fn cfg() -> ProviderConfig {
+        ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap()
+    }
+
+    fn probe(url: &str) -> ProbeResult {
+        ProbeResult {
+            url: url.to_string(),
+            has_input: true,
+            has_send: true,
+            ..Default::default()
+        }
+    }
+
+    #[test]
+    fn a_ready_page_is_available() {
+        let status = classify(&cfg(), &probe("https://chatgpt.com/"), "chromium-cdp");
+        assert_eq!(status.state, SessionState::Available);
+        assert!(status.is_available());
+        assert_eq!(status.browser.as_deref(), Some("chromium-cdp"));
+    }
+
+    #[test]
+    fn login_pages_are_detected_by_url_or_marker() {
+        let by_url = classify(&cfg(), &probe("https://chatgpt.com/auth/login"), "cdp");
+        assert_eq!(by_url.state, SessionState::RequiresLogin);
+        assert_eq!(by_url.as_error().code(), "requires_login");
+
+        let mut markup = probe("https://chatgpt.com/");
+        markup.has_login = true;
+        assert_eq!(
+            classify(&cfg(), &markup, "cdp").state,
+            SessionState::RequiresLogin
+        );
+    }
+
+    #[test]
+    fn captcha_wins_over_everything() {
+        let mut markup = probe("https://chatgpt.com/");
+        markup.has_captcha = true;
+        markup.has_login = true;
+        let status = classify(&cfg(), &markup, "cdp");
+        assert_eq!(status.state, SessionState::Captcha);
+        assert_eq!(status.as_error().http_status(), 403);
+    }
+
+    #[test]
+    fn the_real_signed_out_landing_page_is_reported_as_a_login_page() {
+        // Markup captured from chatgpt.com while signed out: no prompt field,
+        // "Log in" / "Sign up" buttons, no login URL.
+        let mut landing = probe("https://chatgpt.com/");
+        landing.has_input = false;
+        landing.body_text = "chatgpt: chat, work, create & code with ai log in sign up".to_string();
+        let status = classify(&cfg(), &landing, "cdp");
+        assert_eq!(status.state, SessionState::RequiresLogin);
+        assert!(status.detail.as_deref().unwrap().contains("--manual"));
+        assert!(page_is_meaningful(&cfg(), &landing));
+    }
+
+    #[test]
+    fn a_missing_input_field_is_reported_with_the_selector() {
+        let mut markup = probe("https://chatgpt.com/");
+        markup.has_input = false;
+        let status = classify(&cfg(), &markup, "cdp");
+        assert_eq!(status.state, SessionState::Error);
+        assert!(status
+            .detail
+            .as_deref()
+            .unwrap()
+            .contains("prompt-textarea"));
+    }
+}
diff --git a/src/cli.rs b/src/cli.rs
new file mode 100644
index 0000000..0d317fc
--- /dev/null
+++ b/src/cli.rs
@@ -0,0 +1,380 @@
+//! Command line interface definition.
+
+use std::path::PathBuf;
+
+use clap::{Args, Parser, Subcommand};
+
+/// OpenAI-compatible gateway driving a real browser session on LLM web UIs.
+#[derive(Debug, Parser)]
+#[command(
+    name = "llm-gateway",
+    version = crate::VERSION,
+    about = "Expose an OpenAI-compatible API backed by an authenticated browser session",
+    long_about = None,
+    propagate_version = true
+)]
+pub struct Cli {
+    #[command(flatten)]
+    pub global: GlobalArgs,
+
+    #[command(subcommand)]
+    pub command: Option<Command>,
+}
+
+/// Flags accepted by every subcommand.
+#[derive(Debug, Clone, Args, Default)]
+pub struct GlobalArgs {
+    /// Address to bind (default 127.0.0.1).
+    #[arg(long, global = true, env = "LLM_GATEWAY_HOST", value_name = "HOST")]
+    pub host: Option<String>,
+
+    /// Port of the API server (default 8080).
+    #[arg(
+        long,
+        short,
+        global = true,
+        env = "LLM_GATEWAY_PORT",
+        value_name = "PORT"
+    )]
+    pub port: Option<u16>,
+
+    /// Browser family: chrome, chromium, edge, brave.
+    #[arg(long, global = true, value_name = "NAME")]
+    pub browser: Option<String>,
+
+    /// Explicit path to the browser executable.
+    #[arg(long, global = true, value_name = "PATH")]
+    pub browser_path: Option<PathBuf>,
+
+    /// Root directory of the persistent browser profiles.
+    #[arg(long, global = true, value_name = "PATH")]
+    pub profile_dir: Option<PathBuf>,
+
+    /// Restrict the server to a single provider.
+    #[arg(long, global = true, value_name = "NAME")]
+    pub provider: Option<String>,
+
+    /// Run the browser without a window (no manual login possible).
+    #[arg(long, global = true)]
+    pub headless: bool,
+
+    /// Attach to a browser you started instead of launching one.
+    #[arg(long, global = true)]
+    pub attach: bool,
+
+    /// Debug port of the browser to attach to.
+    #[arg(long, global = true, value_name = "PORT")]
+    pub debug_port: Option<u16>,
+
+    /// Automation hiding: off (default), minimal or aggressive.
+    #[arg(long, global = true, value_name = "MODE")]
+    pub stealth: Option<String>,
+
+    /// Log level: trace, debug, info, warn, error.
+    #[arg(long, global = true, env = "LLM_GATEWAY_LOG", value_name = "LEVEL")]
+    pub log_level: Option<String>,
+
+    /// Log format: pretty or json.
+    #[arg(long, global = true, value_name = "FORMAT")]
+    pub log_format: Option<String>,
+
+    /// Configuration file (default <state dir>/config.toml).
+    #[arg(long, global = true, env = "LLM_GATEWAY_CONFIG", value_name = "PATH")]
+    pub config: Option<PathBuf>,
+
+    /// Save screenshots and DOM dumps for every request.
+    #[arg(long, global = true)]
+    pub debug: bool,
+
+    /// Maximum number of tabs per provider.
+    #[arg(long, global = true, value_name = "N")]
+    pub max_tabs: Option<usize>,
+
+    /// Require this bearer token from API clients.
+    #[arg(long, global = true, value_name = "TOKEN")]
+    pub api_key: Option<String>,
+
+    /// Fidelity of the captured answer: auto, clipboard, dom or text.
+    #[arg(long, global = true, value_name = "MODE")]
+    pub markdown: Option<String>,
+
+    /// Skip the confirmation prompts.
+    #[arg(long, short = 'y', global = true)]
+    pub yes: bool,
+}
+
+#[derive(Debug, Subcommand)]
+pub enum Command {
+    /// Start the OpenAI-compatible API server.
+    Serve(ServeArgs),
+    /// Send a prompt to a provider and print the captured answer.
+    Test(TestArgs),
+    /// Check that the configured selectors and the session still work.
+    Selftest(SelftestArgs),
+    /// List the configured providers.
+    List(ListArgs),
+    /// Open a browser window to sign in to a provider.
+    Login(LoginArgs),
+    /// Delete the persistent browser profile of a provider.
+    Logout(LogoutArgs),
+    /// Inspect or clear the persisted conversations.
+    Conversations(ConversationsArgs),
+    /// Ask a running server to reload its configuration.
+    Reload,
+    /// Configuration helpers.
+    Config(ConfigArgs),
+}
+
+#[derive(Debug, Args)]
+pub struct ServeArgs {
+    /// Provider backend: browser (default) or mock (no browser at all).
+    #[arg(long, value_name = "KIND", default_value = "browser")]
+    pub backend: String,
+}
+
+#[derive(Debug, Args)]
+pub struct TestArgs {
+    /// Provider to test, optionally one of its accounts: `chatgpt@perso`.
+    pub provider: Option<String>,
+    /// Test every configured provider.
+    #[arg(long)]
+    pub all: bool,
+    /// Prompt to send.
+    #[arg(long, value_name = "TEXT")]
+    pub prompt: Option<String>,
+    /// Print the result as JSON.
+    #[arg(long)]
+    pub json: bool,
+}
+
+#[derive(Debug, Args)]
+pub struct SelftestArgs {
+    /// Provider to check, optionally one of its accounts.
+    pub provider: Option<String>,
+    /// Check every configured provider.
+    #[arg(long)]
+    pub all: bool,
+    /// Print the report as JSON.
+    #[arg(long)]
+    pub json: bool,
+}
+
+#[derive(Debug, Args)]
+pub struct ListArgs {
+    /// Print the provider list as JSON.
+    #[arg(long)]
+    pub json: bool,
+}
+
+#[derive(Debug, Args)]
+pub struct LoginArgs {
+    /// Provider name, optionally followed by the account: `chatgpt@perso`.
+    pub provider: String,
+
+    /// Account to sign in, when the provider declares several.
+    #[arg(long, value_name = "ID")]
+    pub account: Option<String>,
+
+    /// Print how to sign in from a browser you start yourself.
+    ///
+    /// This is the configuration OAuth providers such as Google accept, since
+    /// no automation flag and no debugging port is involved.
+    #[arg(long)]
+    pub manual: bool,
+
+    /// Start the printed command for you.
+    #[arg(long, requires = "manual")]
+    pub launch: bool,
+}
+
+#[derive(Debug, Args)]
+pub struct LogoutArgs {
+    /// Provider to forget, optionally followed by the account.
+    pub provider: Option<String>,
+    /// Account to forget, when the provider declares several.
+    #[arg(long, value_name = "ID")]
+    pub account: Option<String>,
+    /// Forget every provider, or every account of the named one.
+    #[arg(long)]
+    pub all: bool,
+}
+
+#[derive(Debug, Args)]
+pub struct ConversationsArgs {
+    #[command(subcommand)]
+    pub command: ConversationsCommand,
+}
+
+#[derive(Debug, Subcommand)]
+pub enum ConversationsCommand {
+    /// List the stored conversations.
+    List {
+        /// Provider to filter on, optionally with its account: chatgpt@perso.
+        #[arg(long, value_name = "NAME")]
+        provider: Option<String>,
+        /// Account to filter on; "default" selects the threads of a provider
+        /// that declares no account.
+        #[arg(long, value_name = "ID")]
+        account: Option<String>,
+        #[arg(long)]
+        json: bool,
+    },
+    /// Remove stored conversations.
+    Clear {
+        /// Provider to filter on, optionally with its account: chatgpt@perso.
+        #[arg(long, value_name = "NAME")]
+        provider: Option<String>,
+        /// Account to filter on; "default" selects the threads of a provider
+        /// that declares no account.
+        #[arg(long, value_name = "ID")]
+        account: Option<String>,
+    },
+}
+
+#[derive(Debug, Args)]
+pub struct ConfigArgs {
+    #[command(subcommand)]
+    pub command: ConfigCommand,
+}
+
+#[derive(Debug, Subcommand)]
+pub enum ConfigCommand {
+    /// Print the configuration file path.
+    Path,
+    /// Create the state directory and the default files.
+    Init {
+        /// Overwrite the installed provider files with the shipped defaults.
+        ///
+        /// The previous file is kept as <provider>.toml.bak. Use it after an
+        /// upgrade to pick up refreshed selectors.
+        #[arg(long)]
+        force: bool,
+    },
+    /// Print the effective configuration.
+    Show,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn global_flags_are_accepted_before_and_after_the_subcommand() {
+        let cli = Cli::try_parse_from(["llm-gateway", "--port", "9000", "list"]).unwrap();
+        assert_eq!(cli.global.port, Some(9000));
+        assert!(matches!(cli.command, Some(Command::List(_))));
+
+        let cli = Cli::try_parse_from(["llm-gateway", "list", "--port", "9001"]).unwrap();
+        assert_eq!(cli.global.port, Some(9001));
+    }
+
+    #[test]
+    fn serve_defaults_to_the_browser_backend() {
+        let cli = Cli::try_parse_from(["llm-gateway", "serve"]).unwrap();
+        match cli.command {
+            Some(Command::Serve(args)) => assert_eq!(args.backend, "browser"),
+            other => panic!("unexpected command: {other:?}"),
+        }
+    }
+
+    #[test]
+    fn login_accepts_the_manual_flags() {
+        let cli = Cli::try_parse_from(["llm-gateway", "login", "chatgpt", "--manual", "--launch"])
+            .unwrap();
+        match cli.command {
+            Some(Command::Login(args)) => {
+                assert_eq!(args.provider, "chatgpt");
+                assert!(args.manual);
+                assert!(args.launch);
+            }
+            other => panic!("unexpected: {other:?}"),
+        }
+        assert!(Cli::try_parse_from(["llm-gateway", "login", "chatgpt", "--launch"]).is_err());
+    }
+
+    #[test]
+    fn accounts_can_be_named_on_login_and_logout() {
+        let cli =
+            Cli::try_parse_from(["llm-gateway", "login", "chatgpt", "--account", "perso"]).unwrap();
+        match cli.command {
+            Some(Command::Login(args)) => assert_eq!(args.account.as_deref(), Some("perso")),
+            other => panic!("unexpected: {other:?}"),
+        }
+
+        // The account may also ride along with the provider name.
+        let cli = Cli::try_parse_from(["llm-gateway", "logout", "chatgpt@perso"]).unwrap();
+        match cli.command {
+            Some(Command::Logout(args)) => {
+                assert_eq!(args.provider.as_deref(), Some("chatgpt@perso"));
+                assert_eq!(args.account, None);
+            }
+            other => panic!("unexpected: {other:?}"),
+        }
+    }
+
+    #[test]
+    fn the_markdown_mode_is_a_global_flag() {
+        let cli = Cli::try_parse_from(["llm-gateway", "serve", "--markdown", "clipboard"]).unwrap();
+        assert_eq!(cli.global.markdown.as_deref(), Some("clipboard"));
+    }
+
+    #[test]
+    fn attach_flags_are_global() {
+        let cli = Cli::try_parse_from(["llm-gateway", "serve", "--attach", "--debug-port", "9333"])
+            .unwrap();
+        assert!(cli.global.attach);
+        assert_eq!(cli.global.debug_port, Some(9333));
+    }
+
+    #[test]
+    fn conversations_has_nested_subcommands() {
+        let cli = Cli::try_parse_from(["llm-gateway", "conversations", "clear", "--provider", "x"])
+            .unwrap();
+        match cli.command {
+            Some(Command::Conversations(args)) => match args.command {
+                ConversationsCommand::Clear { provider, account } => {
+                    assert_eq!(provider.as_deref(), Some("x"));
+                    assert_eq!(account, None);
+                }
+                other => panic!("unexpected: {other:?}"),
+            },
+            other => panic!("unexpected: {other:?}"),
+        }
+    }
+
+    #[test]
+    fn conversations_can_be_filtered_by_account() {
+        let cli = Cli::try_parse_from([
+            "llm-gateway",
+            "conversations",
+            "list",
+            "--provider",
+            "chatgpt",
+            "--account",
+            "perso",
+            "--json",
+        ])
+        .unwrap();
+        match cli.command {
+            Some(Command::Conversations(args)) => match args.command {
+                ConversationsCommand::List {
+                    provider,
+                    account,
+                    json,
+                } => {
+                    assert_eq!(provider.as_deref(), Some("chatgpt"));
+                    assert_eq!(account.as_deref(), Some("perso"));
+                    assert!(json);
+                }
+                other => panic!("unexpected: {other:?}"),
+            },
+            other => panic!("unexpected: {other:?}"),
+        }
+    }
+
+    #[test]
+    fn no_subcommand_means_serve() {
+        let cli = Cli::try_parse_from(["llm-gateway"]).unwrap();
+        assert!(cli.command.is_none());
+    }
+}
diff --git a/src/config.rs b/src/config.rs
new file mode 100644
index 0000000..8284217
--- /dev/null
+++ b/src/config.rs
@@ -0,0 +1,562 @@
+//! Global configuration: TOML file, defaults and CLI overrides.
+
+use std::path::{Path, PathBuf};
+
+use serde::{Deserialize, Serialize};
+
+use crate::error::{GatewayError, Result};
+use crate::paths::{self, Layout};
+
+/// When to save screenshots and DOM dumps for debugging.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize, Serialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum ScreenshotMode {
+    Never,
+    #[default]
+    OnError,
+    Always,
+}
+
+/// How a thread is continued on the provider web UI.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize, Serialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum ConversationStrategy {
+    #[default]
+    Auto,
+    Reuse,
+    Replay,
+}
+
+/// Where the client conversation id comes from.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize, Serialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum ConversationIdSource {
+    #[default]
+    Fingerprint,
+    Header,
+    Uuid,
+}
+
+/// How much the browser hides the fact that it is automated.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize, Serialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum StealthMode {
+    /// Leave the page alone. Chromium is launched with a switch that already
+    /// hides navigator.webdriver and the user agent stays genuine, which is
+    /// what sign-in providers such as Google expect.
+    #[default]
+    Off,
+    /// Also patch navigator.webdriver from an injected script.
+    Minimal,
+    /// Full chromiumoxide stealth, including a spoofed user agent.
+    ///
+    /// Warning: it advertises an outdated Chrome version, which is itself a
+    /// bot signal and makes OAuth providers refuse the sign-in.
+    Aggressive,
+}
+
+impl StealthMode {
+    /// Parse the --stealth flag.
+    pub fn parse(raw: &str) -> Result<Self> {
+        match raw.trim().to_lowercase().as_str() {
+            "off" | "none" => Ok(Self::Off),
+            "minimal" | "light" => Ok(Self::Minimal),
+            "aggressive" | "full" => Ok(Self::Aggressive),
+            other => Err(GatewayError::Config(format!(
+                "unknown stealth mode '{other}', expected off, minimal or aggressive"
+            ))),
+        }
+    }
+}
+
+/// How the prompt text is pushed into the web editor.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize, Serialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum InjectMethod {
+    #[default]
+    Auto,
+    InsertText,
+    ExecCommand,
+    TypeStr,
+}
+
+/// Where the final answer text comes from.
+///
+/// A web UI renders its answer as rich HTML, and `innerText` flattens it: code
+/// fences, tables and lists all collapse into plain text. The fidelity pass
+/// runs once, when the answer has settled, and this setting decides how.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize, Serialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum MarkdownMode {
+    /// Clipboard when the provider has a copy button, otherwise the DOM.
+    #[default]
+    Auto,
+    /// Always click the provider copy button and read the clipboard over CDP.
+    /// Falls back to the DOM when the clipboard cannot be read.
+    Clipboard,
+    /// Always convert the answer node's HTML to Markdown.
+    Dom,
+    /// Keep the historical behaviour: the visible text, formatting flattened.
+    Text,
+}
+
+impl MarkdownMode {
+    /// Parse the --markdown flag.
+    pub fn parse(raw: &str) -> Result<Self> {
+        match raw.trim().to_lowercase().as_str() {
+            "auto" => Ok(Self::Auto),
+            "clipboard" | "copy" => Ok(Self::Clipboard),
+            "dom" | "html" => Ok(Self::Dom),
+            "text" | "plain" | "off" => Ok(Self::Text),
+            other => Err(GatewayError::Config(format!(
+                "unknown markdown mode '{other}', expected auto, clipboard, dom or text"
+            ))),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct ServerSection {
+    pub host: String,
+    pub port: u16,
+    pub api_key: String,
+    pub include_warnings: bool,
+    pub request_body_limit: usize,
+}
+
+impl Default for ServerSection {
+    fn default() -> Self {
+        Self {
+            host: "127.0.0.1".to_string(),
+            port: 8080,
+            api_key: String::new(),
+            include_warnings: true,
+            request_body_limit: 32 * 1024 * 1024,
+        }
+    }
+}
+
+impl ServerSection {
+    /// True when the server is reachable from another host.
+    pub fn is_public_bind(&self) -> bool {
+        let host = self.host.trim();
+        !(host == "127.0.0.1" || host == "localhost" || host == "::1")
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct BrowserSection {
+    pub executable: String,
+    pub headless: bool,
+    pub profile_dir: String,
+    /// Concurrent turns allowed per provider account, i.e. tabs kept open.
+    pub max_tabs: usize,
+    /// How long a request waits for a free tab before it is refused with 429.
+    pub busy_wait_s: u64,
+    pub launch_timeout_s: u64,
+    pub request_timeout_s: u64,
+    pub extra_args: Vec<String>,
+    pub stealth: StealthMode,
+    /// Attach to a browser the user started instead of launching one.
+    pub attach: bool,
+    /// Debug port of that browser.
+    pub debug_port: u16,
+}
+
+impl Default for BrowserSection {
+    fn default() -> Self {
+        Self {
+            executable: String::new(),
+            headless: false,
+            profile_dir: String::new(),
+            max_tabs: 1,
+            busy_wait_s: 30,
+            launch_timeout_s: 60,
+            request_timeout_s: 60,
+            extra_args: vec![
+                "--disable-blink-features=AutomationControlled".to_string(),
+                "--no-first-run".to_string(),
+                "--no-default-browser-check".to_string(),
+            ],
+            stealth: StealthMode::Off,
+            attach: false,
+            debug_port: 9222,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct ConversationSection {
+    pub store: String,
+    pub strategy: ConversationStrategy,
+    pub id_source: ConversationIdSource,
+}
+
+impl Default for ConversationSection {
+    fn default() -> Self {
+        Self {
+            store: String::new(),
+            strategy: ConversationStrategy::Auto,
+            id_source: ConversationIdSource::Fingerprint,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct CaptureSection {
+    pub poll_interval_ms: u64,
+    pub quiet_ms: u64,
+    pub response_timeout_s: u64,
+    pub inject_method: InjectMethod,
+    /// Fidelity of the captured answer (see `MarkdownMode`).
+    pub markdown: MarkdownMode,
+    /// How long the clipboard read is given before the DOM conversion wins.
+    pub clipboard_timeout_ms: u64,
+    /// Upper bound accepted for the OpenAI `n` parameter.
+    pub max_variants: u32,
+}
+
+impl Default for CaptureSection {
+    fn default() -> Self {
+        Self {
+            poll_interval_ms: 400,
+            quiet_ms: 1500,
+            response_timeout_s: 180,
+            inject_method: InjectMethod::Auto,
+            markdown: MarkdownMode::Auto,
+            clipboard_timeout_ms: 1500,
+            max_variants: 4,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct TokensSection {
+    pub encoding: String,
+    pub fallback_heuristic: bool,
+}
+
+impl Default for TokensSection {
+    fn default() -> Self {
+        Self {
+            encoding: "o200k_base".to_string(),
+            fallback_heuristic: true,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct DebugSection {
+    pub screenshots: ScreenshotMode,
+    pub dir: String,
+}
+
+impl Default for DebugSection {
+    fn default() -> Self {
+        Self {
+            screenshots: ScreenshotMode::OnError,
+            dir: String::new(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct LoggingSection {
+    pub level: String,
+    pub format: String,
+    pub file: String,
+}
+
+impl Default for LoggingSection {
+    fn default() -> Self {
+        Self {
+            level: "info".to_string(),
+            format: "pretty".to_string(),
+            file: String::new(),
+        }
+    }
+}
+
+/// Root configuration object.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct GlobalConfig {
+    pub server: ServerSection,
+    pub browser: BrowserSection,
+    pub conversation: ConversationSection,
+    pub capture: CaptureSection,
+    pub tokens: TokensSection,
+    pub debug: DebugSection,
+    pub logging: LoggingSection,
+}
+
+impl GlobalConfig {
+    /// Read the configuration file, returning defaults when it does not exist.
+    pub fn load(path: &Path) -> Result<Self> {
+        if !path.exists() {
+            return Ok(Self::default());
+        }
+        let raw = std::fs::read_to_string(path)
+            .map_err(|e| GatewayError::Config(format!("reading {}: {e}", path.display())))?;
+        Self::from_toml(&raw)
+    }
+
+    pub fn from_toml(raw: &str) -> Result<Self> {
+        toml::from_str::<Self>(raw).map_err(|e| GatewayError::Config(e.to_string()))
+    }
+
+    pub fn validate(&self) -> Result<()> {
+        if self.server.port == 0 {
+            return Err(GatewayError::Config("server.port must not be 0".into()));
+        }
+        if self.browser.max_tabs == 0 {
+            return Err(GatewayError::Config(
+                "browser.max_tabs must be at least 1".into(),
+            ));
+        }
+        if self.capture.poll_interval_ms < 50 {
+            return Err(GatewayError::Config(
+                "capture.poll_interval_ms must be at least 50".into(),
+            ));
+        }
+        if self.capture.response_timeout_s == 0 {
+            return Err(GatewayError::Config(
+                "capture.response_timeout_s must not be 0".into(),
+            ));
+        }
+        if self.capture.max_variants == 0 {
+            return Err(GatewayError::Config(
+                "capture.max_variants must be at least 1".into(),
+            ));
+        }
+        if self.browser.attach && self.browser.debug_port == 0 {
+            return Err(GatewayError::Config(
+                "browser.debug_port must be set when browser.attach is true".into(),
+            ));
+        }
+        if self.browser.headless && self.server.api_key.is_empty() {
+            // Not fatal: headless mode simply cannot ask the user to log in.
+            tracing::debug!("headless mode cannot prompt for a manual login");
+        }
+        Ok(())
+    }
+
+    pub fn resolved_profile_root(&self, layout: &Layout) -> PathBuf {
+        non_empty_path(&self.browser.profile_dir)
+            .map(|raw| paths::resolve_against(layout.root(), &raw))
+            .unwrap_or_else(|| layout.profiles_dir())
+    }
+
+    pub fn profile_dir_for(&self, layout: &Layout, provider: &str) -> PathBuf {
+        self.resolved_profile_root(layout)
+            .join(provider)
+            .join("user-data-dir")
+    }
+
+    pub fn resolved_debug_dir(&self, layout: &Layout) -> PathBuf {
+        non_empty_path(&self.debug.dir)
+            .map(|raw| paths::resolve_against(layout.root(), &raw))
+            .unwrap_or_else(|| layout.debug_dir())
+    }
+
+    pub fn resolved_store_path(&self, layout: &Layout) -> PathBuf {
+        non_empty_path(&self.conversation.store)
+            .map(|raw| paths::resolve_against(layout.root(), &raw))
+            .unwrap_or_else(|| layout.conversations_file())
+    }
+
+    pub fn resolved_log_file(&self, layout: &Layout) -> PathBuf {
+        non_empty_path(&self.logging.file)
+            .map(|raw| paths::resolve_against(layout.root(), &raw))
+            .unwrap_or_else(|| layout.logs_dir().join("llm-gateway.log"))
+    }
+}
+
+fn non_empty_path(raw: &str) -> Option<String> {
+    let trimmed = raw.trim();
+    if trimmed.is_empty() {
+        None
+    } else {
+        Some(trimmed.to_string())
+    }
+}
+
+/// Values coming from the command line that override the configuration file.
+#[derive(Debug, Clone, Default)]
+pub struct CliOverrides {
+    pub host: Option<String>,
+    pub port: Option<u16>,
+    pub browser_executable: Option<String>,
+    pub headless: Option<bool>,
+    pub profile_dir: Option<String>,
+    pub max_tabs: Option<usize>,
+    pub debug_screenshots: Option<bool>,
+    pub log_level: Option<String>,
+    pub log_format: Option<String>,
+    pub api_key: Option<String>,
+    pub attach: Option<bool>,
+    pub debug_port: Option<u16>,
+    pub stealth: Option<StealthMode>,
+    pub markdown: Option<MarkdownMode>,
+}
+
+impl GlobalConfig {
+    /// Apply CLI flags on top of the file configuration.
+    pub fn apply(&mut self, overrides: &CliOverrides) {
+        if let Some(host) = &overrides.host {
+            self.server.host = host.clone();
+        }
+        if let Some(port) = overrides.port {
+            self.server.port = port;
+        }
+        if let Some(key) = &overrides.api_key {
+            self.server.api_key = key.clone();
+        }
+        if let Some(exe) = &overrides.browser_executable {
+            self.browser.executable = exe.clone();
+        }
+        if let Some(headless) = overrides.headless {
+            self.browser.headless = headless;
+        }
+        if let Some(dir) = &overrides.profile_dir {
+            self.browser.profile_dir = dir.clone();
+        }
+        if let Some(max_tabs) = overrides.max_tabs {
+            self.browser.max_tabs = max_tabs;
+        }
+        if let Some(debug) = overrides.debug_screenshots {
+            self.debug.screenshots = if debug {
+                ScreenshotMode::Always
+            } else {
+                ScreenshotMode::OnError
+            };
+        }
+        if let Some(level) = &overrides.log_level {
+            self.logging.level = level.clone();
+        }
+        if let Some(format) = &overrides.log_format {
+            self.logging.format = format.clone();
+        }
+        if let Some(attach) = overrides.attach {
+            self.browser.attach = attach;
+        }
+        if let Some(port) = overrides.debug_port {
+            self.browser.debug_port = port;
+        }
+        if let Some(stealth) = overrides.stealth {
+            self.browser.stealth = stealth;
+        }
+        if let Some(markdown) = overrides.markdown {
+            self.capture.markdown = markdown;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn defaults_are_loopback_and_serialised() {
+        let cfg = GlobalConfig::default();
+        assert_eq!(cfg.server.host, "127.0.0.1");
+        assert_eq!(cfg.server.port, 8080);
+        assert_eq!(cfg.browser.max_tabs, 1);
+        assert_eq!(cfg.conversation.strategy, ConversationStrategy::Auto);
+        assert_eq!(cfg.capture.poll_interval_ms, 400);
+        cfg.validate().unwrap();
+        assert!(!cfg.server.is_public_bind());
+    }
+
+    #[test]
+    fn toml_round_trip_and_partial_files() {
+        let full = toml::to_string(&GlobalConfig::default()).unwrap();
+        let parsed = GlobalConfig::from_toml(&full).unwrap();
+        assert_eq!(parsed.server.port, 8080);
+
+        let partial = "[server]\nport = 9999\n";
+        let parsed = GlobalConfig::from_toml(partial).unwrap();
+        assert_eq!(parsed.server.port, 9999);
+        assert_eq!(parsed.server.host, "127.0.0.1");
+    }
+
+    #[test]
+    fn invalid_toml_is_a_config_error() {
+        let err = GlobalConfig::from_toml("port = ").unwrap_err();
+        assert_eq!(err.code(), "invalid_configuration");
+    }
+
+    #[test]
+    fn attach_mode_requires_a_port() {
+        let mut cfg = GlobalConfig::default();
+        assert_eq!(cfg.browser.stealth, StealthMode::Off);
+        assert_eq!(cfg.browser.debug_port, 9222);
+        cfg.browser.attach = true;
+        cfg.validate().unwrap();
+        cfg.browser.debug_port = 0;
+        assert!(cfg.validate().is_err());
+    }
+
+    #[test]
+    fn stealth_mode_is_parsed_from_the_file() {
+        let cfg = GlobalConfig::from_toml("[browser]\nstealth = \"aggressive\"\n").unwrap();
+        assert_eq!(cfg.browser.stealth, StealthMode::Aggressive);
+        let cfg = GlobalConfig::from_toml("[browser]\nstealth = \"minimal\"\n").unwrap();
+        assert_eq!(cfg.browser.stealth, StealthMode::Minimal);
+    }
+
+    #[test]
+    fn markdown_modes_are_parsed_and_default_to_auto() {
+        assert_eq!(
+            MarkdownMode::parse("clipboard").unwrap(),
+            MarkdownMode::Clipboard
+        );
+        assert_eq!(MarkdownMode::parse("DOM").unwrap(), MarkdownMode::Dom);
+        assert_eq!(MarkdownMode::parse(" text ").unwrap(), MarkdownMode::Text);
+        assert!(MarkdownMode::parse("rich").is_err());
+        assert_eq!(GlobalConfig::default().capture.markdown, MarkdownMode::Auto);
+        assert_eq!(GlobalConfig::default().capture.max_variants, 4);
+
+        let cfg = GlobalConfig::from_toml("[capture]\nmarkdown = \"text\"\n").unwrap();
+        assert_eq!(cfg.capture.markdown, MarkdownMode::Text);
+    }
+
+    #[test]
+    fn cli_overrides_win() {
+        let mut cfg = GlobalConfig::default();
+        cfg.apply(&CliOverrides {
+            port: Some(1234),
+            headless: Some(true),
+            debug_screenshots: Some(true),
+            ..Default::default()
+        });
+        assert_eq!(cfg.server.port, 1234);
+        assert!(cfg.browser.headless);
+        assert_eq!(cfg.debug.screenshots, ScreenshotMode::Always);
+    }
+
+    #[test]
+    fn paths_fall_back_to_the_layout() {
+        let layout = Layout::rooted_at(PathBuf::from("/state"));
+        let cfg = GlobalConfig::default();
+        assert_eq!(
+            cfg.resolved_profile_root(&layout),
+            PathBuf::from("/state/profiles")
+        );
+        assert_eq!(
+            cfg.profile_dir_for(&layout, "chatgpt"),
+            PathBuf::from("/state/profiles/chatgpt/user-data-dir")
+        );
+        assert_eq!(
+            cfg.resolved_store_path(&layout),
+            PathBuf::from("/state/conversations.json")
+        );
+    }
+}
diff --git a/src/conversation/fingerprint.rs b/src/conversation/fingerprint.rs
new file mode 100644
index 0000000..71821a9
--- /dev/null
+++ b/src/conversation/fingerprint.rs
@@ -0,0 +1,99 @@
+//! Stable client-side conversation identifiers.
+
+use crate::config::ConversationIdSource;
+use sha2::{Digest, Sha256};
+
+/// Separator that cannot appear in user supplied text.
+const SEP: char = '\u{1f}';
+
+/// Derive a deterministic id from the opening messages of a thread.
+///
+/// OpenAI clients resend the whole history on every call and do not send a
+/// conversation header, so deriving the id from the opening prompt is what
+/// gives them continuity across calls and across server restarts.
+pub fn fingerprint(owner: &str, system: &str, first_user: &str) -> String {
+    let mut hasher = Sha256::new();
+    hasher.update(owner.as_bytes());
+    hasher.update(SEP.to_string().as_bytes());
+    hasher.update(system.as_bytes());
+    hasher.update(SEP.to_string().as_bytes());
+    hasher.update(first_user.as_bytes());
+    let digest = hasher.finalize();
+    let hex = digest
+        .iter()
+        .map(|b| format!("{b:02x}"))
+        .collect::<String>();
+    format!("fp-{}", &hex[..16])
+}
+
+/// Decide which conversation id a request belongs to.
+///
+/// `owner` identifies the provider *and* the account (`chatgpt@perso`): the same
+/// prompt sent to two accounts must map to two different web conversations.
+pub fn resolve_conversation_id(
+    source: ConversationIdSource,
+    header: Option<&str>,
+    owner: &str,
+    system: &str,
+    first_user: &str,
+) -> String {
+    if let Some(id) = header.map(str::trim).filter(|id| !id.is_empty()) {
+        return id.to_string();
+    }
+    match source {
+        ConversationIdSource::Fingerprint => fingerprint(owner, system, first_user),
+        ConversationIdSource::Header | ConversationIdSource::Uuid => {
+            format!("sess-{}", uuid::Uuid::new_v4())
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn fingerprints_are_stable_and_distinct() {
+        let a = fingerprint("chatgpt", "sys", "hello");
+        let b = fingerprint("chatgpt", "sys", "hello");
+        let c = fingerprint("chatgpt", "sys", "hello there");
+        let d = fingerprint("claude", "sys", "hello");
+        assert_eq!(a, b);
+        assert_ne!(a, c);
+        assert_ne!(a, d);
+
+        // Two accounts of the same provider never share a thread.
+        assert_ne!(
+            fingerprint("chatgpt", "s", "m"),
+            fingerprint("chatgpt@perso", "s", "m")
+        );
+        assert!(a.starts_with("fp-"));
+        assert_eq!(a.len(), 19);
+    }
+
+    #[test]
+    fn separator_prevents_ambiguous_joins() {
+        let a = fingerprint("p", "ab", "c");
+        let b = fingerprint("p", "a", "bc");
+        assert_ne!(a, b);
+    }
+
+    #[test]
+    fn header_wins_over_the_configured_source() {
+        let id = resolve_conversation_id(
+            ConversationIdSource::Fingerprint,
+            Some(" client-thread-1 "),
+            "chatgpt",
+            "",
+            "hi",
+        );
+        assert_eq!(id, "client-thread-1");
+
+        let id = resolve_conversation_id(ConversationIdSource::Header, None, "chatgpt", "", "hi");
+        assert!(id.starts_with("sess-"));
+
+        let id =
+            resolve_conversation_id(ConversationIdSource::Fingerprint, None, "chatgpt", "", "hi");
+        assert_eq!(id, fingerprint("chatgpt", "", "hi"));
+    }
+}
diff --git a/src/conversation/mod.rs b/src/conversation/mod.rs
new file mode 100644
index 0000000..97e27b3
--- /dev/null
+++ b/src/conversation/mod.rs
@@ -0,0 +1,7 @@
+//! Multi-turn conversation continuity between an OpenAI client and a web thread.
+
+pub mod fingerprint;
+pub mod store;
+
+pub use fingerprint::{fingerprint, resolve_conversation_id};
+pub use store::{StoreFileSnapshot, ThreadRecord, ThreadState, ThreadStore};
diff --git a/src/conversation/store.rs b/src/conversation/store.rs
new file mode 100644
index 0000000..b6b0e90
--- /dev/null
+++ b/src/conversation/store.rs
@@ -0,0 +1,386 @@
+//! JSON-backed thread store mapping client conversations to web conversations.
+
+use std::collections::BTreeMap;
+use std::io::Write;
+use std::path::{Path, PathBuf};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use serde::{Deserialize, Serialize};
+use tokio::sync::Mutex;
+
+use crate::error::{GatewayError, Result};
+use crate::providers::config::IMPLICIT_ACCOUNT;
+
+/// Whether the web thread can be reused safely.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum ThreadState {
+    /// The last turn finished cleanly: the thread can be continued.
+    #[default]
+    Ready,
+    /// The last turn was interrupted: replay the history instead of reusing.
+    Incomplete,
+}
+
+/// One client conversation and the web conversation backing it.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ThreadRecord {
+    pub provider: String,
+    /// Account of the provider, when it declares several.
+    #[serde(default)]
+    pub account: Option<String>,
+    /// Full URL of the web conversation, when the provider exposes one.
+    #[serde(default)]
+    pub web_url: Option<String>,
+    /// Provider-side conversation identifier extracted from the URL.
+    #[serde(default)]
+    pub web_id: Option<String>,
+    pub created_at: u64,
+    pub last_used_at: u64,
+    #[serde(default)]
+    pub turns: u64,
+    #[serde(default)]
+    pub messages_sent: u64,
+    #[serde(default)]
+    pub state: ThreadState,
+    #[serde(default)]
+    pub note: Option<String>,
+}
+
+impl ThreadRecord {
+    pub fn new(provider: &str) -> Self {
+        let now = now_secs();
+        Self {
+            provider: provider.to_string(),
+            account: None,
+            web_url: None,
+            web_id: None,
+            created_at: now,
+            last_used_at: now,
+            turns: 0,
+            messages_sent: 0,
+            state: ThreadState::Ready,
+            note: None,
+        }
+    }
+
+    /// True when the stored web conversation can be continued.
+    pub fn is_reusable(&self) -> bool {
+        self.state == ThreadState::Ready && self.web_url.is_some()
+    }
+}
+
+/// On-disk representation, versioned so it can evolve.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct StoreFileSnapshot {
+    pub version: u32,
+    #[serde(default)]
+    pub threads: BTreeMap<String, ThreadRecord>,
+}
+
+impl Default for StoreFileSnapshot {
+    fn default() -> Self {
+        Self {
+            version: 1,
+            threads: BTreeMap::new(),
+        }
+    }
+}
+
+/// Thread storage, readable and editable by hand.
+#[derive(Debug)]
+pub struct ThreadStore {
+    path: Option<PathBuf>,
+    inner: Mutex<StoreFileSnapshot>,
+}
+
+impl ThreadStore {
+    /// Open the store, tolerating a missing file.
+    pub async fn open(path: &Path) -> Result<Self> {
+        let snapshot = if path.exists() {
+            let raw = std::fs::read_to_string(path)?;
+            if raw.trim().is_empty() {
+                StoreFileSnapshot::default()
+            } else {
+                serde_json::from_str::<StoreFileSnapshot>(&raw)
+                    .map_err(|e| GatewayError::Config(format!("parsing {}: {e}", path.display())))?
+            }
+        } else {
+            StoreFileSnapshot::default()
+        };
+        Ok(Self {
+            path: Some(path.to_path_buf()),
+            inner: Mutex::new(snapshot),
+        })
+    }
+
+    /// In-memory store, used by tests and by the mock backend.
+    pub fn in_memory() -> Self {
+        Self {
+            path: None,
+            inner: Mutex::new(StoreFileSnapshot::default()),
+        }
+    }
+
+    pub fn path(&self) -> Option<&Path> {
+        self.path.as_deref()
+    }
+
+    pub async fn get(&self, id: &str) -> Option<ThreadRecord> {
+        self.inner.lock().await.threads.get(id).cloned()
+    }
+
+    pub async fn upsert(&self, id: &str, record: ThreadRecord) -> Result<()> {
+        {
+            let mut guard = self.inner.lock().await;
+            guard.threads.insert(id.to_string(), record);
+        }
+        self.flush().await
+    }
+
+    /// Record a completed turn.
+    pub async fn record_turn(
+        &self,
+        id: &str,
+        provider: &str,
+        account: Option<&str>,
+        web_url: Option<String>,
+        web_id: Option<String>,
+        messages_sent: u64,
+    ) -> Result<()> {
+        {
+            let mut guard = self.inner.lock().await;
+            let entry = guard
+                .threads
+                .entry(id.to_string())
+                .or_insert_with(|| ThreadRecord::new(provider));
+            entry.provider = provider.to_string();
+            if account.is_some() {
+                entry.account = account.map(str::to_string);
+            }
+            if web_url.is_some() {
+                entry.web_url = web_url;
+            }
+            if web_id.is_some() {
+                entry.web_id = web_id;
+            }
+            entry.last_used_at = now_secs();
+            entry.turns += 1;
+            entry.messages_sent += messages_sent;
+            entry.state = ThreadState::Ready;
+            entry.note = None;
+        }
+        self.flush().await
+    }
+
+    /// Mark a thread as interrupted so the next turn replays instead of reusing.
+    pub async fn mark_incomplete(&self, id: &str, note: &str) -> Result<()> {
+        {
+            let mut guard = self.inner.lock().await;
+            if let Some(entry) = guard.threads.get_mut(id) {
+                entry.state = ThreadState::Incomplete;
+                entry.note = Some(note.to_string());
+                entry.last_used_at = now_secs();
+            }
+        }
+        self.flush().await
+    }
+
+    /// Stored threads, optionally restricted to one provider and one account.
+    pub async fn list(
+        &self,
+        provider: Option<&str>,
+        account: Option<&str>,
+    ) -> Vec<(String, ThreadRecord)> {
+        self.inner
+            .lock()
+            .await
+            .threads
+            .iter()
+            .filter(|(_, record)| {
+                provider.is_none_or(|p| record.provider == p) && matches_account(record, account)
+            })
+            .map(|(id, record)| (id.clone(), record.clone()))
+            .collect()
+    }
+
+    /// Remove threads, optionally restricted to one provider and one account.
+    /// Returns the count.
+    pub async fn clear(&self, provider: Option<&str>, account: Option<&str>) -> Result<usize> {
+        let removed = {
+            let mut guard = self.inner.lock().await;
+            let before = guard.threads.len();
+            if provider.is_none() && account.is_none() {
+                guard.threads.clear();
+            } else {
+                guard.threads.retain(|_, record| {
+                    !(provider.is_none_or(|p| record.provider == p)
+                        && matches_account(record, account))
+                });
+            }
+            before - guard.threads.len()
+        };
+        self.flush().await?;
+        Ok(removed)
+    }
+
+    /// Persist the current snapshot atomically.
+    pub async fn flush(&self) -> Result<()> {
+        let Some(path) = self.path.clone() else {
+            return Ok(());
+        };
+        let snapshot = self.inner.lock().await.clone();
+        write_atomic(&path, &snapshot)
+    }
+}
+
+/// Does a stored thread belong to the account a command asked for?
+///
+/// A thread recorded without an account was served by the single implicit
+/// account of its provider, which the CLI names `default` everywhere else.
+fn matches_account(record: &ThreadRecord, account: Option<&str>) -> bool {
+    let Some(wanted) = account.map(str::trim).filter(|value| !value.is_empty()) else {
+        return true;
+    };
+    match record.account.as_deref() {
+        Some(account) => account.eq_ignore_ascii_case(wanted),
+        None => wanted.eq_ignore_ascii_case(IMPLICIT_ACCOUNT),
+    }
+}
+
+fn write_atomic(path: &Path, snapshot: &StoreFileSnapshot) -> Result<()> {
+    let parent = path.parent().unwrap_or_else(|| Path::new("."));
+    std::fs::create_dir_all(parent)?;
+    let body = serde_json::to_vec_pretty(snapshot)
+        .map_err(|e| GatewayError::Internal(format!("serialising the thread store: {e}")))?;
+
+    let mut tmp = tempfile::NamedTempFile::new_in(parent)?;
+    tmp.write_all(&body)?;
+    tmp.flush()?;
+    tmp.persist(path).map_err(|e| GatewayError::Io(e.error))?;
+    Ok(())
+}
+
+pub fn now_secs() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs())
+        .unwrap_or(0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn records_turns_and_reloads_from_disk() {
+        let tmp = tempfile::tempdir().unwrap();
+        let path = tmp.path().join("conversations.json");
+        let store = ThreadStore::open(&path).await.unwrap();
+
+        store
+            .record_turn(
+                "fp-1",
+                "chatgpt",
+                None,
+                Some("https://chatgpt.com/c/abc".into()),
+                Some("abc".into()),
+                3,
+            )
+            .await
+            .unwrap();
+
+        let reloaded = ThreadStore::open(&path).await.unwrap();
+        let record = reloaded.get("fp-1").await.unwrap();
+        assert_eq!(record.turns, 1);
+        assert_eq!(record.messages_sent, 3);
+        assert_eq!(record.web_id.as_deref(), Some("abc"));
+        assert!(record.is_reusable());
+    }
+
+    #[tokio::test]
+    async fn incomplete_threads_are_not_reusable() {
+        let store = ThreadStore::in_memory();
+        store
+            .record_turn(
+                "t",
+                "chatgpt",
+                None,
+                Some("https://x/c/1".into()),
+                Some("1".into()),
+                1,
+            )
+            .await
+            .unwrap();
+        store
+            .mark_incomplete("t", "client disconnected")
+            .await
+            .unwrap();
+        let record = store.get("t").await.unwrap();
+        assert!(!record.is_reusable());
+        assert_eq!(record.note.as_deref(), Some("client disconnected"));
+    }
+
+    #[tokio::test]
+    async fn clear_filters_by_provider() {
+        let store = ThreadStore::in_memory();
+        store
+            .record_turn("a", "chatgpt", Some("perso"), None, None, 1)
+            .await
+            .unwrap();
+        store
+            .record_turn("b", "claude", None, None, None, 1)
+            .await
+            .unwrap();
+        assert_eq!(
+            store.get("a").await.unwrap().account.as_deref(),
+            Some("perso")
+        );
+        assert_eq!(store.clear(Some("chatgpt"), None).await.unwrap(), 1);
+        assert_eq!(store.list(None, None).await.len(), 1);
+        assert_eq!(store.clear(None, None).await.unwrap(), 1);
+        assert!(store.list(None, None).await.is_empty());
+    }
+
+    #[tokio::test]
+    async fn listing_and_clearing_filter_by_account() {
+        let store = ThreadStore::in_memory();
+        store
+            .record_turn("perso-1", "chatgpt", Some("perso"), None, None, 1)
+            .await
+            .unwrap();
+        store
+            .record_turn("pro-1", "chatgpt", Some("pro"), None, None, 1)
+            .await
+            .unwrap();
+        // A provider that declares no account stores no account at all.
+        store
+            .record_turn("solo-1", "claude", None, None, None, 1)
+            .await
+            .unwrap();
+
+        assert_eq!(store.list(None, Some("perso")).await.len(), 1);
+        assert_eq!(store.list(Some("chatgpt"), Some("pro")).await.len(), 1);
+        assert!(store.list(Some("claude"), Some("perso")).await.is_empty());
+
+        // "default" is the name of the implicit account in the rest of the CLI.
+        let implicit = store.list(None, Some("default")).await;
+        assert_eq!(implicit.len(), 1);
+        assert_eq!(implicit[0].0, "solo-1");
+
+        assert_eq!(
+            store.clear(Some("chatgpt"), Some("perso")).await.unwrap(),
+            1
+        );
+        assert_eq!(store.list(Some("chatgpt"), None).await.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn corrupt_store_reports_a_config_error() {
+        let tmp = tempfile::tempdir().unwrap();
+        let path = tmp.path().join("conversations.json");
+        std::fs::write(&path, "{not json").unwrap();
+        let err = ThreadStore::open(&path).await.unwrap_err();
+        assert_eq!(err.code(), "invalid_configuration");
+    }
+}
diff --git a/src/dashboard/index.html b/src/dashboard/index.html
new file mode 100644
index 0000000..9fa45a7
--- /dev/null
+++ b/src/dashboard/index.html
@@ -0,0 +1,194 @@
+<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8" />
+<title>llm-gateway dashboard</title>
+<style>
+  :root { color-scheme: dark; }
+  body { margin: 0; font: 14px/1.5 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+         background: #14161a; color: #d8dee9; }
+  header { padding: 12px 18px; background: #1c1f26; border-bottom: 1px solid #2b303b;
+           display: flex; gap: 16px; align-items: center; flex-wrap: wrap; }
+  h1 { font-size: 15px; margin: 0; font-weight: 600; }
+  main { display: grid; grid-template-columns: minmax(320px, 1fr) minmax(360px, 1.2fr); gap: 18px; padding: 18px; }
+  section { background: #1c1f26; border: 1px solid #2b303b; border-radius: 8px; padding: 14px; }
+  h2 { font-size: 13px; text-transform: uppercase; letter-spacing: .08em; color: #8f9bab; margin: 0 0 10px; }
+  table { width: 100%; border-collapse: collapse; }
+  td, th { text-align: left; padding: 5px 6px; border-bottom: 1px solid #262b34; font-size: 13px; }
+  .dot { display: inline-block; width: 9px; height: 9px; border-radius: 50%; margin-right: 7px; background: #6b7280; }
+  .available { background: #22c55e; } .requires_login { background: #f59e0b; }
+  .captcha, .error, .misconfigured { background: #ef4444; } .busy { background: #3b82f6; }
+  #logs { height: 340px; overflow: auto; white-space: pre-wrap; word-break: break-word;
+          background: #101216; border: 1px solid #262b34; border-radius: 6px; padding: 8px; font-size: 12px; }
+  input, textarea, select, button { font: inherit; background: #101216; color: #d8dee9;
+          border: 1px solid #2b303b; border-radius: 5px; padding: 6px 8px; }
+  button { cursor: pointer; background: #23303f; }
+  button:hover { background: #2c3d51; }
+  .row { display: flex; gap: 8px; align-items: center; margin-bottom: 8px; flex-wrap: wrap; }
+  textarea { width: 100%; min-height: 64px; resize: vertical; }
+  pre { background: #101216; border: 1px solid #262b34; border-radius: 6px; padding: 8px;
+        max-height: 240px; overflow: auto; font-size: 12px; }
+  a { color: #7aa2f7; }
+</style>
+</head>
+<body>
+<header>
+  <h1>llm-gateway</h1>
+  <span id="health">loading…</span>
+  <label>API key <input id="apiKey" placeholder="only if configured" size="18" /></label>
+  <button id="reload">Reload configuration</button>
+  <a href="/v1/models" target="_blank">/v1/models</a>
+  <a href="/health" target="_blank">/health</a>
+</header>
+<main>
+  <section>
+    <h2>Providers</h2>
+    <table><thead><tr><th>provider</th><th>state</th><th>url</th><th></th></tr></thead>
+      <tbody id="providers"></tbody></table>
+    <div class="row" style="margin-top:12px">
+      <button data-action="status">Refresh status</button>
+      <button data-action="validate">Validate all</button>
+    </div>
+    <pre id="report"></pre>
+  </section>
+  <section>
+    <h2>Recent logs</h2>
+    <div id="logs"></div>
+  </section>
+  <section style="grid-column: 1 / -1">
+    <h2>Manual test</h2>
+    <div class="row">
+      <select id="model"></select>
+      <label><input type="checkbox" id="stream" checked /> stream</label>
+      <button id="send">Send</button>
+    </div>
+    <textarea id="prompt">Say 'ok'</textarea>
+    <pre id="answer"></pre>
+  </section>
+</main>
+<script>
+const key = () => document.getElementById('apiKey').value.trim();
+const headers = () => key() ? { 'authorization': 'Bearer ' + key() } : {};
+const apiKeyInput = document.getElementById('apiKey');
+apiKeyInput.value = localStorage.getItem('llm-gateway-key') || '';
+apiKeyInput.addEventListener('change', () => localStorage.setItem('llm-gateway-key', apiKeyInput.value));
+
+async function getJson(path, init) {
+  const response = await fetch(path, { ...init, headers: { ...headers(), ...(init?.headers || {}) } });
+  const text = await response.text();
+  try { return { ok: response.ok, status: response.status, body: JSON.parse(text) }; }
+  catch { return { ok: response.ok, status: response.status, body: text }; }
+}
+
+let models = [];
+async function refreshHealth() {
+  const { body } = await getJson('/health');
+  document.getElementById('health').textContent =
+    body && body.status ? body.status + ' · up ' + body.uptime_s + 's · ' + (body.providers || []).length + ' provider(s)' : 'unreachable';
+  models = ((body && body.providers) || []).flatMap(p => [
+    p.name,
+    ...(p.accounts || []).map(a => p.name + '@' + a.id),
+    ...(p.models || []).map(m => p.name + '/' + m),
+  ]);
+  const select = document.getElementById('model');
+  select.innerHTML = models.map(m => '<option>' + m + '</option>').join('');
+}
+
+async function refreshStatus() {
+  const { body } = await getJson('/health');
+  const rows = [];
+  for (const provider of (body && body.providers) || []) {
+    // One row per account: each has its own browser, session and tab pool, so
+    // each is probed on its own - a signed-out second account shows up here
+    // instead of hiding behind the state of the default one.
+    const accounts = provider.accounts && provider.accounts.length
+      ? provider.accounts
+      : [{ id: null, default: true }];
+    for (const account of accounts) {
+      const label = account.id ? provider.name + '@' + account.id : provider.name;
+      const status = await getJson('/v1/providers/' + label + '/status');
+      const state = (status.body && status.body.state) || 'unknown';
+      const identity = account.email || account.label || '';
+      rows.push('<tr><td>' + label + (account.default ? ' *' : '') +
+        (identity ? '<br><small>' + identity + '</small>' : '') + '</td>' +
+        '<td><span class="dot ' + state + '"></span>' + state + '</td>' +
+        '<td>' + (status.body && status.body.url || provider.web_url) + '</td>' +
+        '<td>' + (status.body && status.body.detail ? '<small>' + status.body.detail + '</small>' : '') + '</td></tr>');
+    }
+  }
+  document.getElementById('providers').innerHTML = rows.join('') || '<tr><td colspan="4">no provider configured</td></tr>';
+}
+
+async function validateAll() {
+  const { body } = await getJson('/health');
+  const reports = [];
+  for (const provider of (body && body.providers) || []) {
+    const owners = provider.accounts && provider.accounts.length
+      ? provider.accounts.map(a => provider.name + '@' + a.id)
+      : [provider.name];
+    for (const owner of owners) {
+      const result = await getJson('/v1/providers/' + owner + '/validate', { method: 'POST' });
+      reports.push(result.body);
+    }
+  }
+  document.getElementById('report').textContent = JSON.stringify(reports, null, 2);
+}
+
+async function send() {
+  const model = document.getElementById('model').value;
+  const prompt = document.getElementById('prompt').value;
+  const stream = document.getElementById('stream').checked;
+  const out = document.getElementById('answer');
+  out.textContent = '';
+  const response = await fetch('/v1/chat/completions', {
+    method: 'POST',
+    headers: { ...headers(), 'content-type': 'application/json' },
+    body: JSON.stringify({ model, messages: [{ role: 'user', content: prompt }], stream }),
+  });
+  if (!stream) { out.textContent = JSON.stringify(await response.json(), null, 2); return; }
+  const reader = response.body.getReader();
+  const decoder = new TextDecoder();
+  let buffer = '';
+  for (;;) {
+    const { value, done } = await reader.read();
+    if (done) break;
+    buffer += decoder.decode(value, { stream: true });
+    const parts = buffer.split('\n\n');
+    buffer = parts.pop();
+    for (const part of parts) {
+      const line = part.split('\n').find(l => l.startsWith('data: '));
+      if (!line) continue;
+      const payload = line.slice(6);
+      if (payload === '[DONE]') continue;
+      try {
+        const chunk = JSON.parse(payload);
+        const delta = chunk.choices && chunk.choices[0] && chunk.choices[0].delta && chunk.choices[0].delta.content;
+        if (delta) out.textContent += delta;
+        else if (chunk.error) out.textContent += '\n[error] ' + chunk.error.message;
+      } catch (e) { /* keep the raw stream on screen */ }
+    }
+  }
+}
+
+document.getElementById('reload').addEventListener('click', async () => {
+  const result = await getJson('/v1/admin/reload', { method: 'POST' });
+  document.getElementById('report').textContent = JSON.stringify(result.body, null, 2);
+  await refreshHealth();
+});
+document.querySelector('[data-action="status"]').addEventListener('click', refreshStatus);
+document.querySelector('[data-action="validate"]').addEventListener('click', validateAll);
+document.getElementById('send').addEventListener('click', send);
+
+const logs = document.getElementById('logs');
+const events = new EventSource('/dashboard/events');
+events.onmessage = (event) => {
+  logs.textContent += event.data + '\n';
+  logs.scrollTop = logs.scrollHeight;
+};
+
+refreshHealth();
+refreshStatus();
+setInterval(refreshHealth, 15000);
+</script>
+</body>
+</html>
diff --git a/src/dashboard/mod.rs b/src/dashboard/mod.rs
new file mode 100644
index 0000000..2513f95
--- /dev/null
+++ b/src/dashboard/mod.rs
@@ -0,0 +1,4 @@
+//! The static dashboard page embedded in the binary.
+
+/// Raw HTML of the dashboard.
+pub const INDEX_HTML: &str = include_str!("index.html");
diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..7dbf1d4
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,210 @@
+//! Typed errors mapped onto the OpenAI error payload.
+
+use std::path::PathBuf;
+
+/// Convenience alias used across the crate.
+pub type Result<T, E = GatewayError> = std::result::Result<T, E>;
+
+/// Every failure mode the gateway can surface to a client.
+#[derive(Debug, thiserror::Error)]
+pub enum GatewayError {
+    #[error("model '{0}' does not match any configured provider")]
+    UnknownProvider(String),
+
+    /// The model string named a provider, but not one of its accounts.
+    #[error("{0}")]
+    UnknownAccount(String),
+
+    #[error("parameter '{param}' {detail}")]
+    UnsupportedParameter { param: String, detail: String },
+
+    #[error("{0}")]
+    UnsupportedContentType(String),
+
+    #[error("{0}")]
+    InvalidRequest(String),
+
+    #[error("invalid API key")]
+    InvalidApiKey,
+
+    #[error(
+        "provider '{provider}' is not signed in: run 'llm-gateway login {provider} --manual', sign in inside the window it opens, then close it (Google refuses browsers it sees as automated, so this path avoids that)"
+    )]
+    RequiresLogin { provider: String },
+
+    #[error(
+        "provider '{provider}' is showing a captcha challenge; solve it in the browser window"
+    )]
+    Captcha { provider: String },
+
+    #[error("provider '{provider}' is busy, retry later")]
+    ProviderBusy { provider: String, waited_ms: u64 },
+
+    #[error("provider '{provider}' is rate limiting: {detail}")]
+    UpstreamRateLimited { provider: String, detail: String },
+
+    #[error("browser profile {path} is locked by another browser instance; close it and retry")]
+    BrowserProfileLocked { path: PathBuf },
+
+    #[error("selector '{selector}' not found ({step})")]
+    SelectorMissing { selector: String, step: String },
+
+    #[error("provider '{provider}' reported an error: {message}")]
+    UpstreamError { provider: String, message: String },
+
+    #[error("browser engine unavailable: {0}")]
+    BrowserUnavailable(String),
+
+    #[error("timed out while {stage} after {timeout_s}s")]
+    CaptureTimeout { stage: String, timeout_s: u64 },
+
+    #[error("provider '{provider}' is misconfigured: {detail}")]
+    ProviderMisconfigured { provider: String, detail: String },
+
+    #[error("unsupported browser '{0}': only Chromium-based browsers speak CDP")]
+    UnsupportedBrowser(String),
+
+    #[error("provider '{0}' is not configured")]
+    ProviderNotConfigured(String),
+
+    #[error("HTTP request to {url} failed: {source}")]
+    Http {
+        url: String,
+        #[source]
+        source: reqwest::Error,
+    },
+
+    #[error("I/O error: {0}")]
+    Io(#[from] std::io::Error),
+
+    #[error("invalid configuration: {0}")]
+    Config(String),
+
+    #[error("internal error: {0}")]
+    Internal(String),
+
+    /// The caller went away before the answer was captured. Never serialised:
+    /// there is no client left to read it.
+    #[error("client disconnected before the answer was captured")]
+    Cancelled,
+}
+
+impl GatewayError {
+    pub fn invalid_request(msg: impl Into<String>) -> Self {
+        Self::InvalidRequest(msg.into())
+    }
+
+    pub fn unsupported_param(param: impl Into<String>, detail: impl Into<String>) -> Self {
+        Self::UnsupportedParameter {
+            param: param.into(),
+            detail: detail.into(),
+        }
+    }
+
+    pub fn internal(msg: impl Into<String>) -> Self {
+        Self::Internal(msg.into())
+    }
+
+    /// HTTP status returned to the OpenAI-compatible client.
+    pub fn http_status(&self) -> u16 {
+        match self {
+            Self::UnknownProvider(_) | Self::UnknownAccount(_) => 404,
+            Self::UnsupportedParameter { .. }
+            | Self::UnsupportedContentType(_)
+            | Self::InvalidRequest(_) => 400,
+            Self::InvalidApiKey | Self::RequiresLogin { .. } => 401,
+            Self::Captcha { .. } => 403,
+            Self::ProviderBusy { .. } | Self::UpstreamRateLimited { .. } => 429,
+            Self::BrowserProfileLocked { .. } => 409,
+            Self::BrowserUnavailable(_) | Self::ProviderMisconfigured { .. } => 503,
+            Self::CaptureTimeout { .. } => 504,
+            Self::Cancelled => 499,
+            _ => 500,
+        }
+    }
+
+    /// OpenAI-compatible error type field.
+    pub fn error_type(&self) -> &'static str {
+        match self.http_status() {
+            400 | 401 | 403 | 404 => "invalid_request_error",
+            429 => "rate_limit_error",
+            _ => "api_error",
+        }
+    }
+
+    /// Stable machine-readable code, also used as a log field.
+    pub fn code(&self) -> &'static str {
+        match self {
+            Self::UnknownProvider(_) => "model_not_found",
+            Self::UnknownAccount(_) => "account_not_found",
+            Self::UnsupportedParameter { .. } => "unsupported_parameter",
+            Self::UnsupportedContentType(_) => "unsupported_content_type",
+            Self::InvalidRequest(_) => "invalid_request",
+            Self::InvalidApiKey => "invalid_api_key",
+            Self::RequiresLogin { .. } => "requires_login",
+            Self::Captcha { .. } => "captcha_required",
+            Self::ProviderBusy { .. } => "provider_busy",
+            Self::UpstreamRateLimited { .. } => "upstream_rate_limit",
+            Self::BrowserProfileLocked { .. } => "browser_profile_locked",
+            Self::SelectorMissing { .. } => "selector_missing",
+            Self::UpstreamError { .. } => "upstream_error",
+            Self::BrowserUnavailable(_) => "browser_unavailable",
+            Self::CaptureTimeout { .. } => "upstream_timeout",
+            Self::ProviderMisconfigured { .. } => "provider_misconfigured",
+            Self::UnsupportedBrowser(_) => "unsupported_browser",
+            Self::ProviderNotConfigured(_) => "provider_not_configured",
+            Self::Http { .. } => "upstream_http_error",
+            Self::Io(_) => "io_error",
+            Self::Config(_) => "invalid_configuration",
+            Self::Internal(_) => "internal_error",
+            Self::Cancelled => "client_disconnected",
+        }
+    }
+
+    /// Name of the offending parameter, when the error is parameter-specific.
+    pub fn param(&self) -> Option<&str> {
+        match self {
+            Self::UnsupportedParameter { param, .. } => Some(param.as_str()),
+            _ => None,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::PathBuf;
+
+    #[test]
+    fn codes_and_statuses_are_stable() {
+        let e = GatewayError::RequiresLogin {
+            provider: "chatgpt".into(),
+        };
+        assert_eq!(e.http_status(), 401);
+        assert_eq!(e.code(), "requires_login");
+        assert_eq!(e.error_type(), "invalid_request_error");
+        assert!(e.to_string().contains("llm-gateway login chatgpt"));
+
+        let e = GatewayError::CaptureTimeout {
+            stage: "waiting for the answer".into(),
+            timeout_s: 180,
+        };
+        assert_eq!(e.http_status(), 504);
+        assert_eq!(e.code(), "upstream_timeout");
+
+        let e = GatewayError::unsupported_param("tools", "is not supported by the browser backend");
+        assert_eq!(e.param(), Some("tools"));
+        assert_eq!(e.http_status(), 400);
+
+        let e = GatewayError::BrowserProfileLocked {
+            path: PathBuf::from("/p"),
+        };
+        assert_eq!(e.http_status(), 409);
+
+        let e = GatewayError::UnknownAccount("provider 'chatgpt' has no account 'x'".into());
+        assert_eq!(e.http_status(), 404);
+        assert_eq!(e.code(), "account_not_found");
+        assert_eq!(e.error_type(), "invalid_request_error");
+        assert!(e.to_string().contains("no account 'x'"));
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..2635170
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,29 @@
+//! llm-bridge: an OpenAI-compatible gateway driven by a real browser session.
+
+pub mod browser;
+pub mod cli;
+pub mod config;
+pub mod conversation;
+pub mod dashboard;
+pub mod error;
+pub mod markdown;
+pub mod paths;
+pub mod providers;
+pub mod selftest;
+pub mod server;
+pub mod tokens;
+pub mod util;
+
+/// Version reported by the API.
+pub const API_VERSION: &str = env!("CARGO_PKG_VERSION");
+
+/// Version plus the moment this binary was compiled.
+///
+/// Printed by `llm-gateway --version` and in the start-up banner, so it is
+/// obvious whether an installed binary matches the sources it came from.
+pub const VERSION: &str = concat!(
+    env!("CARGO_PKG_VERSION"),
+    " (built ",
+    env!("LLM_GATEWAY_BUILD_TIME"),
+    ")"
+);
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..7723227
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,1245 @@
+//! llm-gateway command line entry point.
+
+use std::io::Write;
+use std::path::PathBuf;
+use std::process::ExitCode;
+use std::sync::{Arc, OnceLock};
+use std::time::{Duration, Instant};
+
+use anyhow::{anyhow, bail, Context, Result};
+use clap::Parser;
+use llm_bridge::browser::{dom, executable_hint, external_launch, resolve_executable};
+use llm_bridge::cli::{
+    Cli, Command, ConfigCommand, ConversationsCommand, GlobalArgs, ServeArgs, TestArgs,
+};
+use llm_bridge::config::{CliOverrides, GlobalConfig, MarkdownMode, StealthMode};
+use llm_bridge::conversation::ThreadStore;
+use llm_bridge::error::GatewayError;
+use llm_bridge::paths::Layout;
+use llm_bridge::providers::{
+    owner_label, parse_model, ChatBackend, LlmProvider, MockBackend, ProviderRegistry, TurnEvent,
+    TurnRequest, WebUiProvider, IMPLICIT_ACCOUNT,
+};
+use llm_bridge::selftest;
+use llm_bridge::server::{self, AppState, BufferLayer, LogBuffer};
+use llm_bridge::util;
+use tracing_subscriber::prelude::*;
+use tracing_subscriber::{fmt, EnvFilter};
+
+/// Keeps the non-blocking file appender alive for the whole process.
+static FILE_GUARD: OnceLock<tracing_appender::non_blocking::WorkerGuard> = OnceLock::new();
+
+fn main() -> ExitCode {
+    let cli = Cli::parse();
+    let runtime = match tokio::runtime::Builder::new_multi_thread()
+        .enable_all()
+        .build()
+    {
+        Ok(runtime) => runtime,
+        Err(err) => {
+            eprintln!("error: cannot start the async runtime: {err}");
+            return ExitCode::from(1);
+        }
+    };
+    match runtime.block_on(run(cli)) {
+        Ok(code) => code,
+        Err(err) => {
+            eprintln!("error: {err:#}");
+            ExitCode::from(1)
+        }
+    }
+}
+
+async fn run(cli: Cli) -> Result<ExitCode> {
+    let layout = Layout::discover()?;
+    layout.ensure().context("creating the state directory")?;
+
+    let config_path = match &cli.global.config {
+        Some(path) => llm_bridge::paths::expand_tilde(&path.to_string_lossy()),
+        None => layout.config_file(),
+    };
+    let mut config = GlobalConfig::load(&config_path)?;
+    let overrides = build_overrides(&cli.global)?;
+    config.apply(&overrides);
+    config.validate()?;
+
+    let logs = LogBuffer::new(500);
+    init_tracing(&layout, &config, &logs);
+
+    let command = cli.command.unwrap_or(Command::Serve(ServeArgs {
+        backend: "browser".to_string(),
+    }));
+    match command {
+        Command::Serve(args) => {
+            serve(
+                layout,
+                config,
+                overrides.clone(),
+                logs,
+                args,
+                cli.global.provider,
+            )
+            .await
+        }
+        Command::Test(args) => test(layout, config, args).await,
+        Command::Selftest(args) => selftest_command(layout, config, args).await,
+        Command::List(args) => list(layout, config, args.json).await,
+        Command::Login(args) => login(layout, config, args).await,
+        Command::Logout(args) => logout(layout, config, args, cli.global.yes).await,
+        Command::Conversations(args) => {
+            conversations(layout, config, args.command, cli.global.yes).await
+        }
+        Command::Reload => reload(config).await,
+        Command::Config(args) => config_command(layout, config, args.command),
+    }
+}
+
+/// Translate the command line flags into configuration overrides.
+fn build_overrides(global: &GlobalArgs) -> Result<CliOverrides> {
+    let browser_executable = match (&global.browser_path, &global.browser) {
+        (Some(path), _) => Some(path.to_string_lossy().to_string()),
+        (None, Some(name)) => executable_hint(name)?.map(|path| path.to_string_lossy().to_string()),
+        (None, None) => None,
+    };
+
+    let stealth = match &global.stealth {
+        Some(raw) => Some(StealthMode::parse(raw)?),
+        None => None,
+    };
+
+    let markdown = match &global.markdown {
+        Some(raw) => Some(MarkdownMode::parse(raw)?),
+        None => None,
+    };
+
+    Ok(CliOverrides {
+        host: global.host.clone(),
+        port: global.port,
+        browser_executable,
+        headless: if global.headless { Some(true) } else { None },
+        profile_dir: global
+            .profile_dir
+            .as_ref()
+            .map(|path| path.to_string_lossy().to_string()),
+        max_tabs: global.max_tabs,
+        debug_screenshots: if global.debug { Some(true) } else { None },
+        log_level: global.log_level.clone(),
+        log_format: global.log_format.clone(),
+        api_key: global.api_key.clone(),
+        attach: if global.attach { Some(true) } else { None },
+        debug_port: global.debug_port,
+        stealth,
+        markdown,
+    })
+}
+
+/// Split a `provider[@account]` argument into its two parts.
+fn split_owner(raw: &str) -> (String, Option<String>) {
+    let parsed = parse_model(raw);
+    (parsed.provider, parsed.account)
+}
+
+/// Install the tracing subscriber, feeding both stderr and the dashboard buffer.
+fn init_tracing(layout: &Layout, config: &GlobalConfig, logs: &LogBuffer) {
+    let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| {
+        EnvFilter::new(format!(
+            // Some Chrome versions emit CDP events chromiumoxide cannot decode;
+            // they are harmless and very noisy, so keep that target quiet.
+            "{},chromiumoxide=error,hyper=warn,tungstenite=warn,h2=warn",
+            config.logging.level
+        ))
+    });
+
+    let json = config.logging.format.eq_ignore_ascii_case("json");
+    let stderr_layer = if json {
+        fmt::layer().json().with_writer(std::io::stderr).boxed()
+    } else {
+        fmt::layer().with_writer(std::io::stderr).boxed()
+    };
+
+    let file_layer = {
+        let path = config.resolved_log_file(layout);
+        if let Some(parent) = path.parent() {
+            let _ = std::fs::create_dir_all(parent);
+        }
+        match std::fs::File::create(&path) {
+            Ok(file) => {
+                let (writer, guard) = tracing_appender::non_blocking(file);
+                let _ = FILE_GUARD.set(guard);
+                Some(fmt::layer().json().with_writer(writer).boxed())
+            }
+            Err(_) => None,
+        }
+    };
+
+    let _ = tracing_subscriber::registry()
+        .with(filter)
+        .with(stderr_layer)
+        .with(file_layer)
+        .with(BufferLayer::new(logs.clone()))
+        .try_init();
+}
+
+// ---------------------------------------------------------------------------
+// serve
+// ---------------------------------------------------------------------------
+
+async fn serve(
+    layout: Layout,
+    config: GlobalConfig,
+    overrides: CliOverrides,
+    logs: LogBuffer,
+    args: ServeArgs,
+    provider_filter: Option<String>,
+) -> Result<ExitCode> {
+    let mock = match args.backend.to_lowercase().as_str() {
+        "browser" | "cdp" | "chrome" => false,
+        "mock" => true,
+        other => bail!("unknown backend '{other}', expected 'browser' or 'mock'"),
+    };
+
+    let registry = Arc::new(ProviderRegistry::new(layout.clone(), config.clone()));
+    let report = registry.reload().await?;
+    for name in &report.added {
+        tracing::info!(provider = %name, "provider registered");
+    }
+
+    if let Some(name) = &provider_filter {
+        if !registry.retain_only(name).await {
+            bail!(
+                "provider '{name}' is not configured (state directory: {})",
+                layout.providers_dir().display()
+            );
+        }
+    }
+
+    let backend: Arc<dyn ChatBackend> = if mock {
+        tracing::info!("using the mock backend: no browser will be launched");
+        let descriptors = ChatBackend::providers(registry.as_ref());
+        let per_chunk = Duration::from_millis(20);
+        if descriptors.is_empty() {
+            Arc::new(MockBackend::new(
+                vec![("chatgpt", "gpt-4o"), ("claude", "claude-sonnet-4")],
+                per_chunk,
+            ))
+        } else {
+            Arc::new(MockBackend::from_descriptors(descriptors, per_chunk))
+        }
+    } else {
+        registry.clone()
+    };
+
+    let store = Arc::new(ThreadStore::open(&config.resolved_store_path(&layout)).await?);
+    let state = AppState {
+        backend,
+        store,
+        layout: Arc::new(layout.clone()),
+        config: registry.config_handle(),
+        cli_overrides: Arc::new(overrides.clone()),
+        logs: logs.clone(),
+        metrics: Default::default(),
+        started_at: Instant::now(),
+    };
+
+    // Keep the watcher alive for the lifetime of the server.
+    let _watcher = spawn_config_watcher(&layout, Arc::clone(&registry), overrides);
+
+    if config.browser.attach {
+        warn_if_no_browser_is_listening(&config, &layout, &registry);
+    }
+
+    let app = server::router(state);
+    let address = format!("{}:{}", config.server.host, config.server.port);
+    let listener = match tokio::net::TcpListener::bind(&address).await {
+        Ok(listener) => listener,
+        Err(err) => {
+            bail!(
+                "cannot listen on {address}: {err}\n\
+                 Another application is most likely using that port. Either start the \
+                 gateway elsewhere:\n    llm-gateway serve --port 8090\n\
+                 or make it permanent by setting port = 8090 in the [server] section of {}",
+                layout.config_file().display()
+            );
+        }
+    };
+
+    println!(
+        "llm-gateway {VERSION} listening on http://{address}",
+        VERSION = llm_bridge::VERSION
+    );
+    println!("  dashboard   http://{address}/dashboard");
+    println!("  models      http://{address}/v1/models");
+    println!("  state dir   {}", layout.root().display());
+    if let Some(name) = &provider_filter {
+        println!("  provider    {name} (only)");
+    }
+    if config.server.is_public_bind() && config.server.api_key.is_empty() {
+        eprintln!("warning: {address} is reachable from the network and no API key is configured");
+    }
+
+    axum::serve(listener, app)
+        .with_graceful_shutdown(shutdown_signal())
+        .await?;
+    registry.shutdown_all().await;
+    Ok(ExitCode::SUCCESS)
+}
+
+/// Attach mode needs a browser that is already running on the debug port.
+fn warn_if_no_browser_is_listening(
+    config: &GlobalConfig,
+    layout: &Layout,
+    registry: &Arc<ProviderRegistry>,
+) {
+    let address = format!("127.0.0.1:{}", config.browser.debug_port);
+    let reachable = address
+        .parse()
+        .ok()
+        .and_then(|socket| {
+            std::net::TcpStream::connect_timeout(&socket, Duration::from_secs(2)).ok()
+        })
+        .is_some();
+    if reachable {
+        tracing::info!(address = %address, "attach mode: a browser is listening");
+        return;
+    }
+
+    let first = registry.all().first().cloned();
+    let url = first
+        .as_ref()
+        .map(|provider| provider.cfg().web_url().to_string())
+        .unwrap_or_else(|| "about:blank".to_string());
+    let profile = first
+        .as_ref()
+        .map(|provider| config.profile_dir_for(layout, provider.name()))
+        .unwrap_or_else(|| config.resolved_profile_root(layout));
+    let configured = llm_bridge::paths::expand_tilde(&config.browser.executable);
+    let explicit = if config.browser.executable.trim().is_empty() {
+        None
+    } else {
+        Some(&configured)
+    };
+    let executable = resolve_executable(explicit, std::env::var("CHROME").ok());
+
+    eprintln!(
+        "warning: attach mode is on but nothing listens on {address}\n\
+           Start a browser first:\n    {}",
+        external_launch(
+            executable.as_ref(),
+            &profile,
+            &url,
+            Some(config.browser.debug_port)
+        )
+        .command_line()
+    );
+}
+
+/// Watch the provider directory and the configuration file for edits.
+fn spawn_config_watcher(
+    layout: &Layout,
+    registry: Arc<ProviderRegistry>,
+    overrides: CliOverrides,
+) -> Option<notify::RecommendedWatcher> {
+    use notify::{RecursiveMode, Watcher};
+
+    let (tx, mut rx) = tokio::sync::mpsc::channel::<()>(16);
+    let mut watcher = notify::recommended_watcher(move |result: notify::Result<notify::Event>| {
+        if result.is_ok() {
+            let _ = tx.blocking_send(());
+        }
+    })
+    .ok()?;
+
+    if watcher
+        .watch(&layout.providers_dir(), RecursiveMode::NonRecursive)
+        .is_err()
+    {
+        return None;
+    }
+    let _ = watcher.watch(&layout.config_file(), RecursiveMode::NonRecursive);
+
+    let config_path = layout.config_file();
+    let providers_dir = layout.providers_dir();
+    tokio::spawn(async move {
+        while rx.recv().await.is_some() {
+            tokio::time::sleep(Duration::from_millis(500)).await;
+            while rx.try_recv().is_ok() {}
+
+            match GlobalConfig::load(&config_path) {
+                Ok(mut config) => {
+                    config.apply(&overrides);
+                    if let Err(err) = config.validate() {
+                        tracing::warn!(error = %err, "reloaded configuration is invalid, keeping the previous one");
+                    } else {
+                        registry.replace_global(config);
+                    }
+                }
+                Err(err) => tracing::warn!(error = %err, "cannot reload the configuration file"),
+            }
+
+            match registry.reload().await {
+                Ok(report) => {
+                    if !report.added.is_empty()
+                        || !report.updated.is_empty()
+                        || !report.removed.is_empty()
+                    {
+                        tracing::info!(
+                            added = ?report.added,
+                            updated = ?report.updated,
+                            removed = ?report.removed,
+                            "provider configuration reloaded"
+                        );
+                    }
+                }
+                Err(err) => tracing::warn!(error = %err, "cannot reload the providers"),
+            }
+            tracing::debug!(dir = %providers_dir.display(), "watcher woke up");
+        }
+    });
+
+    Some(watcher)
+}
+
+async fn shutdown_signal() {
+    let _ = tokio::signal::ctrl_c().await;
+    println!();
+    tracing::info!("shutting down");
+}
+
+// ---------------------------------------------------------------------------
+// test / selftest / list
+// ---------------------------------------------------------------------------
+
+async fn test(layout: Layout, config: GlobalConfig, args: TestArgs) -> Result<ExitCode> {
+    let registry = build_registry(layout, config).await?;
+    let targets = select_providers(&registry, args.provider.as_deref(), args.all)?;
+    let prompt = args
+        .prompt
+        .unwrap_or_else(|| "Say 'ok' and nothing else.".to_string());
+
+    let mut all_ok = true;
+    let mut results = Vec::new();
+    for (name, account) in targets {
+        let label = owner_label(&name, account.as_deref());
+        let handle = registry
+            .get(&name)
+            .ok_or_else(|| anyhow!("provider '{name}' is not configured"))?;
+        let started = Instant::now();
+        let answer = test_target(&handle, account.as_deref(), &prompt, args.json).await;
+        let elapsed = started.elapsed().as_millis() as u64;
+        // Close the browser this target started before moving on, even when the
+        // turn failed, so a provider with several accounts never keeps more than
+        // one of them alive.
+        shutdown_target(&handle, account.as_deref()).await;
+
+        match answer {
+            Err(err) => {
+                all_ok = false;
+                results.push(serde_json::json!({
+                    "provider": label,
+                    "ok": false,
+                    "elapsed_ms": elapsed,
+                    "error": err.to_string(),
+                }));
+                if !args.json {
+                    println!("failed: {err}");
+                }
+            }
+            Ok(text) => {
+                results.push(serde_json::json!({
+                    "provider": label,
+                    "ok": !text.trim().is_empty(),
+                    "elapsed_ms": elapsed,
+                    "answer": text,
+                }));
+                if !args.json {
+                    println!();
+                    println!(
+                        "-- {label}: {elapsed} ms, {} characters",
+                        text.chars().count()
+                    );
+                }
+            }
+        }
+    }
+
+    if args.json {
+        println!("{}", serde_json::to_string_pretty(&results)?);
+    }
+    Ok(if all_ok {
+        ExitCode::SUCCESS
+    } else {
+        ExitCode::from(2)
+    })
+}
+
+/// Send the probe prompt to one target and return the captured answer.
+///
+/// Deltas are printed as they arrive unless the caller asked for JSON, in which
+/// case only the final text matters.
+async fn test_target(
+    handle: &Arc<WebUiProvider>,
+    account: Option<&str>,
+    prompt: &str,
+    quiet: bool,
+) -> std::result::Result<String, GatewayError> {
+    let session = handle
+        .session(account)
+        .await
+        .map_err(|err| GatewayError::Internal(format!("cannot open a browser session: {err}")))?;
+    let request = TurnRequest {
+        prompt: prompt.to_string(),
+        attachments: Vec::new(),
+        reuse_url: None,
+        replay_history: true,
+        probe: false,
+        trace_id: format!("cli-{}", uuid::Uuid::new_v4().simple()),
+        wait_for_tab: None,
+    };
+
+    if !quiet {
+        print!("{}: ", owner_label(handle.name(), account));
+        let _ = std::io::stdout().flush();
+    }
+
+    let mut stream = handle.run_turn(session, request).await?;
+    let mut text = String::new();
+    while let Some(event) = stream.recv().await {
+        match event {
+            TurnEvent::Delta(delta) => {
+                if !quiet {
+                    print!("{delta}");
+                    let _ = std::io::stdout().flush();
+                }
+                text.push_str(&delta);
+            }
+            TurnEvent::Completed(outcome) => return Ok(outcome.text),
+            TurnEvent::Failed(err) => return Err(err),
+        }
+    }
+    Ok(text)
+}
+
+async fn selftest_command(
+    layout: Layout,
+    config: GlobalConfig,
+    args: llm_bridge::cli::SelftestArgs,
+) -> Result<ExitCode> {
+    let registry = build_registry(layout, config).await?;
+    let names = select_providers(&registry, args.provider.as_deref(), args.all)?;
+    let mut reports = Vec::new();
+    for (name, account) in names {
+        let label = owner_label(&name, account.as_deref());
+        let handle = registry
+            .get(&name)
+            .ok_or_else(|| anyhow!("provider '{name}' is not configured"))?;
+        if !args.json {
+            println!("checking {label}...");
+        }
+        let cfg = handle.cfg();
+        reports.push(selftest::validate_provider(handle.as_ref(), &cfg, account.as_deref()).await?);
+        shutdown_target(&handle, account.as_deref()).await;
+    }
+
+    if args.json {
+        println!("{}", selftest::render_json(&reports));
+    } else {
+        print!("{}", selftest::render_text(&reports));
+    }
+
+    Ok(if selftest::all_ok(&reports) {
+        ExitCode::SUCCESS
+    } else {
+        ExitCode::from(2)
+    })
+}
+
+async fn list(layout: Layout, config: GlobalConfig, json: bool) -> Result<ExitCode> {
+    let registry = build_registry(layout.clone(), config.clone()).await?;
+    let descriptors = ChatBackend::providers(registry.as_ref());
+    if descriptors.is_empty() {
+        println!(
+            "no provider configured in {}",
+            layout.providers_dir().display()
+        );
+        return Ok(ExitCode::SUCCESS);
+    }
+
+    if json {
+        println!("{}", serde_json::to_string_pretty(&descriptors)?);
+        return Ok(ExitCode::SUCCESS);
+    }
+
+    for descriptor in &descriptors {
+        let state = if descriptor.usable {
+            "configured"
+        } else {
+            "misconfigured"
+        };
+        println!(
+            "{:<12} {:<10} {}",
+            descriptor.name, state, descriptor.display_name
+        );
+        println!("{:<12} web      {}", "", descriptor.web_url);
+        if !descriptor.models.is_empty() {
+            println!("{:<12} models   {}", "", descriptor.models.join(", "));
+        }
+        if let Some(browser) = &descriptor.browser {
+            println!("{:<12} engine   {}", "", browser);
+        }
+        for account in &descriptor.accounts {
+            let marker = if account.default { "*" } else { " " };
+            let identity = account
+                .email
+                .clone()
+                .or_else(|| account.label.clone())
+                .unwrap_or_else(|| "-".to_string());
+            println!(
+                "{:<12} {marker} {:<10} {}",
+                "",
+                util::truncate(&account.id, 10),
+                identity
+            );
+        }
+        for problem in &descriptor.problems {
+            println!("{:<12} problem  {}", "", problem);
+        }
+        println!();
+    }
+    println!(
+        "profiles: {}",
+        config.resolved_profile_root(&layout).display()
+    );
+    println!("run 'llm-gateway selftest <provider>' to check a live session");
+    Ok(ExitCode::SUCCESS)
+}
+
+/// Resolve the providers (and accounts) a CLI command must act on.
+///
+/// A name may carry the account: `chatgpt@perso`. With `--all` every provider
+/// is used, and every account each provider declares.
+fn select_providers(
+    registry: &ProviderRegistry,
+    provider: Option<&str>,
+    all: bool,
+) -> Result<Vec<(String, Option<String>)>> {
+    match (provider, all) {
+        (Some(raw), _) => {
+            let (name, account) = split_owner(raw);
+            let Some(handle) = registry.get(&name) else {
+                bail!(
+                    "provider '{name}' is not configured (known: {})",
+                    registry
+                        .all()
+                        .iter()
+                        .map(|provider| provider.name().to_string())
+                        .collect::<Vec<_>>()
+                        .join(", ")
+                );
+            };
+            let cfg = handle.cfg();
+            let account = cfg
+                .resolve_account_id(account.as_deref())
+                .map_err(|detail| anyhow!("{detail}"))?;
+            Ok(vec![(name, account)])
+        }
+        (None, true) => {
+            // Every account is exercised, not just the default one: a provider
+            // that declares several profiles is only fully checked when each of
+            // them answers, and a signed-out second account is exactly the kind
+            // of thing --all exists to catch.
+            let mut targets: Vec<(String, Option<String>)> = Vec::new();
+            for handle in registry.all() {
+                let name = handle.name().to_string();
+                let cfg = handle.cfg();
+                if cfg.has_explicit_accounts() {
+                    for account in cfg.accounts() {
+                        targets.push((name.clone(), Some(account.id.clone())));
+                    }
+                } else {
+                    targets.push((name, None));
+                }
+            }
+            if targets.is_empty() {
+                bail!("no provider is configured");
+            }
+            Ok(targets)
+        }
+        (None, false) => bail!("give a provider name or use --all"),
+    }
+}
+
+/// Stop the browser one CLI target started, without touching its siblings.
+///
+/// A provider with several accounts owns one browser per account, so shutting
+/// the provider down after each of them would close a session the next target
+/// is about to need.
+async fn shutdown_target(handle: &Arc<WebUiProvider>, account: Option<&str>) {
+    let result = match account {
+        Some(account) => handle.shutdown_account(account).await,
+        None => handle.shutdown().await,
+    };
+    if let Err(err) = result {
+        eprintln!(
+            "warning: cannot stop the browser of {}: {err}",
+            owner_label(handle.name(), account)
+        );
+    }
+}
+
+async fn build_registry(layout: Layout, config: GlobalConfig) -> Result<Arc<ProviderRegistry>> {
+    let registry = Arc::new(ProviderRegistry::new(layout, config));
+    let report = registry.reload().await?;
+    for problem in &report.problems {
+        eprintln!("warning: {problem}");
+    }
+    if registry.all().is_empty() {
+        bail!("no provider is configured");
+    }
+    Ok(registry)
+}
+
+// ---------------------------------------------------------------------------
+// login / logout / conversations / reload / config
+// ---------------------------------------------------------------------------
+
+/// Explain how to sign in from a browser the user starts themselves.
+///
+/// This is the configuration OAuth providers such as Google accept: no
+/// automation switch and no debugging port is involved during the sign-in.
+fn print_manual_login(
+    provider: &str,
+    display_name: &str,
+    web_url: &str,
+    profile_dir: &std::path::Path,
+    config: &GlobalConfig,
+) -> Result<llm_bridge::browser::ExternalLaunch> {
+    let configured = llm_bridge::paths::expand_tilde(&config.browser.executable);
+    let explicit = if config.browser.executable.trim().is_empty() {
+        None
+    } else {
+        Some(&configured)
+    };
+    let executable = resolve_executable(explicit, std::env::var("CHROME").ok());
+    let plain = external_launch(executable.as_ref(), profile_dir, web_url, None);
+    let attached = external_launch(
+        executable.as_ref(),
+        profile_dir,
+        web_url,
+        Some(config.browser.debug_port),
+    );
+
+    println!("Sign in from a browser you start yourself: no automation switch and no");
+    println!("debugging port is involved, which is what OAuth providers such as Google");
+    println!("require. The gateway launches its own browser only for later requests.");
+    println!();
+    println!("The command to use (it opens the dedicated profile of {provider}, shown");
+    println!("below, without ever touching your personal Chrome profile):");
+    println!("    {}", plain.command_line());
+    println!();
+    println!("Then sign in to {display_name} in that window.");
+    println!();
+    println!("The session is kept in:");
+    println!("  {}", profile_dir.display());
+    println!();
+    println!("Alternative: keep that window open and let the gateway drive it instead.");
+    println!("Start it with a debugging port and set [browser] attach = true, or pass");
+    println!("--attach:");
+    println!("    {}", attached.command_line());
+    println!();
+    Ok(plain)
+}
+
+/// Ask a yes/no question that defaults to yes.
+async fn confirm_default_yes(question: &str) -> Result<bool> {
+    print!("{question} [Y/n] ");
+    std::io::stdout().flush()?;
+    let line = read_line_blocking().await?;
+    Ok(!matches!(
+        line.trim().to_lowercase().as_str(),
+        "n" | "no" | "non"
+    ))
+}
+
+async fn login(
+    layout: Layout,
+    mut config: GlobalConfig,
+    args: llm_bridge::cli::LoginArgs,
+) -> Result<ExitCode> {
+    let (provider, named_account) = split_owner(&args.provider);
+    // A manual login needs a visible window.
+    config.browser.headless = false;
+    let registry = build_registry(layout.clone(), config.clone()).await?;
+    let handle = registry
+        .get(&provider)
+        .ok_or_else(|| anyhow!("provider '{provider}' is not configured"))?;
+    let cfg = handle.cfg();
+    let requested = args.account.clone().or(named_account);
+    let account = cfg
+        .resolve_account_id(requested.as_deref())
+        .map_err(|detail| anyhow!("{detail}"))?;
+    let label = owner_label(&provider, account.as_deref());
+    let profile_dir = handle
+        .profile_dir(account.as_deref())
+        .ok_or_else(|| anyhow!("provider '{provider}' has no browser profile"))?;
+    if cfg.has_explicit_accounts() {
+        println!("signing in {label} (profile {})", profile_dir.display());
+    }
+
+    if args.manual {
+        let launch = print_manual_login(
+            &label,
+            cfg.display_name(),
+            cfg.web_url(),
+            &profile_dir,
+            &config,
+        )?;
+
+        // Starting the window for the user is the whole point of this mode, but
+        // ask first so a scripted run can do it by hand.
+        if args.launch || confirm_default_yes("Open that browser window now?").await? {
+            match launch.spawn() {
+                Ok(child) => println!("browser started (pid {})", child.id()),
+                Err(err) => eprintln!(
+                    "cannot start the browser ({err}); run the command printed above by hand"
+                ),
+            }
+        }
+
+        println!();
+        println!(
+            "IMPORTANT: sign in to {} in that window first.",
+            cfg.display_name()
+        );
+        println!("  1. sign in with Google (or with an email address and password);");
+        println!("  2. wait until the chat interface is displayed;");
+        println!("  3. CLOSE that window completely, then press Enter here.");
+        println!();
+        read_line_blocking().await?;
+    }
+
+    let session = match handle.session(account.as_deref()).await {
+        Ok(session) => session,
+        Err(GatewayError::BrowserProfileLocked { .. }) => {
+            eprintln!(
+                "the profile is still in use: close the browser window you opened, then run \
+                 'llm-gateway login {label}' again"
+            );
+            return Ok(ExitCode::from(2));
+        }
+        Err(err) => return Err(err.into()),
+    };
+    let page = session.page_handle();
+    dom::goto(&page, cfg.web_url(), Duration::from_secs(60)).await?;
+
+    if !args.manual {
+        println!("A browser window is open on {}", cfg.web_url());
+        println!("Sign in once and complete any captcha; the session is kept in:");
+        println!("  {}", profile_dir.display());
+        println!("Press Enter here when you are signed in.");
+        read_line_blocking().await?;
+    }
+
+    let status = handle
+        .validate_session(account.as_deref(), &session)
+        .await?;
+    println!("session state: {}", status.state.as_str());
+    if let Some(detail) = &status.detail {
+        println!("detail: {detail}");
+    }
+
+    if !status.is_available() {
+        println!();
+        println!("The session is still not signed in. The sign-in has to happen inside the");
+        println!("window while it is open, before it is closed:");
+        println!("  llm-gateway login {label} --manual");
+        println!("  -> answer Y to open the window, sign in, wait for the chat to appear,");
+        println!("     then close the window and press Enter.");
+    }
+
+    handle.shutdown().await?;
+    Ok(if status.is_available() {
+        ExitCode::SUCCESS
+    } else {
+        ExitCode::from(2)
+    })
+}
+
+async fn logout(
+    layout: Layout,
+    config: GlobalConfig,
+    args: llm_bridge::cli::LogoutArgs,
+    yes: bool,
+) -> Result<ExitCode> {
+    let root = config.resolved_profile_root(&layout);
+    let (named_provider, named_account) = match &args.provider {
+        Some(raw) => {
+            let (provider, account) = split_owner(raw);
+            (Some(provider), account)
+        }
+        None => (None, None),
+    };
+    let account = args.account.clone().or(named_account);
+
+    // Every (label, directory) pair the command must remove.
+    let mut targets: Vec<(String, PathBuf)> = Vec::new();
+    match (&named_provider, &account, args.all) {
+        (Some(provider), Some(account), _) => {
+            let registry = build_registry(layout.clone(), config.clone()).await?;
+            let handle = registry
+                .get(provider)
+                .ok_or_else(|| anyhow!("provider '{provider}' is not configured"))?;
+            let cfg = handle.cfg();
+            let resolved = cfg
+                .resolve_account_id(Some(account))
+                .map_err(|detail| anyhow!("{detail}"))?;
+            let dir = handle
+                .profile_dir(resolved.as_deref())
+                .ok_or_else(|| anyhow!("provider '{provider}' has no browser profile"))?;
+            targets.push((owner_label(provider, resolved.as_deref()), dir));
+        }
+        (Some(provider), None, true) => {
+            targets.push((provider.clone(), root.join(provider)));
+        }
+        (Some(provider), None, false) => {
+            let registry = build_registry(layout.clone(), config.clone()).await?;
+            let handle = registry
+                .get(provider)
+                .ok_or_else(|| anyhow!("provider '{provider}' is not configured"))?;
+            let cfg = handle.cfg();
+            if cfg.has_explicit_accounts() {
+                let known: Vec<String> = cfg
+                    .accounts()
+                    .map(|account| {
+                        format!(
+                            "{} ({})",
+                            account.id,
+                            account.email.clone().unwrap_or_else(|| "-".into())
+                        )
+                    })
+                    .collect();
+                println!(
+                    "{provider} declares several accounts; name one with --account, or remove \
+                     them all with --all"
+                );
+                println!("  accounts: {}", known.join(", "));
+                return Ok(ExitCode::SUCCESS);
+            }
+            let dir = handle
+                .profile_dir(None)
+                .ok_or_else(|| anyhow!("provider '{provider}' has no browser profile"))?;
+            targets.push((provider.clone(), dir));
+        }
+        (None, _, true) => {
+            let entries = std::fs::read_dir(&root)
+                .map(|entries| {
+                    entries
+                        .flatten()
+                        .filter(|entry| entry.path().is_dir())
+                        .map(|entry| {
+                            (
+                                entry.file_name().to_string_lossy().to_string(),
+                                entry.path(),
+                            )
+                        })
+                        .collect::<Vec<_>>()
+                })
+                .unwrap_or_default();
+            targets = entries;
+        }
+        (None, _, false) => bail!("give a provider name or use --all"),
+    }
+
+    if targets.is_empty() {
+        println!("no stored profile in {}", root.display());
+        return Ok(ExitCode::SUCCESS);
+    }
+
+    for (label, dir) in targets {
+        if !dir.exists() {
+            println!("{label}: no stored profile");
+            continue;
+        }
+        if !confirm(
+            &format!("delete the browser profile of {label} ({})?", dir.display()),
+            yes,
+        )
+        .await?
+        {
+            println!("{label}: skipped");
+            continue;
+        }
+        match std::fs::remove_dir_all(&dir) {
+            Ok(()) => println!("{label}: profile deleted"),
+            Err(err) => eprintln!(
+                "{label}: cannot delete {} ({err}); close the browser window opened by llm-gateway and retry",
+                dir.display()
+            ),
+        }
+    }
+    Ok(ExitCode::SUCCESS)
+}
+
+async fn conversations(
+    layout: Layout,
+    config: GlobalConfig,
+    command: ConversationsCommand,
+    yes: bool,
+) -> Result<ExitCode> {
+    let store = ThreadStore::open(&config.resolved_store_path(&layout)).await?;
+    match command {
+        ConversationsCommand::List {
+            provider,
+            account,
+            json,
+        } => {
+            let (provider, account) = conversation_filter(provider.as_deref(), account);
+            let threads = store.list(provider.as_deref(), account.as_deref()).await;
+            if json {
+                let value: Vec<serde_json::Value> = threads
+                    .iter()
+                    .map(|(id, record)| {
+                        serde_json::json!({ "conversation_id": id, "thread": record })
+                    })
+                    .collect();
+                println!("{}", serde_json::to_string_pretty(&value)?);
+                return Ok(ExitCode::SUCCESS);
+            }
+            if threads.is_empty() {
+                println!("no stored conversation");
+                return Ok(ExitCode::SUCCESS);
+            }
+            println!(
+                "{:<22} {:<10} {:<10} {:>6} {:<11} web conversation",
+                "conversation", "provider", "account", "turns", "state"
+            );
+            for (id, record) in threads {
+                println!(
+                    "{:<22} {:<10} {:<10} {:>6} {:<11} {}",
+                    util::truncate(&id, 20),
+                    record.provider,
+                    record.account.as_deref().unwrap_or(IMPLICIT_ACCOUNT),
+                    record.turns,
+                    match record.state {
+                        llm_bridge::conversation::ThreadState::Ready => "ready",
+                        llm_bridge::conversation::ThreadState::Incomplete => "incomplete",
+                    },
+                    record.web_url.unwrap_or_else(|| "-".to_string())
+                );
+            }
+        }
+        ConversationsCommand::Clear { provider, account } => {
+            let (provider, account) = conversation_filter(provider.as_deref(), account);
+            let scope = match (&provider, &account) {
+                (Some(provider), Some(account)) => format!("{provider}@{account}"),
+                (Some(provider), None) => provider.clone(),
+                (None, Some(account)) => format!("account '{account}' of every provider"),
+                (None, None) => "every provider".to_string(),
+            };
+            if confirm(&format!("delete the stored conversations of {scope}?"), yes).await? {
+                let removed = store.clear(provider.as_deref(), account.as_deref()).await?;
+                println!("{removed} conversation(s) removed");
+            } else {
+                println!("nothing removed");
+            }
+        }
+    }
+    Ok(ExitCode::SUCCESS)
+}
+
+/// Split a `provider[@account]` conversation filter into the two parts a store
+/// query takes. An explicit `--account` wins over the one in the provider name.
+fn conversation_filter(
+    provider: Option<&str>,
+    account: Option<String>,
+) -> (Option<String>, Option<String>) {
+    match provider {
+        Some(raw) => {
+            let (name, named) = split_owner(raw);
+            (Some(name), account.or(named))
+        }
+        None => (None, account),
+    }
+}
+
+async fn reload(config: GlobalConfig) -> Result<ExitCode> {
+    let url = format!(
+        "http://{}:{}/v1/admin/reload",
+        config.server.host, config.server.port
+    );
+    let client = reqwest::Client::new();
+    let mut request = client.post(&url);
+    if !config.server.api_key.is_empty() {
+        request = request.bearer_auth(&config.server.api_key);
+    }
+    let response = request.send().await.with_context(|| {
+        format!(
+            "POST {url} failed: is the server running, and on that port? start it with the \
+                 same --port (or set [server] port in the configuration file)"
+        )
+    })?;
+    let status = response.status();
+    let body = response.text().await.unwrap_or_default();
+    if status.is_success() {
+        println!("{body}");
+        Ok(ExitCode::SUCCESS)
+    } else {
+        bail!("reload failed with HTTP {status}: {body}")
+    }
+}
+
+fn config_command(
+    layout: Layout,
+    config: GlobalConfig,
+    command: ConfigCommand,
+) -> Result<ExitCode> {
+    match command {
+        ConfigCommand::Path => println!("{}", layout.config_file().display()),
+        ConfigCommand::Init { force } => {
+            layout.ensure()?;
+            println!("state directory ready: {}", layout.root().display());
+            println!("  config    {}", layout.config_file().display());
+            println!("  providers {}", layout.providers_dir().display());
+
+            if force {
+                let written = layout.install_default_providers(true)?;
+                if written.is_empty() {
+                    println!("no provider file was replaced");
+                }
+                for path in written {
+                    println!(
+                        "  refreshed {} (previous version kept as {}.bak)",
+                        path.display(),
+                        path.display()
+                    );
+                }
+            }
+        }
+        ConfigCommand::Show => {
+            println!("{}", toml::to_string_pretty(&config)?);
+        }
+    }
+    Ok(ExitCode::SUCCESS)
+}
+
+// ---------------------------------------------------------------------------
+// helpers
+// ---------------------------------------------------------------------------
+
+async fn confirm(question: &str, assume_yes: bool) -> Result<bool> {
+    if assume_yes {
+        return Ok(true);
+    }
+    print!("{question} [y/N] ");
+    std::io::stdout().flush()?;
+    let line = read_line_blocking().await?;
+    Ok(matches!(
+        line.trim().to_lowercase().as_str(),
+        "y" | "yes" | "o" | "oui"
+    ))
+}
+
+async fn read_line_blocking() -> Result<String> {
+    tokio::task::spawn_blocking(|| {
+        let mut line = String::new();
+        std::io::stdin().read_line(&mut line)?;
+        Ok::<String, std::io::Error>(line)
+    })
+    .await
+    .context("waiting for input")?
+    .context("reading input")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A registry with a two-account provider and a single-account one.
+    async fn registry_with_accounts() -> (Arc<ProviderRegistry>, tempfile::TempDir) {
+        let tmp = tempfile::tempdir().unwrap();
+        let layout = Layout::rooted_at(tmp.path().join("state"));
+        layout.ensure().unwrap();
+        for name in ["chatgpt", "claude", "deepseek"] {
+            std::fs::remove_file(layout.provider_config(name)).ok();
+        }
+        let accounts = r#"
+[[accounts]]
+id = "perso"
+email = "bruno.charest@gmail.com"
+default = true
+
+[[accounts]]
+id = "pro"
+email = "brunocharest.bc@gmail.com"
+"#;
+        std::fs::write(
+            layout.provider_config("chatgpt"),
+            format!("{}{accounts}", include_str!("../providers/chatgpt.toml")),
+        )
+        .unwrap();
+        std::fs::write(
+            layout.provider_config("claude"),
+            include_str!("../providers/claude.toml"),
+        )
+        .unwrap();
+
+        let registry = Arc::new(ProviderRegistry::new(layout, GlobalConfig::default()));
+        registry.reload().await.unwrap();
+        (registry, tmp)
+    }
+
+    #[tokio::test]
+    async fn a_named_account_is_resolved_from_the_provider_argument() {
+        let (registry, _tmp) = registry_with_accounts().await;
+        let targets = select_providers(&registry, Some("chatgpt@pro"), false).unwrap();
+        assert_eq!(
+            targets,
+            vec![("chatgpt".to_string(), Some("pro".to_string()))]
+        );
+
+        // The default account is used when the name carries none.
+        let targets = select_providers(&registry, Some("chatgpt"), false).unwrap();
+        assert_eq!(
+            targets,
+            vec![("chatgpt".to_string(), Some("perso".to_string()))]
+        );
+
+        let err = select_providers(&registry, Some("chatgpt@nobody"), false).unwrap_err();
+        assert!(err.to_string().contains("no account 'nobody'"), "{err}");
+    }
+
+    #[tokio::test]
+    async fn all_covers_every_account_of_every_provider() {
+        let (registry, _tmp) = registry_with_accounts().await;
+        let targets = select_providers(&registry, None, true).unwrap();
+        assert_eq!(
+            targets,
+            vec![
+                ("chatgpt".to_string(), Some("perso".to_string())),
+                ("chatgpt".to_string(), Some("pro".to_string())),
+                // A provider without accounts keeps its single implicit one.
+                ("claude".to_string(), None),
+            ]
+        );
+    }
+
+    #[test]
+    fn the_conversation_filter_splits_the_provider_and_the_account() {
+        assert_eq!(
+            conversation_filter(Some("chatgpt@perso"), None),
+            (Some("chatgpt".to_string()), Some("perso".to_string()))
+        );
+        assert_eq!(
+            conversation_filter(Some("claude"), None),
+            (Some("claude".to_string()), None)
+        );
+        assert_eq!(
+            conversation_filter(None, Some("pro".to_string())),
+            (None, Some("pro".to_string()))
+        );
+        // An explicit flag wins over the one riding along with the provider.
+        assert_eq!(
+            conversation_filter(Some("chatgpt@perso"), Some("pro".to_string())),
+            (Some("chatgpt".to_string()), Some("pro".to_string()))
+        );
+    }
+}
diff --git a/src/markdown.rs b/src/markdown.rs
new file mode 100644
index 0000000..e66cb99
--- /dev/null
+++ b/src/markdown.rs
@@ -0,0 +1,1380 @@
+//! HTML to Markdown conversion for captured answers.
+//!
+//! The gateway reads answers from a signed-in browser page, so the text it
+//! forwards was written for a human looking at rendered HTML. `innerText` keeps
+//! the words and drops the structure: a table collapses into a column of
+//! unrelated lines and a code block loses its fences, so the next model in the
+//! chain cannot tell code from prose. Capturing `innerHTML` instead keeps that
+//! structure, and this module turns it back into Markdown.
+//!
+//! The converter is deliberately self-contained: no browser, no network and no
+//! HTML parser crate, because the markup is whatever a third party UI happens
+//! to ship. The tokenizer is tolerant by design, so malformed markup degrades
+//! into the readable text around it, and both parsing and rendering run on
+//! explicit stacks, so no input can overflow the stack, spin forever or panic.
+
+/// Depth beyond which start tags are ignored.
+///
+/// Real answers nest a handful of levels; the cap only stops a hostile page
+/// from making the converter allocate without bound.
+const MAX_DEPTH: usize = 128;
+
+/// Elements whose content is text rather than markup, so it is skipped whole.
+const RAW_TEXT_ELEMENTS: [&str; 4] = ["script", "style", "textarea", "title"];
+
+/// Elements that never have children and never need a closing tag.
+const VOID_ELEMENTS: [&str; 14] = [
+    "area", "base", "br", "col", "embed", "hr", "img", "input", "link", "meta", "param", "source",
+    "track", "wbr",
+];
+
+/// Elements that are a block of their own and are followed by a blank line.
+const BLOCK_ELEMENTS: [&str; 12] = [
+    "p",
+    "div",
+    "section",
+    "article",
+    "header",
+    "footer",
+    "main",
+    "aside",
+    "figure",
+    "figcaption",
+    "dd",
+    "dt",
+];
+
+/// Convert the inner HTML of one answer node into Markdown.
+pub fn html_to_markdown(html: &str) -> String {
+    if html.trim().is_empty() {
+        return String::new();
+    }
+    let root = parse(html);
+    tidy(&render(&root.children))
+}
+
+/// True when the HTML contains a construct a plain text extraction would lose
+/// (a fenced code block, a table row, a list item, a heading, a link).
+pub fn has_rich_structure(html: &str) -> bool {
+    // Callers use this to choose between `innerText` and `innerHTML`, so a cheap
+    // approximate scan is enough; an exact answer would mean parsing twice.
+    const MARKERS: [&str; 12] = [
+        "<pre", "<table", "<ul", "<ol", "<li", "<h1", "<h2", "<h3", "<h4", "<h5", "<h6", "<a ",
+    ];
+    let lower = html.to_ascii_lowercase();
+    MARKERS.iter().any(|marker| lower.contains(marker))
+}
+
+/// Collapse the whitespace of a Markdown document without touching fenced code
+/// blocks: trim trailing spaces per line, drop runs of more than two blank
+/// lines down to one blank line, and end with exactly one newline (or an empty
+/// string when there is no content).
+pub fn tidy(markdown: &str) -> String {
+    let mut out = String::with_capacity(markdown.len());
+    let mut pending_blank = false;
+    let mut fence: Option<String> = None;
+
+    for raw_line in markdown.split('\n') {
+        // A carriage return only survives a CRLF document: line ending noise.
+        let line = raw_line.strip_suffix('\r').unwrap_or(raw_line);
+
+        if let Some(opening) = fence.as_deref() {
+            // Inside a fence the text is code the user wrote, so it is copied
+            // through untouched, blank lines, indentation and trailing spaces
+            // included.
+            out.push_str(line);
+            out.push('\n');
+            if closes_fence(line, opening) {
+                fence = None;
+            }
+            continue;
+        }
+
+        let line = line.trim_end_matches([' ', '\t']);
+        if line.is_empty() {
+            // Remembered rather than written: a blank line only exists when
+            // something follows it, which also drops the ones at the end.
+            pending_blank = true;
+            continue;
+        }
+        if let Some(opening) = opening_fence(line) {
+            fence = Some(opening);
+        }
+        if pending_blank && !out.is_empty() {
+            out.push('\n');
+        }
+        pending_blank = false;
+        out.push_str(line);
+        out.push('\n');
+    }
+
+    out
+}
+
+/// The run of backticks that opens a fenced block, when a line starts one.
+fn opening_fence(line: &str) -> Option<String> {
+    let run: String = line
+        .trim_start()
+        .chars()
+        .take_while(|character| *character == '`')
+        .collect();
+    if run.len() >= 3 {
+        Some(run)
+    } else {
+        None
+    }
+}
+
+/// True when a line closes the fence it is inside.
+fn closes_fence(line: &str, opening: &str) -> bool {
+    let trimmed = line.trim();
+    trimmed.len() >= opening.len() && trimmed.chars().all(|character| character == '`')
+}
+
+/// One node of the parsed document.
+#[derive(Debug)]
+enum Node {
+    Element(Element),
+    /// Entity-decoded text, otherwise exactly as written: whitespace is only
+    /// collapsed when the text is rendered, so a fenced block still reads it
+    /// verbatim.
+    Text(String),
+}
+
+/// One element: a lowercased name, decoded attributes and its children.
+#[derive(Debug, Default)]
+struct Element {
+    name: String,
+    attributes: Vec<(String, String)>,
+    children: Vec<Node>,
+}
+
+impl Element {
+    /// The value of an attribute, matched by its lowercased name.
+    fn attr(&self, name: &str) -> Option<&str> {
+        self.attributes
+            .iter()
+            .find(|(key, _)| key == name)
+            .map(|(_, value)| value.as_str())
+    }
+}
+
+/// Parse HTML into a tree, tolerating anything.
+///
+/// Text that no rule understands still ends up somewhere sensible, and an
+/// unterminated construct simply ends the document: a broken page must never
+/// cost an answer that is already half readable.
+fn parse(html: &str) -> Element {
+    let mut stack: Vec<Element> = vec![Element::default()];
+    let bytes = html.as_bytes();
+    let mut cursor = 0usize;
+
+    while cursor < bytes.len() {
+        if bytes.get(cursor) != Some(&b'<') {
+            let start = cursor;
+            while let Some(byte) = bytes.get(cursor) {
+                if *byte == b'<' {
+                    break;
+                }
+                cursor += 1;
+            }
+            if let Some(text) = html.get(start..cursor) {
+                push_text_node(&mut stack, text);
+            }
+            continue;
+        }
+
+        let rest = html.get(cursor..).unwrap_or("");
+
+        // Comments, doctypes and processing instructions carry no answer text.
+        if rest.starts_with("<!--") {
+            cursor = match rest.find("-->") {
+                Some(offset) => cursor + offset + 3,
+                None => bytes.len(),
+            };
+            continue;
+        }
+        if rest.starts_with("<!") || rest.starts_with("<?") {
+            cursor = match rest.find('>') {
+                Some(offset) => cursor + offset + 1,
+                None => bytes.len(),
+            };
+            continue;
+        }
+
+        if rest.starts_with("</") {
+            let name_start = cursor + 2;
+            let mut end = name_start;
+            while let Some(byte) = bytes.get(end) {
+                if byte.is_ascii_whitespace() || *byte == b'>' {
+                    break;
+                }
+                end += 1;
+            }
+            let name = html.get(name_start..end).unwrap_or("").to_ascii_lowercase();
+            cursor = match html.get(end..).and_then(|tail| tail.find('>')) {
+                Some(offset) => end + offset + 1,
+                None => bytes.len(),
+            };
+            close_element(&mut stack, &name);
+            continue;
+        }
+
+        if rest
+            .as_bytes()
+            .get(1)
+            .is_some_and(|byte| byte.is_ascii_alphabetic())
+        {
+            let (name, attributes, self_closing, end) = read_start_tag(html, cursor);
+            cursor = end;
+            if name.is_empty() {
+                continue;
+            }
+            if RAW_TEXT_ELEMENTS.contains(&name.as_str()) && !self_closing {
+                cursor = skip_raw_text(html, end, &name);
+                continue;
+            }
+            let element = Element {
+                name: name.clone(),
+                attributes,
+                children: Vec::new(),
+            };
+            if self_closing || VOID_ELEMENTS.contains(&name.as_str()) || stack.len() >= MAX_DEPTH {
+                // A void element, a self-closing tag, or markup nested deeper
+                // than any real answer goes: the content is kept, the wrapper
+                // is not.
+                if let Some(parent) = stack.last_mut() {
+                    parent.children.push(Node::Element(element));
+                }
+            } else {
+                stack.push(element);
+            }
+            continue;
+        }
+
+        // A `<` that opens nothing is text, which is what a browser shows too.
+        push_text_node(&mut stack, "<");
+        cursor += 1;
+    }
+
+    close_until(&mut stack, 1);
+    stack.pop().unwrap_or_default()
+}
+
+/// Read one start tag: its lowercased name, its decoded attributes, whether it
+/// closes itself, and the position just past the final `>`.
+fn read_start_tag(html: &str, start: usize) -> (String, Vec<(String, String)>, bool, usize) {
+    let bytes = html.as_bytes();
+    let mut cursor = start + 1;
+    let name_start = cursor;
+    while let Some(byte) = bytes.get(cursor) {
+        if byte.is_ascii_whitespace() || *byte == b'>' || *byte == b'/' {
+            break;
+        }
+        cursor += 1;
+    }
+    let name = html
+        .get(name_start..cursor)
+        .unwrap_or("")
+        .to_ascii_lowercase();
+
+    let mut attributes: Vec<(String, String)> = Vec::new();
+    let mut self_closing = false;
+
+    loop {
+        let before = cursor;
+        while let Some(byte) = bytes.get(cursor) {
+            if byte.is_ascii_whitespace() {
+                cursor += 1;
+            } else {
+                break;
+            }
+        }
+
+        match bytes.get(cursor).copied() {
+            None => break,
+            Some(b'>') => {
+                cursor += 1;
+                break;
+            }
+            Some(b'/') => {
+                self_closing = true;
+                cursor += 1;
+            }
+            Some(_) => {
+                let attribute_start = cursor;
+                while let Some(byte) = bytes.get(cursor) {
+                    if byte.is_ascii_whitespace() || *byte == b'=' || *byte == b'>' || *byte == b'/'
+                    {
+                        break;
+                    }
+                    cursor += 1;
+                }
+                let attribute = html
+                    .get(attribute_start..cursor)
+                    .unwrap_or("")
+                    .to_ascii_lowercase();
+                while let Some(byte) = bytes.get(cursor) {
+                    if byte.is_ascii_whitespace() {
+                        cursor += 1;
+                    } else {
+                        break;
+                    }
+                }
+
+                let mut value = String::new();
+                if bytes.get(cursor) == Some(&b'=') {
+                    cursor += 1;
+                    while let Some(byte) = bytes.get(cursor) {
+                        if byte.is_ascii_whitespace() {
+                            cursor += 1;
+                        } else {
+                            break;
+                        }
+                    }
+                    match bytes.get(cursor).copied() {
+                        Some(quote) if quote == b'"' || quote == b'\'' => {
+                            cursor += 1;
+                            let value_start = cursor;
+                            while let Some(byte) = bytes.get(cursor) {
+                                if *byte == quote {
+                                    break;
+                                }
+                                cursor += 1;
+                            }
+                            value = html.get(value_start..cursor).unwrap_or("").to_string();
+                            // An unterminated quote runs to the end of the
+                            // document; the value stays a best effort.
+                            if bytes.get(cursor) == Some(&quote) {
+                                cursor += 1;
+                            }
+                        }
+                        None | Some(b'>') => {}
+                        Some(_) => {
+                            let value_start = cursor;
+                            while let Some(byte) = bytes.get(cursor) {
+                                if byte.is_ascii_whitespace() || *byte == b'>' {
+                                    break;
+                                }
+                                cursor += 1;
+                            }
+                            value = html.get(value_start..cursor).unwrap_or("").to_string();
+                        }
+                    }
+                }
+
+                if !attribute.is_empty() {
+                    attributes.push((attribute, decode_entities(&value)));
+                }
+            }
+        }
+
+        // Every turn consumes at least one byte; the guard is what keeps that
+        // true even for markup this reader has not thought of.
+        if cursor == before {
+            cursor += 1;
+        }
+    }
+
+    (name, attributes, self_closing, cursor)
+}
+
+/// Append a text node, decoding its entities on the way in.
+fn push_text_node(stack: &mut [Element], text: &str) {
+    if let Some(parent) = stack.last_mut() {
+        parent.children.push(Node::Text(decode_entities(text)));
+    }
+}
+
+/// Close the innermost open element with this name.
+///
+/// A stray end tag is ignored, while one that closes an outer element also
+/// closes the elements it still contains, which is what a browser does with
+/// mismatched markup.
+fn close_element(stack: &mut Vec<Element>, name: &str) {
+    if name.is_empty() {
+        return;
+    }
+    if let Some(index) = stack.iter().rposition(|element| element.name == name) {
+        close_until(stack, index);
+    }
+}
+
+/// Pop open elements down to `keep`, attaching each one to its new parent.
+fn close_until(stack: &mut Vec<Element>, keep: usize) {
+    while stack.len() > keep {
+        match stack.pop() {
+            Some(element) => {
+                if let Some(parent) = stack.last_mut() {
+                    parent.children.push(Node::Element(element));
+                }
+            }
+            None => return,
+        }
+    }
+}
+
+/// Skip the content of a raw text element, returning the position just past its
+/// end tag.
+fn skip_raw_text(html: &str, from: usize, name: &str) -> usize {
+    let needle = format!("</{name}");
+    match find_ascii_case_insensitive(html.as_bytes(), needle.as_bytes(), from) {
+        Some(index) => match html.get(index..).and_then(|tail| tail.find('>')) {
+            Some(offset) => index + offset + 1,
+            None => html.len(),
+        },
+        None => html.len(),
+    }
+}
+
+/// Find `needle` in `haystack` from `from`, comparing ASCII case-insensitively.
+fn find_ascii_case_insensitive(haystack: &[u8], needle: &[u8], from: usize) -> Option<usize> {
+    if needle.is_empty() || haystack.len() < needle.len() {
+        return None;
+    }
+    let last = haystack.len() - needle.len();
+    let mut index = from;
+    while index <= last {
+        let window = haystack.get(index..index + needle.len())?;
+        if window.eq_ignore_ascii_case(needle) {
+            return Some(index);
+        }
+        index += 1;
+    }
+    None
+}
+
+/// Decode the HTML entities that show up in captured answers.
+///
+/// Anything unrecognised is left exactly as it was written, because a stray
+/// ampersand in prose is far more common than an entity this table has missed.
+fn decode_entities(text: &str) -> String {
+    if !text.contains('&') {
+        return text.to_string();
+    }
+    let mut out = String::with_capacity(text.len());
+    let mut rest = text;
+    while let Some(index) = rest.find('&') {
+        out.push_str(rest.get(..index).unwrap_or(""));
+        let tail = rest.get(index..).unwrap_or("");
+        match decode_one(tail) {
+            Some((decoded, consumed)) => {
+                out.push(decoded);
+                rest = tail.get(consumed..).unwrap_or("");
+            }
+            None => {
+                out.push('&');
+                rest = tail.get(1..).unwrap_or("");
+            }
+        }
+    }
+    out.push_str(rest);
+    out
+}
+
+/// Decode the single entity a string starts with, with its length in bytes.
+fn decode_one(tail: &str) -> Option<(char, usize)> {
+    let body = tail.strip_prefix('&')?;
+    let end = body.find(';')?;
+    let name = body.get(..end)?;
+    // A bare ampersand must not swallow the rest of a sentence, so only a short
+    // reference is considered at all.
+    if name.is_empty() || name.len() > 32 {
+        return None;
+    }
+
+    let decoded = if let Some(digits) = name.strip_prefix('#') {
+        let code = match digits.strip_prefix(['x', 'X']) {
+            Some(hex) => u32::from_str_radix(hex, 16).ok()?,
+            None => digits.parse::<u32>().ok()?,
+        };
+        match char::from_u32(code) {
+            // Out of range or a lone surrogate: the replacement character is
+            // the honest answer, and it cannot panic.
+            Some(character) if character != '\0' => character,
+            _ => '\u{fffd}',
+        }
+    } else {
+        named_entity(name)?
+    };
+
+    Some((decoded, end + 2))
+}
+
+/// The character behind a named entity, or `None` when it is not one we know.
+fn named_entity(name: &str) -> Option<char> {
+    // Matching ignores case: pages spell `&AMP;` and `&Nbsp;` too.
+    let character = match name.to_ascii_lowercase().as_str() {
+        "amp" => '&',
+        "lt" => '<',
+        "gt" => '>',
+        "quot" => '"',
+        "apos" => '\'',
+        "nbsp" => '\u{a0}',
+        "mdash" => '—',
+        "ndash" => '–',
+        "hellip" => '…',
+        "laquo" => '«',
+        "raquo" => '»',
+        "times" => '×',
+        "copy" => '©',
+        "reg" => '®',
+        "deg" => '°',
+        "middot" => '·',
+        "bull" => '•',
+        "eacute" => 'é',
+        "egrave" => 'è',
+        "agrave" => 'à',
+        "ccedil" => 'ç',
+        "uuml" => 'ü',
+        "ouml" => 'ö',
+        "auml" => 'ä',
+        _ => return None,
+    };
+    Some(character)
+}
+
+/// Collapse runs of layout whitespace into a single space, the way HTML itself
+/// does. A non-breaking space is content rather than layout and survives.
+fn collapse_whitespace(text: &str) -> String {
+    let mut out = String::with_capacity(text.len());
+    let mut in_space = false;
+    for character in text.chars() {
+        match character {
+            ' ' | '\t' | '\n' | '\r' | '\u{c}' => {
+                if !in_space {
+                    out.push(' ');
+                    in_space = true;
+                }
+            }
+            _ => {
+                out.push(character);
+                in_space = false;
+            }
+        }
+    }
+    out
+}
+
+/// One unit of work for the iterative renderer.
+enum Work<'a> {
+    /// Render a node of the parsed tree.
+    Node(&'a Node),
+    /// Append literal Markdown.
+    Emit(String),
+    /// Start a new line when the current one already holds something.
+    Break,
+    /// Push a buffer that the matching `Finish` will consume.
+    Capture(Capture),
+    /// Close the innermost capture and turn it into Markdown.
+    Finish,
+}
+
+/// Why a buffer is being captured: the text has to be complete before it can be
+/// wrapped (a link label), prefixed (a quote or a list item) or cut into cells.
+enum Capture {
+    Link { href: String },
+    Quote,
+    Item { ordered: bool, index: usize },
+    Row { header: bool, cells: Vec<String> },
+    Cell { colspan: usize },
+}
+
+/// Render a slice of nodes into Markdown.
+///
+/// The walk runs on an explicit stack of work items - a node becomes the items
+/// that produce its Markdown - so the traversal stays flat however deeply the
+/// document nests.
+fn render(nodes: &[Node]) -> String {
+    let mut buffers: Vec<String> = vec![String::new()];
+    let mut captures: Vec<Capture> = Vec::new();
+    let mut work: Vec<Work<'_>> = nodes.iter().rev().map(Work::Node).collect();
+
+    while let Some(item) = work.pop() {
+        match item {
+            Work::Emit(text) => push_text(&mut buffers, &text),
+            Work::Break => ensure_newline(&mut buffers),
+            Work::Capture(capture) => {
+                captures.push(capture);
+                buffers.push(String::new());
+            }
+            Work::Finish => finish_capture(&mut buffers, &mut captures),
+            Work::Node(Node::Text(text)) => {
+                let collapsed = collapse_whitespace(text);
+                // The indentation of the markup must not become a leading space
+                // on a fresh line, while on a line in progress it is what keeps
+                // `a <b>b</b>` from running into `ab`.
+                let collapsed = if at_line_start(&buffers) {
+                    collapsed.trim_start_matches(' ')
+                } else {
+                    collapsed.as_str()
+                };
+                if !collapsed.is_empty() {
+                    push_text(&mut buffers, collapsed);
+                }
+            }
+            Work::Node(Node::Element(element)) => push_element(element, &mut work),
+        }
+    }
+
+    // A capture left open would swallow its text, so anything still pending is
+    // unwound into the buffer below it.
+    while buffers.len() > 1 {
+        finish_capture(&mut buffers, &mut captures);
+    }
+    buffers.pop().unwrap_or_default()
+}
+
+/// Turn one element into the work items that render it.
+fn push_element<'a>(element: &'a Element, work: &mut Vec<Work<'a>>) {
+    let mut parts: Vec<Work<'a>> = Vec::new();
+
+    match element.name.as_str() {
+        // Markdown's hard break is two trailing spaces. `tidy` trims them, so
+        // the caller sees a plain newline, which is what a reader expects.
+        "br" => parts.push(Work::Emit("  \n".to_string())),
+        "hr" => {
+            parts.push(Work::Break);
+            parts.push(Work::Emit("---\n\n".to_string()));
+        }
+        "img" => {
+            let image = image_markdown(element);
+            if !image.is_empty() {
+                parts.push(Work::Emit(image));
+            }
+        }
+        // Fenced blocks and inline code spans read their own text, so their
+        // children are never walked as markup.
+        "pre" => {
+            parts.push(Work::Break);
+            parts.push(Work::Emit(fenced_block(element)));
+        }
+        "code" => {
+            let span = inline_code(element);
+            if !span.is_empty() {
+                parts.push(Work::Emit(span));
+            }
+        }
+        "blockquote" => {
+            parts.push(Work::Break);
+            parts.push(Work::Capture(Capture::Quote));
+            parts.extend(children(element));
+            parts.push(Work::Finish);
+        }
+        "ul" | "ol" => {
+            parts.push(Work::Break);
+            push_list(element, element.name == "ol", &mut parts);
+        }
+        "table" => {
+            parts.push(Work::Break);
+            push_table(element, &mut parts);
+        }
+        "a" => {
+            let href = element.attr("href").unwrap_or_default().to_string();
+            parts.push(Work::Capture(Capture::Link { href }));
+            parts.extend(children(element));
+            parts.push(Work::Finish);
+        }
+        "h1" | "h2" | "h3" | "h4" | "h5" | "h6" => {
+            let level = heading_level(&element.name);
+            parts.push(Work::Break);
+            parts.push(Work::Emit(format!("{} ", "#".repeat(level))));
+            parts.extend(children(element));
+            parts.push(Work::Emit("\n\n".to_string()));
+        }
+        "strong" | "b" => parts.extend(wrapped("**", element)),
+        "em" | "i" => parts.extend(wrapped("*", element)),
+        "del" | "s" | "strike" => parts.extend(wrapped("~~", element)),
+        name if BLOCK_ELEMENTS.contains(&name) => {
+            parts.push(Work::Break);
+            parts.extend(children(element));
+            parts.push(Work::Emit("\n\n".to_string()));
+        }
+        // Unknown elements, and cells or items met outside their table or list,
+        // keep their content and nothing else.
+        _ => parts.extend(children(element)),
+    }
+
+    // The stack is popped from the back, so the parts go on in reverse.
+    for part in parts.into_iter().rev() {
+        work.push(part);
+    }
+}
+
+/// The heading level of an `h1`..`h6` element.
+fn heading_level(name: &str) -> usize {
+    name.as_bytes()
+        .last()
+        .map_or(1, |digit| usize::from(digit.saturating_sub(b'0')))
+        .clamp(1, 6)
+}
+
+/// Emphasised or struck-through content: a marker on either side.
+fn wrapped<'a>(marker: &str, element: &'a Element) -> Vec<Work<'a>> {
+    let mut parts = vec![Work::Emit(marker.to_string())];
+    parts.extend(children(element));
+    parts.push(Work::Emit(marker.to_string()));
+    parts
+}
+
+/// One work item per child, in document order.
+fn children<'a>(element: &'a Element) -> Vec<Work<'a>> {
+    element.children.iter().map(Work::Node).collect()
+}
+
+/// Add the items that render a `ul` or `ol`.
+fn push_list<'a>(element: &'a Element, ordered: bool, parts: &mut Vec<Work<'a>>) {
+    let mut index = 0usize;
+    for child in &element.children {
+        match child {
+            Node::Element(item) if item.name == "li" => {
+                parts.push(Work::Capture(Capture::Item { ordered, index }));
+                parts.extend(children(item));
+                parts.push(Work::Finish);
+                index += 1;
+            }
+            // Anything a list holds besides its items is kept as it is.
+            other => parts.push(Work::Node(other)),
+        }
+    }
+    // A list is followed by a blank line, so the next block starts cleanly.
+    parts.push(Work::Emit("\n".to_string()));
+}
+
+/// Add the items that render a `table`.
+fn push_table<'a>(element: &'a Element, parts: &mut Vec<Work<'a>>) {
+    let rows = table_rows(element);
+    if rows.is_empty() {
+        // A table with no rows holds nothing a reader would miss.
+        return;
+    }
+    // Markdown tables need a header row; when the markup names none, the first
+    // row takes that role, which is what a reader of the page would assume.
+    let has_header = rows.iter().any(|(_, header)| *header);
+    for (index, (row, header)) in rows.iter().enumerate() {
+        let header = *header || (!has_header && index == 0);
+        parts.push(Work::Capture(Capture::Row {
+            header,
+            cells: Vec::new(),
+        }));
+        for cell in row_cells(row) {
+            parts.push(Work::Capture(Capture::Cell {
+                colspan: colspan(cell),
+            }));
+            parts.extend(children(cell));
+            parts.push(Work::Finish);
+        }
+        parts.push(Work::Finish);
+    }
+    parts.push(Work::Emit("\n".to_string()));
+}
+
+/// The rows of a table in document order, each with the flag telling whether it
+/// is a header row (inside `thead`, or holding `th` cells).
+fn table_rows(table: &Element) -> Vec<(&Element, bool)> {
+    let mut rows = Vec::new();
+    for child in &table.children {
+        let Node::Element(child) = child else {
+            continue;
+        };
+        match child.name.as_str() {
+            "tr" => rows.push((child, row_has_th(child))),
+            "thead" | "tbody" | "tfoot" => {
+                let in_header = child.name == "thead";
+                for row in &child.children {
+                    if let Node::Element(row) = row {
+                        if row.name == "tr" {
+                            rows.push((row, in_header || row_has_th(row)));
+                        }
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+    rows
+}
+
+/// True when a row holds header cells of its own.
+fn row_has_th(row: &Element) -> bool {
+    row_cells(row).iter().any(|cell| cell.name == "th")
+}
+
+/// The cells of a row, in document order.
+fn row_cells(row: &Element) -> Vec<&Element> {
+    row.children
+        .iter()
+        .filter_map(|child| match child {
+            Node::Element(cell) if cell.name == "th" || cell.name == "td" => Some(cell),
+            _ => None,
+        })
+        .collect()
+}
+
+/// How many columns a cell covers; a missing or silly value means one, and the
+/// cap keeps a hostile `colspan` from asking for an enormous row.
+fn colspan(cell: &Element) -> usize {
+    cell.attr("colspan")
+        .and_then(|value| value.trim().parse::<usize>().ok())
+        .filter(|span| *span > 0)
+        .map_or(1, |span| span.min(64))
+}
+
+/// Close the innermost capture and append its Markdown to the buffer below it.
+fn finish_capture(buffers: &mut Vec<String>, captures: &mut Vec<Capture>) {
+    let text = match buffers.pop() {
+        Some(text) => text,
+        None => return,
+    };
+
+    match captures.pop() {
+        Some(Capture::Link { href }) => {
+            let label = text.trim();
+            let rendered = if href.is_empty() {
+                label.to_string()
+            } else if label == href {
+                href
+            } else if label.is_empty() {
+                String::new()
+            } else {
+                format!("[{label}]({href})")
+            };
+            push_text(buffers, &rendered);
+        }
+        Some(Capture::Quote) => {
+            let mut quoted = String::new();
+            let body = text.trim();
+            if !body.is_empty() {
+                for line in body.split('\n') {
+                    let line = line.trim_end();
+                    if line.is_empty() {
+                        quoted.push_str(">\n");
+                    } else {
+                        quoted.push_str("> ");
+                        quoted.push_str(line);
+                        quoted.push('\n');
+                    }
+                }
+                quoted.push('\n');
+            }
+            push_text(buffers, &quoted);
+        }
+        Some(Capture::Item { ordered, index }) => {
+            // The bullet shares its line with the first line of the item; the
+            // rest continues indented under it, two spaces per level.
+            let bullet = if ordered {
+                format!("{}.", index + 1)
+            } else {
+                "-".to_string()
+            };
+            let mut rendered = String::new();
+            for (number, line) in text.trim().split('\n').enumerate() {
+                let line = line.trim_end();
+                if number == 0 {
+                    rendered.push_str(&bullet);
+                    rendered.push(' ');
+                    rendered.push_str(line.trim_start());
+                } else if !line.is_empty() {
+                    rendered.push_str("  ");
+                    rendered.push_str(line);
+                }
+                rendered.push('\n');
+            }
+            push_text(buffers, &rendered);
+        }
+        Some(Capture::Row { header, cells }) => {
+            let mut rendered = String::new();
+            if !cells.is_empty() {
+                rendered.push_str("| ");
+                rendered.push_str(&cells.join(" | "));
+                rendered.push_str(" |\n");
+                if header {
+                    rendered.push_str("| ");
+                    rendered.push_str(&vec!["---"; cells.len()].join(" | "));
+                    rendered.push_str(" |\n");
+                }
+            }
+            push_text(buffers, &rendered);
+        }
+        Some(Capture::Cell { colspan }) => {
+            // A cell is a single line: newlines inside it become spaces, and a
+            // pipe would otherwise cut the row into extra columns.
+            let cell = text
+                .split_whitespace()
+                .collect::<Vec<_>>()
+                .join(" ")
+                .replace('|', "\\|");
+            match captures.last_mut() {
+                Some(Capture::Row { cells, .. }) => {
+                    for _ in 0..colspan {
+                        cells.push(cell.clone());
+                    }
+                }
+                _ => push_text(buffers, &cell),
+            }
+        }
+        None => push_text(buffers, &text),
+    }
+}
+
+/// An image with its alternative text, as Markdown.
+fn image_markdown(element: &Element) -> String {
+    let alt = element.attr("alt").unwrap_or_default();
+    let src = element.attr("src").unwrap_or_default();
+    if alt.is_empty() && src.is_empty() {
+        // A decorative spacer: nothing a reader would miss.
+        return String::new();
+    }
+    format!("![{alt}]({src})")
+}
+
+/// An inline code span: one backtick, or two when the text contains one.
+fn inline_code(element: &Element) -> String {
+    let text = text_content(element);
+    let text = text.trim();
+    if text.is_empty() {
+        return String::new();
+    }
+    let ticks = if text.contains('`') { "``" } else { "`" };
+    format!("{ticks}{text}{ticks}")
+}
+
+/// A `pre` as a fenced block, named with the language of an inner `code`
+/// element when the page declares one.
+fn fenced_block(element: &Element) -> String {
+    let text = text_content(element);
+    let text = text.trim_matches(['\n', '\r']);
+    let language = code_language(element).unwrap_or_default();
+    let fence = fence_for(text);
+    format!("{fence}{language}\n{text}\n{fence}\n\n")
+}
+
+/// A fence longer than any run of backticks in the text, and at least three.
+fn fence_for(text: &str) -> String {
+    let mut longest = 0usize;
+    let mut run = 0usize;
+    for character in text.chars() {
+        if character == '`' {
+            run += 1;
+            longest = longest.max(run);
+        } else {
+            run = 0;
+        }
+    }
+    "`".repeat(longest.max(2) + 1)
+}
+
+/// The language named by `class="language-xxx"` on the `code` child of a `pre`.
+fn code_language(element: &Element) -> Option<String> {
+    let code = element.children.iter().find_map(|child| match child {
+        Node::Element(child) if child.name == "code" => Some(child),
+        _ => None,
+    })?;
+    code.attr("class")?
+        .split_whitespace()
+        .find_map(|token| token.strip_prefix("language-"))
+        .filter(|language| !language.is_empty())
+        .map(|language| language.to_string())
+}
+
+/// The text of a subtree, with its whitespace exactly as written.
+///
+/// Fenced blocks and code spans use this instead of the renderer, because
+/// Markdown code is literal text rather than markup.
+fn text_content(element: &Element) -> String {
+    let mut out = String::new();
+    let mut stack: Vec<&Node> = element.children.iter().rev().collect();
+    while let Some(node) = stack.pop() {
+        match node {
+            Node::Text(text) => out.push_str(text),
+            Node::Element(child) => {
+                if child.name == "br" {
+                    out.push('\n');
+                }
+                stack.extend(child.children.iter().rev());
+            }
+        }
+    }
+    out
+}
+
+/// Append text to the innermost buffer.
+fn push_text(buffers: &mut [String], text: &str) {
+    if let Some(buffer) = buffers.last_mut() {
+        buffer.push_str(text);
+    }
+}
+
+/// End the current line when it already holds something.
+fn ensure_newline(buffers: &mut [String]) {
+    if let Some(buffer) = buffers.last_mut() {
+        if !buffer.is_empty() && !buffer.ends_with('\n') {
+            buffer.push('\n');
+        }
+    }
+}
+
+/// True when nothing has been written on the current line yet.
+fn at_line_start(buffers: &[String]) -> bool {
+    buffers
+        .last()
+        .is_none_or(|buffer| buffer.is_empty() || buffer.ends_with('\n'))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_input_produces_empty_output() {
+        assert_eq!(html_to_markdown(""), "");
+        assert_eq!(html_to_markdown("   \n\t  "), "");
+    }
+
+    #[test]
+    fn paragraphs_keep_their_text_without_the_markup() {
+        assert_eq!(html_to_markdown("<p>Hello world</p>"), "Hello world\n");
+    }
+
+    #[test]
+    fn two_paragraphs_are_separated_by_a_blank_line() {
+        assert_eq!(html_to_markdown("<p>One</p><p>Two</p>"), "One\n\nTwo\n");
+    }
+
+    #[test]
+    fn layout_whitespace_never_leaves_blank_runs() {
+        assert_eq!(html_to_markdown("<p>a</p>\n\n\n<p>b</p>\n\n\n"), "a\n\nb\n");
+    }
+
+    #[test]
+    fn line_break_ends_the_line() {
+        // The renderer writes Markdown's two-space hard break; `tidy` trims the
+        // trailing spaces, so the caller sees a plain newline.
+        assert_eq!(html_to_markdown("<p>one<br>two</p>"), "one\ntwo\n");
+        assert_eq!(html_to_markdown("<p>one<br/>two</p>"), "one\ntwo\n");
+    }
+
+    #[test]
+    fn headings_use_one_hash_per_level() {
+        assert_eq!(
+            html_to_markdown("<h1>Title</h1><h4>Deep</h4>"),
+            "# Title\n\n#### Deep\n"
+        );
+    }
+
+    #[test]
+    fn emphasis_becomes_markdown_markers() {
+        let html =
+            "<p><strong>bold</strong> <b>also bold</b> <em>italic</em> <i>also</i> <del>gone</del></p>";
+        assert_eq!(
+            html_to_markdown(html),
+            "**bold** **also bold** *italic* *also* ~~gone~~\n"
+        );
+    }
+
+    #[test]
+    fn inline_code_uses_one_backtick() {
+        assert_eq!(
+            html_to_markdown("<p>run <code>cargo test</code> now</p>"),
+            "run `cargo test` now\n"
+        );
+    }
+
+    #[test]
+    fn inline_code_containing_a_backtick_uses_two() {
+        assert_eq!(
+            html_to_markdown("<p><code>x `y` z</code></p>"),
+            "``x `y` z``\n"
+        );
+    }
+
+    #[test]
+    fn fenced_code_block_without_a_language() {
+        assert_eq!(
+            html_to_markdown("<pre>fn main() {}</pre>"),
+            "```\nfn main() {}\n```\n"
+        );
+    }
+
+    #[test]
+    fn fenced_code_block_takes_the_language_from_the_code_class() {
+        let html = r#"<pre><code class="language-rust hljs">let x = 1;</code></pre>"#;
+        assert_eq!(html_to_markdown(html), "```rust\nlet x = 1;\n```\n");
+    }
+
+    #[test]
+    fn fenced_code_block_leaves_its_text_alone() {
+        let html = "<pre><code>a &lt; b &amp;&amp; c\n   indented\n</code></pre>";
+        assert_eq!(
+            html_to_markdown(html),
+            "```\na < b && c\n   indented\n```\n"
+        );
+    }
+
+    #[test]
+    fn fence_grows_when_the_code_contains_backticks() {
+        assert_eq!(
+            html_to_markdown("<pre>a ``` b</pre>"),
+            "````\na ``` b\n````\n"
+        );
+    }
+
+    #[test]
+    fn named_and_numeric_entities_are_decoded() {
+        assert_eq!(
+            html_to_markdown("<p>a &amp; b &lt;tag&gt; &#65;&#x42;</p>"),
+            "a & b <tag> AB\n"
+        );
+        assert_eq!(html_to_markdown("<p>&#x1F600;</p>"), "\u{1f600}\n");
+    }
+
+    #[test]
+    fn punctuation_entities_are_decoded() {
+        assert_eq!(
+            html_to_markdown("<p>5 &times; 3 &mdash; caf&eacute;</p>"),
+            "5 × 3 — café\n"
+        );
+    }
+
+    #[test]
+    fn unknown_entities_are_left_alone() {
+        assert_eq!(
+            html_to_markdown("<p>a &unknown; b & c</p>"),
+            "a &unknown; b & c\n"
+        );
+    }
+
+    #[test]
+    fn invalid_numeric_references_do_not_panic() {
+        assert_eq!(
+            html_to_markdown("<p>&#xD800;&#x110000;</p>"),
+            "\u{fffd}\u{fffd}\n"
+        );
+    }
+
+    #[test]
+    fn non_breaking_spaces_are_kept() {
+        assert_eq!(html_to_markdown("<p>a&nbsp;b</p>"), "a\u{a0}b\n");
+    }
+
+    #[test]
+    fn attributes_are_decoded() {
+        let html = r#"<a href="https://x.test/?a=1&amp;b=2">docs</a>"#;
+        assert_eq!(html_to_markdown(html), "[docs](https://x.test/?a=1&b=2)\n");
+    }
+
+    #[test]
+    fn attribute_names_are_case_insensitive() {
+        let html = r#"<a HREF="https://e.test">https://e.test</a>"#;
+        assert_eq!(html_to_markdown(html), "https://e.test\n");
+    }
+
+    #[test]
+    fn attribute_values_may_be_quoted_or_bare() {
+        assert_eq!(
+            html_to_markdown("<a href='https://s.test'>x</a>"),
+            "[x](https://s.test)\n"
+        );
+        assert_eq!(
+            html_to_markdown("<img src=/u/pic.png alt=pic>"),
+            "![pic](/u/pic.png)\n"
+        );
+    }
+
+    #[test]
+    fn nested_lists_are_indented() {
+        let html = "<ul><li>one<ul><li>inner</li></ul></li><li>two</li></ul>";
+        assert_eq!(html_to_markdown(html), "- one\n  - inner\n- two\n");
+    }
+
+    #[test]
+    fn ordered_list_items_are_numbered() {
+        assert_eq!(
+            html_to_markdown("<ol><li>first</li><li>second</li></ol>"),
+            "1. first\n2. second\n"
+        );
+    }
+
+    #[test]
+    fn list_item_blocks_continue_on_indented_lines() {
+        assert_eq!(
+            html_to_markdown("<ul><li>first<p>second</p></li></ul>"),
+            "- first\n  second\n"
+        );
+    }
+
+    #[test]
+    fn blockquote_prefixes_every_line() {
+        let html = "<blockquote><p>first</p><p>second</p></blockquote>";
+        assert_eq!(html_to_markdown(html), "> first\n>\n> second\n");
+    }
+
+    #[test]
+    fn link_with_a_different_text_uses_the_markdown_form() {
+        let html = r#"<p>see <a href="https://e.test">the docs</a></p>"#;
+        assert_eq!(html_to_markdown(html), "see [the docs](https://e.test)\n");
+    }
+
+    #[test]
+    fn link_whose_text_is_its_href_collapses_to_the_url() {
+        let html = r#"<p><a href="https://e.test">https://e.test</a></p>"#;
+        assert_eq!(html_to_markdown(html), "https://e.test\n");
+    }
+
+    #[test]
+    fn image_uses_its_alt_text_and_source() {
+        let html = r#"<p><img src="/pic.png" alt="A picture"></p>"#;
+        assert_eq!(html_to_markdown(html), "![A picture](/pic.png)\n");
+    }
+
+    #[test]
+    fn horizontal_rule_gets_its_own_line() {
+        assert_eq!(
+            html_to_markdown("<p>above</p><hr><p>below</p>"),
+            "above\n\n---\n\nbelow\n"
+        );
+    }
+
+    #[test]
+    fn table_with_a_header_becomes_a_github_table() {
+        let html = "<table><thead><tr><th>Name</th><th>Value</th></tr></thead>\
+                    <tbody><tr><td>a</td><td>1</td></tr></tbody></table>";
+        assert_eq!(
+            html_to_markdown(html),
+            "| Name | Value |\n| --- | --- |\n| a | 1 |\n"
+        );
+    }
+
+    #[test]
+    fn table_without_a_header_promotes_the_first_row() {
+        let html = "<table><tr><td>h1</td><td>h2</td></tr><tr><td>a</td><td>b</td></tr></table>";
+        assert_eq!(
+            html_to_markdown(html),
+            "| h1 | h2 |\n| --- | --- |\n| a | b |\n"
+        );
+    }
+
+    #[test]
+    fn pipes_inside_a_cell_are_escaped() {
+        let html = "<table><tr><th>a</th><th>b</th></tr><tr><td>x | y</td><td>z</td></tr></table>";
+        assert_eq!(
+            html_to_markdown(html),
+            "| a | b |\n| --- | --- |\n| x \\| y | z |\n"
+        );
+    }
+
+    #[test]
+    fn colspan_repeats_the_cell_content() {
+        let html =
+            r#"<table><tr><th>a</th><th>b</th></tr><tr><td colspan="2">span</td></tr></table>"#;
+        assert_eq!(
+            html_to_markdown(html),
+            "| a | b |\n| --- | --- |\n| span | span |\n"
+        );
+    }
+
+    #[test]
+    fn a_table_without_rows_produces_nothing() {
+        assert_eq!(html_to_markdown("<table></table>"), "");
+    }
+
+    #[test]
+    fn unknown_elements_keep_their_content() {
+        let html = r#"<answer><span data-x="1">text</span></answer>"#;
+        assert_eq!(html_to_markdown(html), "text\n");
+    }
+
+    #[test]
+    fn comments_doctypes_and_raw_text_are_dropped() {
+        let html = "<!doctype html><!-- hidden --><style>p{color:red}</style>\
+                    <script>var x = 1;</script><p>kept</p>";
+        assert_eq!(html_to_markdown(html), "kept\n");
+    }
+
+    #[test]
+    fn an_unclosed_tag_keeps_the_text() {
+        assert_eq!(html_to_markdown("<p>hello <b>world"), "hello **world**\n");
+    }
+
+    #[test]
+    fn a_stray_angle_bracket_is_text() {
+        assert_eq!(
+            html_to_markdown("<p>2 < 3 and 4 > 1</p>"),
+            "2 < 3 and 4 > 1\n"
+        );
+    }
+
+    #[test]
+    fn an_unterminated_attribute_quote_stops_at_the_end() {
+        // The quoted value runs to the end of the document: everything before it
+        // is still rendered and nothing hangs.
+        let html = "<p>visible</p><a href=\"broken>tail";
+        assert_eq!(html_to_markdown(html), "visible\n");
+    }
+
+    #[test]
+    fn a_stray_end_tag_is_ignored() {
+        assert_eq!(html_to_markdown("<p><b>bold</i></p>"), "**bold**\n");
+    }
+
+    #[test]
+    fn unterminated_constructs_terminate() {
+        assert_eq!(html_to_markdown("<>&&&"), "<>&&&\n");
+        assert_eq!(html_to_markdown("<p>a</p><!-- open"), "a\n");
+        assert_eq!(html_to_markdown("<p>a"), "a\n");
+    }
+
+    #[test]
+    fn deeply_nested_markup_is_bounded() {
+        let mut html = String::new();
+        for _ in 0..5_000 {
+            html.push_str("<div>");
+        }
+        html.push_str("deep");
+        assert_eq!(html_to_markdown(&html), "deep\n");
+    }
+
+    #[test]
+    fn tidy_trims_trailing_spaces_and_collapses_blank_lines() {
+        assert_eq!(tidy("a   \n\n\n\nb  \n\n\n"), "a\n\nb\n");
+    }
+
+    #[test]
+    fn tidy_ends_with_exactly_one_newline() {
+        assert_eq!(tidy("text"), "text\n");
+        assert_eq!(tidy("text\n\n\n"), "text\n");
+    }
+
+    #[test]
+    fn tidy_of_whitespace_only_input_is_empty() {
+        assert_eq!(tidy(""), "");
+        assert_eq!(tidy("\n\n   \n"), "");
+    }
+
+    #[test]
+    fn tidy_does_not_touch_fenced_code_blocks() {
+        let input = "text  \n\n```rust\nlet a = 1;   \n\n\nlet b = 2;\n```\n\n\n";
+        let expected = "text\n\n```rust\nlet a = 1;   \n\n\nlet b = 2;\n```\n";
+        assert_eq!(tidy(input), expected);
+    }
+
+    #[test]
+    fn has_rich_structure_detects_structure() {
+        assert!(has_rich_structure("<pre>code</pre>"));
+        assert!(has_rich_structure("<TABLE><tr><td>x</td></tr></TABLE>"));
+        assert!(has_rich_structure("<ul><li>a</li></ul>"));
+        assert!(has_rich_structure("<ol><li>a</li></ol>"));
+        assert!(has_rich_structure("<h3>title</h3>"));
+        assert!(has_rich_structure(
+            "see <a href=\"https://e.test\">the docs</a>"
+        ));
+    }
+
+    #[test]
+    fn has_rich_structure_is_false_for_plain_markup() {
+        assert!(!has_rich_structure(""));
+        assert!(!has_rich_structure("just words"));
+        assert!(!has_rich_structure("<p>just <b>words</b></p>"));
+        assert!(!has_rich_structure("<div><span>text</span></div>"));
+    }
+}
diff --git a/src/paths.rs b/src/paths.rs
new file mode 100644
index 0000000..a14408b
--- /dev/null
+++ b/src/paths.rs
@@ -0,0 +1,251 @@
+//! Filesystem layout of the gateway state directory (default: `~/.llm-gateway`).
+
+use std::path::{Path, PathBuf};
+
+use anyhow::{Context, Result};
+
+/// Environment variable overriding the state directory.
+pub const HOME_ENV: &str = "LLM_GATEWAY_HOME";
+
+/// Default provider configurations, materialised on first run.
+const DEFAULT_PROVIDER_CONFIGS: &[(&str, &str)] = &[
+    ("chatgpt", include_str!("../providers/chatgpt.toml")),
+    ("claude", include_str!("../providers/claude.toml")),
+    ("deepseek", include_str!("../providers/deepseek.toml")),
+];
+
+/// Names of the provider files shipped with this build.
+pub fn default_provider_names() -> Vec<&'static str> {
+    DEFAULT_PROVIDER_CONFIGS
+        .iter()
+        .map(|(name, _)| *name)
+        .collect()
+}
+
+/// Default global configuration, materialised on first run.
+const DEFAULT_CONFIG: &str = include_str!("../config.toml.example");
+
+/// Resolved locations of every file the gateway reads or writes.
+#[derive(Debug, Clone)]
+pub struct Layout {
+    root: PathBuf,
+}
+
+impl Layout {
+    /// Discover the layout, honouring the environment override then `~/.llm-gateway`.
+    pub fn discover() -> Result<Self> {
+        if let Some(raw) = std::env::var_os(HOME_ENV) {
+            let raw = raw.to_string_lossy().to_string();
+            if !raw.trim().is_empty() {
+                return Ok(Self {
+                    root: expand_tilde(&raw),
+                });
+            }
+        }
+        let home = dirs::home_dir().context("cannot determine the home directory")?;
+        Ok(Self {
+            root: home.join(".llm-gateway"),
+        })
+    }
+
+    /// Build a layout rooted at an explicit directory (used by tests).
+    pub fn rooted_at(root: impl Into<PathBuf>) -> Self {
+        Self { root: root.into() }
+    }
+
+    pub fn root(&self) -> &Path {
+        &self.root
+    }
+
+    /// Root of all browser profiles.
+    pub fn profiles_dir(&self) -> PathBuf {
+        self.root.join("profiles")
+    }
+
+    /// Chrome user-data-dir of a provider. A dedicated directory is used so the
+    /// personal browser profile of the user is never touched.
+    ///
+    /// This is the layout of a provider without declared accounts; a provider
+    /// that declares accounts keeps one directory per account under
+    /// `profiles/<provider>/accounts/` (see `account_profile_dir`).
+    pub fn profile_dir(&self, provider: &str) -> PathBuf {
+        self.profiles_dir().join(provider).join("user-data-dir")
+    }
+
+    /// Chrome user-data-dir of one account of a provider.
+    pub fn account_profile_dir(&self, provider: &str, account: &str) -> PathBuf {
+        self.profiles_dir()
+            .join(provider)
+            .join("accounts")
+            .join(account)
+            .join("user-data-dir")
+    }
+
+    /// Directory holding the accounts of a provider.
+    pub fn accounts_dir(&self, provider: &str) -> PathBuf {
+        self.profiles_dir().join(provider).join("accounts")
+    }
+
+    pub fn providers_dir(&self) -> PathBuf {
+        self.root.join("providers")
+    }
+
+    pub fn provider_config(&self, provider: &str) -> PathBuf {
+        self.providers_dir().join(format!("{provider}.toml"))
+    }
+
+    pub fn conversations_file(&self) -> PathBuf {
+        self.root.join("conversations.json")
+    }
+
+    pub fn debug_dir(&self) -> PathBuf {
+        self.root.join("debug")
+    }
+
+    pub fn logs_dir(&self) -> PathBuf {
+        self.root.join("logs")
+    }
+
+    pub fn config_file(&self) -> PathBuf {
+        self.root.join("config.toml")
+    }
+
+    /// Create the directory tree and materialise the embedded defaults.
+    ///
+    /// Existing files are never overwritten: user edits always win.
+    pub fn ensure(&self) -> Result<()> {
+        for dir in [
+            self.root.clone(),
+            self.profiles_dir(),
+            self.providers_dir(),
+            self.debug_dir(),
+            self.logs_dir(),
+        ] {
+            std::fs::create_dir_all(&dir).with_context(|| format!("creating {}", dir.display()))?;
+        }
+
+        let config = self.config_file();
+        if !config.exists() {
+            std::fs::write(&config, DEFAULT_CONFIG)
+                .with_context(|| format!("writing {}", config.display()))?;
+        }
+
+        self.install_default_providers(false)?;
+
+        Ok(())
+    }
+
+    /// Write the embedded provider defaults.
+    ///
+    /// Without `force`, an already installed file is left alone: your edits win.
+    /// With `force`, the previous file is kept as `<name>.toml.bak`, which is
+    /// how an upgraded build ships refreshed selectors.
+    pub fn install_default_providers(&self, force: bool) -> Result<Vec<PathBuf>> {
+        let mut written = Vec::new();
+        for (name, body) in DEFAULT_PROVIDER_CONFIGS {
+            let path = self.provider_config(name);
+            if path.exists() {
+                if !force {
+                    continue;
+                }
+                let backup = path.with_extension("toml.bak");
+                std::fs::copy(&path, &backup)
+                    .with_context(|| format!("backing up {}", path.display()))?;
+            }
+            std::fs::write(&path, body).with_context(|| format!("writing {}", path.display()))?;
+            written.push(path);
+        }
+        Ok(written)
+    }
+}
+
+/// Expand a leading tilde into the user home directory.
+pub fn expand_tilde(raw: &str) -> PathBuf {
+    let trimmed = raw.trim();
+    if trimmed == "~" {
+        return dirs::home_dir().unwrap_or_else(|| PathBuf::from(trimmed));
+    }
+    let rest = trimmed
+        .strip_prefix("~/")
+        .or_else(|| trimmed.strip_prefix("~\\"));
+    if let Some(rest) = rest {
+        if let Some(home) = dirs::home_dir() {
+            return home.join(rest);
+        }
+    }
+    PathBuf::from(trimmed)
+}
+
+/// Resolve a configuration path against the layout root when it is relative.
+pub fn resolve_against(root: &Path, raw: &str) -> PathBuf {
+    let expanded = expand_tilde(raw);
+    if expanded.is_absolute() {
+        expanded
+    } else {
+        root.join(expanded)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn tilde_is_expanded() {
+        let home = dirs::home_dir().unwrap();
+        assert_eq!(expand_tilde("~"), home);
+        assert_eq!(expand_tilde("~/.llm-gateway"), home.join(".llm-gateway"));
+        assert_eq!(expand_tilde("/tmp/x"), PathBuf::from("/tmp/x"));
+    }
+
+    #[test]
+    fn ensure_creates_layout_without_overwriting() {
+        let tmp = tempfile::tempdir().unwrap();
+        let layout = Layout::rooted_at(tmp.path().join("state"));
+        layout.ensure().unwrap();
+        assert!(layout.providers_dir().join("chatgpt.toml").is_file());
+        for name in default_provider_names() {
+            assert!(
+                layout
+                    .providers_dir()
+                    .join(format!("{name}.toml"))
+                    .is_file(),
+                "{name}.toml was not installed"
+            );
+        }
+        assert!(layout.profiles_dir().is_dir());
+        assert!(layout.debug_dir().is_dir());
+        assert!(layout.logs_dir().is_dir());
+
+        let custom = layout.provider_config("chatgpt");
+        std::fs::write(&custom, "# edited by the user\n").unwrap();
+        layout.ensure().unwrap();
+        assert_eq!(
+            std::fs::read_to_string(&custom).unwrap(),
+            "# edited by the user\n"
+        );
+    }
+
+    #[test]
+    fn accounts_get_their_own_profile_directory() {
+        let layout = Layout::rooted_at(PathBuf::from("/state"));
+        assert_eq!(
+            layout.profile_dir("chatgpt"),
+            PathBuf::from("/state/profiles/chatgpt/user-data-dir")
+        );
+        assert_eq!(
+            layout.account_profile_dir("chatgpt", "perso"),
+            PathBuf::from("/state/profiles/chatgpt/accounts/perso/user-data-dir")
+        );
+    }
+
+    #[test]
+    fn relative_paths_resolve_against_root() {
+        let root = PathBuf::from("/state");
+        assert_eq!(
+            resolve_against(&root, "debug"),
+            PathBuf::from("/state/debug")
+        );
+        assert_eq!(resolve_against(&root, "/abs"), PathBuf::from("/abs"));
+    }
+}
diff --git a/src/providers/backend.rs b/src/providers/backend.rs
new file mode 100644
index 0000000..f4117fd
--- /dev/null
+++ b/src/providers/backend.rs
@@ -0,0 +1,127 @@
+//! The seam the HTTP layer talks to.
+//!
+//! `RegistryBackend` drives real browsers; `MockBackend` answers from memory so
+//! the API can be exercised without Chrome, network or a login.
+
+use async_trait::async_trait;
+use serde::{Deserialize, Serialize};
+
+use crate::browser::{SessionState, SessionStatus};
+use crate::error::Result;
+use crate::providers::config::Capabilities;
+use crate::providers::{AccountInfo, TurnRequest, TurnStream};
+
+/// Timing of one validation step.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct StepTiming {
+    pub step: String,
+    pub ms: u64,
+    pub ok: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub detail: Option<String>,
+}
+
+/// Result of a provider validation run.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ValidationReport {
+    pub provider: String,
+    pub ok: bool,
+    /// ok | login_required | captcha | selector_missing | rate_limited | timeout | error | misconfigured
+    pub status: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub message: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub response_excerpt: Option<String>,
+    pub duration_ms: u64,
+    pub checked_at: u64,
+    pub steps: Vec<StepTiming>,
+}
+
+/// Public description of a configured provider.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ProviderDescriptor {
+    pub name: String,
+    pub display_name: String,
+    pub web_url: String,
+    pub models: Vec<String>,
+    pub enabled: bool,
+    pub usable: bool,
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
+    pub problems: Vec<String>,
+    pub capabilities: Capabilities,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub browser: Option<String>,
+    /// Declared accounts; empty when the provider has a single implicit one.
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
+    pub accounts: Vec<AccountInfo>,
+}
+
+/// A `model` string resolved to one provider and one of its accounts.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ResolvedModel {
+    pub provider: ProviderDescriptor,
+    /// Account id, when the provider declares accounts.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub account: Option<String>,
+    /// Model name asked for after the `/`, echoed back to the client.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub model: Option<String>,
+}
+
+impl ResolvedModel {
+    /// Provider and account, as used in logs and errors.
+    pub fn owner(&self) -> String {
+        match &self.account {
+            Some(account) => format!("{}@{account}", self.provider.name),
+            None => self.provider.name.clone(),
+        }
+    }
+}
+
+/// Outcome of a configuration reload.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct ReloadReport {
+    pub added: Vec<String>,
+    pub updated: Vec<String>,
+    pub removed: Vec<String>,
+    pub problems: Vec<String>,
+}
+
+/// Everything the HTTP layer needs from the provider layer.
+#[async_trait]
+pub trait ChatBackend: Send + Sync {
+    /// Run one turn on `provider`, optionally on one of its accounts.
+    async fn complete(
+        &self,
+        provider: &str,
+        account: Option<&str>,
+        request: TurnRequest,
+    ) -> Result<TurnStream>;
+    /// Session state of one account, or of the default one when `account` is
+    /// None. An unknown account is reported as a misconfigured status rather
+    /// than an error, so a monitor still gets a body to look at.
+    async fn status(&self, provider: &str, account: Option<&str>) -> SessionStatus;
+    /// Validate one account, or the default one when `account` is None.
+    async fn validate(&self, provider: &str, account: Option<&str>) -> Result<ValidationReport>;
+    async fn reload(&self) -> Result<ReloadReport>;
+    fn providers(&self) -> Vec<ProviderDescriptor>;
+    /// Resolve a model string to a provider, an account and a model name.
+    fn resolve(&self, model: &str) -> Result<ResolvedModel>;
+    async fn shutdown(&self);
+}
+
+/// `provider` or `provider@account`, as printed in logs and reports.
+pub fn owner_label(provider: &str, account: Option<&str>) -> String {
+    match account.map(str::trim).filter(|value| !value.is_empty()) {
+        Some(account) => format!("{provider}@{account}"),
+        None => provider.to_string(),
+    }
+}
+
+/// Build the status of a provider that is not configured at all.
+pub fn unknown_provider_status(provider: &str) -> SessionStatus {
+    let mut status =
+        SessionStatus::error(provider, format!("provider '{provider}' is not configured"));
+    status.state = SessionState::Misconfigured;
+    status
+}
diff --git a/src/providers/config.rs b/src/providers/config.rs
new file mode 100644
index 0000000..130afa4
--- /dev/null
+++ b/src/providers/config.rs
@@ -0,0 +1,882 @@
+//! Provider configuration loaded from `~/.llm-gateway/providers/*.toml`.
+//!
+//! Selectors live here and nowhere else: a provider UI change must never
+//! require a code change.
+
+use std::path::{Path, PathBuf};
+
+use serde::{Deserialize, Serialize};
+
+use crate::error::{GatewayError, Result};
+
+/// CSS selectors used to drive the provider page.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct Selectors {
+    /// Editable prompt area.
+    pub input_field: String,
+    /// Submit button.
+    pub send_button: String,
+    /// One node per assistant answer, in document order.
+    pub response_container: String,
+    /// Element that only exists while the answer is being generated.
+    pub streaming_indicator: String,
+    /// Hidden `input[type=file]` used for attachments.
+    pub file_input: String,
+    /// Control that starts a brand new conversation.
+    pub new_chat_button: String,
+    /// Element that only exists on the sign-in page.
+    pub login_page_indicator: String,
+    /// Bot challenge frame.
+    pub captcha_indicator: String,
+    /// Visible upstream error message.
+    pub error_banner: String,
+    /// Model picker (reserved: not driven yet).
+    pub model_selector: String,
+    /// Attachment chip shown after an upload completed.
+    pub attachment_indicator: String,
+    /// Copy button inside one answer node, looked up relative to that node.
+    ///
+    /// Clicking it is what gives the gateway the provider's own Markdown
+    /// rendering instead of the flattened visible text.
+    pub copy_button: String,
+}
+
+impl Selectors {
+    /// Selectors without which no turn can be executed.
+    pub fn missing_required(&self) -> Vec<&'static str> {
+        let mut missing = Vec::new();
+        if self.input_field.trim().is_empty() {
+            missing.push("selectors.input_field");
+        }
+        if self.send_button.trim().is_empty() {
+            missing.push("selectors.send_button");
+        }
+        if self.response_container.trim().is_empty() {
+            missing.push("selectors.response_container");
+        }
+        missing
+    }
+}
+
+/// Identity and entry points of the web UI.
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct ProviderMeta {
+    pub name: String,
+    #[serde(default)]
+    pub display_name: Option<String>,
+    pub web_url: String,
+    #[serde(default)]
+    pub new_conversation_url: Option<String>,
+    /// Regex with one capture group extracting the web conversation id.
+    #[serde(default)]
+    pub conversation_url_pattern: Option<String>,
+    #[serde(default)]
+    pub default_models: Vec<String>,
+    #[serde(default = "default_true")]
+    pub enabled: bool,
+}
+
+fn default_true() -> bool {
+    true
+}
+
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct LoginRules {
+    /// Substrings that identify a sign-in URL.
+    pub url_patterns: Vec<String>,
+    /// Lowercase substrings of the visible page text that reveal a signed-out
+    /// page. They are only consulted when no prompt field is present, so a chat
+    /// page that happens to mention "log in" somewhere is never misclassified.
+    pub text_patterns: Vec<String>,
+}
+
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct RateLimitRules {
+    /// Lowercase substrings that reveal upstream throttling.
+    pub text_patterns: Vec<String>,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct Timeouts {
+    pub page_load: u64,
+    pub response_generation: u64,
+    pub response_timeout: u64,
+}
+
+impl Default for Timeouts {
+    fn default() -> Self {
+        Self {
+            page_load: 30,
+            response_generation: 120,
+            response_timeout: 180,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct InputOptions {
+    pub poll_interval_ms: u64,
+    pub quiet_ms: u64,
+    pub inject_method: crate::config::InjectMethod,
+    /// Overrides the global `[capture] markdown` for this provider.
+    pub markdown: crate::config::MarkdownMode,
+}
+
+impl Default for InputOptions {
+    fn default() -> Self {
+        Self {
+            poll_interval_ms: 400,
+            quiet_ms: 1500,
+            inject_method: crate::config::InjectMethod::Auto,
+            markdown: crate::config::MarkdownMode::Auto,
+        }
+    }
+}
+
+/// One signed-in account of a provider.
+///
+/// A web UI account is a browser profile: two ChatGPT accounts are two
+/// profiles, two sessions and two tabs. Declaring them here is what lets a
+/// single provider file serve `model = "chatgpt"` and
+/// `model = "chatgpt@brunocharest.bc@gmail.com"` at the same time.
+#[derive(Debug, Clone, Default, Deserialize, Serialize)]
+#[serde(default)]
+pub struct AccountConfig {
+    /// Short name used in the model string, e.g. "perso" in `chatgpt@perso`.
+    pub id: String,
+    /// Address of the account, also accepted in the model string.
+    pub email: Option<String>,
+    /// Free-form human label, shown by `llm-gateway list`.
+    pub label: Option<String>,
+    /// Directory name of the browser profile. Defaults to the account id.
+    pub profile: Option<String>,
+    /// The account used when a request names the provider alone.
+    #[serde(default)]
+    pub default: bool,
+    #[serde(default = "default_true")]
+    pub enabled: bool,
+}
+
+impl AccountConfig {
+    /// Directory name of this account's browser profile.
+    pub fn profile_name(&self) -> String {
+        let raw = self
+            .profile
+            .as_deref()
+            .map(str::trim)
+            .filter(|value| !value.is_empty())
+            .unwrap_or(&self.id);
+        sanitise_profile_name(raw)
+    }
+
+    /// Every string that may be used to address this account.
+    pub fn aliases(&self) -> Vec<String> {
+        let mut out = vec![self.id.clone()];
+        for extra in [self.email.as_deref(), self.label.as_deref()] {
+            if let Some(value) = extra.map(str::trim).filter(|value| !value.is_empty()) {
+                out.push(value.to_string());
+            }
+        }
+        out
+    }
+
+    /// True when `key` designates this account (case-insensitive).
+    pub fn matches(&self, key: &str) -> bool {
+        let key = key.trim();
+        !key.is_empty()
+            && self
+                .aliases()
+                .iter()
+                .any(|alias| alias.eq_ignore_ascii_case(key))
+    }
+}
+
+/// Name of the single implicit account of a provider that declares none.
+pub const IMPLICIT_ACCOUNT: &str = "default";
+
+/// Keep a profile directory name usable on every platform.
+///
+/// A profile name becomes one path segment under `profiles/<provider>/accounts`,
+/// so separators and reserved characters are folded into underscores rather
+/// than escaping the directory.
+fn sanitise_profile_name(raw: &str) -> String {
+    raw.chars()
+        .map(|c| match c {
+            '/' | '\\' | ':' | '*' | '?' | '"' | '<' | '>' | '|' => '_',
+            other => other,
+        })
+        .collect()
+}
+
+/// What the web UI of this provider can do.
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(default)]
+pub struct Capabilities {
+    pub supports_images: bool,
+    pub supports_streaming: bool,
+    pub supports_new_chat: bool,
+}
+
+impl Default for Capabilities {
+    fn default() -> Self {
+        Self {
+            supports_images: false,
+            supports_streaming: true,
+            supports_new_chat: true,
+        }
+    }
+}
+
+/// Raw `providers/<name>.toml` document.
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct ProviderFile {
+    pub provider: ProviderMeta,
+    /// Signed-in accounts. Empty means a single implicit one.
+    #[serde(default)]
+    pub accounts: Vec<AccountConfig>,
+    #[serde(default)]
+    pub selectors: Selectors,
+    #[serde(default)]
+    pub login: LoginRules,
+    #[serde(default)]
+    pub rate_limit: RateLimitRules,
+    #[serde(default)]
+    pub timeouts: Timeouts,
+    #[serde(default)]
+    pub input: InputOptions,
+    #[serde(default)]
+    pub options: Capabilities,
+}
+
+impl ProviderFile {
+    /// Canonical TOML of this document, used to detect real changes on reload.
+    pub fn serialized(&self) -> String {
+        toml::to_string(self).unwrap_or_default()
+    }
+}
+
+/// Validated provider configuration, ready to be handed to a provider.
+#[derive(Debug, Clone)]
+pub struct ProviderConfig {
+    pub file: ProviderFile,
+    pub source: PathBuf,
+    pattern: Option<regex::Regex>,
+    pub problems: Vec<String>,
+}
+
+impl ProviderConfig {
+    pub fn name(&self) -> &str {
+        &self.file.provider.name
+    }
+
+    pub fn display_name(&self) -> &str {
+        self.file
+            .provider
+            .display_name
+            .as_deref()
+            .unwrap_or(&self.file.provider.name)
+    }
+
+    pub fn web_url(&self) -> &str {
+        &self.file.provider.web_url
+    }
+
+    pub fn new_conversation_url(&self) -> &str {
+        self.file
+            .provider
+            .new_conversation_url
+            .as_deref()
+            .unwrap_or(&self.file.provider.web_url)
+    }
+
+    pub fn enabled(&self) -> bool {
+        self.file.provider.enabled
+    }
+
+    pub fn default_models(&self) -> &[String] {
+        &self.file.provider.default_models
+    }
+
+    pub fn default_model(&self) -> String {
+        self.file
+            .provider
+            .default_models
+            .first()
+            .cloned()
+            .unwrap_or_else(|| self.name().to_string())
+    }
+
+    pub fn selectors(&self) -> &Selectors {
+        &self.file.selectors
+    }
+
+    pub fn capabilities(&self) -> &Capabilities {
+        &self.file.options
+    }
+
+    /// Declared accounts, enabled ones only, in configuration order.
+    pub fn accounts(&self) -> impl Iterator<Item = &AccountConfig> {
+        self.file.accounts.iter().filter(|account| account.enabled)
+    }
+
+    /// True when the provider file declares its own accounts.
+    pub fn has_explicit_accounts(&self) -> bool {
+        !self.file.accounts.is_empty()
+    }
+
+    /// Account id used by a request that names the provider alone.
+    pub fn default_account_id(&self) -> Option<&str> {
+        if !self.has_explicit_accounts() {
+            return None;
+        }
+        self.accounts()
+            .find(|account| account.default)
+            .or_else(|| self.accounts().next())
+            .map(|account| account.id.as_str())
+    }
+
+    /// Look up an account by id, e-mail address or label.
+    pub fn find_account(&self, key: &str) -> Option<&AccountConfig> {
+        self.accounts().find(|account| account.matches(key))
+    }
+
+    /// Resolve the account of a request into an account id.
+    ///
+    /// `None` (or an empty key) means "the default account"; it is accepted
+    /// only when the provider actually has one, so that a typo in a model name
+    /// is never silently routed to the wrong profile.
+    pub fn resolve_account_id(
+        &self,
+        key: Option<&str>,
+    ) -> std::result::Result<Option<String>, String> {
+        let explicit = key.map(str::trim).filter(|value| !value.is_empty());
+        if !self.has_explicit_accounts() {
+            return match explicit {
+                None => Ok(None),
+                Some(name) if name.eq_ignore_ascii_case(IMPLICIT_ACCOUNT) => Ok(None),
+                Some(name) => Err(format!(
+                    "provider '{}' has a single account; '{name}' does not select one. \
+                     Declare it in an [[accounts]] table of {} to give it its own profile",
+                    self.name(),
+                    self.source.display()
+                )),
+            };
+        }
+        match explicit {
+            None => Ok(self.default_account_id().map(str::to_string)),
+            Some(name) => self
+                .find_account(name)
+                .map(|account| Some(account.id.clone()))
+                .ok_or_else(|| {
+                    format!(
+                        "provider '{}' has no account '{name}' (known: {})",
+                        self.name(),
+                        self.accounts()
+                            .map(|account| match &account.email {
+                                Some(email) => format!("{} <{email}>", account.id),
+                                None => account.id.clone(),
+                            })
+                            .collect::<Vec<_>>()
+                            .join(", ")
+                    )
+                }),
+        }
+    }
+
+    pub fn is_usable(&self) -> bool {
+        self.problems.is_empty()
+    }
+
+    /// True when the page is a sign-in screen rather than a chat UI.
+    ///
+    /// The URL and the markup marker are trusted at any time; the text patterns
+    /// are a fallback for the marketing page a signed-out visitor lands on, and
+    /// are only used when the prompt field is missing.
+    pub fn is_signed_out_page(
+        &self,
+        url: &str,
+        body_text_lowercase: &str,
+        login_marker: bool,
+        has_input: bool,
+    ) -> bool {
+        if login_marker || self.is_login_url(url) {
+            return true;
+        }
+        if has_input {
+            return false;
+        }
+        self.file.login.text_patterns.iter().any(|pattern| {
+            let pattern = pattern.trim().to_lowercase();
+            !pattern.is_empty() && body_text_lowercase.contains(&pattern)
+        })
+    }
+
+    /// True when the page URL identifies a sign-in screen.
+    pub fn is_login_url(&self, url: &str) -> bool {
+        let lower = url.to_lowercase();
+        self.file
+            .login
+            .url_patterns
+            .iter()
+            .any(|p| !p.is_empty() && lower.contains(&p.to_lowercase()))
+    }
+
+    /// Extract the provider-side conversation id from a page URL.
+    pub fn conversation_id_from_url(&self, url: &str) -> Option<String> {
+        let pattern = self.pattern.as_ref()?;
+        pattern
+            .captures(url)?
+            .get(1)
+            .map(|m| m.as_str().to_string())
+    }
+
+    /// Effective answer fidelity: the provider file wins when it sets one.
+    pub fn markdown_mode(
+        &self,
+        global: crate::config::MarkdownMode,
+    ) -> crate::config::MarkdownMode {
+        match self.file.input.markdown {
+            crate::config::MarkdownMode::Auto => global,
+            explicit => explicit,
+        }
+    }
+
+    /// True when the provider exposes a per-answer copy button.
+    pub fn has_copy_button(&self) -> bool {
+        !self.file.selectors.copy_button.trim().is_empty()
+    }
+
+    /// Detect an upstream throttling notice in the visible page text.
+    pub fn rate_limit_hit(&self, body_text_lowercase: &str) -> Option<String> {
+        self.file
+            .rate_limit
+            .text_patterns
+            .iter()
+            .find(|p| !p.is_empty() && body_text_lowercase.contains(&p.to_lowercase()))
+            .cloned()
+    }
+
+    /// Parse a TOML document and validate it.
+    pub fn parse(raw: &str, source: impl Into<PathBuf>) -> Result<Self> {
+        let file: ProviderFile =
+            toml::from_str(raw).map_err(|e| GatewayError::Config(e.to_string()))?;
+        Ok(Self::from_file(file, source.into()))
+    }
+
+    pub fn from_file(file: ProviderFile, source: PathBuf) -> Self {
+        let mut problems = Vec::new();
+
+        if file.provider.name.trim().is_empty() {
+            problems.push("provider.name must not be empty".to_string());
+        }
+        let url = file.provider.web_url.as_str();
+        if !(url.starts_with("http://")
+            || url.starts_with("https://")
+            || url.starts_with("file://"))
+        {
+            problems.push("provider.web_url must be an absolute http(s) or file URL".to_string());
+        }
+        for missing in file.selectors.missing_required() {
+            problems.push(format!("{missing} is required"));
+        }
+        if file.timeouts.response_timeout == 0 {
+            problems.push("timeouts.response_timeout must not be 0".to_string());
+        }
+        if file.input.poll_interval_ms < 50 {
+            problems.push("input.poll_interval_ms must be at least 50".to_string());
+        }
+
+        // Accounts: unique ids, and at most one default so that a request which
+        // names the provider alone is never ambiguous.
+        let mut seen_ids: Vec<String> = Vec::new();
+        let mut defaults = 0usize;
+        let mut profile_names: Vec<String> = Vec::new();
+        for (index, account) in file.accounts.iter().enumerate() {
+            let id = account.id.trim();
+            if id.is_empty() {
+                problems.push(format!("accounts[{index}].id must not be empty"));
+                continue;
+            }
+            let lower = id.to_lowercase();
+            if seen_ids.contains(&lower) {
+                problems.push(format!("duplicate account id '{id}'"));
+            }
+            seen_ids.push(lower);
+            if account.default {
+                defaults += 1;
+            }
+            // Two accounts sharing a profile would share one signed-in session.
+            let profile = account.profile_name();
+            if profile_names.contains(&profile) {
+                problems.push(format!(
+                    "accounts[{index}] reuses the profile directory '{profile}'"
+                ));
+            }
+            profile_names.push(profile);
+        }
+        if defaults > 1 {
+            problems.push("at most one account may set default = true".to_string());
+        }
+
+        let pattern = match file.provider.conversation_url_pattern.as_deref() {
+            Some(raw) if !raw.trim().is_empty() => match regex::Regex::new(raw) {
+                Ok(re) => {
+                    if re.captures_len() < 2 {
+                        problems.push(
+                            "provider.conversation_url_pattern needs one capture group".to_string(),
+                        );
+                        None
+                    } else {
+                        Some(re)
+                    }
+                }
+                Err(e) => {
+                    problems.push(format!("provider.conversation_url_pattern is invalid: {e}"));
+                    None
+                }
+            },
+            _ => None,
+        };
+
+        Self {
+            file,
+            source,
+            pattern,
+            problems,
+        }
+    }
+
+    /// Load one provider file.
+    pub fn load(path: &Path) -> Result<Self> {
+        let raw = std::fs::read_to_string(path)
+            .map_err(|e| GatewayError::Config(format!("reading {}: {e}", path.display())))?;
+        Self::parse(&raw, path.to_path_buf())
+    }
+
+    /// Load every `*.toml` of a directory, sorted by file name for stable output.
+    pub fn load_dir(dir: &Path) -> Vec<(PathBuf, Result<Self>)> {
+        let mut out = Vec::new();
+        let Ok(entries) = std::fs::read_dir(dir) else {
+            return out;
+        };
+        let mut paths: Vec<PathBuf> = entries
+            .flatten()
+            .map(|entry| entry.path())
+            .filter(|path| path.extension().is_some_and(|ext| ext == "toml"))
+            .collect();
+        paths.sort();
+        for path in paths {
+            let result = Self::load(&path);
+            out.push((path, result));
+        }
+        out
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const CHATGPT: &str = include_str!("../../providers/chatgpt.toml");
+
+    #[test]
+    fn embedded_chatgpt_config_is_valid() {
+        let cfg = ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap();
+        assert_eq!(cfg.name(), "chatgpt");
+        assert!(cfg.is_usable(), "problems: {:?}", cfg.problems);
+        assert!(cfg.enabled());
+        assert_eq!(cfg.default_model(), "gpt-4o");
+        assert!(cfg.capabilities().supports_images);
+        assert_eq!(
+            cfg.selectors().input_field,
+            "div#prompt-textarea, div.ProseMirror[contenteditable='true']"
+        );
+        assert_eq!(cfg.new_conversation_url(), "https://chatgpt.com/");
+    }
+
+    #[test]
+    fn conversation_ids_are_extracted_from_the_url() {
+        let cfg = ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap();
+        let id = cfg
+            .conversation_id_from_url("https://chatgpt.com/c/68f0a1b2-1111-2222-3333-abcdefabcdef");
+        assert_eq!(id.as_deref(), Some("68f0a1b2-1111-2222-3333-abcdefabcdef"));
+        assert!(cfg
+            .conversation_id_from_url("https://chatgpt.com/")
+            .is_none());
+    }
+
+    #[test]
+    fn a_signed_out_landing_page_is_recognised_without_a_marker() {
+        let raw = r#"
+[provider]
+name = "x"
+web_url = "https://example.com"
+
+[selectors]
+input_field = "div#prompt"
+send_button = "button#send"
+response_container = "div.answer"
+
+[login]
+url_patterns = ["/auth/login"]
+text_patterns = ["log in", "sign up"]
+"#;
+        let cfg = ProviderConfig::parse(raw, "x.toml").unwrap();
+
+        // The real chatgpt.com landing page: no prompt field, "Log in" buttons.
+        let body = "chatgpt: chat, work, create & code with ai log in sign up";
+        assert!(cfg.is_signed_out_page("https://example.com/", body, false, false));
+
+        // A chat page that merely mentions "log in" somewhere stays available.
+        assert!(!cfg.is_signed_out_page("https://example.com/", body, false, true));
+
+        // A neutral page with the editor present is obviously fine.
+        assert!(!cfg.is_signed_out_page("https://example.com/", "hello", false, true));
+
+        // Nothing matches: not a login page.
+        assert!(!cfg.is_signed_out_page("https://example.com/", "hello", false, false));
+
+        // Markers and URLs are always trusted.
+        assert!(cfg.is_signed_out_page("https://example.com/", "", true, true));
+        assert!(cfg.is_signed_out_page("https://example.com/auth/login", "", false, true));
+    }
+
+    #[test]
+    fn login_urls_and_rate_limits_are_detected() {
+        let cfg = ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap();
+        assert!(cfg.is_login_url("https://chatgpt.com/auth/login"));
+        assert!(cfg.is_login_url("https://accounts.google.com/o/oauth2"));
+        assert!(!cfg.is_login_url("https://chatgpt.com/c/abc"));
+        assert!(cfg
+            .rate_limit_hit("you are sending too many requests")
+            .is_some());
+        assert!(cfg.rate_limit_hit("hello there").is_none());
+    }
+
+    #[test]
+    fn only_absolute_urls_are_accepted() {
+        let raw = r#"
+[provider]
+name = "x"
+web_url = "chatgpt.com"
+
+[selectors]
+input_field = "a"
+send_button = "b"
+response_container = "c"
+"#;
+        let cfg = ProviderConfig::parse(raw, "x.toml").unwrap();
+        assert!(cfg.problems.iter().any(|p| p.contains("web_url")));
+
+        let local = ProviderConfig::parse(
+            &raw.replace("chatgpt.com", "file:///tmp/fixture.html"),
+            "x.toml",
+        )
+        .unwrap();
+        assert!(local.is_usable(), "{:?}", local.problems);
+    }
+
+    #[test]
+    fn missing_selectors_are_reported_not_fatal() {
+        let raw = r#"
+[provider]
+name = "broken"
+web_url = "https://example.com"
+
+[selectors]
+send_button = "button#send"
+"#;
+        let cfg = ProviderConfig::parse(raw, "broken.toml").unwrap();
+        assert!(!cfg.is_usable());
+        assert!(cfg.problems.iter().any(|p| p.contains("input_field")));
+        assert!(cfg
+            .problems
+            .iter()
+            .any(|p| p.contains("response_container")));
+    }
+
+    const WITH_ACCOUNTS: &str = r#"
+[provider]
+name = "chatgpt"
+web_url = "https://chatgpt.com/"
+
+[selectors]
+input_field = "div#prompt"
+send_button = "button#send"
+response_container = "div.answer"
+
+[[accounts]]
+id = "perso"
+email = "bruno.charest@gmail.com"
+default = true
+
+[[accounts]]
+id = "pro"
+email = "brunocharest.bc@gmail.com"
+label = "Work"
+"#;
+
+    #[test]
+    fn a_provider_without_accounts_has_a_single_implicit_one() {
+        let cfg = ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap();
+        assert!(!cfg.has_explicit_accounts());
+        assert_eq!(cfg.accounts().count(), 0);
+        assert_eq!(cfg.default_account_id(), None);
+        assert_eq!(cfg.resolve_account_id(None).unwrap(), None);
+        assert_eq!(cfg.resolve_account_id(Some("default")).unwrap(), None);
+        assert_eq!(cfg.resolve_account_id(Some(" ")).unwrap(), None);
+        let err = cfg.resolve_account_id(Some("perso")).unwrap_err();
+        assert!(err.contains("single account"), "{err}");
+    }
+
+    #[test]
+    fn declared_accounts_are_addressed_by_id_email_or_label() {
+        let cfg = ProviderConfig::parse(WITH_ACCOUNTS, "chatgpt.toml").unwrap();
+        assert!(cfg.is_usable(), "problems: {:?}", cfg.problems);
+        assert_eq!(cfg.accounts().count(), 2);
+        assert_eq!(cfg.default_account_id(), Some("perso"));
+        assert_eq!(
+            cfg.resolve_account_id(None).unwrap().as_deref(),
+            Some("perso")
+        );
+        assert_eq!(
+            cfg.resolve_account_id(Some("PRO")).unwrap().as_deref(),
+            Some("pro")
+        );
+        assert_eq!(
+            cfg.resolve_account_id(Some("brunocharest.bc@gmail.com"))
+                .unwrap()
+                .as_deref(),
+            Some("pro")
+        );
+        assert_eq!(
+            cfg.resolve_account_id(Some("Work")).unwrap().as_deref(),
+            Some("pro")
+        );
+        let err = cfg.resolve_account_id(Some("nobody")).unwrap_err();
+        assert!(err.contains("no account 'nobody'"), "{err}");
+        assert!(err.contains("perso"), "{err}");
+    }
+
+    #[test]
+    fn the_first_enabled_account_is_the_default_when_none_is_marked() {
+        let raw = WITH_ACCOUNTS.replace("default = true", "enabled = false");
+        let cfg = ProviderConfig::parse(&raw, "chatgpt.toml").unwrap();
+        // "perso" is disabled, so the default is the first enabled account.
+        assert_eq!(cfg.default_account_id(), Some("pro"));
+        assert_eq!(cfg.accounts().count(), 1);
+    }
+
+    #[test]
+    fn accounts_reuse_is_reported() {
+        let raw = WITH_ACCOUNTS.replace("id = \"pro\"", "id = \"perso\"");
+        let cfg = ProviderConfig::parse(&raw, "chatgpt.toml").unwrap();
+        assert!(!cfg.is_usable());
+        assert!(cfg
+            .problems
+            .iter()
+            .any(|p| p.contains("duplicate account id")));
+        assert!(cfg.problems.iter().any(|p| p.contains("profile directory")));
+
+        let two_defaults = WITH_ACCOUNTS.replace("label = \"Work\"", "default = true");
+        let cfg = ProviderConfig::parse(&two_defaults, "chatgpt.toml").unwrap();
+        assert!(cfg
+            .problems
+            .iter()
+            .any(|p| p.contains("at most one account")));
+
+        let nameless = WITH_ACCOUNTS.replace("id = \"pro\"", "id = \"\"");
+        let cfg = ProviderConfig::parse(&nameless, "chatgpt.toml").unwrap();
+        assert!(cfg.problems.iter().any(|p| p.contains("must not be empty")));
+    }
+
+    #[test]
+    fn profile_directory_names_are_safe_path_segments() {
+        let account = AccountConfig {
+            id: "a/b:c".to_string(),
+            ..Default::default()
+        };
+        assert_eq!(account.profile_name(), "a_b_c");
+
+        let explicit = AccountConfig {
+            id: "perso".to_string(),
+            profile: Some("  my profile  ".to_string()),
+            ..Default::default()
+        };
+        assert_eq!(explicit.profile_name(), "my profile");
+    }
+
+    #[test]
+    fn the_markdown_mode_falls_back_to_the_global_one() {
+        use crate::config::MarkdownMode;
+        let cfg = ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap();
+        assert_eq!(cfg.markdown_mode(MarkdownMode::Dom), MarkdownMode::Dom);
+
+        let raw = r#"
+[provider]
+name = "x"
+web_url = "https://example.com"
+
+[selectors]
+input_field = "a"
+send_button = "b"
+response_container = "c"
+
+[input]
+markdown = "text"
+"#;
+        let cfg = ProviderConfig::parse(raw, "x.toml").unwrap();
+        assert_eq!(
+            cfg.markdown_mode(MarkdownMode::Clipboard),
+            MarkdownMode::Text
+        );
+    }
+
+    #[test]
+    fn the_copy_button_is_optional() {
+        let cfg = ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap();
+        assert!(cfg.has_copy_button());
+        // Blank the key by name rather than by matching the whole line: the
+        // shipped selector list is edited as the provider UIs change, and this
+        // test is about the key being optional, not about its current value.
+        let raw = CHATGPT
+            .lines()
+            .map(|line| {
+                if line.trim_start().starts_with("copy_button") {
+                    "copy_button = \"\""
+                } else {
+                    line
+                }
+            })
+            .collect::<Vec<_>>()
+            .join("\n");
+        let cfg = ProviderConfig::parse(&raw, "chatgpt.toml").unwrap();
+        assert!(!cfg.has_copy_button());
+        assert!(cfg.is_usable(), "the copy button is never required");
+    }
+
+    #[test]
+    fn invalid_regex_is_reported() {
+        let raw = r#"
+[provider]
+name = "x"
+web_url = "https://example.com"
+conversation_url_pattern = "("
+
+[selectors]
+input_field = "a"
+send_button = "b"
+response_container = "c"
+"#;
+        let cfg = ProviderConfig::parse(raw, "x.toml").unwrap();
+        assert!(cfg
+            .problems
+            .iter()
+            .any(|p| p.contains("conversation_url_pattern")));
+    }
+}
diff --git a/src/providers/mock.rs b/src/providers/mock.rs
new file mode 100644
index 0000000..70c1fef
--- /dev/null
+++ b/src/providers/mock.rs
@@ -0,0 +1,290 @@
+//! An in-memory backend: no browser, no network, no login.
+//!
+//! It serves the CLI demo and the HTTP integration tests, and keeps the API
+//! exercisable on a machine without Chrome.
+
+use std::time::Duration;
+
+use async_trait::async_trait;
+use tokio::sync::mpsc;
+
+use crate::browser::{SessionState, SessionStatus};
+use crate::error::{GatewayError, Result};
+use crate::providers::backend::{
+    owner_label, ChatBackend, ProviderDescriptor, ReloadReport, ResolvedModel, StepTiming,
+    ValidationReport,
+};
+use crate::providers::config::{Capabilities, IMPLICIT_ACCOUNT};
+use crate::providers::model::parse_model;
+use crate::providers::{AccountInfo, TurnEvent, TurnOutcome, TurnRequest, TurnStream};
+use crate::util;
+
+/// Canned backend used by tests and by `serve --backend mock`.
+pub struct MockBackend {
+    providers: Vec<ProviderDescriptor>,
+    per_chunk: Duration,
+    answers: Vec<String>,
+}
+
+impl Default for MockBackend {
+    fn default() -> Self {
+        Self::new(
+            vec![("chatgpt", "gpt-4o"), ("claude", "claude-sonnet-4")],
+            Duration::from_millis(20),
+        )
+    }
+}
+
+impl MockBackend {
+    /// Mirror the providers that are actually configured.
+    pub fn from_descriptors(mut descriptors: Vec<ProviderDescriptor>, per_chunk: Duration) -> Self {
+        for descriptor in &mut descriptors {
+            descriptor.browser = Some("mock".to_string());
+            descriptor.enabled = true;
+            descriptor.usable = true;
+        }
+        Self {
+            providers: descriptors,
+            per_chunk,
+            answers: MockBackend::default().answers,
+        }
+    }
+
+    pub fn new(providers: Vec<(&str, &str)>, per_chunk: Duration) -> Self {
+        let providers = providers
+            .into_iter()
+            .map(|(name, model)| ProviderDescriptor {
+                name: name.to_string(),
+                display_name: name.to_string(),
+                web_url: format!("https://{name}.example/"),
+                models: vec![model.to_string()],
+                enabled: true,
+                usable: true,
+                problems: Vec::new(),
+                capabilities: Capabilities {
+                    supports_images: true,
+                    supports_streaming: true,
+                    supports_new_chat: true,
+                },
+                browser: Some("mock".to_string()),
+                accounts: Vec::new(),
+            })
+            .collect();
+        Self {
+            providers,
+            per_chunk,
+            answers: vec![
+                "ok".to_string(),
+                "This answer comes from the mock backend: no browser was launched.".to_string(),
+            ],
+        }
+    }
+
+    /// Declare accounts on one provider, to exercise multi-account routing.
+    pub fn with_accounts(mut self, provider: &str, accounts: Vec<AccountInfo>) -> Self {
+        if let Some(descriptor) = self.providers.iter_mut().find(|p| p.name == provider) {
+            descriptor.accounts = accounts;
+        }
+        self
+    }
+
+    fn find(&self, provider: &str) -> Result<&ProviderDescriptor> {
+        self.providers
+            .iter()
+            .find(|p| p.name == provider)
+            .ok_or_else(|| GatewayError::UnknownProvider(provider.to_string()))
+    }
+
+    /// Resolve an account key against a descriptor, tolerating an id, an
+    /// e-mail address or a label.
+    fn account_of(descriptor: &ProviderDescriptor, key: Option<&str>) -> Result<Option<String>> {
+        if descriptor.accounts.is_empty() {
+            return match key.map(str::trim).filter(|value| !value.is_empty()) {
+                None => Ok(None),
+                Some(name) if name.eq_ignore_ascii_case(IMPLICIT_ACCOUNT) => Ok(None),
+                Some(name) => Err(GatewayError::UnknownAccount(format!(
+                    "provider '{}' has a single account; '{name}' does not select one",
+                    descriptor.name
+                ))),
+            };
+        }
+        let default = descriptor
+            .accounts
+            .iter()
+            .find(|account| account.default)
+            .or_else(|| descriptor.accounts.first())
+            .map(|account| account.id.clone());
+        match key.map(str::trim).filter(|value| !value.is_empty()) {
+            None => Ok(default),
+            Some(name) => descriptor
+                .accounts
+                .iter()
+                .find(|account| {
+                    account.id.eq_ignore_ascii_case(name)
+                        || account
+                            .email
+                            .as_deref()
+                            .is_some_and(|email| email.eq_ignore_ascii_case(name))
+                        || account
+                            .label
+                            .as_deref()
+                            .is_some_and(|label| label.eq_ignore_ascii_case(name))
+                })
+                .map(|account| Some(account.id.clone()))
+                .ok_or_else(|| {
+                    GatewayError::UnknownAccount(format!(
+                        "provider '{}' has no account '{name}' (known: {})",
+                        descriptor.name,
+                        descriptor
+                            .accounts
+                            .iter()
+                            .map(|account| account.id.clone())
+                            .collect::<Vec<_>>()
+                            .join(", ")
+                    ))
+                }),
+        }
+    }
+}
+
+#[async_trait]
+impl ChatBackend for MockBackend {
+    async fn complete(
+        &self,
+        provider: &str,
+        account: Option<&str>,
+        request: TurnRequest,
+    ) -> Result<TurnStream> {
+        let descriptor = self.find(provider)?;
+        MockBackend::account_of(descriptor, account)?;
+        let answer = if request.probe {
+            self.answers[0].clone()
+        } else {
+            self.answers.last().cloned().unwrap_or_default()
+        };
+        let per_chunk = self.per_chunk;
+        let reused = request.reuse_url.is_some();
+        let web_id = request
+            .reuse_url
+            .as_deref()
+            .and_then(|url| url.rsplit('/').next().map(str::to_string))
+            .unwrap_or_else(|| format!("mock-{}", uuid::Uuid::new_v4().simple()));
+        let web_url = format!("{}c/{}", descriptor.web_url, web_id);
+        let (tx, rx) = mpsc::channel(16);
+
+        tokio::spawn(async move {
+            let started = std::time::Instant::now();
+            let mut deltas = 0u32;
+            for chunk in answer.as_bytes().chunks(8) {
+                let piece = String::from_utf8_lossy(chunk).to_string();
+                if tx.send(TurnEvent::Delta(piece)).await.is_err() {
+                    return;
+                }
+                deltas += 1;
+                tokio::time::sleep(per_chunk).await;
+            }
+            let _ = tx
+                .send(TurnEvent::Completed(TurnOutcome {
+                    text: answer,
+                    web_url: Some(web_url),
+                    web_id: Some(web_id),
+                    elapsed_ms: started.elapsed().as_millis() as u64,
+                    deltas,
+                    fidelity: "text".to_string(),
+                }))
+                .await;
+        });
+
+        let _ = reused;
+        Ok(TurnStream::new(rx))
+    }
+
+    async fn status(&self, provider: &str, account: Option<&str>) -> SessionStatus {
+        let descriptor = match self.find(provider) {
+            Ok(descriptor) => descriptor,
+            Err(_) => {
+                let mut status = SessionStatus::error(provider, "provider is not configured");
+                status.state = SessionState::Misconfigured;
+                return status;
+            }
+        };
+        let account = match MockBackend::account_of(descriptor, account) {
+            Ok(account) => account,
+            Err(err) => {
+                let label = owner_label(provider, account);
+                let mut status = SessionStatus::error(&label, err.to_string());
+                status.state = SessionState::Misconfigured;
+                return status;
+            }
+        };
+        SessionStatus::available(
+            &owner_label(provider, account.as_deref()),
+            Some(descriptor.web_url.clone()),
+        )
+        .with_browser("mock")
+    }
+
+    async fn validate(&self, provider: &str, account: Option<&str>) -> Result<ValidationReport> {
+        let descriptor = self.find(provider)?;
+        let account = MockBackend::account_of(descriptor, account)?;
+        let started = std::time::Instant::now();
+        Ok(ValidationReport {
+            provider: owner_label(provider, account.as_deref()),
+            ok: true,
+            status: "ok".to_string(),
+            message: None,
+            response_excerpt: Some("ok".to_string()),
+            duration_ms: started.elapsed().as_millis() as u64,
+            checked_at: util::now_secs(),
+            steps: vec![
+                StepTiming {
+                    step: "session".into(),
+                    ms: 0,
+                    ok: true,
+                    detail: None,
+                },
+                StepTiming {
+                    step: "probe_prompt".into(),
+                    ms: 1,
+                    ok: true,
+                    detail: None,
+                },
+            ],
+        })
+    }
+
+    async fn reload(&self) -> Result<ReloadReport> {
+        Ok(ReloadReport::default())
+    }
+
+    fn providers(&self) -> Vec<ProviderDescriptor> {
+        self.providers.clone()
+    }
+
+    fn resolve(&self, model: &str) -> Result<ResolvedModel> {
+        let reference = parse_model(model);
+        let descriptor = if let Ok(descriptor) = self.find(&reference.provider) {
+            descriptor.clone()
+        } else if self.providers.len() == 1 {
+            self.providers[0].clone()
+        } else {
+            return Err(GatewayError::UnknownProvider(format!(
+                "{} (mock providers: {})",
+                reference.original(),
+                self.providers
+                    .iter()
+                    .map(|p| p.name.clone())
+                    .collect::<Vec<_>>()
+                    .join(", ")
+            )));
+        };
+        let account = MockBackend::account_of(&descriptor, reference.account.as_deref())?;
+        Ok(ResolvedModel {
+            provider: descriptor,
+            account,
+            model: reference.model,
+        })
+    }
+
+    async fn shutdown(&self) {}
+}
diff --git a/src/providers/mod.rs b/src/providers/mod.rs
new file mode 100644
index 0000000..3db842e
--- /dev/null
+++ b/src/providers/mod.rs
@@ -0,0 +1,23 @@
+//! Providers: configuration, the browser-driven implementation and the registry.
+
+pub mod backend;
+pub mod config;
+pub mod mock;
+pub mod model;
+pub mod registry;
+pub mod r#trait;
+pub mod webui;
+
+pub use backend::{
+    owner_label, ChatBackend, ProviderDescriptor, ReloadReport, ResolvedModel, StepTiming,
+    ValidationReport,
+};
+pub use config::{AccountConfig, Capabilities, ProviderConfig, Selectors, IMPLICIT_ACCOUNT};
+pub use mock::MockBackend;
+pub use model::{parse_model, ModelRef};
+pub use r#trait::{
+    AccountInfo, Attachment, AttachmentKind, LlmProvider, TurnEvent, TurnOutcome, TurnRequest,
+    TurnStream,
+};
+pub use registry::ProviderRegistry;
+pub use webui::{CaptureDefaults, WebUiProvider};
diff --git a/src/providers/model.rs b/src/providers/model.rs
new file mode 100644
index 0000000..f17cdd9
--- /dev/null
+++ b/src/providers/model.rs
@@ -0,0 +1,132 @@
+//! Parsing of the `model` string a client sends.
+//!
+//! The OpenAI API has a single field to select a model, and this gateway uses it
+//! for two things: the provider and, when the provider declares several, the
+//! account to answer from.
+//!
+//! ```text
+//! chatgpt                              provider, default account
+//! chatgpt@perso                        provider, account "perso"
+//! chatgpt@bruno.charest@gmail.com      provider, account by e-mail
+//! chatgpt/gpt-4o                       provider, model name
+//! chatgpt@perso/gpt-4o                 all three
+//! ```
+//!
+//! The account is parsed before the model name, so an address that itself
+//! contains an `@` still works.
+
+/// A `model` string broken into its parts.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct ModelRef {
+    /// Everything before the account marker: the provider name or a model name.
+    pub provider: String,
+    /// Account requested with `@`, when one is.
+    pub account: Option<String>,
+    /// Model name after the first `/`, when one is.
+    pub model: Option<String>,
+}
+
+impl ModelRef {
+    /// Rebuild the string, for error messages.
+    pub fn original(&self) -> String {
+        let mut out = self.provider.clone();
+        if let Some(account) = &self.account {
+            out.push('@');
+            out.push_str(account);
+        }
+        if let Some(model) = &self.model {
+            out.push('/');
+            out.push_str(model);
+        }
+        out
+    }
+}
+
+/// Split a model string into provider, account and model name.
+pub fn parse_model(raw: &str) -> ModelRef {
+    let trimmed = raw.trim();
+    let (head, model) = match trimmed.split_once('/') {
+        Some((head, model)) => (head, Some(model.trim()).filter(|value| !value.is_empty())),
+        None => (trimmed, None),
+    };
+    let (provider, account) = match head.split_once('@') {
+        Some((provider, account)) => (
+            provider.trim(),
+            Some(account.trim()).filter(|value| !value.is_empty()),
+        ),
+        None => (head.trim(), None),
+    };
+
+    ModelRef {
+        provider: provider.to_string(),
+        account: account.map(str::to_string),
+        model: model.map(str::to_string),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn a_bare_provider_has_no_account_and_no_model() {
+        let parsed = parse_model("chatgpt");
+        assert_eq!(parsed.provider, "chatgpt");
+        assert_eq!(parsed.account, None);
+        assert_eq!(parsed.model, None);
+        assert_eq!(parsed.original(), "chatgpt");
+    }
+
+    #[test]
+    fn the_model_name_follows_a_slash() {
+        let parsed = parse_model("chatgpt/gpt-4o");
+        assert_eq!(parsed.provider, "chatgpt");
+        assert_eq!(parsed.account, None);
+        assert_eq!(parsed.model.as_deref(), Some("gpt-4o"));
+    }
+
+    #[test]
+    fn the_account_follows_an_at_sign() {
+        let parsed = parse_model("chatgpt@perso");
+        assert_eq!(parsed.provider, "chatgpt");
+        assert_eq!(parsed.account.as_deref(), Some("perso"));
+        assert_eq!(parsed.model, None);
+
+        let both = parse_model("chatgpt@perso/gpt-4o");
+        assert_eq!(both.provider, "chatgpt");
+        assert_eq!(both.account.as_deref(), Some("perso"));
+        assert_eq!(both.model.as_deref(), Some("gpt-4o"));
+        assert_eq!(both.original(), "chatgpt@perso/gpt-4o");
+    }
+
+    #[test]
+    fn an_e_mail_address_survives_parsing() {
+        let parsed = parse_model("chatgpt@bruno.charest@gmail.com");
+        assert_eq!(parsed.provider, "chatgpt");
+        assert_eq!(parsed.account.as_deref(), Some("bruno.charest@gmail.com"));
+        assert_eq!(parsed.model, None);
+
+        let with_model = parse_model("chatgpt@bruno.charest@gmail.com/gpt-4o");
+        assert_eq!(with_model.provider, "chatgpt");
+        assert_eq!(
+            with_model.account.as_deref(),
+            Some("bruno.charest@gmail.com")
+        );
+        assert_eq!(with_model.model.as_deref(), Some("gpt-4o"));
+    }
+
+    #[test]
+    fn blanks_and_trailing_slashes_are_tolerated() {
+        let parsed = parse_model("  chatgpt  ");
+        assert_eq!(parsed.provider, "chatgpt");
+
+        let parsed = parse_model("chatgpt/");
+        assert_eq!(parsed.provider, "chatgpt");
+        assert_eq!(parsed.model, None);
+
+        let parsed = parse_model("chatgpt@/gpt-4o");
+        assert_eq!(parsed.provider, "chatgpt");
+        assert_eq!(parsed.account, None);
+        assert_eq!(parsed.model.as_deref(), Some("gpt-4o"));
+    }
+}
diff --git a/src/providers/registry.rs b/src/providers/registry.rs
new file mode 100644
index 0000000..44485e4
--- /dev/null
+++ b/src/providers/registry.rs
@@ -0,0 +1,591 @@
+//! Provider registry: loads provider files and builds browser-driven providers.
+
+use std::collections::{BTreeMap, BTreeSet};
+use std::sync::{Arc, RwLock};
+use std::time::Duration;
+
+use arc_swap::ArcSwap;
+use async_trait::async_trait;
+
+use crate::browser::{resolve_executable, DebugRecorder, SessionStatus};
+use crate::config::GlobalConfig;
+use crate::error::{GatewayError, Result};
+use crate::paths::{expand_tilde, Layout};
+use crate::providers::backend::{
+    owner_label, ChatBackend, ProviderDescriptor, ReloadReport, ResolvedModel, ValidationReport,
+};
+use crate::providers::config::ProviderConfig;
+use crate::providers::model::parse_model;
+use crate::providers::webui::{CaptureDefaults, WebUiProvider};
+use crate::providers::{LlmProvider, TurnRequest, TurnStream};
+use crate::selftest::runner::validate_provider;
+
+/// Public description of one configured provider, with its accounts.
+pub fn descriptor_of(provider: &WebUiProvider) -> ProviderDescriptor {
+    let cfg = provider.cfg();
+    ProviderDescriptor {
+        name: cfg.name().to_string(),
+        display_name: cfg.display_name().to_string(),
+        web_url: cfg.web_url().to_string(),
+        models: cfg.default_models().to_vec(),
+        enabled: cfg.enabled(),
+        usable: cfg.is_usable(),
+        problems: cfg.problems.clone(),
+        capabilities: cfg.capabilities().clone(),
+        browser: Some(provider.browser().to_string()),
+        accounts: provider.accounts(),
+    }
+}
+
+/// Owns every configured provider and their browser processes.
+pub struct ProviderRegistry {
+    layout: Layout,
+    config: Arc<ArcSwap<GlobalConfig>>,
+    providers: RwLock<BTreeMap<String, Arc<WebUiProvider>>>,
+}
+
+impl ProviderRegistry {
+    pub fn new(layout: Layout, config: GlobalConfig) -> Self {
+        Self {
+            layout,
+            config: Arc::new(ArcSwap::from_pointee(config)),
+            providers: RwLock::new(BTreeMap::new()),
+        }
+    }
+
+    /// Shared configuration handle: the HTTP layer reads the same snapshot.
+    pub fn config_handle(&self) -> Arc<ArcSwap<GlobalConfig>> {
+        Arc::clone(&self.config)
+    }
+
+    pub fn layout(&self) -> &Layout {
+        &self.layout
+    }
+
+    pub fn global(&self) -> Arc<GlobalConfig> {
+        self.config.load_full()
+    }
+
+    /// Swap in a reloaded global configuration (browser settings need a restart
+    /// to take effect; capture settings apply immediately).
+    pub fn replace_global(&self, config: GlobalConfig) {
+        self.config.store(Arc::new(config));
+    }
+
+    pub fn get(&self, name: &str) -> Option<Arc<WebUiProvider>> {
+        self.providers
+            .read()
+            .ok()
+            .and_then(|map| map.get(name).cloned())
+    }
+
+    pub fn all(&self) -> Vec<Arc<WebUiProvider>> {
+        self.providers
+            .read()
+            .map(|map| map.values().cloned().collect())
+            .unwrap_or_default()
+    }
+
+    fn browser_settings(&self, provider: &str) -> crate::browser::BrowserSettings {
+        let global = self.config.load();
+        let configured = global.browser.executable.trim();
+        let executable = if configured.is_empty() {
+            resolve_executable(None, std::env::var("CHROME").ok())
+        } else {
+            let path = expand_tilde(configured);
+            Some(path)
+        };
+        crate::browser::BrowserSettings {
+            provider: provider.to_string(),
+            account: None,
+            executable,
+            headless: global.browser.headless,
+            // The historical, single-account profile directory. A provider that
+            // declares accounts replaces it with a per-account one.
+            profile_dir: global.profile_dir_for(&self.layout, provider),
+            max_tabs: global.browser.max_tabs.max(1),
+            busy_wait: Duration::from_secs(global.browser.busy_wait_s.max(1)),
+            launch_timeout: Duration::from_secs(global.browser.launch_timeout_s.max(5)),
+            request_timeout: Duration::from_secs(global.browser.request_timeout_s.max(5)),
+            extra_args: global.browser.extra_args.clone(),
+            stealth: global.browser.stealth,
+            attach: global.browser.attach,
+            debug_port: global.browser.debug_port,
+        }
+    }
+
+    fn build_provider(&self, cfg: ProviderConfig) -> Arc<WebUiProvider> {
+        let name = cfg.name().to_string();
+        let global = self.config.load_full();
+        let settings = self.browser_settings(&name);
+        let profiles_root = settings
+            .profile_dir
+            .parent()
+            .map(|path| path.to_path_buf())
+            .unwrap_or_else(|| global.resolved_profile_root(&self.layout).join(&name));
+        let recorder = DebugRecorder::new(
+            global.resolved_debug_dir(&self.layout),
+            global.debug.screenshots,
+        );
+        let defaults = CaptureDefaults::from_config(&global);
+        if global.browser.max_tabs > 1 {
+            tracing::info!(
+                provider = %name,
+                max_tabs = global.browser.max_tabs,
+                "concurrent turns per account"
+            );
+        }
+        Arc::new(WebUiProvider::new(
+            cfg,
+            settings,
+            profiles_root,
+            recorder,
+            defaults,
+        ))
+    }
+
+    /// Load (or reload) every provider file. Returns what changed.
+    ///
+    /// The provider map is never held across an await: reloading an account can
+    /// stop a browser, which is asynchronous work.
+    pub async fn reload(&self) -> Result<ReloadReport> {
+        let mut report = ReloadReport::default();
+        let mut seen: BTreeSet<String> = BTreeSet::new();
+        let mut to_update: Vec<(Arc<WebUiProvider>, ProviderConfig)> = Vec::new();
+        let mut to_add: Vec<ProviderConfig> = Vec::new();
+
+        for (path, result) in ProviderConfig::load_dir(&self.layout.providers_dir()) {
+            let cfg = match result {
+                Ok(cfg) => cfg,
+                Err(err) => {
+                    report.problems.push(format!("{}: {err}", path.display()));
+                    tracing::error!(path = %path.display(), error = %err, "cannot load the provider configuration");
+                    continue;
+                }
+            };
+
+            if !cfg.enabled() {
+                tracing::debug!(provider = %cfg.name(), "provider disabled in its configuration file");
+                continue;
+            }
+            if !cfg.is_usable() {
+                for problem in &cfg.problems {
+                    report.problems.push(format!("{}: {problem}", cfg.name()));
+                }
+            }
+            let name = cfg.name().to_string();
+            if !seen.insert(name.clone()) {
+                report
+                    .problems
+                    .push(format!("duplicate provider '{name}' in {}", path.display()));
+                continue;
+            }
+
+            match self.get(&name) {
+                Some(existing) => {
+                    if existing.cfg().file.serialized() != cfg.file.serialized() {
+                        report.updated.push(name);
+                        to_update.push((existing, cfg));
+                    }
+                }
+                None => {
+                    report.added.push(name);
+                    to_add.push(cfg);
+                }
+            }
+        }
+
+        let mut removed: Vec<Arc<WebUiProvider>> = Vec::new();
+        {
+            let mut map = self.providers.write().expect("provider map poisoned");
+            for cfg in to_add {
+                let provider = self.build_provider(cfg);
+                map.insert(provider.name().to_string(), provider);
+            }
+            let stale: Vec<String> = map
+                .keys()
+                .filter(|key| !seen.contains(*key))
+                .cloned()
+                .collect();
+            for name in stale {
+                if let Some(provider) = map.remove(&name) {
+                    removed.push(provider);
+                    report.removed.push(name);
+                }
+            }
+        }
+
+        for (provider, cfg) in to_update {
+            provider.replace_config(cfg).await;
+        }
+
+        // Shut the removed providers down outside the lock: it awaits.
+        for provider in removed {
+            if let Err(err) = provider.shutdown().await {
+                tracing::warn!(provider = %provider.name(), error = %err, "cannot stop the removed provider");
+            }
+        }
+
+        for name in &report.added {
+            tracing::info!(provider = %name, "provider registered");
+        }
+        if !report.problems.is_empty() {
+            tracing::warn!(problems = ?report.problems, "provider configuration problems");
+        }
+        Ok(report)
+    }
+
+    /// Drop every provider except one. Returns false when the name is unknown.
+    pub async fn retain_only(&self, keep: &str) -> bool {
+        let mut removed = Vec::new();
+        {
+            let mut map = self.providers.write().expect("provider map poisoned");
+            let names: Vec<String> = map
+                .keys()
+                .filter(|name| name.as_str() != keep)
+                .cloned()
+                .collect();
+            for name in names {
+                if let Some(provider) = map.remove(&name) {
+                    removed.push(provider);
+                }
+            }
+        }
+        let found = self.get(keep).is_some();
+        for provider in removed {
+            let _ = provider.shutdown().await;
+        }
+        found
+    }
+
+    /// Stop every browser process owned by the registry.
+    pub async fn shutdown_all(&self) {
+        for provider in self.all() {
+            if let Err(err) = provider.shutdown().await {
+                tracing::debug!(provider = %provider.name(), error = %err, "shutdown failed");
+            }
+        }
+    }
+
+    /// Human readable status of one provider account, for the CLI and the API.
+    pub async fn status_of(&self, provider: &str, account: Option<&str>) -> SessionStatus {
+        let Some(handle) = self.get(provider) else {
+            let mut status =
+                SessionStatus::error(provider, format!("provider '{provider}' is not configured"));
+            status.state = crate::browser::SessionState::Misconfigured;
+            return status;
+        };
+        // A bare provider name selects its default account; the report says
+        // which account was actually probed, exactly like a validation report.
+        let cfg = handle.cfg();
+        let account = match cfg.resolve_account_id(account) {
+            Ok(account) => account,
+            Err(detail) => return SessionStatus::error(&owner_label(provider, account), detail),
+        };
+        let label = owner_label(provider, account.as_deref());
+        let mut status = match handle.probe_session(account.as_deref()).await {
+            Ok(session) => handle
+                .validate_session(account.as_deref(), &session)
+                .await
+                .unwrap_or_else(|err| SessionStatus::error(&label, err.to_string())),
+            Err(err) => SessionStatus::error(&label, err.to_string()),
+        };
+        // The page probe only knows the provider name; the label is what tells
+        // two accounts of the same provider apart.
+        status.provider = label;
+        status
+    }
+
+    /// Occupancy of every tab pool, for the status endpoints.
+    pub fn tab_stats(&self) -> Vec<(String, crate::browser::TabStats)> {
+        self.all()
+            .iter()
+            .flat_map(|provider| {
+                let name = provider.name().to_string();
+                provider
+                    .tab_stats()
+                    .into_iter()
+                    .map(move |(account, stats)| (format!("{name}@{account}"), stats))
+                    .collect::<Vec<_>>()
+            })
+            .collect()
+    }
+}
+
+#[async_trait]
+impl ChatBackend for ProviderRegistry {
+    async fn complete(
+        &self,
+        provider: &str,
+        account: Option<&str>,
+        request: TurnRequest,
+    ) -> Result<TurnStream> {
+        let handle = self
+            .get(provider)
+            .ok_or_else(|| GatewayError::UnknownProvider(provider.to_string()))?;
+        let cfg = handle.cfg();
+        if !cfg.is_usable() {
+            return Err(GatewayError::ProviderMisconfigured {
+                provider: provider.to_string(),
+                detail: cfg.problems.join("; "),
+            });
+        }
+
+        // Admission control lives in the provider account's tab pool: the lease
+        // is held for the whole capture and released when it ends.
+        let wait = request
+            .wait_for_tab
+            .unwrap_or_else(|| handle.busy_wait(account));
+        let session = handle.session_with_wait(account, wait).await?;
+        handle.run_turn(session, request).await
+    }
+
+    async fn status(&self, provider: &str, account: Option<&str>) -> SessionStatus {
+        self.status_of(provider, account).await
+    }
+
+    async fn validate(&self, provider: &str, account: Option<&str>) -> Result<ValidationReport> {
+        let handle = self
+            .get(provider)
+            .ok_or_else(|| GatewayError::UnknownProvider(provider.to_string()))?;
+        let cfg = handle.cfg();
+        // An unknown account is a 404, not a report: the caller named an
+        // account that does not exist rather than one that fails to answer.
+        let account = cfg
+            .resolve_account_id(account)
+            .map_err(GatewayError::UnknownAccount)?;
+        validate_provider(handle.as_ref(), &cfg, account.as_deref()).await
+    }
+
+    async fn reload(&self) -> Result<ReloadReport> {
+        ProviderRegistry::reload(self).await
+    }
+
+    fn providers(&self) -> Vec<ProviderDescriptor> {
+        self.all()
+            .into_iter()
+            .map(|provider| descriptor_of(&provider))
+            .collect()
+    }
+
+    fn resolve(&self, model: &str) -> Result<ResolvedModel> {
+        let reference = parse_model(model);
+        let map = self.providers.read().expect("provider map poisoned");
+
+        let provider = match map.get(&reference.provider) {
+            Some(provider) => provider,
+            None if map.len() == 1 => {
+                let only = map.values().next().expect("one provider");
+                tracing::debug!(
+                    model = %reference.original(),
+                    provider = %only.name(),
+                    "routing to the only configured provider"
+                );
+                only
+            }
+            None if map.is_empty() => {
+                return Err(GatewayError::UnknownProvider(format!(
+                    "{} (no provider is configured: check {})",
+                    reference.original(),
+                    self.layout.providers_dir().display()
+                )))
+            }
+            None => {
+                return Err(GatewayError::UnknownProvider(format!(
+                    "{} (configured providers: {})",
+                    reference.original(),
+                    map.keys().cloned().collect::<Vec<_>>().join(", ")
+                )))
+            }
+        };
+
+        let cfg = provider.cfg();
+        let account = cfg
+            .resolve_account_id(reference.account.as_deref())
+            .map_err(|detail| {
+                GatewayError::UnknownAccount(format!("{detail} (model '{}')", reference.original()))
+            })?;
+
+        Ok(ResolvedModel {
+            provider: descriptor_of(provider),
+            account,
+            model: reference.model,
+        })
+    }
+
+    async fn shutdown(&self) {
+        self.shutdown_all().await;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::providers::config::IMPLICIT_ACCOUNT;
+
+    /// A registry with two providers, one of them multi-account.
+    fn registry() -> (ProviderRegistry, tempfile::TempDir) {
+        let tmp = tempfile::tempdir().unwrap();
+        let layout = Layout::rooted_at(tmp.path().join("state"));
+        layout.ensure().unwrap();
+        std::fs::remove_file(layout.provider_config("chatgpt")).ok();
+        std::fs::remove_file(layout.provider_config("claude")).ok();
+        std::fs::remove_file(layout.provider_config("deepseek")).ok();
+
+        let accounts = r#"
+[[accounts]]
+id = "perso"
+email = "bruno.charest@gmail.com"
+default = true
+
+[[accounts]]
+id = "pro"
+email = "brunocharest.bc@gmail.com"
+"#;
+        std::fs::write(
+            layout.provider_config("chatgpt"),
+            format!("{}{accounts}", include_str!("../../providers/chatgpt.toml")),
+        )
+        .unwrap();
+        std::fs::write(
+            layout.provider_config("claude"),
+            include_str!("../../providers/claude.toml"),
+        )
+        .unwrap();
+
+        (ProviderRegistry::new(layout, GlobalConfig::default()), tmp)
+    }
+
+    #[tokio::test]
+    async fn the_shipped_providers_are_registered() {
+        let (registry, _tmp) = registry();
+        let report = registry.reload().await.unwrap();
+        assert!(report.problems.is_empty(), "{:?}", report.problems);
+        let mut names: Vec<String> = report.added;
+        names.sort();
+        assert_eq!(names, vec!["chatgpt".to_string(), "claude".to_string()]);
+    }
+
+    #[tokio::test]
+    async fn a_model_string_selects_provider_account_and_model() {
+        let (registry, _tmp) = registry();
+        registry.reload().await.unwrap();
+
+        let plain = registry.resolve("claude").unwrap();
+        assert_eq!(plain.provider.name, "claude");
+        assert_eq!(plain.account, None);
+        assert_eq!(plain.owner(), "claude");
+
+        let named = registry.resolve("chatgpt@pro/claude-sonnet-4").unwrap();
+        assert_eq!(named.provider.name, "chatgpt");
+        assert_eq!(named.account.as_deref(), Some("pro"));
+        assert_eq!(named.model.as_deref(), Some("claude-sonnet-4"));
+        assert_eq!(named.owner(), "chatgpt@pro");
+
+        // The default account is used when none is named.
+        let default = registry.resolve("chatgpt").unwrap();
+        assert_eq!(default.account.as_deref(), Some("perso"));
+
+        // An address works as well as an id.
+        let by_email = registry
+            .resolve("chatgpt@brunocharest.bc@gmail.com")
+            .unwrap();
+        assert_eq!(by_email.account.as_deref(), Some("pro"));
+    }
+
+    #[tokio::test]
+    async fn unknown_providers_and_accounts_are_404s() {
+        let (registry, _tmp) = registry();
+        registry.reload().await.unwrap();
+
+        let err = registry.resolve("gemini").unwrap_err();
+        assert_eq!(err.code(), "model_not_found");
+        assert_eq!(err.http_status(), 404);
+        assert!(err.to_string().contains("chatgpt"), "{err}");
+
+        let err = registry.resolve("chatgpt@nobody").unwrap_err();
+        assert_eq!(err.code(), "account_not_found");
+        assert_eq!(err.http_status(), 404);
+        assert!(err.to_string().contains("no account 'nobody'"), "{err}");
+        assert!(err.to_string().contains("chatgpt@nobody"), "{err}");
+    }
+
+    #[tokio::test]
+    async fn every_account_is_described_with_its_own_profile() {
+        let (registry, _tmp) = registry();
+        registry.reload().await.unwrap();
+        let descriptor = registry.resolve("chatgpt").unwrap().provider;
+        assert_eq!(descriptor.accounts.len(), 2);
+        assert_eq!(
+            descriptor.accounts[0].email.as_deref(),
+            Some("bruno.charest@gmail.com")
+        );
+        assert!(descriptor.accounts[0].default);
+        assert!(!descriptor.accounts[1].default);
+        assert_ne!(
+            descriptor.accounts[0].profile,
+            descriptor.accounts[1].profile
+        );
+
+        // A single-account provider reports no account list at all.
+        let claude = registry.resolve("claude").unwrap().provider;
+        assert!(claude.accounts.is_empty());
+    }
+
+    #[tokio::test]
+    async fn a_single_provider_still_answers_to_a_bare_model_name() {
+        let tmp = tempfile::tempdir().unwrap();
+        let layout = Layout::rooted_at(tmp.path().join("state"));
+        layout.ensure().unwrap();
+        std::fs::remove_file(layout.provider_config("chatgpt")).ok();
+        std::fs::remove_file(layout.provider_config("claude")).ok();
+        std::fs::remove_file(layout.provider_config("deepseek")).ok();
+        std::fs::write(
+            layout.provider_config("chatgpt"),
+            include_str!("../../providers/chatgpt.toml"),
+        )
+        .unwrap();
+
+        let registry = ProviderRegistry::new(layout, GlobalConfig::default());
+        registry.reload().await.unwrap();
+        let resolved = registry.resolve("gpt-4o").unwrap();
+        assert_eq!(resolved.provider.name, "chatgpt");
+        assert_eq!(resolved.account, None);
+
+        // A provider that declares no account refuses a named one.
+        let err = registry.resolve("chatgpt@perso").unwrap_err();
+        assert!(err.to_string().contains("single account"), "{err}");
+    }
+
+    #[tokio::test]
+    async fn the_implicit_account_keeps_the_legacy_profile_directory() {
+        let tmp = tempfile::tempdir().unwrap();
+        let layout = Layout::rooted_at(tmp.path().join("state"));
+        layout.ensure().unwrap();
+        std::fs::remove_file(layout.provider_config("chatgpt")).ok();
+        std::fs::remove_file(layout.provider_config("claude")).ok();
+        std::fs::remove_file(layout.provider_config("deepseek")).ok();
+        std::fs::write(
+            layout.provider_config("chatgpt"),
+            include_str!("../../providers/chatgpt.toml"),
+        )
+        .unwrap();
+
+        let registry = ProviderRegistry::new(layout.clone(), GlobalConfig::default());
+        registry.reload().await.unwrap();
+        let provider = registry.get("chatgpt").unwrap();
+        assert_eq!(
+            provider.profile_dir(None).unwrap(),
+            layout.profile_dir("chatgpt")
+        );
+        assert_eq!(
+            provider.profile_dir(None).unwrap(),
+            layout.profiles_dir().join("chatgpt").join("user-data-dir")
+        );
+    }
+
+    #[test]
+    fn the_implicit_account_name_is_stable() {
+        assert_eq!(IMPLICIT_ACCOUNT, "default");
+    }
+}
diff --git a/src/providers/trait.rs b/src/providers/trait.rs
new file mode 100644
index 0000000..f1a98a0
--- /dev/null
+++ b/src/providers/trait.rs
@@ -0,0 +1,199 @@
+//! The provider contract: one browser-driven chat turn.
+
+use std::path::PathBuf;
+use std::sync::Arc;
+use std::time::Duration;
+
+use async_trait::async_trait;
+use serde::{Deserialize, Serialize};
+use tokio::sync::mpsc;
+
+use crate::browser::{Session, SessionStatus};
+use crate::error::Result;
+use crate::providers::config::{Capabilities, ProviderConfig};
+
+/// A file materialised on disk, ready to be attached in the web UI.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Attachment {
+    pub path: PathBuf,
+    pub mime: String,
+    pub kind: AttachmentKind,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AttachmentKind {
+    Image,
+    Document,
+}
+
+/// Everything needed to run one turn.
+#[derive(Debug, Clone)]
+pub struct TurnRequest {
+    /// Text actually pushed into the editor (history replayed when needed).
+    pub prompt: String,
+    pub attachments: Vec<Attachment>,
+    /// Web conversation to reopen, when the thread is being continued.
+    pub reuse_url: Option<String>,
+    /// Force a fresh web conversation and inject the whole history.
+    pub replay_history: bool,
+    /// Probe turns (selftest/validate) skip the thread bookkeeping.
+    pub probe: bool,
+    pub trace_id: String,
+    /// How long this turn may wait for a free tab.
+    ///
+    /// `None` uses the configured `browser.busy_wait_s`: a client request that
+    /// arrives while the account is busy should get a 429 rather than queue for
+    /// minutes. The extra variants of one request are our own concurrency, so
+    /// they wait for their turn instead of failing.
+    pub wait_for_tab: Option<Duration>,
+}
+
+impl TurnRequest {
+    pub fn probe(trace_id: impl Into<String>) -> Self {
+        Self {
+            prompt: "Answer with the single word: ok".to_string(),
+            attachments: Vec::new(),
+            reuse_url: None,
+            replay_history: true,
+            probe: true,
+            trace_id: trace_id.into(),
+            wait_for_tab: None,
+        }
+    }
+}
+
+/// Incremental result of a turn.
+#[derive(Debug)]
+pub enum TurnEvent {
+    /// Newly generated text, appended to the previous deltas.
+    Delta(String),
+    /// Terminal event carrying the full answer.
+    Completed(TurnOutcome),
+    /// Terminal error: the capture failed after the stream started.
+    Failed(crate::error::GatewayError),
+}
+
+/// Final result of a turn.
+#[derive(Debug, Clone, Default)]
+pub struct TurnOutcome {
+    pub text: String,
+    pub web_url: Option<String>,
+    pub web_id: Option<String>,
+    pub elapsed_ms: u64,
+    pub deltas: u32,
+    /// Where the final text comes from: `clipboard`, `dom` or `text`.
+    pub fidelity: String,
+}
+
+/// One declared account of a provider, as reported by the API.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AccountInfo {
+    pub id: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub email: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub label: Option<String>,
+    /// True for the account a request naming the provider alone reaches.
+    pub default: bool,
+    /// Directory of the browser profile holding this account's session.
+    pub profile: String,
+}
+
+/// Stream of turn events.
+pub struct TurnStream {
+    rx: mpsc::Receiver<TurnEvent>,
+}
+
+impl Unpin for TurnStream {}
+
+impl futures::Stream for TurnStream {
+    type Item = TurnEvent;
+
+    fn poll_next(
+        self: std::pin::Pin<&mut Self>,
+        cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Option<Self::Item>> {
+        self.get_mut().rx.poll_recv(cx)
+    }
+}
+
+impl TurnStream {
+    pub fn new(rx: mpsc::Receiver<TurnEvent>) -> Self {
+        Self { rx }
+    }
+
+    pub async fn recv(&mut self) -> Option<TurnEvent> {
+        self.rx.recv().await
+    }
+
+    pub fn into_receiver(self) -> mpsc::Receiver<TurnEvent> {
+        self.rx
+    }
+
+    /// Drain the stream, returning the final outcome.
+    pub async fn collect(mut self) -> Result<TurnOutcome> {
+        while let Some(event) = self.rx.recv().await {
+            match event {
+                TurnEvent::Completed(outcome) => return Ok(outcome),
+                TurnEvent::Failed(err) => return Err(err),
+                TurnEvent::Delta(_) => {}
+            }
+        }
+        Err(crate::error::GatewayError::internal(
+            "the provider task ended without producing an answer",
+        ))
+    }
+}
+
+/// A chat provider backed by a web UI.
+#[async_trait]
+pub trait LlmProvider: Send + Sync {
+    /// Configured name, e.g. "chatgpt".
+    fn name(&self) -> &str;
+
+    /// Current configuration snapshot (hot reloaded).
+    fn cfg(&self) -> Arc<ProviderConfig>;
+
+    /// What the web UI supports.
+    fn capabilities(&self) -> Capabilities {
+        self.cfg().capabilities().clone()
+    }
+
+    /// True when the configuration has no problems.
+    fn is_configured(&self) -> bool {
+        self.cfg().is_usable()
+    }
+
+    /// Accounts declared by the configuration. Empty when the provider has a
+    /// single implicit one.
+    fn accounts(&self) -> Vec<AccountInfo> {
+        Vec::new()
+    }
+
+    /// Browser session of one account, starting the browser when needed.
+    ///
+    /// `account` is an account id; `None` selects the default account.
+    async fn session(&self, account: Option<&str>) -> Result<Session>;
+
+    /// Read the current page status.
+    async fn validate_session(
+        &self,
+        account: Option<&str>,
+        session: &Session,
+    ) -> Result<SessionStatus>;
+
+    /// Execute one turn. Returns immediately with a stream of events.
+    async fn run_turn(&self, session: Session, request: TurnRequest) -> Result<TurnStream>;
+
+    /// Start a brand new web conversation, returning its URL when known.
+    async fn new_conversation(&self, session: &Session) -> Result<Option<String>>;
+
+    /// Attach files in the web UI.
+    async fn upload_files(&self, session: &Session, files: &[Attachment]) -> Result<()>;
+
+    /// Close the browser process owned by this provider, every account.
+    async fn shutdown(&self) -> Result<()>;
+
+    /// Close the browser of one account only.
+    async fn shutdown_account(&self, account: &str) -> Result<()>;
+}
diff --git a/src/providers/webui.rs b/src/providers/webui.rs
new file mode 100644
index 0000000..0dacc8f
--- /dev/null
+++ b/src/providers/webui.rs
@@ -0,0 +1,1247 @@
+//! Generic browser-driven provider.
+//!
+//! One implementation drives every provider: the whole site specific behaviour
+//! lives in `providers/*.toml` (URLs, selectors, timeouts, capabilities), so
+//! porting the gateway to a new chat web UI is a configuration change.
+//!
+//! A provider may declare several accounts. An account is a browser profile,
+//! therefore a browser process, a session and a pool of tabs: two ChatGPT
+//! accounts are two engines, and a request picks one with `model =
+//! "chatgpt@perso"`.
+
+use std::collections::BTreeMap;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use arc_swap::ArcSwap;
+use async_trait::async_trait;
+use chromiumoxide::cdp::browser_protocol::input::InsertTextParams;
+use chromiumoxide::Page;
+
+use crate::browser::session::classify;
+use crate::browser::{
+    dom, js, BrowserEngine, CdpEngine, DebugRecorder, Session, SessionStatus, TabStats,
+};
+use crate::config::{GlobalConfig, InjectMethod, MarkdownMode};
+use crate::error::{GatewayError, Result};
+use crate::markdown;
+use crate::providers::config::{ProviderConfig, IMPLICIT_ACCOUNT};
+use crate::providers::{
+    AccountInfo, Attachment, LlmProvider, TurnEvent, TurnOutcome, TurnRequest, TurnStream,
+};
+use crate::util;
+
+/// Global capture knobs, used when a provider does not override them.
+#[derive(Debug, Clone)]
+pub struct CaptureDefaults {
+    pub poll_interval: Duration,
+    pub quiet: Duration,
+    pub response_timeout: Duration,
+    pub inject_method: InjectMethod,
+    /// Fidelity of the final answer text.
+    pub markdown: MarkdownMode,
+    /// How long the clipboard read is given before the DOM wins.
+    pub clipboard_timeout: Duration,
+}
+
+impl Default for CaptureDefaults {
+    fn default() -> Self {
+        Self {
+            poll_interval: Duration::from_millis(400),
+            quiet: Duration::from_millis(1500),
+            response_timeout: Duration::from_secs(180),
+            inject_method: InjectMethod::Auto,
+            markdown: MarkdownMode::Auto,
+            clipboard_timeout: Duration::from_millis(1500),
+        }
+    }
+}
+
+impl CaptureDefaults {
+    pub fn from_config(cfg: &GlobalConfig) -> Self {
+        Self {
+            poll_interval: Duration::from_millis(cfg.capture.poll_interval_ms.max(50)),
+            quiet: Duration::from_millis(cfg.capture.quiet_ms),
+            response_timeout: Duration::from_secs(cfg.capture.response_timeout_s.max(1)),
+            inject_method: cfg.capture.inject_method,
+            markdown: cfg.capture.markdown,
+            clipboard_timeout: Duration::from_millis(cfg.capture.clipboard_timeout_ms.max(100)),
+        }
+    }
+}
+
+/// Snapshot handed to the spawned turn task.
+struct TurnContext {
+    cfg: Arc<ProviderConfig>,
+    recorder: DebugRecorder,
+    defaults: CaptureDefaults,
+}
+
+/// One account of a provider: its browser, its tabs and its session.
+struct AccountRuntime {
+    id: String,
+    info: AccountInfo,
+    engine: Arc<dyn BrowserEngine>,
+}
+
+/// A provider whose answers come from a chat web UI.
+pub struct WebUiProvider {
+    name: String,
+    cfg: ArcSwap<ProviderConfig>,
+    accounts: ArcSwap<BTreeMap<String, Arc<AccountRuntime>>>,
+    /// Settings shared by every account; the profile directory is per account.
+    base_settings: crate::browser::BrowserSettings,
+    /// `profiles/<provider>`, parent of the per-account directories.
+    profiles_root: PathBuf,
+    recorder: DebugRecorder,
+    defaults: CaptureDefaults,
+}
+
+impl WebUiProvider {
+    pub fn new(
+        cfg: ProviderConfig,
+        base_settings: crate::browser::BrowserSettings,
+        profiles_root: PathBuf,
+        recorder: DebugRecorder,
+        defaults: CaptureDefaults,
+    ) -> Self {
+        let accounts = build_accounts(&cfg, &base_settings, &profiles_root, &BTreeMap::new()).0;
+        Self {
+            name: cfg.name().to_string(),
+            cfg: ArcSwap::from_pointee(cfg),
+            accounts: ArcSwap::from_pointee(accounts),
+            base_settings,
+            profiles_root,
+            recorder,
+            defaults,
+        }
+    }
+
+    /// Swap in a configuration reloaded from disk.
+    ///
+    /// Accounts that did not change keep their browser and their signed-in
+    /// session; the ones that disappeared are shut down.
+    pub async fn replace_config(&self, cfg: ProviderConfig) {
+        let problems = cfg.problems.clone();
+        let existing = self.accounts.load_full();
+        let (accounts, removed) =
+            build_accounts(&cfg, &self.base_settings, &self.profiles_root, &existing);
+        self.cfg.store(Arc::new(cfg));
+        self.accounts.store(Arc::new(accounts));
+        for account in removed {
+            if let Err(err) = account.engine.shutdown().await {
+                tracing::warn!(
+                    provider = %self.name,
+                    account = %account.id,
+                    error = %err,
+                    "cannot stop the browser of a removed account"
+                );
+            }
+        }
+        if !problems.is_empty() {
+            tracing::warn!(provider = %self.name, ?problems, "provider configuration has problems");
+        }
+    }
+
+    pub fn browser(&self) -> &'static str {
+        "chromium-cdp"
+    }
+
+    /// True when at least one browser process is alive.
+    pub async fn is_running(&self) -> bool {
+        for account in self.accounts.load().values() {
+            if account.engine.is_running().await {
+                return true;
+            }
+        }
+        false
+    }
+
+    /// Occupancy of every account's tab pool.
+    pub fn tab_stats(&self) -> Vec<(String, TabStats)> {
+        self.accounts
+            .load()
+            .values()
+            .map(|account| (account.id.clone(), account.engine.stats()))
+            .collect()
+    }
+
+    /// Runtime of one account.
+    fn runtime(&self, account: Option<&str>) -> Result<Arc<AccountRuntime>> {
+        let key = account_key(account);
+        let accounts = self.accounts.load();
+        accounts.get(key).cloned().ok_or_else(|| {
+            let known: Vec<&str> = accounts.keys().map(String::as_str).collect();
+            GatewayError::UnknownAccount(format!(
+                "provider '{}' has no account '{key}' (known: {})",
+                self.name,
+                known.join(", ")
+            ))
+        })
+    }
+
+    /// Open a tab for one turn, waiting for a free one.
+    pub async fn session(&self, account: Option<&str>) -> Result<Session> {
+        let runtime = self.runtime(account)?;
+        let wait = runtime.engine.settings().busy_wait;
+        self.lease_session(&runtime, wait).await
+    }
+
+    /// Open a tab for one turn, with an explicit wait budget.
+    pub async fn session_with_wait(
+        &self,
+        account: Option<&str>,
+        wait: Duration,
+    ) -> Result<Session> {
+        let runtime = self.runtime(account)?;
+        self.lease_session(&runtime, wait).await
+    }
+
+    /// Wait budget configured for one account.
+    pub fn busy_wait(&self, account: Option<&str>) -> Duration {
+        self.accounts
+            .load()
+            .get(account_key(account))
+            .map(|runtime| runtime.engine.settings().busy_wait)
+            .unwrap_or_else(|| Duration::from_secs(30))
+    }
+
+    /// Open a tab for a status probe: a busy account answers immediately
+    /// instead of queueing behind a generation in progress.
+    pub async fn probe_session(&self, account: Option<&str>) -> Result<Session> {
+        let runtime = self.runtime(account)?;
+        self.lease_session(&runtime, Duration::from_secs(2)).await
+    }
+
+    async fn lease_session(
+        &self,
+        runtime: &Arc<AccountRuntime>,
+        wait: Duration,
+    ) -> Result<Session> {
+        let lease = runtime.engine.acquire_page(wait).await?;
+        Ok(Session::new(
+            self.name.clone(),
+            runtime.engine.kind(),
+            Arc::clone(&runtime.engine),
+            lease,
+        ))
+    }
+
+    /// Directory of the browser profile of one account.
+    pub fn profile_dir(&self, account: Option<&str>) -> Option<PathBuf> {
+        self.accounts
+            .load()
+            .get(account_key(account))
+            .map(|runtime| runtime.engine.settings().profile_dir.clone())
+    }
+}
+
+/// Account id used as a map key: the implicit account when none is named.
+fn account_key(account: Option<&str>) -> &str {
+    account
+        .map(str::trim)
+        .filter(|value| !value.is_empty())
+        .unwrap_or(IMPLICIT_ACCOUNT)
+}
+
+/// Build the account runtimes, reusing the engines that did not change.
+///
+/// Returns the new map and the runtimes that are no longer configured.
+fn build_accounts(
+    cfg: &ProviderConfig,
+    base: &crate::browser::BrowserSettings,
+    profiles_root: &Path,
+    existing: &BTreeMap<String, Arc<AccountRuntime>>,
+) -> (
+    BTreeMap<String, Arc<AccountRuntime>>,
+    Vec<Arc<AccountRuntime>>,
+) {
+    let mut wanted: Vec<(String, AccountInfo, PathBuf)> = Vec::new();
+
+    if cfg.has_explicit_accounts() {
+        let default_id = cfg.default_account_id().map(str::to_string);
+        for account in cfg.accounts() {
+            let profile_dir = profiles_root
+                .join("accounts")
+                .join(account.profile_name())
+                .join("user-data-dir");
+            let info = AccountInfo {
+                id: account.id.clone(),
+                email: account.email.clone(),
+                label: account.label.clone(),
+                default: default_id.as_deref() == Some(account.id.as_str()),
+                profile: profile_dir.display().to_string(),
+            };
+            wanted.push((account.id.clone(), info, profile_dir));
+        }
+    } else {
+        // Historical single-account layout: the profile stays where it was, so
+        // an existing signed-in session keeps working after an upgrade.
+        let profile_dir = base.profile_dir.clone();
+        let info = AccountInfo {
+            id: IMPLICIT_ACCOUNT.to_string(),
+            email: None,
+            label: None,
+            default: true,
+            profile: profile_dir.display().to_string(),
+        };
+        wanted.push((IMPLICIT_ACCOUNT.to_string(), info, profile_dir));
+    }
+
+    let mut map = BTreeMap::new();
+    let mut kept: Vec<String> = Vec::new();
+    for (id, info, profile_dir) in wanted {
+        let reuse = existing.get(&id).filter(|runtime| {
+            runtime.engine.settings().profile_dir == profile_dir
+                && runtime.engine.settings().max_tabs == base.max_tabs
+        });
+        let runtime = match reuse {
+            Some(runtime) => Arc::new(AccountRuntime {
+                id: id.clone(),
+                info,
+                engine: Arc::clone(&runtime.engine),
+            }),
+            None => {
+                let mut settings = base.clone();
+                settings.account = if id == IMPLICIT_ACCOUNT && !cfg.has_explicit_accounts() {
+                    None
+                } else {
+                    Some(id.clone())
+                };
+                settings.profile_dir = profile_dir;
+                Arc::new(AccountRuntime {
+                    id: id.clone(),
+                    info,
+                    engine: Arc::new(CdpEngine::new(settings)),
+                })
+            }
+        };
+        kept.push(id.clone());
+        map.insert(id, runtime);
+    }
+
+    let removed = existing
+        .iter()
+        .filter(|(id, _)| !kept.contains(id))
+        .map(|(_, runtime)| Arc::clone(runtime))
+        .collect();
+    (map, removed)
+}
+
+#[async_trait]
+impl LlmProvider for WebUiProvider {
+    fn name(&self) -> &str {
+        &self.name
+    }
+
+    fn cfg(&self) -> Arc<ProviderConfig> {
+        self.cfg.load_full()
+    }
+
+    fn accounts(&self) -> Vec<AccountInfo> {
+        // A provider without declared accounts keeps its single implicit one
+        // private: there is nothing for a client to select.
+        if !self.cfg.load().has_explicit_accounts() {
+            return Vec::new();
+        }
+        self.accounts
+            .load()
+            .values()
+            .map(|runtime| runtime.info.clone())
+            .collect()
+    }
+
+    async fn session(&self, account: Option<&str>) -> Result<Session> {
+        WebUiProvider::session(self, account).await
+    }
+
+    async fn validate_session(
+        &self,
+        account: Option<&str>,
+        session: &Session,
+    ) -> Result<SessionStatus> {
+        let _ = account;
+        let cfg = self.cfg();
+        let page_load = Duration::from_secs(cfg.file.timeouts.page_load.max(5));
+
+        // A brand new session sits on about:blank: open the provider page
+        // before judging it, otherwise every status check waits for the page
+        // load budget and then reports a missing selector.
+        if let Err(err) = ensure_on_provider_page(session.page(), &cfg, page_load).await {
+            return Ok(SessionStatus::error(cfg.name(), err.to_string()));
+        }
+
+        Ok(session.status(&cfg, page_load).await)
+    }
+
+    async fn run_turn(&self, session: Session, request: TurnRequest) -> Result<TurnStream> {
+        let cfg = self.cfg();
+        if !cfg.is_usable() {
+            return Err(GatewayError::ProviderMisconfigured {
+                provider: cfg.name().to_string(),
+                detail: cfg.problems.join("; "),
+            });
+        }
+        if !request.attachments.is_empty() && !cfg.capabilities().supports_images {
+            return Err(GatewayError::UnsupportedContentType(format!(
+                "provider '{}' does not support images or attachments",
+                cfg.name()
+            )));
+        }
+
+        let context = TurnContext {
+            cfg,
+            recorder: self.recorder.clone(),
+            defaults: self.defaults.clone(),
+        };
+        let (tx, rx) = tokio::sync::mpsc::channel(64);
+        tokio::spawn(async move {
+            drive_turn(context, session, request, tx).await;
+        });
+        Ok(TurnStream::new(rx))
+    }
+
+    async fn new_conversation(&self, session: &Session) -> Result<Option<String>> {
+        let cfg = self.cfg();
+        let page = session.page_handle();
+        let page_load = Duration::from_secs(cfg.file.timeouts.page_load.max(5));
+
+        if cfg.capabilities().supports_new_chat
+            && !cfg.selectors().new_chat_button.trim().is_empty()
+        {
+            if let Ok(button) = page.find_element(&cfg.selectors().new_chat_button).await {
+                if session
+                    .engine()
+                    .click(session.page(), &button)
+                    .await
+                    .is_ok()
+                {
+                    tokio::time::sleep(Duration::from_millis(800)).await;
+                    let url = dom::page_url(&page).await.ok();
+                    session.set_web_url(url.clone()).await;
+                    return Ok(url);
+                }
+            }
+        }
+
+        dom::goto(&page, cfg.new_conversation_url(), page_load).await?;
+        let url = dom::page_url(&page).await.ok();
+        session.set_web_url(url.clone()).await;
+        Ok(url)
+    }
+
+    async fn upload_files(&self, session: &Session, files: &[Attachment]) -> Result<()> {
+        let cfg = self.cfg();
+        upload_attachments(&cfg, session.page(), files).await
+    }
+
+    async fn shutdown(&self) -> Result<()> {
+        let mut first_error = None;
+        for account in self.accounts.load().values() {
+            if let Err(err) = account.engine.shutdown().await {
+                tracing::debug!(account = %account.id, error = %err, "shutdown failed");
+                first_error.get_or_insert(err);
+            }
+        }
+        match first_error {
+            Some(err) => Err(err),
+            None => Ok(()),
+        }
+    }
+
+    async fn shutdown_account(&self, account: &str) -> Result<()> {
+        self.runtime(Some(account))?.engine.shutdown().await
+    }
+}
+
+/// Run the whole turn, forwarding deltas and finishing with exactly one terminal
+/// event.
+async fn drive_turn(
+    context: TurnContext,
+    session: Session,
+    request: TurnRequest,
+    tx: tokio::sync::mpsc::Sender<TurnEvent>,
+) {
+    match run_steps(&context, &session, &request, &tx).await {
+        Ok(outcome) => {
+            // `debug.screenshots = "always"` (the --debug flag) promises a dump
+            // for every request, not only the failing ones. A successful turn is
+            // where the answer, its container and its copy button can be
+            // observed, which is exactly what a selector hunt needs.
+            if context.recorder.should_capture(false) {
+                let artifacts = context
+                    .recorder
+                    .capture(
+                        &session.owner(),
+                        &request.trace_id,
+                        session.page(),
+                        "captured because debug.screenshots = always",
+                    )
+                    .await;
+                tracing::debug!(
+                    provider = %session.owner(),
+                    screenshot = ?artifacts.screenshot,
+                    html = ?artifacts.html,
+                    "turn captured"
+                );
+            }
+            let _ = tx.send(TurnEvent::Completed(outcome)).await;
+        }
+        Err(GatewayError::Cancelled) => {
+            tracing::info!(
+                provider = %session.owner(),
+                trace_id = %request.trace_id,
+                "client disconnected, capture abandoned"
+            );
+        }
+        Err(err) => {
+            if context.recorder.should_capture(true) {
+                let artifacts = context
+                    .recorder
+                    .capture(
+                        &session.owner(),
+                        &request.trace_id,
+                        session.page(),
+                        &err.to_string(),
+                    )
+                    .await;
+                tracing::warn!(
+                    provider = %session.owner(),
+                    code = err.code(),
+                    error = %err,
+                    screenshot = ?artifacts.screenshot,
+                    html = ?artifacts.html,
+                    "turn failed"
+                );
+            }
+            let _ = tx.send(TurnEvent::Failed(err)).await;
+        }
+    }
+}
+
+async fn run_steps(
+    context: &TurnContext,
+    session: &Session,
+    request: &TurnRequest,
+    tx: &tokio::sync::mpsc::Sender<TurnEvent>,
+) -> Result<TurnOutcome> {
+    let cfg = &context.cfg;
+    let sel = cfg.selectors();
+    // The page handle serves the DOM helpers; everything that dispatches input
+    // goes through the session, so the engine can serialise it.
+    let page = session.page_handle();
+    let started = Instant::now();
+    let page_load = Duration::from_secs(cfg.file.timeouts.page_load.max(5));
+    let provider = session.owner();
+
+    tracing::debug!(
+        provider = %provider,
+        tab = session.tab_slot(),
+        reuse = request.reuse_url.is_some(),
+        replay = request.replay_history,
+        "turn started"
+    );
+
+    // 1. Open the thread, or a fresh conversation when the history is replayed.
+    let reuse_url = request
+        .reuse_url
+        .as_deref()
+        .filter(|_| !request.replay_history);
+    match reuse_url {
+        Some(url) => {
+            if let Err(err) = dom::goto(&page, url, page_load).await {
+                tracing::warn!(error = %err, url, "cannot reopen the web conversation, starting a new one");
+                dom::goto(&page, cfg.new_conversation_url(), page_load).await?;
+            }
+        }
+        None => dom::goto(&page, cfg.new_conversation_url(), page_load).await?,
+    }
+
+    tracing::debug!(provider = %provider, tab = session.tab_slot(), "page opened");
+
+    // 2. Wait until the page shows something usable (editor, sign-in screen or
+    //    challenge), then classify it. A page that is still hydrating must not be
+    //    reported as a broken selector.
+    let probe = session.settled_probe(cfg, page_load).await?;
+    tracing::debug!(
+        provider = %provider,
+        tab = session.tab_slot(),
+        url = %probe.url,
+        has_input = probe.has_input,
+        "page probed"
+    );
+    if !probe.has_input
+        && !probe.has_captcha
+        && !cfg.is_signed_out_page(
+            &probe.url,
+            &probe.body_text,
+            probe.has_login,
+            probe.has_input,
+        )
+    {
+        return Err(GatewayError::SelectorMissing {
+            selector: sel.input_field.clone(),
+            step: "the prompt field is not present on the page".to_string(),
+        });
+    }
+    let status = classify(cfg, &probe, session.browser());
+    if !status.is_available() {
+        return Err(status.as_error());
+    }
+    if let Some(pattern) = cfg.rate_limit_hit(&probe.body_text) {
+        return Err(GatewayError::UpstreamRateLimited {
+            provider,
+            detail: pattern,
+        });
+    }
+
+    dom::wait_for_selector(
+        &page,
+        &sel.input_field,
+        "waiting for the prompt field",
+        page_load,
+    )
+    .await?;
+
+    // 3. Attachments first: the UI needs them processed before sending.
+    if !request.attachments.is_empty() {
+        upload_attachments(cfg, &page, &request.attachments).await?;
+    }
+
+    let baseline = probe.response_count;
+    let prompt_len = request.prompt.trim().chars().count();
+
+    // 4. Inject the prompt and submit it.
+    inject_prompt(
+        cfg,
+        session,
+        &request.prompt,
+        context.defaults.inject_method,
+    )
+    .await?;
+    submit_prompt(cfg, session, baseline, prompt_len).await?;
+
+    // 5. Capture the answer, then read it again with full fidelity.
+    let mut outcome = poll_answer(context, &page, baseline, &provider, tx).await?;
+    let (text, fidelity) = finalize_answer(context, session, baseline, &outcome.text).await;
+    outcome.text = text;
+    outcome.fidelity = fidelity.to_string();
+
+    let elapsed_ms = started.elapsed().as_millis() as u64;
+    tracing::info!(
+        provider = %provider,
+        web_id = outcome.web_id.as_deref().unwrap_or("-"),
+        deltas = outcome.deltas,
+        chars = outcome.text.chars().count(),
+        fidelity,
+        elapsed_ms,
+        "turn completed"
+    );
+
+    outcome.elapsed_ms = elapsed_ms;
+    Ok(outcome)
+}
+
+/// Open the provider page when the tab is not on it yet.
+///
+/// Status checks and the selftest start from a fresh tab (about:blank); probing
+/// that page reports a missing selector instead of the real state.
+async fn ensure_on_provider_page(
+    page: &Page,
+    cfg: &ProviderConfig,
+    timeout: Duration,
+) -> Result<()> {
+    let current = dom::page_url(page).await.unwrap_or_default();
+    let blank = current.is_empty() || current == "about:blank";
+    if blank || host_of(&current) != host_of(cfg.web_url()) {
+        tracing::debug!(
+            from = %current,
+            to = cfg.web_url(),
+            "opening the provider page before probing it"
+        );
+        dom::goto(page, cfg.web_url(), timeout).await?;
+    }
+    Ok(())
+}
+
+/// Host part of a URL, without pulling a URL crate into the capture path.
+fn host_of(url: &str) -> Option<&str> {
+    let (_, rest) = url.split_once("://")?;
+    let host = rest.split(['/', '?', '#']).next().unwrap_or(rest);
+    if host.is_empty() {
+        None
+    } else {
+        Some(host)
+    }
+}
+
+/// Effective polling, quiet period and budget for one provider.
+fn effective_timings(
+    cfg: &ProviderConfig,
+    defaults: &CaptureDefaults,
+) -> (Duration, Duration, Duration) {
+    let poll = if cfg.file.input.poll_interval_ms >= 50 {
+        Duration::from_millis(cfg.file.input.poll_interval_ms)
+    } else {
+        defaults.poll_interval
+    };
+    let quiet = if cfg.file.input.quiet_ms > 0 {
+        Duration::from_millis(cfg.file.input.quiet_ms)
+    } else {
+        defaults.quiet
+    };
+    let budget = if cfg.file.timeouts.response_timeout > 0 {
+        Duration::from_secs(cfg.file.timeouts.response_timeout)
+    } else {
+        defaults.response_timeout
+    };
+    (poll, quiet, budget)
+}
+
+async fn poll_answer(
+    context: &TurnContext,
+    page: &Page,
+    baseline: usize,
+    provider: &str,
+    tx: &tokio::sync::mpsc::Sender<TurnEvent>,
+) -> Result<TurnOutcome> {
+    let cfg = &context.cfg;
+    let (poll, quiet, budget) = effective_timings(cfg, &context.defaults);
+    let first_token_budget = Duration::from_secs(cfg.file.timeouts.response_generation.max(5));
+    let script = js::read_response_script(cfg.selectors(), baseline);
+
+    let started = Instant::now();
+    let first_token_deadline = started + first_token_budget;
+    let deadline = started + budget;
+
+    let mut emitted = String::new();
+    let mut final_text = String::new();
+    let mut last_change = Instant::now();
+    let mut deltas = 0u32;
+    let mut saw_text = false;
+    let mut warned_rewrite = false;
+
+    loop {
+        if Instant::now() >= deadline {
+            return Err(GatewayError::CaptureTimeout {
+                stage: format!(
+                    "waiting for the answer to settle ({} characters captured)",
+                    final_text.chars().count()
+                ),
+                timeout_s: budget.as_secs(),
+            });
+        }
+
+        let read: js::ReadResponseResult = dom::evaluate_json(page, &script).await?;
+
+        if read.has_captcha {
+            return Err(GatewayError::Captcha {
+                provider: provider.to_string(),
+            });
+        }
+        if read.has_login && !saw_text {
+            return Err(GatewayError::RequiresLogin {
+                provider: provider.to_string(),
+            });
+        }
+        if let Some(banner) = read
+            .error_text
+            .as_deref()
+            .map(str::trim)
+            .filter(|t| !t.is_empty())
+        {
+            if let Some(pattern) = cfg.rate_limit_hit(&banner.to_lowercase()) {
+                return Err(GatewayError::UpstreamRateLimited {
+                    provider: provider.to_string(),
+                    detail: pattern,
+                });
+            }
+            if !saw_text && !read.streaming {
+                return Err(GatewayError::UpstreamError {
+                    provider: provider.to_string(),
+                    message: util::truncate(banner, 300),
+                });
+            }
+        }
+
+        let text = read.text.trim_end().to_string();
+        if text != final_text {
+            if text.len() > emitted.len() && text.starts_with(emitted.as_str()) {
+                let delta = text[emitted.len()..].to_string();
+                if !delta.is_empty() {
+                    deltas += 1;
+                    let _ = tx.send(TurnEvent::Delta(delta)).await;
+                }
+                emitted = text.clone();
+            } else if text.len() != emitted.len() && !warned_rewrite {
+                warned_rewrite = true;
+                tracing::warn!(
+                    provider,
+                    emitted_chars = emitted.chars().count(),
+                    current_chars = text.chars().count(),
+                    "the provider rewrote the answer mid-stream; streamed deltas may contain stale text"
+                );
+            }
+            if !text.trim().is_empty() {
+                saw_text = true;
+            }
+            final_text = text;
+            last_change = Instant::now();
+        }
+
+        let complete =
+            !read.streaming && !final_text.trim().is_empty() && last_change.elapsed() >= quiet;
+        if complete {
+            break;
+        }
+
+        if tx.is_closed() {
+            return Err(GatewayError::Cancelled);
+        }
+
+        if !saw_text && Instant::now() >= first_token_deadline {
+            return Err(GatewayError::CaptureTimeout {
+                stage: "waiting for the first token".to_string(),
+                timeout_s: first_token_budget.as_secs(),
+            });
+        }
+
+        tokio::time::sleep(poll).await;
+    }
+
+    let text = final_text.trim().to_string();
+    if text.is_empty() {
+        return Err(GatewayError::UpstreamError {
+            provider: provider.to_string(),
+            message: "the provider returned an empty answer".to_string(),
+        });
+    }
+
+    let web_url = dom::page_url(page).await.ok().filter(|u| !u.is_empty());
+    let web_id = web_url
+        .as_deref()
+        .and_then(|url| cfg.conversation_id_from_url(url));
+
+    Ok(TurnOutcome {
+        text,
+        web_url,
+        web_id,
+        elapsed_ms: started.elapsed().as_millis() as u64,
+        deltas,
+        fidelity: "text".to_string(),
+    })
+}
+
+/// Read the settled answer again for maximum fidelity.
+///
+/// The polling loop only ever sees `innerText`, which flattens tables, lists
+/// and code fences. Once the answer is final the gateway asks the page for the
+/// same text twice more: through the provider's own copy button (the clipboard
+/// then holds exactly the Markdown the UI rendered) and, failing that, by
+/// converting the answer node's HTML. The plain text remains the last resort.
+async fn finalize_answer(
+    context: &TurnContext,
+    session: &Session,
+    index: usize,
+    plain: &str,
+) -> (String, &'static str) {
+    let cfg = &context.cfg;
+    let mode = cfg.markdown_mode(context.defaults.markdown);
+    if mode == MarkdownMode::Text {
+        return (plain.to_string(), "text");
+    }
+
+    let page = session.page();
+    let sel = cfg.selectors();
+
+    if mode != MarkdownMode::Dom && cfg.has_copy_button() {
+        // Chrome refuses a clipboard read unless the permission was granted
+        // over CDP first.
+        let _ = session.grant_clipboard_access().await;
+        let script = js::copy_answer_script(
+            sel,
+            index,
+            context.defaults.clipboard_timeout.as_millis() as u64,
+        );
+        match dom::evaluate_json::<js::ClipboardResult>(page, &script).await {
+            Ok(result) => {
+                let copied = result.clipboard.unwrap_or_default();
+                let copied = markdown::tidy(&copied);
+                if !copied.trim().is_empty() {
+                    tracing::debug!(
+                        chars = copied.chars().count(),
+                        "the provider copy button gave the answer as Markdown"
+                    );
+                    return (copied, "clipboard");
+                }
+                tracing::debug!(
+                    clicked = result.clicked,
+                    error = result.error.as_deref().unwrap_or("-"),
+                    "the clipboard did not yield a usable answer"
+                );
+            }
+            Err(err) => {
+                tracing::debug!(error = %err, "the clipboard read failed");
+            }
+        }
+    }
+
+    match dom::evaluate_json::<js::AnswerHtml>(page, &js::read_answer_html_script(sel, index)).await
+    {
+        Ok(answer) if answer.found && !answer.html.trim().is_empty() => {
+            let converted = markdown::html_to_markdown(&answer.html);
+            if !converted.trim().is_empty() {
+                return (converted, "dom");
+            }
+            tracing::debug!("the HTML conversion produced nothing, keeping the visible text");
+        }
+        Ok(_) => tracing::debug!("the answer node could not be read back"),
+        Err(err) => tracing::debug!(error = %err, "cannot read the answer markup"),
+    }
+
+    (plain.to_string(), "text")
+}
+
+/// Number of characters that must be present to consider an injection successful.
+const MIN_VERIFIED_CHARS: usize = 8;
+
+async fn verify_input(cfg: &ProviderConfig, page: &Page, expected_len: usize) -> bool {
+    let script = js::verify_input_script(cfg.selectors(), expected_len.min(MIN_VERIFIED_CHARS));
+    match dom::evaluate_json::<js::InjectionResult>(page, &script).await {
+        Ok(result) => result.ok,
+        Err(err) => {
+            tracing::debug!(error = %err, "cannot verify the editor content");
+            false
+        }
+    }
+}
+
+async fn inject_prompt(
+    cfg: &ProviderConfig,
+    session: &Session,
+    text: &str,
+    method: InjectMethod,
+) -> Result<()> {
+    let sel = cfg.selectors();
+    let page = session.page();
+    let input = dom::wait_for_selector(
+        page,
+        &sel.input_field,
+        "focusing the prompt field",
+        Duration::from_secs(15),
+    )
+    .await?;
+    // A real mouse event, dispatched through the engine: it serialises input
+    // browser wide, because two tabs clicking at once wedge Chrome.
+    session.engine().click(page, &input).await?;
+
+    // A reused tab may still hold text from an earlier turn.
+    if verify_input(cfg, page, 1).await {
+        let script = js::clear_input_script(sel);
+        match dom::evaluate_json::<js::InjectionResult>(page, &script).await {
+            Ok(result) if result.ok => tracing::debug!("cleared the editor before injecting"),
+            Ok(result) => tracing::debug!(reason = ?result.reason, "could not clear the editor"),
+            Err(err) => tracing::debug!(error = %err, "could not clear the editor"),
+        }
+    }
+
+    let attempts: Vec<InjectMethod> = match method {
+        InjectMethod::Auto => {
+            vec![
+                InjectMethod::InsertText,
+                InjectMethod::ExecCommand,
+                InjectMethod::TypeStr,
+            ]
+        }
+        other => vec![other],
+    };
+
+    let mut last_reason = String::from("no injection method was attempted");
+    for attempt in attempts {
+        let outcome: std::result::Result<(), String> = match attempt {
+            InjectMethod::InsertText | InjectMethod::Auto => page
+                .execute(InsertTextParams::new(text.to_string()))
+                .await
+                .map(|_| ())
+                .map_err(|err| err.to_string()),
+            InjectMethod::ExecCommand => {
+                let script = js::exec_command_insert_script(text);
+                match dom::evaluate_json::<js::InjectionResult>(page, &script).await {
+                    Ok(result) if result.ok => Ok(()),
+                    Ok(result) => Err(result.reason.unwrap_or_else(|| {
+                        "document.execCommand refused the insertion".to_string()
+                    })),
+                    Err(err) => Err(err.to_string()),
+                }
+            }
+            InjectMethod::TypeStr => session
+                .engine()
+                .type_text(&input, text)
+                .await
+                .map_err(|err| err.to_string()),
+        };
+
+        if let Err(reason) = outcome {
+            last_reason = format!("{attempt:?}: {reason}");
+            continue;
+        }
+        if verify_input(cfg, page, text.chars().count()).await {
+            tracing::debug!(method = ?attempt, "prompt injected");
+            return Ok(());
+        }
+        last_reason = format!("{attempt:?}: the editor stayed empty");
+    }
+
+    Err(GatewayError::SelectorMissing {
+        selector: sel.input_field.clone(),
+        step: format!("injecting the prompt ({last_reason})"),
+    })
+}
+
+async fn submit_prompt(
+    cfg: &ProviderConfig,
+    session: &Session,
+    baseline: usize,
+    prompt_len: usize,
+) -> Result<()> {
+    let sel = cfg.selectors();
+    let page = session.page();
+    let engine = session.engine();
+
+    if !sel.send_button.trim().is_empty() {
+        if let Ok(button) = page.find_element(&sel.send_button).await {
+            if engine.click(page, &button).await.is_ok()
+                && wait_for_submission(cfg, page, baseline, prompt_len, Duration::from_secs(6))
+                    .await
+            {
+                return Ok(());
+            }
+        }
+    }
+
+    let input = dom::wait_for_selector(
+        page,
+        &sel.input_field,
+        "submitting the prompt",
+        Duration::from_secs(5),
+    )
+    .await?;
+    engine.click(page, &input).await?;
+    engine.press_key(&input, "Enter").await?;
+
+    if wait_for_submission(cfg, page, baseline, prompt_len, Duration::from_secs(10)).await {
+        return Ok(());
+    }
+
+    Err(GatewayError::SelectorMissing {
+        selector: sel.send_button.clone(),
+        step: "submitting the prompt (the send button did nothing and Enter did not submit)"
+            .to_string(),
+    })
+}
+
+/// Wait until the UI shows that a request is actually running: a spinner, a new
+/// answer node, or an editor that no longer holds the prompt.
+async fn wait_for_submission(
+    cfg: &ProviderConfig,
+    page: &Page,
+    baseline: usize,
+    prompt_len: usize,
+    timeout: Duration,
+) -> bool {
+    let sel = cfg.selectors();
+    let script = js::read_response_script(sel, baseline);
+    let deadline = Instant::now() + timeout;
+    loop {
+        if let Ok(read) = dom::evaluate_json::<js::ReadResponseResult>(page, &script).await {
+            if read.streaming || read.count > baseline {
+                return true;
+            }
+        }
+        if prompt_len > 0 {
+            let verify = js::verify_input_script(sel, prompt_len.min(MIN_VERIFIED_CHARS));
+            if let Ok(result) = dom::evaluate_json::<js::InjectionResult>(page, &verify).await {
+                if !result.ok {
+                    // The editor was cleared: the web UI accepted the prompt.
+                    return true;
+                }
+            }
+        }
+        if Instant::now() >= deadline {
+            return false;
+        }
+        tokio::time::sleep(Duration::from_millis(250)).await;
+    }
+}
+
+async fn upload_attachments(
+    cfg: &ProviderConfig,
+    page: &Page,
+    attachments: &[Attachment],
+) -> Result<()> {
+    if attachments.is_empty() {
+        return Ok(());
+    }
+    let sel = cfg.selectors();
+    if sel.file_input.trim().is_empty() {
+        return Err(GatewayError::SelectorMissing {
+            selector: "selectors.file_input".to_string(),
+            step: "attaching files".to_string(),
+        });
+    }
+
+    let paths: Vec<PathBuf> = attachments.iter().map(|a| a.path.clone()).collect();
+    dom::set_file_input_files(page, &sel.file_input, &paths).await?;
+
+    if !sel.attachment_indicator.trim().is_empty() {
+        let _ = dom::wait_for_selector(
+            page,
+            &sel.attachment_indicator,
+            "waiting for the attachments to be ready",
+            Duration::from_secs(30),
+        )
+        .await;
+    }
+    // The web UI needs a moment to ingest the files before accepting the prompt.
+    tokio::time::sleep(Duration::from_millis(1500)).await;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::browser::BrowserSettings;
+    use crate::providers::config::ProviderConfig;
+
+    const CHATGPT: &str = include_str!("../../providers/chatgpt.toml");
+
+    fn cfg() -> ProviderConfig {
+        ProviderConfig::parse(CHATGPT, "chatgpt.toml").unwrap()
+    }
+
+    fn provider(raw: &str) -> (WebUiProvider, tempfile::TempDir) {
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path().join("profiles").join("chatgpt");
+        let settings = BrowserSettings {
+            provider: "chatgpt".to_string(),
+            profile_dir: root.join("user-data-dir"),
+            ..BrowserSettings::default()
+        };
+        let provider = WebUiProvider::new(
+            ProviderConfig::parse(raw, "chatgpt.toml").unwrap(),
+            settings,
+            root,
+            DebugRecorder::new(
+                tmp.path().join("debug"),
+                crate::config::ScreenshotMode::Never,
+            ),
+            CaptureDefaults::default(),
+        );
+        (provider, tmp)
+    }
+
+    #[test]
+    fn provider_timings_win_over_the_defaults() {
+        let defaults = CaptureDefaults::default();
+        let (poll, quiet, budget) = effective_timings(&cfg(), &defaults);
+        assert_eq!(poll, Duration::from_millis(400));
+        assert_eq!(quiet, Duration::from_millis(1500));
+        assert_eq!(budget, Duration::from_secs(180));
+    }
+
+    #[test]
+    fn hosts_decide_whether_the_page_must_be_opened() {
+        assert_eq!(
+            host_of("https://chatgpt.com/c/abc?x=1#y"),
+            Some("chatgpt.com")
+        );
+        assert_eq!(host_of("https://chatgpt.com"), Some("chatgpt.com"));
+        assert_eq!(
+            host_of("https://accounts.google.com/o/oauth2"),
+            Some("accounts.google.com")
+        );
+        assert_eq!(host_of("about:blank"), None);
+        assert_eq!(host_of("file:///C:/tmp/fixture.html"), None);
+        assert_eq!(host_of(""), None);
+    }
+
+    #[test]
+    fn capture_defaults_come_from_the_global_config() {
+        let mut global = GlobalConfig::default();
+        global.capture.poll_interval_ms = 250;
+        global.capture.quiet_ms = 3000;
+        global.capture.response_timeout_s = 90;
+        global.capture.markdown = MarkdownMode::Dom;
+        global.capture.clipboard_timeout_ms = 800;
+        let defaults = CaptureDefaults::from_config(&global);
+        assert_eq!(defaults.poll_interval, Duration::from_millis(250));
+        assert_eq!(defaults.quiet, Duration::from_millis(3000));
+        assert_eq!(defaults.response_timeout, Duration::from_secs(90));
+        assert_eq!(defaults.markdown, MarkdownMode::Dom);
+        assert_eq!(defaults.clipboard_timeout, Duration::from_millis(800));
+    }
+
+    #[tokio::test]
+    async fn a_provider_without_accounts_keeps_the_historical_profile() {
+        let (provider, _tmp) = provider(CHATGPT);
+        assert!(
+            provider.accounts().is_empty(),
+            "the implicit account is not addressable"
+        );
+        let profile = provider.profile_dir(None).unwrap();
+        assert!(profile.ends_with("user-data-dir"), "{}", profile.display());
+        assert!(
+            !profile.to_string_lossy().contains("accounts"),
+            "the historical profile directory must not move: {}",
+            profile.display()
+        );
+        // The implicit account stays reachable under its own name.
+        assert_eq!(
+            provider.profile_dir(Some(IMPLICIT_ACCOUNT)).unwrap(),
+            profile
+        );
+    }
+
+    #[tokio::test]
+    async fn declared_accounts_get_one_profile_each() {
+        let raw = format!(
+            "{CHATGPT}\n[[accounts]]\nid = \"perso\"\nemail = \"a@example.com\"\ndefault = true\n\n[[accounts]]\nid = \"pro\"\nemail = \"b@example.com\"\n"
+        );
+        let (provider, _tmp) = provider(&raw);
+        let accounts = provider.accounts();
+        assert_eq!(accounts.len(), 2);
+        assert_eq!(accounts[0].id, "perso");
+        assert_eq!(accounts[0].email.as_deref(), Some("a@example.com"));
+        assert!(accounts[0].default);
+        assert!(!accounts[1].default);
+        assert!(accounts[0]
+            .profile
+            .replace('\\', "/")
+            .contains("accounts/perso"));
+        assert!(accounts[1]
+            .profile
+            .replace('\\', "/")
+            .contains("accounts/pro"));
+        assert_ne!(accounts[0].profile, accounts[1].profile);
+    }
+
+    #[tokio::test]
+    async fn an_unknown_account_is_refused_with_the_known_ones() {
+        let raw = format!("{CHATGPT}\n[[accounts]]\nid = \"perso\"\n");
+        let (provider, _tmp) = provider(&raw);
+        let err = provider.session(Some("nope")).await.unwrap_err();
+        assert_eq!(err.code(), "account_not_found");
+        assert_eq!(err.http_status(), 404);
+        assert!(err.to_string().contains("has no account 'nope'"), "{err}");
+        assert!(err.to_string().contains("perso"), "{err}");
+    }
+
+    #[test]
+    fn the_account_key_of_an_unnamed_request_is_the_implicit_one() {
+        assert_eq!(account_key(None), IMPLICIT_ACCOUNT);
+        assert_eq!(account_key(Some("")), IMPLICIT_ACCOUNT);
+        assert_eq!(account_key(Some("  ")), IMPLICIT_ACCOUNT);
+        assert_eq!(account_key(Some("perso")), "perso");
+    }
+}
diff --git a/src/selftest/mod.rs b/src/selftest/mod.rs
new file mode 100644
index 0000000..e31f17a
--- /dev/null
+++ b/src/selftest/mod.rs
@@ -0,0 +1,79 @@
+//! Selector and session validation, exposed by the CLI and the HTTP API.
+
+pub mod runner;
+
+pub use runner::{validate_provider, PROBE_PROMPT};
+
+use crate::error::{GatewayError, Result};
+use crate::providers::{parse_model, LlmProvider, ProviderRegistry, ValidationReport};
+
+/// Validate one provider, or every provider when `only` is None.
+///
+/// `only` accepts the same `provider[@account]` spelling as the command line,
+/// and every report names the account it probed.
+pub async fn run(registry: &ProviderRegistry, only: Option<&str>) -> Result<Vec<ValidationReport>> {
+    let wanted = only.map(parse_model);
+    let mut reports = Vec::new();
+    for provider in registry.all() {
+        let account = match &wanted {
+            Some(reference) => {
+                if provider.name() != reference.provider {
+                    continue;
+                }
+                reference.account.clone()
+            }
+            None => None,
+        };
+        let cfg = provider.cfg();
+        let account = cfg
+            .resolve_account_id(account.as_deref())
+            .map_err(GatewayError::Config)?;
+        reports.push(validate_provider(provider.as_ref(), &cfg, account.as_deref()).await?);
+    }
+    Ok(reports)
+}
+
+/// Human readable report, one line per provider plus the step timings.
+pub fn render_text(reports: &[ValidationReport]) -> String {
+    let mut out = String::new();
+    if reports.is_empty() {
+        out.push_str("no provider configured\n");
+        return out;
+    }
+    for report in reports {
+        let marker = if report.ok { "OK  " } else { "FAIL" };
+        out.push_str(&format!(
+            "{marker} {:<12} {:<18} {} ms\n",
+            report.provider, report.status, report.duration_ms
+        ));
+        for step in &report.steps {
+            out.push_str(&format!(
+                "       - {:<14} {:>7} ms  {}{}\n",
+                step.step,
+                step.ms,
+                if step.ok { "ok" } else { "failed" },
+                step.detail
+                    .as_ref()
+                    .map(|d| format!("  ({d})"))
+                    .unwrap_or_default()
+            ));
+        }
+        if let Some(message) = &report.message {
+            out.push_str(&format!("       ! {message}\n"));
+        }
+        if let Some(excerpt) = &report.response_excerpt {
+            out.push_str(&format!("       = {excerpt}\n"));
+        }
+    }
+    out
+}
+
+/// JSON report, for scripts.
+pub fn render_json(reports: &[ValidationReport]) -> String {
+    serde_json::to_string_pretty(reports).unwrap_or_else(|_| "[]".to_string())
+}
+
+/// True when every report succeeded.
+pub fn all_ok(reports: &[ValidationReport]) -> bool {
+    reports.iter().all(|report| report.ok)
+}
diff --git a/src/selftest/runner.rs b/src/selftest/runner.rs
new file mode 100644
index 0000000..e858da9
--- /dev/null
+++ b/src/selftest/runner.rs
@@ -0,0 +1,271 @@
+//! Provider validation: proves that a configured web UI can still be driven.
+//!
+//! This is the selector non-regression test: it opens the provider page, checks
+//! the login state and the required selectors, then sends a probe prompt and
+//! verifies that a non-empty answer comes back.
+
+use std::time::Instant;
+
+use crate::browser::SessionState;
+use crate::error::{GatewayError, Result};
+use crate::providers::backend::{StepTiming, ValidationReport};
+use crate::providers::config::ProviderConfig;
+use crate::providers::{LlmProvider, TurnRequest};
+use crate::util;
+
+/// Prompt used to check that generation still works end to end.
+pub const PROBE_PROMPT: &str = "Answer with the single word: ok";
+
+/// Validate one provider account without any HTTP involvement.
+pub async fn validate_provider(
+    provider: &dyn LlmProvider,
+    cfg: &ProviderConfig,
+    account: Option<&str>,
+) -> Result<ValidationReport> {
+    let started = Instant::now();
+    let name = match account {
+        Some(account) => format!("{}@{account}", cfg.name()),
+        None => cfg.name().to_string(),
+    };
+    let mut steps: Vec<StepTiming> = Vec::new();
+
+    if !cfg.is_usable() {
+        return Ok(finish(
+            name,
+            false,
+            "misconfigured",
+            Some(cfg.problems.join("; ")),
+            None,
+            steps,
+            started,
+        ));
+    }
+
+    // 1. Browser session.
+    let step_started = Instant::now();
+    let session = match provider.session(account).await {
+        Ok(session) => {
+            steps.push(StepTiming {
+                step: "session".to_string(),
+                ms: step_started.elapsed().as_millis() as u64,
+                ok: true,
+                detail: Some(format!("{} browser ready", session.browser())),
+            });
+            session
+        }
+        Err(err) => {
+            steps.push(failed_step("session", step_started, &err));
+            return Ok(failure_from_error(name, err, steps, started));
+        }
+    };
+
+    // 2. Page state: login, captcha, prompt field.
+    let step_started = Instant::now();
+    match provider.validate_session(account, &session).await {
+        Ok(status) if status.is_available() => steps.push(StepTiming {
+            step: "page_probe".to_string(),
+            ms: step_started.elapsed().as_millis() as u64,
+            ok: true,
+            detail: status.url.clone(),
+        }),
+        Ok(status) => {
+            steps.push(StepTiming {
+                step: "page_probe".to_string(),
+                ms: step_started.elapsed().as_millis() as u64,
+                ok: false,
+                detail: status.detail.clone(),
+            });
+            return Ok(finish(
+                name,
+                false,
+                state_to_status(status.state),
+                status.detail,
+                None,
+                steps,
+                started,
+            ));
+        }
+        Err(err) => {
+            steps.push(failed_step("page_probe", step_started, &err));
+            return Ok(failure_from_error(name, err, steps, started));
+        }
+    }
+
+    // 3. Real turn with a probe prompt.
+    let step_started = Instant::now();
+    let request = TurnRequest {
+        prompt: PROBE_PROMPT.to_string(),
+        attachments: Vec::new(),
+        reuse_url: None,
+        replay_history: true,
+        probe: true,
+        trace_id: format!("selftest-{}", uuid::Uuid::new_v4().simple()),
+        wait_for_tab: None,
+    };
+
+    let stream = match provider.run_turn(session, request).await {
+        Ok(stream) => stream,
+        Err(err) => {
+            steps.push(failed_step("probe_prompt", step_started, &err));
+            return Ok(failure_from_error(name, err, steps, started));
+        }
+    };
+
+    match stream.collect().await {
+        Ok(outcome) => {
+            let text = outcome.text.trim().to_string();
+            let answered = !text.is_empty();
+            let matched = text.to_lowercase().contains("ok");
+            steps.push(StepTiming {
+                step: "probe_prompt".to_string(),
+                ms: step_started.elapsed().as_millis() as u64,
+                ok: answered,
+                detail: Some(format!("{} characters captured", text.chars().count())),
+            });
+            let (ok, status, message) = if !answered {
+                (
+                    false,
+                    "empty_answer",
+                    Some("the provider returned an empty answer".to_string()),
+                )
+            } else if !matched {
+                (
+                    true,
+                    "ok",
+                    Some(
+                        "the answer did not contain the probe word but generation works"
+                            .to_string(),
+                    ),
+                )
+            } else {
+                (true, "ok", None)
+            };
+            Ok(finish(
+                name,
+                ok,
+                status,
+                message,
+                Some(util::truncate(&text, 200)),
+                steps,
+                started,
+            ))
+        }
+        Err(err) => {
+            steps.push(failed_step("probe_prompt", step_started, &err));
+            Ok(failure_from_error(name, err, steps, started))
+        }
+    }
+}
+
+fn failed_step(step: &str, started: Instant, err: &GatewayError) -> StepTiming {
+    StepTiming {
+        step: step.to_string(),
+        ms: started.elapsed().as_millis() as u64,
+        ok: false,
+        detail: Some(err.to_string()),
+    }
+}
+
+fn failure_from_error(
+    provider: String,
+    err: GatewayError,
+    steps: Vec<StepTiming>,
+    started: Instant,
+) -> ValidationReport {
+    let status = error_to_status(&err);
+    finish(
+        provider,
+        false,
+        status,
+        Some(err.to_string()),
+        None,
+        steps,
+        started,
+    )
+}
+
+fn finish(
+    provider: String,
+    ok: bool,
+    status: &str,
+    message: Option<String>,
+    response_excerpt: Option<String>,
+    steps: Vec<StepTiming>,
+    started: Instant,
+) -> ValidationReport {
+    ValidationReport {
+        provider,
+        ok,
+        status: status.to_string(),
+        message,
+        response_excerpt,
+        duration_ms: started.elapsed().as_millis() as u64,
+        checked_at: util::now_secs(),
+        steps,
+    }
+}
+
+/// Map a gateway error onto a selftest status.
+pub fn error_to_status(err: &GatewayError) -> &'static str {
+    match err.code() {
+        "requires_login" => "login_required",
+        "captcha_required" => "captcha",
+        "upstream_rate_limit" => "rate_limited",
+        "upstream_timeout" => "timeout",
+        "selector_missing" => "selector_missing",
+        "provider_misconfigured" => "misconfigured",
+        "browser_profile_locked" | "browser_unavailable" => "browser_unavailable",
+        _ => "error",
+    }
+}
+
+fn state_to_status(state: SessionState) -> &'static str {
+    match state {
+        SessionState::Available => "ok",
+        SessionState::RequiresLogin => "login_required",
+        SessionState::Captcha => "captcha",
+        SessionState::Busy => "busy",
+        SessionState::Misconfigured => "misconfigured",
+        SessionState::Error => "error",
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn errors_map_to_selftest_statuses() {
+        let err = GatewayError::RequiresLogin {
+            provider: "chatgpt".into(),
+        };
+        assert_eq!(error_to_status(&err), "login_required");
+        let err = GatewayError::SelectorMissing {
+            selector: "a".into(),
+            step: "b".into(),
+        };
+        assert_eq!(error_to_status(&err), "selector_missing");
+        let err = GatewayError::CaptureTimeout {
+            stage: "x".into(),
+            timeout_s: 1,
+        };
+        assert_eq!(error_to_status(&err), "timeout");
+        let err = GatewayError::Captcha {
+            provider: "p".into(),
+        };
+        assert_eq!(error_to_status(&err), "captcha");
+    }
+
+    #[test]
+    fn states_map_to_selftest_statuses() {
+        assert_eq!(
+            state_to_status(SessionState::RequiresLogin),
+            "login_required"
+        );
+        assert_eq!(state_to_status(SessionState::Available), "ok");
+        assert_eq!(
+            state_to_status(SessionState::Misconfigured),
+            "misconfigured"
+        );
+    }
+}
diff --git a/src/server/error.rs b/src/server/error.rs
new file mode 100644
index 0000000..e0b252e
--- /dev/null
+++ b/src/server/error.rs
@@ -0,0 +1,88 @@
+//! Mapping gateway errors onto OpenAI error responses.
+
+use axum::http::StatusCode;
+use axum::response::{IntoResponse, Response};
+use axum::Json;
+use serde::Serialize;
+
+use crate::error::GatewayError;
+
+#[derive(Debug, Clone, Serialize)]
+pub struct OpenAiError {
+    pub message: String,
+    #[serde(rename = "type")]
+    pub kind: &'static str,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub param: Option<String>,
+    pub code: &'static str,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct OpenAiErrorBody {
+    pub error: OpenAiError,
+}
+
+impl OpenAiErrorBody {
+    pub fn from_error(err: &GatewayError) -> Self {
+        Self {
+            error: OpenAiError {
+                message: err.to_string(),
+                kind: err.error_type(),
+                param: err.param().map(str::to_string),
+                code: err.code(),
+            },
+        }
+    }
+
+    pub fn new(message: impl Into<String>, kind: &'static str, code: &'static str) -> Self {
+        Self {
+            error: OpenAiError {
+                message: message.into(),
+                kind,
+                param: None,
+                code,
+            },
+        }
+    }
+
+    pub fn to_json(&self) -> String {
+        serde_json::to_string(self).unwrap_or_else(|_| {
+            r#"{"error":{"message":"internal error","type":"api_error","code":"internal_error"}}"#
+                .to_string()
+        })
+    }
+}
+
+impl IntoResponse for GatewayError {
+    fn into_response(self) -> Response {
+        let status =
+            StatusCode::from_u16(self.http_status()).unwrap_or(StatusCode::INTERNAL_SERVER_ERROR);
+        tracing::warn!(code = self.code(), status = self.http_status(), error = %self, "request failed");
+        (status, Json(OpenAiErrorBody::from_error(&self))).into_response()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn errors_serialise_into_the_openai_shape() {
+        let err = GatewayError::RequiresLogin {
+            provider: "chatgpt".into(),
+        };
+        let body = OpenAiErrorBody::from_error(&err);
+        let value = serde_json::to_value(&body).unwrap();
+        assert_eq!(value["error"]["type"], "invalid_request_error");
+        assert_eq!(value["error"]["code"], "requires_login");
+        assert!(value["error"]["message"]
+            .as_str()
+            .unwrap()
+            .contains("llm-gateway login"));
+
+        let err = GatewayError::unsupported_param("tools", "is not supported");
+        let body = OpenAiErrorBody::from_error(&err);
+        assert_eq!(body.error.param.as_deref(), Some("tools"));
+        assert_eq!(body.error.code, "unsupported_parameter");
+    }
+}
diff --git a/src/server/logbuf.rs b/src/server/logbuf.rs
new file mode 100644
index 0000000..cf1dae5
--- /dev/null
+++ b/src/server/logbuf.rs
@@ -0,0 +1,141 @@
+//! Recent log lines, replayed on the dashboard.
+
+use std::collections::VecDeque;
+use std::sync::{Arc, Mutex};
+
+use tokio::sync::broadcast;
+use tracing::field::{Field, Visit};
+use tracing::{Event, Subscriber};
+use tracing_subscriber::layer::{Context, Layer};
+
+/// Ring buffer plus live fan-out of the formatted log lines.
+#[derive(Clone)]
+pub struct LogBuffer {
+    capacity: usize,
+    recent: Arc<Mutex<VecDeque<String>>>,
+    sender: broadcast::Sender<String>,
+}
+
+impl LogBuffer {
+    pub fn new(capacity: usize) -> Self {
+        let (sender, _) = broadcast::channel(256);
+        Self {
+            capacity,
+            recent: Arc::new(Mutex::new(VecDeque::with_capacity(capacity))),
+            sender,
+        }
+    }
+
+    pub fn push(&self, line: String) {
+        if let Ok(mut recent) = self.recent.lock() {
+            if recent.len() == self.capacity {
+                recent.pop_front();
+            }
+            recent.push_back(line.clone());
+        }
+        let _ = self.sender.send(line);
+    }
+
+    pub fn subscribe(&self) -> broadcast::Receiver<String> {
+        self.sender.subscribe()
+    }
+
+    pub fn recent(&self) -> Vec<String> {
+        self.recent
+            .lock()
+            .map(|recent| recent.iter().cloned().collect())
+            .unwrap_or_default()
+    }
+}
+
+/// Tracing layer feeding a LogBuffer.
+pub struct BufferLayer {
+    buffer: LogBuffer,
+}
+
+impl BufferLayer {
+    pub fn new(buffer: LogBuffer) -> Self {
+        Self { buffer }
+    }
+}
+
+impl<S: Subscriber> Layer<S> for BufferLayer {
+    fn on_event(&self, event: &Event<'_>, _context: Context<'_, S>) {
+        let metadata = event.metadata();
+        let mut visitor = LineVisitor::default();
+        event.record(&mut visitor);
+
+        let mut line = format!("{} {}", metadata.level(), metadata.target());
+        if let Some(message) = visitor.message {
+            line.push_str(": ");
+            line.push_str(&message);
+        }
+        for (key, value) in visitor.fields {
+            line.push(' ');
+            line.push_str(&key);
+            line.push('=');
+            line.push_str(&value);
+        }
+        self.buffer.push(line);
+    }
+}
+
+#[derive(Default)]
+struct LineVisitor {
+    message: Option<String>,
+    fields: Vec<(String, String)>,
+}
+
+impl Visit for LineVisitor {
+    fn record_str(&mut self, field: &Field, value: &str) {
+        self.record(field, value.to_string());
+    }
+
+    fn record_debug(&mut self, field: &Field, value: &dyn std::fmt::Debug) {
+        self.record(field, format!("{value:?}"));
+    }
+
+    fn record_i64(&mut self, field: &Field, value: i64) {
+        self.record(field, value.to_string());
+    }
+
+    fn record_u64(&mut self, field: &Field, value: u64) {
+        self.record(field, value.to_string());
+    }
+
+    fn record_bool(&mut self, field: &Field, value: bool) {
+        self.record(field, value.to_string());
+    }
+}
+
+impl LineVisitor {
+    fn record(&mut self, field: &Field, value: String) {
+        if field.name() == "message" {
+            self.message = Some(value);
+        } else {
+            self.fields.push((field.name().to_string(), value));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ring_buffer_keeps_the_most_recent_lines() {
+        let buffer = LogBuffer::new(3);
+        for index in 0..5 {
+            buffer.push(format!("line {index}"));
+        }
+        assert_eq!(buffer.recent(), vec!["line 2", "line 3", "line 4"]);
+    }
+
+    #[test]
+    fn subscribers_receive_new_lines() {
+        let buffer = LogBuffer::new(4);
+        let mut receiver = buffer.subscribe();
+        buffer.push("hello".to_string());
+        assert_eq!(receiver.try_recv().unwrap(), "hello");
+    }
+}
diff --git a/src/server/middleware.rs b/src/server/middleware.rs
new file mode 100644
index 0000000..40d59f7
--- /dev/null
+++ b/src/server/middleware.rs
@@ -0,0 +1,69 @@
+//! Optional bearer-token authentication.
+
+use axum::extract::{Request, State};
+use axum::http::header::AUTHORIZATION;
+use axum::middleware::Next;
+use axum::response::{IntoResponse, Response};
+
+use crate::error::GatewayError;
+use crate::server::state::AppState;
+
+/// Reject requests that do not carry the configured API key.
+pub async fn require_api_key(
+    State(state): State<AppState>,
+    request: Request,
+    next: Next,
+) -> Response {
+    let expected = state.config().server.api_key.clone();
+    if expected.is_empty() || is_open_path(request.uri().path()) {
+        return next.run(request).await;
+    }
+
+    let provided = request
+        .headers()
+        .get(AUTHORIZATION)
+        .and_then(|value| value.to_str().ok())
+        .and_then(|value| value.strip_prefix("Bearer "))
+        .map(str::trim);
+
+    match provided {
+        Some(token) if constant_time_eq(token, &expected) => next.run(request).await,
+        _ => GatewayError::InvalidApiKey.into_response(),
+    }
+}
+
+/// Paths that stay reachable without a key: health and the dashboard.
+fn is_open_path(path: &str) -> bool {
+    matches!(path, "/health" | "/dashboard" | "/dashboard/events")
+}
+
+/// Compare two secrets without leaking their length through timing.
+fn constant_time_eq(a: &str, b: &str) -> bool {
+    let (a, b) = (a.as_bytes(), b.as_bytes());
+    if a.len() != b.len() {
+        return false;
+    }
+    let mut diff = 0u8;
+    for (x, y) in a.iter().zip(b.iter()) {
+        diff |= x ^ y;
+    }
+    diff == 0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn secrets_are_compared_exactly() {
+        assert!(constant_time_eq("secret", "secret"));
+        assert!(!constant_time_eq("secret", "secrez"));
+        assert!(!constant_time_eq("secret", "secret-longer"));
+    }
+
+    #[test]
+    fn open_paths_are_limited() {
+        assert!(is_open_path("/health"));
+        assert!(!is_open_path("/v1/models"));
+    }
+}
diff --git a/src/server/mod.rs b/src/server/mod.rs
new file mode 100644
index 0000000..cf7480c
--- /dev/null
+++ b/src/server/mod.rs
@@ -0,0 +1,53 @@
+//! HTTP layer: OpenAI-compatible routes, SSE and the local dashboard.
+
+pub mod error;
+pub mod logbuf;
+pub mod middleware;
+pub mod models;
+pub mod routes;
+pub mod sse;
+pub mod state;
+
+pub use logbuf::{BufferLayer, LogBuffer};
+pub use state::{AppState, Metrics};
+
+use axum::extract::DefaultBodyLimit;
+use axum::routing::{get, post};
+use axum::Router;
+use tower_http::cors::CorsLayer;
+use tower_http::trace::TraceLayer;
+
+/// Build the application router with every route wired up.
+pub fn router(state: AppState) -> Router {
+    let body_limit = state.config().server.request_body_limit.max(1024);
+
+    let open = Router::new()
+        .route("/health", get(routes::health))
+        .route("/metrics", get(routes::metrics))
+        .route("/dashboard", get(routes::dashboard))
+        .route("/dashboard/events", get(routes::dashboard_events));
+
+    let api = Router::new()
+        .route("/v1/chat/completions", post(routes::chat_completions))
+        .route("/v1/completions", post(routes::completions))
+        .route("/v1/models", get(routes::models))
+        .route(
+            "/v1/providers/{provider}/status",
+            get(routes::provider_status),
+        )
+        .route(
+            "/v1/providers/{provider}/validate",
+            post(routes::provider_validate),
+        )
+        .route("/v1/admin/reload", post(routes::admin_reload))
+        .route_layer(axum::middleware::from_fn_with_state(
+            state.clone(),
+            middleware::require_api_key,
+        ));
+
+    open.merge(api)
+        .layer(DefaultBodyLimit::max(body_limit))
+        .layer(CorsLayer::permissive())
+        .layer(TraceLayer::new_for_http())
+        .with_state(state)
+}
diff --git a/src/server/models.rs b/src/server/models.rs
new file mode 100644
index 0000000..8c64c3a
--- /dev/null
+++ b/src/server/models.rs
@@ -0,0 +1,449 @@
+//! OpenAI-compatible request and response types.
+
+use serde::{Deserialize, Serialize};
+
+/// Content of a message: either a plain string or an array of typed parts.
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum MessageContent {
+    Text(String),
+    Parts(Vec<ContentPart>),
+}
+
+impl Default for MessageContent {
+    fn default() -> Self {
+        Self::Text(String::new())
+    }
+}
+
+impl MessageContent {
+    /// Concatenated text of every text part.
+    pub fn text(&self) -> String {
+        match self {
+            Self::Text(text) => text.clone(),
+            Self::Parts(parts) => parts
+                .iter()
+                .filter(|part| part.kind == "text" || part.kind == "input_text")
+                .filter_map(|part| part.text.clone())
+                .collect::<Vec<_>>()
+                .join("\n"),
+        }
+    }
+
+    /// Image parts, in order.
+    pub fn images(&self) -> Vec<&ImageUrl> {
+        match self {
+            Self::Text(_) => Vec::new(),
+            Self::Parts(parts) => parts
+                .iter()
+                .filter(|part| part.kind == "image_url" || part.kind == "input_image")
+                .filter_map(|part| part.image_url.as_ref())
+                .collect(),
+        }
+    }
+
+    pub fn has_images(&self) -> bool {
+        !self.images().is_empty()
+    }
+}
+
+/// One element of a multimodal content array.
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct ContentPart {
+    #[serde(rename = "type")]
+    pub kind: String,
+    #[serde(default)]
+    pub text: Option<String>,
+    #[serde(default)]
+    pub image_url: Option<ImageUrl>,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct ImageUrl {
+    pub url: String,
+    #[serde(default)]
+    pub detail: Option<String>,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct ChatMessage {
+    pub role: String,
+    #[serde(default)]
+    pub content: MessageContent,
+    #[serde(default)]
+    pub name: Option<String>,
+    #[serde(default)]
+    pub tool_call_id: Option<String>,
+}
+
+/// `POST /v1/chat/completions` body.
+#[derive(Debug, Clone, Deserialize)]
+pub struct ChatCompletionRequest {
+    pub model: String,
+    #[serde(default)]
+    pub messages: Vec<ChatMessage>,
+    #[serde(default)]
+    pub stream: bool,
+    #[serde(default)]
+    pub n: Option<u32>,
+    #[serde(default)]
+    pub tools: Option<serde_json::Value>,
+    #[serde(default)]
+    pub functions: Option<serde_json::Value>,
+    #[serde(default)]
+    pub tool_choice: Option<serde_json::Value>,
+    #[serde(default)]
+    pub temperature: Option<f64>,
+    #[serde(default)]
+    pub top_p: Option<f64>,
+    #[serde(default)]
+    pub max_tokens: Option<u32>,
+    #[serde(default)]
+    pub max_completion_tokens: Option<u32>,
+    #[serde(default)]
+    pub stop: Option<serde_json::Value>,
+    #[serde(default)]
+    pub response_format: Option<serde_json::Value>,
+    #[serde(default)]
+    pub seed: Option<i64>,
+    #[serde(default)]
+    pub presence_penalty: Option<f64>,
+    #[serde(default)]
+    pub frequency_penalty: Option<f64>,
+    #[serde(default)]
+    pub logit_bias: Option<serde_json::Value>,
+    #[serde(default)]
+    pub logprobs: Option<bool>,
+    #[serde(default)]
+    pub user: Option<String>,
+    #[serde(default)]
+    pub stream_options: Option<serde_json::Value>,
+}
+
+impl ChatCompletionRequest {
+    /// Parameters the browser backend accepts but cannot honour.
+    pub fn ignored_parameters(&self) -> Vec<String> {
+        let mut out = Vec::new();
+        let mut note = |present: bool, name: &str| {
+            if present {
+                out.push(format!("{name} is ignored by the browser backend"));
+            }
+        };
+        note(self.temperature.is_some(), "temperature");
+        note(self.top_p.is_some(), "top_p");
+        note(self.max_tokens.is_some(), "max_tokens");
+        note(
+            self.max_completion_tokens.is_some(),
+            "max_completion_tokens",
+        );
+        note(self.stop.is_some(), "stop");
+        note(self.response_format.is_some(), "response_format");
+        note(self.seed.is_some(), "seed");
+        note(self.presence_penalty.is_some(), "presence_penalty");
+        note(self.frequency_penalty.is_some(), "frequency_penalty");
+        note(self.logit_bias.is_some(), "logit_bias");
+        note(self.logprobs.is_some(), "logprobs");
+        note(self.user.is_some(), "user");
+        note(self.stream_options.is_some(), "stream_options");
+        out
+    }
+
+    /// Parameters that make the request impossible to serve.
+    pub fn unsupported_parameter(&self) -> Option<(&'static str, &'static str)> {
+        if self.tools.as_ref().is_some_and(|value| !value.is_null()) {
+            return Some((
+                "tools",
+                "tool calling is not available through the browser backend",
+            ));
+        }
+        if self
+            .functions
+            .as_ref()
+            .is_some_and(|value| !value.is_null())
+        {
+            return Some((
+                "functions",
+                "function calling is not available through the browser backend",
+            ));
+        }
+        if self
+            .tool_choice
+            .as_ref()
+            .is_some_and(|value| !value.is_null())
+        {
+            return Some((
+                "tool_choice",
+                "tool calling is not available through the browser backend",
+            ));
+        }
+        if self.n == Some(0) {
+            return Some(("n", "must be at least 1"));
+        }
+        None
+    }
+
+    /// Number of completions to produce, clamped to `max_variants`.
+    ///
+    /// Returns the count and, when the request asked for more than the gateway
+    /// accepts, the warning explaining the clamp.
+    pub fn variants(&self, max_variants: u32) -> (u32, Option<String>) {
+        let requested = self.n.unwrap_or(1).max(1);
+        let limit = max_variants.max(1);
+        if requested > limit {
+            return (
+                limit,
+                Some(format!(
+                    "n = {requested} was clamped to {limit} (capture.max_variants)"
+                )),
+            );
+        }
+        (requested, None)
+    }
+}
+
+/// Legacy `POST /v1/completions` body.
+#[derive(Debug, Clone, Deserialize)]
+pub struct CompletionRequest {
+    pub model: String,
+    #[serde(default)]
+    pub prompt: PromptInput,
+    #[serde(default)]
+    pub stream: bool,
+    #[serde(default)]
+    pub max_tokens: Option<u32>,
+    #[serde(default)]
+    pub temperature: Option<f64>,
+    #[serde(default)]
+    pub stop: Option<serde_json::Value>,
+}
+
+#[derive(Debug, Clone, Deserialize)]
+#[serde(untagged)]
+pub enum PromptInput {
+    Text(String),
+    Parts(Vec<String>),
+}
+
+impl Default for PromptInput {
+    fn default() -> Self {
+        Self::Text(String::new())
+    }
+}
+
+impl PromptInput {
+    pub fn joined(&self) -> String {
+        match self {
+            Self::Text(text) => text.clone(),
+            Self::Parts(parts) => parts.join("\n"),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct Usage {
+    pub prompt_tokens: usize,
+    pub completion_tokens: usize,
+    pub total_tokens: usize,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ResponseMessage {
+    pub role: &'static str,
+    pub content: String,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ChatChoice {
+    pub index: u32,
+    pub message: ResponseMessage,
+    pub finish_reason: &'static str,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub logprobs: Option<serde_json::Value>,
+}
+
+/// Non-streaming chat completion payload.
+#[derive(Debug, Clone, Serialize)]
+pub struct ChatCompletion {
+    pub id: String,
+    pub object: &'static str,
+    pub created: u64,
+    pub model: String,
+    pub choices: Vec<ChatChoice>,
+    pub usage: Usage,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub system_fingerprint: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub x_gateway_warnings: Option<Vec<String>>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ChunkDelta {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub role: Option<&'static str>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub content: Option<String>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ChunkChoice {
+    pub index: u32,
+    pub delta: ChunkDelta,
+    pub finish_reason: Option<&'static str>,
+}
+
+/// One SSE chunk of a streamed chat completion.
+#[derive(Debug, Clone, Serialize)]
+pub struct ChatCompletionChunk {
+    pub id: String,
+    pub object: &'static str,
+    pub created: u64,
+    pub model: String,
+    pub choices: Vec<ChunkChoice>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub usage: Option<Usage>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct TextChoice {
+    pub text: String,
+    pub index: u32,
+    pub finish_reason: &'static str,
+    pub logprobs: Option<serde_json::Value>,
+}
+
+/// Non-streaming legacy completion payload.
+#[derive(Debug, Clone, Serialize)]
+pub struct TextCompletion {
+    pub id: String,
+    pub object: &'static str,
+    pub created: u64,
+    pub model: String,
+    pub choices: Vec<TextChoice>,
+    pub usage: Usage,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ModelEntry {
+    pub id: String,
+    pub object: &'static str,
+    pub created: u64,
+    pub owned_by: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub x_status: Option<String>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn multimodal_content_is_flattened() {
+        let raw = r#"[
+          {"type": "text", "text": "describe this"},
+          {"type": "image_url", "image_url": {"url": "data:image/png;base64,AAA"}}
+        ]"#;
+        let content: MessageContent = serde_json::from_str(raw).unwrap();
+        assert_eq!(content.text(), "describe this");
+        assert!(content.has_images());
+        assert_eq!(content.images()[0].url, "data:image/png;base64,AAA");
+    }
+
+    #[test]
+    fn plain_string_content_still_works() {
+        let content: MessageContent = serde_json::from_str("\"hello\"").unwrap();
+        assert_eq!(content.text(), "hello");
+        assert!(!content.has_images());
+    }
+
+    #[test]
+    fn request_parses_a_realistic_payload() {
+        let raw = r#"{
+          "model": "chatgpt",
+          "messages": [
+            {"role": "system", "content": "be brief"},
+            {"role": "user", "content": "hi"}
+          ],
+          "stream": true,
+          "temperature": 0.2,
+          "max_tokens": 100,
+          "user": "abc"
+        }"#;
+        let request: ChatCompletionRequest = serde_json::from_str(raw).unwrap();
+        assert_eq!(request.model, "chatgpt");
+        assert!(request.stream);
+        assert_eq!(request.messages.len(), 2);
+        assert!(request.unsupported_parameter().is_none());
+        let ignored = request.ignored_parameters();
+        assert!(ignored.iter().any(|w| w.contains("temperature")));
+        assert!(ignored.iter().any(|w| w.contains("max_tokens")));
+    }
+
+    #[test]
+    fn tool_calling_is_rejected() {
+        let raw = r#"{"model": "chatgpt", "messages": [], "tools": [{"type": "function"}]}"#;
+        let request: ChatCompletionRequest = serde_json::from_str(raw).unwrap();
+        assert_eq!(request.unsupported_parameter().unwrap().0, "tools");
+    }
+
+    #[test]
+    fn n_is_accepted_clamped_and_never_zero() {
+        let request = |n: u32| {
+            serde_json::from_str::<ChatCompletionRequest>(&format!(
+                r#"{{"model": "chatgpt", "messages": [], "n": {n}}}"#
+            ))
+            .unwrap()
+        };
+
+        assert!(request(1).unsupported_parameter().is_none());
+        assert_eq!(request(1).variants(4), (1, None));
+        assert_eq!(request(3).variants(4), (3, None));
+
+        let (count, warning) = request(9).variants(4);
+        assert_eq!(count, 4);
+        assert!(warning.unwrap().contains("clamped"));
+
+        // n = 0 is a client mistake, not a clamp.
+        assert_eq!(request(0).unsupported_parameter().unwrap().0, "n");
+
+        // No n at all means one completion.
+        let absent: ChatCompletionRequest =
+            serde_json::from_str(r#"{"model": "chatgpt", "messages": []}"#).unwrap();
+        assert_eq!(absent.variants(4), (1, None));
+    }
+
+    #[test]
+    fn responses_serialise_with_the_openai_shape() {
+        let body = ChatCompletion {
+            id: "chatcmpl-1".into(),
+            object: "chat.completion",
+            created: 1,
+            model: "chatgpt".into(),
+            choices: vec![ChatChoice {
+                index: 0,
+                message: ResponseMessage {
+                    role: "assistant",
+                    content: "hi".to_string(),
+                },
+                finish_reason: "stop",
+                logprobs: None,
+            }],
+            usage: Usage {
+                prompt_tokens: 1,
+                completion_tokens: 1,
+                total_tokens: 2,
+            },
+            system_fingerprint: None,
+            x_gateway_warnings: Some(vec!["temperature is ignored by the browser backend".into()]),
+        };
+        let value = serde_json::to_value(&body).unwrap();
+        assert_eq!(value["object"], "chat.completion");
+        assert_eq!(value["choices"][0]["message"]["role"], "assistant");
+        assert_eq!(value["choices"][0]["finish_reason"], "stop");
+        assert_eq!(value["usage"]["total_tokens"], 2);
+        assert!(value["choices"][0].get("logprobs").is_none());
+        assert_eq!(
+            value["x_gateway_warnings"][0],
+            "temperature is ignored by the browser backend"
+        );
+    }
+}
diff --git a/src/server/routes.rs b/src/server/routes.rs
new file mode 100644
index 0000000..542e62e
--- /dev/null
+++ b/src/server/routes.rs
@@ -0,0 +1,1137 @@
+//! HTTP routes: the OpenAI-compatible surface, health, status and the dashboard.
+
+use std::convert::Infallible;
+use std::path::PathBuf;
+use std::sync::Arc;
+use std::time::Duration;
+
+use axum::extract::rejection::JsonRejection;
+use axum::extract::{Path, State};
+use axum::http::{HeaderMap, HeaderValue};
+use axum::response::sse::{Event, KeepAlive, Sse};
+use axum::response::{Html, IntoResponse, Response};
+use axum::Json;
+use futures::{Stream, StreamExt};
+use serde_json::json;
+
+use crate::config::{ConversationStrategy, GlobalConfig};
+use crate::conversation::resolve_conversation_id;
+use crate::error::GatewayError;
+use crate::providers::{
+    parse_model, Attachment, AttachmentKind, ResolvedModel, TurnEvent, TurnOutcome, TurnRequest,
+    TurnStream,
+};
+use crate::server::models::{
+    ChatChoice, ChatCompletion, ChatCompletionRequest, ChatMessage, CompletionRequest, ImageUrl,
+    MessageContent, ResponseMessage, Usage,
+};
+use crate::server::sse::{self, CancelFlag, CancelGuard, StreamMeta, TokenCounts};
+use crate::server::state::AppState;
+use crate::tokens;
+use crate::util;
+
+const MAX_ATTACHMENT_BYTES: usize = 20 * 1024 * 1024;
+const MAX_ATTACHMENTS: usize = 4;
+
+/// Everything resolved from a request before the browser is touched.
+struct PreparedTurn {
+    conversation_id: String,
+    provider: String,
+    /// Account the request is routed to, when the provider declares several.
+    account: Option<String>,
+    prompt: String,
+    prompt_tokens: usize,
+    reuse_url: Option<String>,
+    replay: bool,
+    warnings: Vec<String>,
+    messages: usize,
+    attachments: Vec<Attachment>,
+    temp: TempFiles,
+    trace_id: String,
+    include_usage: bool,
+    /// Number of completions to produce (the OpenAI `n` parameter).
+    variants: u32,
+}
+
+impl PreparedTurn {
+    /// Provider and account, as used in logs.
+    fn owner(&self) -> String {
+        match &self.account {
+            Some(account) => format!("{}@{account}", self.provider),
+            None => self.provider.clone(),
+        }
+    }
+
+    /// The turn request for one of the `n` completions.
+    ///
+    /// Asking for several completions means several answers to the same
+    /// question: every variant starts from the full history in its own web
+    /// conversation, and only the first one becomes the client's thread.
+    fn turn_request(&self, variant: u32) -> TurnRequest {
+        let single = self.variants <= 1;
+        TurnRequest {
+            prompt: self.prompt.clone(),
+            attachments: self.attachments.clone(),
+            reuse_url: if single { self.reuse_url.clone() } else { None },
+            replay_history: if single { self.replay } else { true },
+            probe: false,
+            trace_id: if variant == 0 {
+                self.trace_id.clone()
+            } else {
+                format!("{}-v{variant}", self.trace_id)
+            },
+            // Extra variants are our own concurrency: they queue for a tab
+            // instead of being refused while a sibling still runs.
+            wait_for_tab: if single {
+                None
+            } else {
+                Some(self.variant_wait())
+            },
+        }
+    }
+
+    /// How long an extra variant may wait for a free tab.
+    fn variant_wait(&self) -> Duration {
+        Duration::from_secs(self.variants as u64 * 240 + 60)
+    }
+}
+
+/// Temporary files removed when the turn is over.
+#[derive(Debug, Default)]
+struct TempFiles {
+    paths: Vec<PathBuf>,
+}
+
+impl TempFiles {
+    fn push(&mut self, path: PathBuf) {
+        self.paths.push(path);
+    }
+}
+
+impl Drop for TempFiles {
+    fn drop(&mut self) {
+        for path in &self.paths {
+            let _ = std::fs::remove_file(path);
+        }
+    }
+}
+
+/// Keeps the temporary attachments and the cancellation guard alive while the
+/// response body is being served.
+struct StreamKeepAlive {
+    _temp: TempFiles,
+    _guard: CancelGuard,
+}
+
+// ---------------------------------------------------------------------------
+// Handlers
+// ---------------------------------------------------------------------------
+
+/// POST /v1/chat/completions
+pub async fn chat_completions(
+    State(state): State<AppState>,
+    headers: HeaderMap,
+    body: Result<Json<ChatCompletionRequest>, JsonRejection>,
+) -> Result<Response, GatewayError> {
+    state.metrics.record_request();
+    let request = match body {
+        Ok(Json(request)) => request,
+        Err(rejection) => return Err(body_error(rejection)),
+    };
+    let result = chat_inner(state.clone(), headers, request).await;
+    if let Err(err) = &result {
+        state.metrics.record_error(err.code());
+    }
+    result
+}
+
+/// POST /v1/completions (legacy). Streaming is not supported on this endpoint.
+pub async fn completions(
+    State(state): State<AppState>,
+    headers: HeaderMap,
+    body: Result<Json<CompletionRequest>, JsonRejection>,
+) -> Result<Response, GatewayError> {
+    state.metrics.record_request();
+    let request = match body {
+        Ok(Json(request)) => request,
+        Err(rejection) => return Err(body_error(rejection)),
+    };
+    if request.stream {
+        return Err(GatewayError::unsupported_param(
+            "stream",
+            "is not supported on /v1/completions, use /v1/chat/completions",
+        ));
+    }
+
+    let prompt = request.prompt.joined();
+    let chat = ChatCompletionRequest {
+        model: request.model,
+        messages: vec![ChatMessage {
+            role: "user".to_string(),
+            content: MessageContent::Text(prompt),
+            name: None,
+            tool_call_id: None,
+        }],
+        stream: false,
+        n: None,
+        tools: None,
+        functions: None,
+        tool_choice: None,
+        temperature: request.temperature,
+        top_p: None,
+        max_tokens: request.max_tokens,
+        max_completion_tokens: None,
+        stop: request.stop,
+        response_format: None,
+        seed: None,
+        presence_penalty: None,
+        frequency_penalty: None,
+        logit_bias: None,
+        logprobs: None,
+        user: None,
+        stream_options: None,
+    };
+
+    let response = match chat_inner(state.clone(), headers, chat).await {
+        Ok(response) => response,
+        Err(err) => {
+            state.metrics.record_error(err.code());
+            return Err(err);
+        }
+    };
+
+    // Re-shape the chat completion into a legacy text completion.
+    let (parts, body) = response.into_parts();
+    let bytes = axum::body::to_bytes(body, usize::MAX)
+        .await
+        .map_err(|err| GatewayError::internal(format!("reading the response body: {err}")))?;
+    let value: serde_json::Value = serde_json::from_slice(&bytes)
+        .map_err(|err| GatewayError::internal(format!("decoding the response body: {err}")))?;
+    let text = value["choices"][0]["message"]["content"]
+        .as_str()
+        .unwrap_or_default()
+        .to_string();
+    let usage = &value["usage"];
+    let legacy = json!({
+        "id": value["id"],
+        "object": "text_completion",
+        "created": value["created"],
+        "model": value["model"],
+        "choices": [{ "text": text, "index": 0, "finish_reason": "stop", "logprobs": null }],
+        "usage": {
+            "prompt_tokens": usage["prompt_tokens"],
+            "completion_tokens": usage["completion_tokens"],
+            "total_tokens": usage["total_tokens"],
+        },
+    });
+    let mut response = Json(legacy).into_response();
+    *response.status_mut() = parts.status;
+    for (name, value) in parts.headers.iter() {
+        response.headers_mut().insert(name, value.clone());
+    }
+    Ok(response)
+}
+
+/// GET /v1/models
+pub async fn models(State(state): State<AppState>) -> Json<serde_json::Value> {
+    let created = util::now_secs().saturating_sub(state.uptime_secs());
+    let mut data = Vec::new();
+    for provider in state.backend.providers() {
+        let status = if provider.usable {
+            "configured"
+        } else {
+            "misconfigured"
+        };
+        data.push(json!({
+            "id": provider.name,
+            "object": "model",
+            "created": created,
+            "owned_by": provider.name,
+            "x_status": status,
+        }));
+        // One entry per declared account, so a client can pick one.
+        for account in &provider.accounts {
+            data.push(json!({
+                "id": format!("{}@{}", provider.name, account.id),
+                "object": "model",
+                "created": created,
+                "owned_by": provider.name,
+                "x_status": status,
+                "x_account": {
+                    "id": account.id,
+                    "email": account.email,
+                    "label": account.label,
+                    "default": account.default,
+                },
+            }));
+        }
+        for model in &provider.models {
+            data.push(json!({
+                "id": format!("{}/{}", provider.name, model),
+                "object": "model",
+                "created": created,
+                "owned_by": provider.name,
+                "x_status": status,
+            }));
+        }
+    }
+    Json(json!({ "object": "list", "data": data }))
+}
+
+/// GET /health
+pub async fn health(State(state): State<AppState>) -> Json<serde_json::Value> {
+    let providers: Vec<serde_json::Value> = state
+        .backend
+        .providers()
+        .into_iter()
+        .map(|provider| {
+            json!({
+                "name": provider.name,
+                "display_name": provider.display_name,
+                "web_url": provider.web_url,
+                "models": provider.models,
+                "enabled": provider.enabled,
+                "usable": provider.usable,
+                "problems": provider.problems,
+                "browser": provider.browser,
+                "capabilities": provider.capabilities,
+                "accounts": provider.accounts,
+            })
+        })
+        .collect();
+    let status = if providers.is_empty() {
+        "no_providers"
+    } else {
+        "ok"
+    };
+    Json(json!({
+        "status": status,
+        "version": env!("CARGO_PKG_VERSION"),
+        "uptime_s": state.uptime_secs(),
+        "state_dir": state.layout.root().display().to_string(),
+        "providers": providers,
+    }))
+}
+
+/// GET /v1/providers/{provider}/status
+///
+/// The path segment may name an account: `/v1/providers/chatgpt@perso/status`.
+/// Without one, the default account of the provider is probed and the answer
+/// says which account it was.
+pub async fn provider_status(
+    State(state): State<AppState>,
+    Path(owner): Path<String>,
+) -> Result<Json<serde_json::Value>, GatewayError> {
+    let resolved = resolve_owner(&state, &owner)?;
+    let status = state
+        .backend
+        .status(&resolved.provider.name, resolved.account.as_deref())
+        .await;
+    Ok(Json(
+        serde_json::to_value(status).unwrap_or_else(|_| json!({})),
+    ))
+}
+
+/// POST /v1/providers/{provider}/validate
+///
+/// Accepts the same `provider[@account]` segment as the status route.
+pub async fn provider_validate(
+    State(state): State<AppState>,
+    Path(owner): Path<String>,
+) -> Result<Json<serde_json::Value>, GatewayError> {
+    let resolved = resolve_owner(&state, &owner)?;
+    let report = state
+        .backend
+        .validate(&resolved.provider.name, resolved.account.as_deref())
+        .await?;
+    Ok(Json(
+        serde_json::to_value(report).unwrap_or_else(|_| json!({})),
+    ))
+}
+
+/// Resolve a `provider[@account]` path segment.
+///
+/// An unknown provider is a 404 that lists what is configured, and an unknown
+/// account a 404 that lists the accounts of that provider - both come from the
+/// model resolver, so the HTTP surface and the model names agree on the rules.
+fn resolve_owner(state: &AppState, owner: &str) -> Result<ResolvedModel, GatewayError> {
+    let reference = parse_model(owner);
+    if !state.provider_exists(&reference.provider) {
+        return Err(GatewayError::UnknownProvider(reference.provider));
+    }
+    state.backend.resolve(owner)
+}
+
+/// POST /v1/admin/reload
+pub async fn admin_reload(
+    State(state): State<AppState>,
+) -> Result<Json<serde_json::Value>, GatewayError> {
+    let mut config = GlobalConfig::load(&state.layout.config_file())?;
+    config.apply(&state.cli_overrides);
+    config.validate()?;
+    state.config.store(Arc::new(config));
+    let report = state.backend.reload().await?;
+    Ok(Json(json!({
+        "config": "reloaded",
+        "providers_added": report.added,
+        "providers_updated": report.updated,
+        "providers_removed": report.removed,
+        "problems": report.problems,
+    })))
+}
+
+/// GET /metrics
+pub async fn metrics(State(state): State<AppState>) -> Json<serde_json::Value> {
+    Json(state.metrics.snapshot())
+}
+
+/// GET /dashboard
+pub async fn dashboard() -> Html<&'static str> {
+    Html(include_str!("../dashboard/index.html"))
+}
+
+/// GET /dashboard/events
+pub async fn dashboard_events(State(state): State<AppState>) -> Response {
+    let mut receiver = state.logs.subscribe();
+    let initial = state.logs.recent();
+    let stream = async_stream::stream! {
+        for line in initial {
+            yield Ok::<Event, Infallible>(Event::default().data(line));
+        }
+        loop {
+            match receiver.recv().await {
+                Ok(line) => yield Ok(Event::default().data(line)),
+                Err(tokio::sync::broadcast::error::RecvError::Lagged(_)) => continue,
+                Err(_) => break,
+            }
+        }
+    };
+    Sse::new(stream)
+        .keep_alive(KeepAlive::default())
+        .into_response()
+}
+
+// ---------------------------------------------------------------------------
+// Turn execution
+// ---------------------------------------------------------------------------
+
+async fn chat_inner(
+    state: AppState,
+    headers: HeaderMap,
+    request: ChatCompletionRequest,
+) -> Result<Response, GatewayError> {
+    let prepared = prepare_turn(&state, &headers, &request).await?;
+
+    tracing::info!(
+        provider = %prepared.owner(),
+        conversation = %prepared.conversation_id,
+        replay = prepared.replay,
+        attachments = prepared.attachments.len(),
+        variants = prepared.variants,
+        stream = request.stream,
+        prompt_chars = prepared.prompt.chars().count(),
+        "chat completion requested"
+    );
+
+    let id = format!("chatcmpl-{}", uuid::Uuid::new_v4().simple());
+    let created = util::now_secs();
+    let meta = StreamMeta {
+        id: id.clone(),
+        model: request.model.clone(),
+        created,
+        choices: prepared.variants,
+    };
+
+    if request.stream {
+        return stream_completion(state, prepared, meta).await;
+    }
+
+    let outcomes = complete_variants(&state, &prepared).await?;
+    // Only the first variant becomes the client's thread: the others are
+    // throwaway samples the client never continues.
+    if let Some(first) = outcomes.first() {
+        state
+            .store
+            .record_turn(
+                &prepared.conversation_id,
+                &prepared.provider,
+                prepared.account.as_deref(),
+                first.web_url.clone(),
+                first.web_id.clone(),
+                prepared.messages as u64,
+            )
+            .await?;
+    }
+
+    state
+        .metrics
+        .completions
+        .fetch_add(outcomes.len() as u64, std::sync::atomic::Ordering::Relaxed);
+    let captured: usize = outcomes.iter().map(|o| o.text.chars().count()).sum();
+    state
+        .metrics
+        .captured_chars
+        .fetch_add(captured as u64, std::sync::atomic::Ordering::Relaxed);
+
+    let encoding = state.config().tokens.clone();
+    let completion_tokens: usize = outcomes
+        .iter()
+        .map(|outcome| tokens::count_tokens(&outcome.text, &encoding))
+        .sum();
+    let choices: Vec<ChatChoice> = outcomes
+        .into_iter()
+        .enumerate()
+        .map(|(index, outcome)| ChatChoice {
+            index: index as u32,
+            message: ResponseMessage {
+                role: "assistant",
+                content: outcome.text,
+            },
+            finish_reason: "stop",
+            logprobs: None,
+        })
+        .collect();
+
+    let completion = ChatCompletion {
+        id,
+        object: "chat.completion",
+        created,
+        model: request.model.clone(),
+        choices,
+        usage: Usage {
+            prompt_tokens: prepared.prompt_tokens,
+            completion_tokens,
+            total_tokens: prepared.prompt_tokens + completion_tokens,
+        },
+        system_fingerprint: None,
+        x_gateway_warnings: gateway_warnings(&state, &prepared.warnings),
+    };
+
+    let mut response = Json(completion).into_response();
+    apply_headers(&mut response, &prepared.conversation_id, &prepared.trace_id);
+    Ok(response)
+}
+
+/// Run the `n` completions of one request.
+///
+/// Every variant runs on its own web conversation. The futures are joined so a
+/// single-threaded account serves them one after the other while a
+/// `max_tabs > 1` account serves them in parallel.
+async fn complete_variants(
+    state: &AppState,
+    prepared: &PreparedTurn,
+) -> Result<Vec<TurnOutcome>, GatewayError> {
+    let futures = (0..prepared.variants).map(|variant| {
+        let backend = Arc::clone(&state.backend);
+        let request = prepared.turn_request(variant);
+        let provider = prepared.provider.clone();
+        let account = prepared.account.clone();
+        async move {
+            let stream = backend
+                .complete(&provider, account.as_deref(), request)
+                .await?;
+            stream.collect().await
+        }
+    });
+
+    let results = futures::future::join_all(futures).await;
+    let mut outcomes = Vec::with_capacity(results.len());
+    for result in results {
+        outcomes.push(result?);
+    }
+    Ok(outcomes)
+}
+
+/// Serve a streamed completion, merging the variants when there are several.
+async fn stream_completion(
+    state: AppState,
+    prepared: PreparedTurn,
+    meta: StreamMeta,
+) -> Result<Response, GatewayError> {
+    let flag = CancelFlag::new();
+    let guard = CancelGuard::new(
+        Arc::clone(&state.store),
+        prepared.conversation_id.clone(),
+        flag.clone(),
+    );
+    let counts = TokenCounts {
+        prompt_tokens: prepared.prompt_tokens,
+        encoding: state.config().tokens.clone(),
+        include_usage: prepared.include_usage,
+    };
+    let conversation_header = prepared.conversation_id.clone();
+    let trace_header = prepared.trace_id.clone();
+
+    // One variant: an early failure is still an HTTP status, as it always was.
+    if prepared.variants <= 1 {
+        let mut stream = state
+            .backend
+            .complete(
+                &prepared.provider,
+                prepared.account.as_deref(),
+                prepared.turn_request(0),
+            )
+            .await?;
+        let first = match stream.recv().await {
+            Some(TurnEvent::Failed(err)) => {
+                state.metrics.record_error(err.code());
+                return Err(err);
+            }
+            Some(event) => vec![(0u32, event)],
+            None => {
+                return Err(GatewayError::internal(
+                    "the provider task produced no event",
+                ));
+            }
+        };
+        let merged = futures::stream::iter(first).chain(store_updates(
+            &state,
+            &prepared,
+            merge_indexed(vec![(0, stream)]),
+        ));
+        let keep = StreamKeepAlive {
+            _temp: prepared.temp,
+            _guard: guard,
+        };
+        return Ok(sse_response(
+            merged,
+            meta,
+            counts,
+            flag,
+            keep,
+            &conversation_header,
+            &trace_header,
+        ));
+    }
+    let _ = &guard;
+
+    // Several variants: they are captured concurrently and tagged with their
+    // index, and a failure is reported in band like any other mid-stream error.
+    let (tx, rx) = tokio::sync::mpsc::channel::<sse::IndexedEvent>(256);
+    for variant in 0..prepared.variants {
+        let backend = Arc::clone(&state.backend);
+        let request = prepared.turn_request(variant);
+        let provider = prepared.provider.clone();
+        let account = prepared.account.clone();
+        let tx = tx.clone();
+        tokio::spawn(async move {
+            match backend
+                .complete(&provider, account.as_deref(), request)
+                .await
+            {
+                Ok(mut stream) => {
+                    while let Some(event) = stream.recv().await {
+                        if tx.send((variant, event)).await.is_err() {
+                            return;
+                        }
+                    }
+                }
+                Err(err) => {
+                    let _ = tx.send((variant, TurnEvent::Failed(err))).await;
+                }
+            }
+        });
+    }
+    drop(tx);
+
+    let merged = store_updates(
+        &state,
+        &prepared,
+        tokio_stream::wrappers::ReceiverStream::new(rx),
+    );
+    let keep = StreamKeepAlive {
+        _temp: prepared.temp,
+        _guard: guard,
+    };
+    Ok(sse_response(
+        merged,
+        meta,
+        counts,
+        flag,
+        keep,
+        &conversation_header,
+        &trace_header,
+    ))
+}
+
+/// Build the SSE response around a merged event stream.
+#[allow(clippy::too_many_arguments)]
+fn sse_response<S>(
+    merged: S,
+    meta: StreamMeta,
+    counts: TokenCounts,
+    flag: CancelFlag,
+    keep: StreamKeepAlive,
+    conversation_id: &str,
+    trace_id: &str,
+) -> Response
+where
+    S: Stream<Item = sse::IndexedEvent> + Unpin + Send + 'static,
+{
+    let events = sse::chat_event_stream(merged, meta, counts, flag);
+    let body = events.map(move |event| {
+        let _keep_alive = &keep;
+        event
+    });
+    let mut response = Sse::new(body)
+        .keep_alive(KeepAlive::default())
+        .into_response();
+    apply_headers(&mut response, conversation_id, trace_id);
+    response
+}
+
+/// Merge the variants of one request into a single indexed event stream.
+fn merge_indexed(streams: Vec<(u32, TurnStream)>) -> tokio_stream::StreamMap<u32, TurnStream> {
+    let mut map = tokio_stream::StreamMap::new();
+    for (index, stream) in streams {
+        map.insert(index, stream);
+    }
+    map
+}
+
+/// Persist the conversation mapping when a turn completes.
+///
+/// Only the first variant is recorded: it is the web conversation the client
+/// continues on its next call.
+fn store_updates<S>(
+    state: &AppState,
+    prepared: &PreparedTurn,
+    stream: S,
+) -> impl Stream<Item = sse::IndexedEvent>
+where
+    S: Stream<Item = sse::IndexedEvent> + Unpin,
+{
+    let store = Arc::clone(&state.store);
+    let conversation_id = prepared.conversation_id.clone();
+    let provider = prepared.provider.clone();
+    let account = prepared.account.clone();
+    let messages = prepared.messages as u64;
+    stream.map(move |(index, event)| {
+        if index == 0 {
+            if let TurnEvent::Completed(outcome) = &event {
+                let store = Arc::clone(&store);
+                let conversation_id = conversation_id.clone();
+                let provider = provider.clone();
+                let account = account.clone();
+                let web_url = outcome.web_url.clone();
+                let web_id = outcome.web_id.clone();
+                tokio::spawn(async move {
+                    let _ = store
+                        .record_turn(
+                            &conversation_id,
+                            &provider,
+                            account.as_deref(),
+                            web_url,
+                            web_id,
+                            messages,
+                        )
+                        .await;
+                });
+            }
+        }
+        (index, event)
+    })
+}
+
+/// Explain a body that did not parse, including the usual shell mistake.
+fn body_error(rejection: JsonRejection) -> GatewayError {
+    GatewayError::invalid_request(format!(
+        "{} - check that your shell did not mangle the JSON body: in PowerShell wrap \
+         it in single quotes without backslashes, or build it with ConvertTo-Json",
+        rejection.body_text()
+    ))
+}
+
+fn apply_headers(response: &mut Response, conversation_id: &str, trace_id: &str) {
+    if let Ok(value) = HeaderValue::from_str(conversation_id) {
+        response.headers_mut().insert("x-conversation-id", value);
+    }
+    if let Ok(value) = HeaderValue::from_str(trace_id) {
+        response.headers_mut().insert("x-trace-id", value);
+    }
+}
+
+fn gateway_warnings(state: &AppState, warnings: &[String]) -> Option<Vec<String>> {
+    let config = state.config();
+    if config.server.include_warnings && !warnings.is_empty() {
+        Some(warnings.to_vec())
+    } else {
+        None
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Request preparation
+// ---------------------------------------------------------------------------
+
+async fn prepare_turn(
+    state: &AppState,
+    headers: &HeaderMap,
+    request: &ChatCompletionRequest,
+) -> Result<PreparedTurn, GatewayError> {
+    if let Some((param, detail)) = request.unsupported_parameter() {
+        return Err(GatewayError::unsupported_param(param, detail));
+    }
+    if request.messages.is_empty() {
+        return Err(GatewayError::invalid_request("messages must not be empty"));
+    }
+
+    let route = state.backend.resolve(&request.model)?;
+    let provider_name = route.provider.name.clone();
+    let account = route.account.clone();
+    let capabilities = route.provider.capabilities.clone();
+    let config = state.config();
+    let (variants, clamp_warning) = request.variants(config.capture.max_variants);
+
+    // Provider and account both take part in the thread identity: the same
+    // prompt sent to two accounts must not share one web conversation.
+    let owner = route.owner();
+    let header_id = headers
+        .get("x-conversation-id")
+        .and_then(|value| value.to_str().ok());
+    let (system_text, first_user_text) = openers(&request.messages);
+    let conversation_id = resolve_conversation_id(
+        config.conversation.id_source,
+        header_id,
+        &owner,
+        &system_text,
+        &first_user_text,
+    );
+
+    let record = state.store.get(&conversation_id).await;
+    let messages_sent = record
+        .as_ref()
+        .map(|record| record.messages_sent as usize)
+        .unwrap_or(0);
+    let reusable = record.as_ref().is_some_and(|record| record.is_reusable());
+
+    let mut replay = match config.conversation.strategy {
+        ConversationStrategy::Replay => true,
+        ConversationStrategy::Reuse => !reusable && record.is_none(),
+        ConversationStrategy::Auto => !reusable,
+    };
+    // Several completions mean several answers to the same question, so each
+    // variant replays the history into a brand new web conversation.
+    if variants > 1 {
+        replay = true;
+    }
+    let from_index = if replay {
+        0
+    } else if request.messages.len() > messages_sent {
+        messages_sent
+    } else {
+        request.messages.len().saturating_sub(1)
+    };
+    let prompt = build_prompt(&request.messages, from_index);
+    if prompt.trim().is_empty() {
+        return Err(GatewayError::invalid_request(
+            "the last message contains no text to send",
+        ));
+    }
+
+    let reuse_url = if replay {
+        None
+    } else {
+        record.as_ref().and_then(|record| record.web_url.clone())
+    };
+
+    let mut warnings = request.ignored_parameters();
+    if let Some(warning) = clamp_warning {
+        warnings.push(warning);
+    }
+    if variants > 1 {
+        warnings.push(format!(
+            "n = {variants} starts {variants} independent web conversations; the thread is not continued"
+        ));
+        if record.is_some() {
+            warnings.push(
+                "the stored conversation of this thread is not reused while n > 1".to_string(),
+            );
+        }
+    }
+    if let Some(model) = &route.model {
+        if !route.provider.models.iter().any(|known| known == model) {
+            warnings.push(format!(
+                "the web UI keeps its current model: '{model}' is recorded but not selected"
+            ));
+        }
+    }
+
+    let images: Vec<&ImageUrl> = request
+        .messages
+        .iter()
+        .rev()
+        .find(|message| message.role == "user")
+        .map(|message| message.content.images())
+        .unwrap_or_default();
+
+    let mut temp = TempFiles::default();
+    let attachments = if images.is_empty() {
+        Vec::new()
+    } else if !capabilities.supports_images {
+        return Err(GatewayError::UnsupportedContentType(format!(
+            "provider '{provider_name}' does not support images"
+        )));
+    } else {
+        materialise_attachments(&images, &mut temp).await?
+    };
+
+    let prompt_tokens = tokens::count_tokens(&prompt, &config.tokens);
+    let include_usage = request
+        .stream_options
+        .as_ref()
+        .and_then(|options| options.get("include_usage"))
+        .and_then(|value| value.as_bool())
+        .unwrap_or(false);
+
+    Ok(PreparedTurn {
+        conversation_id,
+        provider: provider_name,
+        account,
+        prompt,
+        prompt_tokens,
+        reuse_url,
+        replay,
+        warnings,
+        messages: request.messages.len(),
+        attachments,
+        temp,
+        trace_id: format!("{:016x}", uuid::Uuid::new_v4().as_u128() as u64),
+        include_usage,
+        variants,
+    })
+}
+
+/// System prompt and first user message, used for the conversation fingerprint.
+fn openers(messages: &[ChatMessage]) -> (String, String) {
+    let system = messages
+        .iter()
+        .filter(|message| message.role == "system" || message.role == "developer")
+        .map(|message| message.content.text())
+        .collect::<Vec<_>>()
+        .join(
+            "
+",
+        );
+    let first_user = messages
+        .iter()
+        .find(|message| message.role == "user")
+        .map(|message| message.content.text())
+        .unwrap_or_default();
+    (system, first_user)
+}
+
+/// Render the messages from an index into a single prompt.
+fn build_prompt(messages: &[ChatMessage], from_index: usize) -> String {
+    let slice = &messages[from_index.min(messages.len())..];
+    let effective = if slice.is_empty() { messages } else { slice };
+
+    let has_system = effective
+        .iter()
+        .any(|message| message.role == "system" || message.role == "developer");
+    let single_user = effective.len() == 1 && effective[0].role == "user";
+    if single_user && !has_system {
+        return effective[0].content.text().trim().to_string();
+    }
+
+    let mut out = String::new();
+    for message in effective {
+        let text = message.content.text();
+        if text.trim().is_empty() {
+            continue;
+        }
+        let label = match message.role.as_str() {
+            "system" | "developer" => "System",
+            "assistant" => "Assistant",
+            "tool" | "function" => "Tool",
+            "user" => "User",
+            other => other,
+        };
+        out.push_str(label);
+        out.push_str(": ");
+        out.push_str(text.trim());
+        out.push_str(
+            "
+
+",
+        );
+    }
+    out.trim_end().to_string()
+}
+
+/// Write inline images and downloaded URLs to temporary files.
+async fn materialise_attachments(
+    images: &[&ImageUrl],
+    temp: &mut TempFiles,
+) -> Result<Vec<Attachment>, GatewayError> {
+    let dir = std::env::temp_dir().join("llm-gateway-attachments");
+    std::fs::create_dir_all(&dir)?;
+
+    let mut attachments = Vec::new();
+    for (index, image) in images.iter().take(MAX_ATTACHMENTS).enumerate() {
+        let (bytes, mime) = fetch_image(&image.url).await?;
+        if bytes.len() > MAX_ATTACHMENT_BYTES {
+            return Err(GatewayError::UnsupportedContentType(format!(
+                "attachment {index} is larger than {} MB",
+                MAX_ATTACHMENT_BYTES / 1024 / 1024
+            )));
+        }
+        let extension = mime_guess::get_mime_extensions_str(&mime)
+            .and_then(|extensions| extensions.first())
+            .copied()
+            .unwrap_or("bin");
+        let path = dir.join(format!(
+            "{}-{index}.{extension}",
+            uuid::Uuid::new_v4().simple()
+        ));
+        std::fs::write(&path, &bytes)?;
+        temp.push(path.clone());
+        attachments.push(Attachment {
+            path,
+            mime: mime.clone(),
+            kind: if mime.starts_with("image/") {
+                AttachmentKind::Image
+            } else {
+                AttachmentKind::Document
+            },
+        });
+    }
+    Ok(attachments)
+}
+
+async fn fetch_image(url: &str) -> Result<(Vec<u8>, String), GatewayError> {
+    if let Some(rest) = url.strip_prefix("data:") {
+        let (header, payload) = rest
+            .split_once(',')
+            .ok_or_else(|| GatewayError::invalid_request("malformed data URL"))?;
+        let mime = header
+            .split(';')
+            .next()
+            .unwrap_or("application/octet-stream")
+            .to_string();
+        if header.contains("base64") {
+            use base64::Engine;
+            let bytes = base64::engine::general_purpose::STANDARD
+                .decode(payload.trim())
+                .map_err(|err| {
+                    GatewayError::invalid_request(format!("invalid base64 image: {err}"))
+                })?;
+            return Ok((bytes, mime));
+        }
+        return Err(GatewayError::invalid_request(
+            "only base64 data URLs are supported for inline images",
+        ));
+    }
+
+    if !url.starts_with("http://") && !url.starts_with("https://") {
+        return Err(GatewayError::invalid_request(format!(
+            "unsupported image URL scheme: {url}"
+        )));
+    }
+
+    let client = reqwest::Client::builder()
+        .timeout(std::time::Duration::from_secs(30))
+        .build()
+        .map_err(|err| GatewayError::internal(err.to_string()))?;
+    let response = client
+        .get(url)
+        .send()
+        .await
+        .map_err(|source| GatewayError::Http {
+            url: url.to_string(),
+            source,
+        })?;
+    if !response.status().is_success() {
+        return Err(GatewayError::invalid_request(format!(
+            "cannot download the image: HTTP {}",
+            response.status()
+        )));
+    }
+    let mime = response
+        .headers()
+        .get(reqwest::header::CONTENT_TYPE)
+        .and_then(|value| value.to_str().ok())
+        .map(|value| value.split(';').next().unwrap_or(value).trim().to_string())
+        .unwrap_or_else(|| "application/octet-stream".to_string());
+    let bytes = response
+        .bytes()
+        .await
+        .map_err(|source| GatewayError::Http {
+            url: url.to_string(),
+            source,
+        })?;
+    Ok((bytes.to_vec(), mime))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn message(role: &str, text: &str) -> ChatMessage {
+        ChatMessage {
+            role: role.to_string(),
+            content: MessageContent::Text(text.to_string()),
+            name: None,
+            tool_call_id: None,
+        }
+    }
+
+    #[test]
+    fn a_single_user_message_is_sent_as_is() {
+        let messages = vec![message("user", "hello")];
+        assert_eq!(build_prompt(&messages, 0), "hello");
+    }
+
+    #[test]
+    fn a_full_history_becomes_a_labelled_transcript() {
+        let messages = vec![
+            message("system", "be brief"),
+            message("user", "hello"),
+            message("assistant", "hi"),
+            message("user", "again"),
+        ];
+        let prompt = build_prompt(&messages, 0);
+        assert_eq!(
+            prompt,
+            "System: be brief
+
+User: hello
+
+Assistant: hi
+
+User: again"
+        );
+    }
+
+    #[test]
+    fn only_the_new_turns_are_replayed_on_a_continued_thread() {
+        let messages = vec![
+            message("user", "hello"),
+            message("assistant", "hi"),
+            message("user", "again"),
+        ];
+        assert_eq!(build_prompt(&messages, 2), "again");
+    }
+
+    #[test]
+    fn openers_extract_system_and_first_user_message() {
+        let messages = vec![
+            message("system", "s"),
+            message("user", "u1"),
+            message("user", "u2"),
+        ];
+        let (system, first) = openers(&messages);
+        assert_eq!(system, "s");
+        assert_eq!(first, "u1");
+    }
+
+    #[test]
+    fn data_urls_are_decoded() {
+        let runtime = tokio::runtime::Runtime::new().unwrap();
+        let (bytes, mime) = runtime
+            .block_on(fetch_image("data:image/png;base64,aGVsbG8="))
+            .unwrap();
+        assert_eq!(bytes, b"hello");
+        assert_eq!(mime, "image/png");
+    }
+}
diff --git a/src/server/sse.rs b/src/server/sse.rs
new file mode 100644
index 0000000..d901ad1
--- /dev/null
+++ b/src/server/sse.rs
@@ -0,0 +1,404 @@
+//! Server-sent events for streamed completions.
+
+use std::convert::Infallible;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+
+use axum::response::sse::Event;
+use futures::{Stream, StreamExt};
+use serde_json::json;
+
+use crate::config::TokensSection;
+use crate::conversation::ThreadStore;
+use crate::providers::TurnEvent;
+use crate::server::models::Usage;
+use crate::tokens;
+use crate::util;
+
+/// Identity shared by every chunk of one completion.
+#[derive(Debug, Clone)]
+pub struct StreamMeta {
+    pub id: String,
+    pub model: String,
+    pub created: u64,
+    /// How many completions the stream carries (`n`, at least 1).
+    pub choices: u32,
+}
+
+/// Token accounting for the final usage block.
+#[derive(Debug, Clone)]
+pub struct TokenCounts {
+    pub prompt_tokens: usize,
+    pub encoding: TokensSection,
+    pub include_usage: bool,
+}
+
+/// Shared flag telling the cancellation guard that the turn finished.
+#[derive(Clone, Default)]
+pub struct CancelFlag(Arc<AtomicBool>);
+
+impl CancelFlag {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn mark_done(&self) {
+        self.0.store(true, Ordering::SeqCst);
+    }
+
+    pub fn is_done(&self) -> bool {
+        self.0.load(Ordering::SeqCst)
+    }
+}
+
+/// Marks a thread as interrupted when the client vanishes mid-generation.
+pub struct CancelGuard {
+    store: Arc<ThreadStore>,
+    conversation_id: String,
+    flag: CancelFlag,
+}
+
+impl CancelGuard {
+    pub fn new(store: Arc<ThreadStore>, conversation_id: String, flag: CancelFlag) -> Self {
+        Self {
+            store,
+            conversation_id,
+            flag,
+        }
+    }
+}
+
+impl Drop for CancelGuard {
+    fn drop(&mut self) {
+        if self.flag.is_done() {
+            return;
+        }
+        let store = Arc::clone(&self.store);
+        let conversation_id = self.conversation_id.clone();
+        if let Ok(handle) = tokio::runtime::Handle::try_current() {
+            handle.spawn(async move {
+                let _ = store
+                    .mark_incomplete(&conversation_id, "client disconnected mid-generation")
+                    .await;
+            });
+        }
+    }
+}
+
+fn chunk_event(value: &serde_json::Value) -> Result<Event, Infallible> {
+    Ok(Event::default().data(value.to_string()))
+}
+
+/// One event tagged with the completion (`n`) it belongs to.
+pub type IndexedEvent = (u32, TurnEvent);
+
+/// Build the SSE stream of a chat completion.
+///
+/// With `n > 1` several completions are produced at once: every chunk carries
+/// the index of the choice it belongs to, exactly like the OpenAI API, and the
+/// stream ends once the last one has finished.
+pub fn chat_event_stream<S>(
+    mut stream: S,
+    meta: StreamMeta,
+    counts: TokenCounts,
+    flag: CancelFlag,
+) -> impl Stream<Item = Result<Event, Infallible>>
+where
+    S: Stream<Item = IndexedEvent> + Unpin,
+{
+    let choices = meta.choices.max(1);
+    async_stream::stream! {
+        // One opening chunk per choice, each announcing its assistant role.
+        for index in 0..choices {
+            yield chunk_event(&json!({
+                "id": meta.id,
+                "object": "chat.completion.chunk",
+                "created": meta.created,
+                "model": meta.model,
+                "choices": [{ "index": index, "delta": { "role": "assistant" }, "finish_reason": null }],
+            }));
+        }
+
+        let mut texts: Vec<String> = vec![String::new(); choices as usize];
+        let mut finished = 0u32;
+
+        while let Some((index, event)) = stream.next().await {
+            let slot = texts.get_mut(index as usize);
+            match event {
+                TurnEvent::Delta(delta) => {
+                    if let Some(text) = slot {
+                        text.push_str(&delta);
+                    }
+                    yield chunk_event(&json!({
+                        "id": meta.id,
+                        "object": "chat.completion.chunk",
+                        "created": meta.created,
+                        "model": meta.model,
+                        "choices": [{ "index": index, "delta": { "content": delta }, "finish_reason": null }],
+                    }));
+                }
+                TurnEvent::Completed(outcome) => {
+                    if let Some(text) = slot {
+                        if !outcome.text.is_empty() {
+                            *text = outcome.text;
+                        }
+                    }
+                    finished += 1;
+                    yield chunk_event(&json!({
+                        "id": meta.id,
+                        "object": "chat.completion.chunk",
+                        "created": meta.created,
+                        "model": meta.model,
+                        "choices": [{ "index": index, "delta": {}, "finish_reason": "stop" }],
+                    }));
+                    if finished >= choices {
+                        flag.mark_done();
+                        if counts.include_usage {
+                            let completion_tokens: usize = texts
+                                .iter()
+                                .map(|text| tokens::count_tokens(text, &counts.encoding))
+                                .sum();
+                            let usage = Usage {
+                                prompt_tokens: counts.prompt_tokens,
+                                completion_tokens,
+                                total_tokens: counts.prompt_tokens + completion_tokens,
+                            };
+                            yield chunk_event(&json!({
+                                "id": meta.id,
+                                "object": "chat.completion.chunk",
+                                "created": meta.created,
+                                "model": meta.model,
+                                "choices": [],
+                                "usage": usage,
+                            }));
+                        }
+                        break;
+                    }
+                }
+                TurnEvent::Failed(err) => {
+                    tracing::warn!(
+                        index,
+                        code = err.code(),
+                        error = %err,
+                        "stream failed after it started"
+                    );
+                    yield chunk_event(&json!({
+                        "error": {
+                            "message": util::truncate(&err.to_string(), 500),
+                            "type": err.error_type(),
+                            "code": err.code(),
+                        }
+                    }));
+                    break;
+                }
+            }
+        }
+
+        yield Ok(Event::default().data("[DONE]"));
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::providers::TurnOutcome;
+    use axum::response::sse::Sse;
+    use axum::response::IntoResponse;
+    use tokio::sync::mpsc;
+    use tokio_stream::wrappers::ReceiverStream;
+
+    /// A stream of events tagged with the choice they belong to.
+    fn indexed(rx: mpsc::Receiver<IndexedEvent>) -> ReceiverStream<IndexedEvent> {
+        ReceiverStream::new(rx)
+    }
+
+    fn counts() -> TokenCounts {
+        TokenCounts {
+            prompt_tokens: 3,
+            encoding: TokensSection {
+                encoding: "heuristic".into(),
+                fallback_heuristic: true,
+            },
+            include_usage: false,
+        }
+    }
+
+    /// Render every SSE event of a stream into the raw wire payload.
+    async fn collect_sse<S>(stream: S) -> String
+    where
+        S: Stream<Item = Result<Event, Infallible>> + Send + 'static,
+    {
+        let response = Sse::new(stream).into_response();
+        let bytes = axum::body::to_bytes(response.into_body(), usize::MAX)
+            .await
+            .unwrap();
+        String::from_utf8_lossy(&bytes).to_string()
+    }
+
+    #[tokio::test]
+    async fn deltas_become_chunks_and_the_stream_ends_with_done() {
+        let (tx, rx) = mpsc::channel(8);
+        tokio::spawn(async move {
+            tx.send((0, TurnEvent::Delta("Hel".into()))).await.unwrap();
+            tx.send((0, TurnEvent::Delta("lo".into()))).await.unwrap();
+            tx.send((
+                0,
+                TurnEvent::Completed(TurnOutcome {
+                    text: "Hello".into(),
+                    ..Default::default()
+                }),
+            ))
+            .await
+            .unwrap();
+        });
+        let flag = CancelFlag::new();
+        let stream = chat_event_stream(
+            indexed(rx),
+            StreamMeta {
+                id: "chatcmpl-1".into(),
+                model: "chatgpt".into(),
+                created: 1,
+                choices: 1,
+            },
+            counts(),
+            flag.clone(),
+        );
+        let joined = collect_sse(stream).await;
+        assert!(joined.contains(r#""content":"Hel""#), "{joined}");
+        assert!(joined.contains(r#""content":"lo""#), "{joined}");
+        assert!(joined.contains(r#""role":"assistant""#), "{joined}");
+        assert!(joined.contains(r#""finish_reason":"stop""#), "{joined}");
+        assert!(joined.contains("data: [DONE]"), "{joined}");
+        assert!(flag.is_done());
+    }
+
+    #[tokio::test]
+    async fn an_error_after_the_stream_started_is_reported_in_band() {
+        let (tx, rx) = mpsc::channel(8);
+        tokio::spawn(async move {
+            tx.send((0, TurnEvent::Delta("partial".into())))
+                .await
+                .unwrap();
+            tx.send((
+                0,
+                TurnEvent::Failed(crate::error::GatewayError::Captcha {
+                    provider: "chatgpt".into(),
+                }),
+            ))
+            .await
+            .unwrap();
+        });
+        let flag = CancelFlag::new();
+        let stream = chat_event_stream(
+            indexed(rx),
+            StreamMeta {
+                id: "chatcmpl-2".into(),
+                model: "chatgpt".into(),
+                created: 1,
+                choices: 1,
+            },
+            counts(),
+            flag,
+        );
+        let joined = collect_sse(stream).await;
+        assert!(joined.contains(r#""content":"partial""#), "{joined}");
+        assert!(joined.contains("captcha_required"), "{joined}");
+        // The stream is still terminated properly so that clients do not hang.
+        assert!(joined.contains("data: [DONE]"), "{joined}");
+    }
+
+    #[tokio::test]
+    async fn two_variants_stream_under_their_own_index_and_end_when_both_do() {
+        let (tx, rx) = mpsc::channel(8);
+        tokio::spawn(async move {
+            tx.send((0, TurnEvent::Delta("first".into())))
+                .await
+                .unwrap();
+            tx.send((1, TurnEvent::Delta("second".into())))
+                .await
+                .unwrap();
+            tx.send((
+                0,
+                TurnEvent::Completed(TurnOutcome {
+                    text: "first".into(),
+                    ..Default::default()
+                }),
+            ))
+            .await
+            .unwrap();
+            tx.send((
+                1,
+                TurnEvent::Completed(TurnOutcome {
+                    text: "second".into(),
+                    ..Default::default()
+                }),
+            ))
+            .await
+            .unwrap();
+        });
+        let flag = CancelFlag::new();
+        let stream = chat_event_stream(
+            indexed(rx),
+            StreamMeta {
+                id: "chatcmpl-3".into(),
+                model: "chatgpt".into(),
+                created: 1,
+                choices: 2,
+            },
+            counts(),
+            flag.clone(),
+        );
+        let joined = collect_sse(stream).await;
+
+        // Both choices announce their role, and each delta keeps its index.
+        assert!(joined.contains(r#""index":0"#), "{joined}");
+        assert!(joined.contains(r#""index":1"#), "{joined}");
+        assert!(joined.contains(r#""content":"first""#), "{joined}");
+        assert!(joined.contains(r#""content":"second""#), "{joined}");
+        assert_eq!(joined.matches(r#""finish_reason":"stop""#).count(), 2);
+        // The flag is only set once nothing more can arrive.
+        assert!(flag.is_done());
+        assert!(joined.contains("data: [DONE]"), "{joined}");
+    }
+
+    #[tokio::test]
+    async fn usage_counts_every_variant() {
+        let (tx, rx) = mpsc::channel(8);
+        tokio::spawn(async move {
+            for index in 0..2u32 {
+                tx.send((
+                    index,
+                    TurnEvent::Completed(TurnOutcome {
+                        text: "hello world hello world".into(),
+                        ..Default::default()
+                    }),
+                ))
+                .await
+                .unwrap();
+            }
+        });
+        let mut counts = counts();
+        counts.include_usage = true;
+        let stream = chat_event_stream(
+            indexed(rx),
+            StreamMeta {
+                id: "chatcmpl-4".into(),
+                model: "chatgpt".into(),
+                created: 1,
+                choices: 2,
+            },
+            counts,
+            CancelFlag::new(),
+        );
+        let joined = collect_sse(stream).await;
+        let usage: serde_json::Value = joined
+            .lines()
+            .filter_map(|line| line.strip_prefix("data: "))
+            .filter(|payload| *payload != "[DONE]")
+            .filter_map(|payload| serde_json::from_str::<serde_json::Value>(payload).ok())
+            .find(|chunk| chunk.get("usage").is_some())
+            .expect("a usage chunk");
+        let completion_tokens = usage["usage"]["completion_tokens"].as_u64().unwrap();
+        assert!(completion_tokens >= 2, "{usage}");
+    }
+}
diff --git a/src/server/state.rs b/src/server/state.rs
new file mode 100644
index 0000000..72516a9
--- /dev/null
+++ b/src/server/state.rs
@@ -0,0 +1,107 @@
+//! Shared server state.
+
+use std::collections::BTreeMap;
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::{Arc, Mutex};
+use std::time::Instant;
+
+use arc_swap::ArcSwap;
+
+use crate::config::{CliOverrides, GlobalConfig};
+use crate::conversation::ThreadStore;
+use crate::paths::Layout;
+use crate::providers::ChatBackend;
+use crate::server::logbuf::LogBuffer;
+
+/// Cheap counters exposed by GET /metrics.
+#[derive(Debug, Default)]
+pub struct Metrics {
+    pub requests: AtomicU64,
+    pub errors: AtomicU64,
+    pub completions: AtomicU64,
+    pub streamed_chunks: AtomicU64,
+    pub captured_chars: AtomicU64,
+    error_codes: Mutex<BTreeMap<String, u64>>,
+}
+
+impl Metrics {
+    pub fn record_request(&self) {
+        self.requests.fetch_add(1, Ordering::Relaxed);
+    }
+
+    pub fn record_error(&self, code: &str) {
+        self.errors.fetch_add(1, Ordering::Relaxed);
+        if let Ok(mut map) = self.error_codes.lock() {
+            *map.entry(code.to_string()).or_insert(0) += 1;
+        }
+    }
+
+    pub fn snapshot(&self) -> serde_json::Value {
+        let codes = self
+            .error_codes
+            .lock()
+            .map(|map| map.clone())
+            .unwrap_or_default();
+        serde_json::json!({
+            "requests_total": self.requests.load(Ordering::Relaxed),
+            "errors_total": self.errors.load(Ordering::Relaxed),
+            "completions_total": self.completions.load(Ordering::Relaxed),
+            "streamed_chunks_total": self.streamed_chunks.load(Ordering::Relaxed),
+            "captured_characters_total": self.captured_chars.load(Ordering::Relaxed),
+            "errors_by_code": codes,
+        })
+    }
+}
+
+/// Everything the HTTP handlers need.
+#[derive(Clone)]
+pub struct AppState {
+    pub backend: Arc<dyn ChatBackend>,
+    pub store: Arc<ThreadStore>,
+    pub layout: Arc<Layout>,
+    pub config: Arc<ArcSwap<GlobalConfig>>,
+    /// CLI flags are re-applied after every configuration reload.
+    pub cli_overrides: Arc<CliOverrides>,
+    pub logs: LogBuffer,
+    pub metrics: Arc<Metrics>,
+    pub started_at: Instant,
+}
+
+impl AppState {
+    /// Assemble the state from its parts (used by the CLI and by tests).
+    #[allow(clippy::too_many_arguments)]
+    pub fn new(
+        backend: Arc<dyn ChatBackend>,
+        store: Arc<ThreadStore>,
+        layout: Layout,
+        config: Arc<ArcSwap<GlobalConfig>>,
+        cli_overrides: CliOverrides,
+        logs: LogBuffer,
+    ) -> Self {
+        Self {
+            backend,
+            store,
+            layout: Arc::new(layout),
+            config,
+            cli_overrides: Arc::new(cli_overrides),
+            logs,
+            metrics: Arc::new(Metrics::default()),
+            started_at: Instant::now(),
+        }
+    }
+
+    pub fn config(&self) -> Arc<GlobalConfig> {
+        self.config.load_full()
+    }
+
+    pub fn uptime_secs(&self) -> u64 {
+        self.started_at.elapsed().as_secs()
+    }
+
+    pub fn provider_exists(&self, name: &str) -> bool {
+        self.backend
+            .providers()
+            .iter()
+            .any(|provider| provider.name == name)
+    }
+}
diff --git a/src/tokens.rs b/src/tokens.rs
new file mode 100644
index 0000000..9b009d6
--- /dev/null
+++ b/src/tokens.rs
@@ -0,0 +1,101 @@
+//! Token estimation for the OpenAI-compatible usage block.
+
+use std::sync::{Mutex, OnceLock};
+
+use crate::config::TokensSection;
+
+/// Encoding name and its lazily loaded BPE table.
+type EncoderCache = Mutex<Option<(String, Option<tiktoken_rs::CoreBPE>)>>;
+
+static CACHE: OnceLock<EncoderCache> = OnceLock::new();
+static WARNED: OnceLock<()> = OnceLock::new();
+
+/// Estimate the number of tokens in a piece of text.
+///
+/// Uses the real BPE encoding when it can be loaded and falls back to a
+/// characters/4 heuristic otherwise: tiktoken fetches its vocabulary files on
+/// first use, which fails on an offline machine.
+pub fn count_tokens(text: &str, cfg: &TokensSection) -> usize {
+    if text.is_empty() {
+        return 0;
+    }
+    if cfg.encoding != "heuristic" {
+        if let Some(count) = bpe_count(text, &cfg.encoding) {
+            return count;
+        }
+    }
+    heuristic(text)
+}
+
+/// Characters/4 approximation, never below 1 for non-empty text.
+pub fn heuristic(text: &str) -> usize {
+    let chars = text.chars().count();
+    if chars == 0 {
+        0
+    } else {
+        chars.div_ceil(4).max(1)
+    }
+}
+
+fn bpe_count(text: &str, encoding: &str) -> Option<usize> {
+    let cache = CACHE.get_or_init(|| Mutex::new(None));
+    let mut guard = cache.lock().ok()?;
+    let stale = guard
+        .as_ref()
+        .map(|(name, _)| name != encoding)
+        .unwrap_or(true);
+    if stale {
+        let loaded = load_bpe(encoding);
+        if loaded.is_none() {
+            WARNED.get_or_init(|| {
+                tracing::warn!(
+                    encoding,
+                    "token encoding unavailable (offline?); falling back to a characters/4 estimate"
+                );
+            });
+        }
+        *guard = Some((encoding.to_string(), loaded));
+    }
+    guard
+        .as_ref()
+        .and_then(|(_, bpe)| bpe.as_ref())
+        .map(|bpe| bpe.encode_with_special_tokens(text).len())
+}
+
+fn load_bpe(encoding: &str) -> Option<tiktoken_rs::CoreBPE> {
+    let result = match encoding {
+        "cl100k_base" => tiktoken_rs::cl100k_base(),
+        "p50k_base" => tiktoken_rs::p50k_base(),
+        "r50k_base" => tiktoken_rs::r50k_base(),
+        _ => tiktoken_rs::o200k_base(),
+    };
+    match result {
+        Ok(bpe) => Some(bpe),
+        Err(err) => {
+            tracing::debug!(error = %err, "could not load the BPE encoding");
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn heuristic_is_monotonic() {
+        assert_eq!(heuristic(""), 0);
+        assert_eq!(heuristic("a"), 1);
+        assert!(heuristic("a longer sentence with words") >= 6);
+    }
+
+    #[test]
+    fn counting_never_returns_zero_for_text() {
+        let cfg = TokensSection {
+            encoding: "heuristic".into(),
+            fallback_heuristic: true,
+        };
+        assert_eq!(count_tokens("", &cfg), 0);
+        assert!(count_tokens("bonjour le monde", &cfg) >= 1);
+    }
+}
diff --git a/src/util.rs b/src/util.rs
new file mode 100644
index 0000000..5a19208
--- /dev/null
+++ b/src/util.rs
@@ -0,0 +1,100 @@
+//! Small shared helpers (time formatting, text diffing).
+
+use std::time::{SystemTime, UNIX_EPOCH};
+
+/// Seconds since the Unix epoch.
+pub fn now_secs() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs())
+        .unwrap_or(0)
+}
+
+/// Convert days since 1970-01-01 into a civil date (Howard Hinnant's algorithm).
+fn civil_from_days(days: i64) -> (i64, u32, u32) {
+    let z = days + 719_468;
+    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
+    let doe = z - era * 146_097; // [0, 146096]
+    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
+    let y = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let d = (doy - (153 * mp + 2) / 5 + 1) as u32;
+    let m = if mp < 10 { mp + 3 } else { mp - 9 } as u32;
+    (if m <= 2 { y + 1 } else { y }, m, d)
+}
+
+/// `YYYYmmdd_HHMMSS` in UTC, used in debug file names.
+pub fn format_compact_utc(secs: u64) -> String {
+    let days = (secs / 86_400) as i64;
+    let rem = secs % 86_400;
+    let (year, month, day) = civil_from_days(days);
+    format!(
+        "{year:04}{month:02}{day:02}_{:02}{:02}{:02}",
+        rem / 3600,
+        (rem % 3600) / 60,
+        rem % 60
+    )
+}
+
+/// `YYYY-MM-DDTHH:MM:SSZ`, used in reports and logs.
+pub fn format_rfc3339(secs: u64) -> String {
+    let days = (secs / 86_400) as i64;
+    let rem = secs % 86_400;
+    let (year, month, day) = civil_from_days(days);
+    format!(
+        "{year:04}-{month:02}-{day:02}T{:02}:{:02}:{:02}Z",
+        rem / 3600,
+        (rem % 3600) / 60,
+        rem % 60
+    )
+}
+
+/// Truncate on a character boundary, appending an ellipsis when cut.
+pub fn truncate(text: &str, max_chars: usize) -> String {
+    if text.chars().count() <= max_chars {
+        return text.to_string();
+    }
+    let mut out: String = text.chars().take(max_chars).collect();
+    out.push('…');
+    out
+}
+
+/// Length in bytes of the longest common prefix of two strings.
+pub fn longest_common_prefix_len(a: &str, b: &str) -> usize {
+    let mut len = 0;
+    for (x, y) in a.chars().zip(b.chars()) {
+        if x != y {
+            break;
+        }
+        len += x.len_utf8();
+    }
+    len
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn timestamps_are_human_readable() {
+        assert_eq!(format_compact_utc(0), "19700101_000000");
+        assert_eq!(format_compact_utc(1_735_689_600), "20250101_000000");
+        assert_eq!(format_rfc3339(1_735_689_600), "2025-01-01T00:00:00Z");
+        assert_eq!(format_compact_utc(1_735_693_261), "20250101_010101");
+    }
+
+    #[test]
+    fn lcp_is_on_char_boundaries() {
+        assert_eq!(longest_common_prefix_len("abc", "abd"), 2);
+        assert_eq!(longest_common_prefix_len("éé", "éa"), 2);
+        assert_eq!(longest_common_prefix_len("", "abc"), 0);
+        assert_eq!(longest_common_prefix_len("abc", "abc"), 3);
+    }
+
+    #[test]
+    fn truncate_respects_chars() {
+        assert_eq!(truncate("hello", 10), "hello");
+        assert_eq!(truncate("hello", 3), "hel…");
+    }
+}
diff --git a/tests/api_integration.rs b/tests/api_integration.rs
new file mode 100644
index 0000000..ecc4e61
--- /dev/null
+++ b/tests/api_integration.rs
@@ -0,0 +1,764 @@
+//! HTTP integration tests against the mock backend: no browser, no network.
+
+use std::sync::Arc;
+use std::time::Duration;
+
+use arc_swap::ArcSwap;
+use axum::body::Body;
+use axum::http::{HeaderMap, Request, StatusCode};
+use axum::Router;
+use http_body_util::BodyExt;
+use llm_bridge::config::{CliOverrides, GlobalConfig, ScreenshotMode};
+use llm_bridge::conversation::ThreadStore;
+use llm_bridge::paths::Layout;
+use llm_bridge::providers::{AccountInfo, ChatBackend, MockBackend};
+use llm_bridge::server::{router, AppState, LogBuffer};
+use serde_json::{json, Value};
+use tower::ServiceExt;
+
+struct Harness {
+    app: Router,
+    store: Arc<ThreadStore>,
+    state: AppState,
+}
+
+/// The two accounts of the mock ChatGPT provider.
+fn mock_accounts() -> Vec<AccountInfo> {
+    vec![
+        AccountInfo {
+            id: "perso".to_string(),
+            email: Some("bruno.charest@gmail.com".to_string()),
+            label: None,
+            default: true,
+            profile: "profiles/chatgpt/accounts/perso/user-data-dir".to_string(),
+        },
+        AccountInfo {
+            id: "pro".to_string(),
+            email: Some("brunocharest.bc@gmail.com".to_string()),
+            label: Some("Work".to_string()),
+            default: false,
+            profile: "profiles/chatgpt/accounts/pro/user-data-dir".to_string(),
+        },
+    ]
+}
+
+fn mock_backend(accounts: bool) -> MockBackend {
+    let backend = MockBackend::new(
+        vec![("chatgpt", "gpt-4o"), ("claude", "claude-sonnet-4")],
+        Duration::from_millis(1),
+    );
+    if accounts {
+        backend.with_accounts("chatgpt", mock_accounts())
+    } else {
+        backend
+    }
+}
+
+fn harness_with(config: GlobalConfig) -> Harness {
+    harness_with_backend(config, mock_backend(false))
+}
+
+fn harness_with_backend(config: GlobalConfig, backend: MockBackend) -> Harness {
+    let backend: Arc<dyn ChatBackend> = Arc::new(backend);
+    let store = Arc::new(ThreadStore::in_memory());
+    let layout = Layout::rooted_at(std::env::temp_dir().join("llm-gateway-tests"));
+    let state = AppState::new(
+        backend,
+        Arc::clone(&store),
+        layout,
+        Arc::new(ArcSwap::from_pointee(config)),
+        CliOverrides::default(),
+        LogBuffer::new(32),
+    );
+    Harness {
+        app: router(state.clone()),
+        store,
+        state,
+    }
+}
+
+fn harness() -> Harness {
+    harness_with(GlobalConfig::default())
+}
+
+/// A harness whose ChatGPT provider declares two accounts.
+fn harness_with_accounts(config: GlobalConfig) -> Harness {
+    harness_with_backend(config, mock_backend(true))
+}
+
+async fn send(app: &Router, request: Request<Body>) -> (StatusCode, HeaderMap, String) {
+    let response = app
+        .clone()
+        .oneshot(request)
+        .await
+        .expect("router call failed");
+    let status = response.status();
+    let headers = response.headers().clone();
+    let bytes = response
+        .into_body()
+        .collect()
+        .await
+        .expect("body")
+        .to_bytes();
+    (status, headers, String::from_utf8_lossy(&bytes).to_string())
+}
+
+async fn get_json(app: &Router, path: &str) -> (StatusCode, Value) {
+    let request = Request::builder().uri(path).body(Body::empty()).unwrap();
+    let (status, _, body) = send(app, request).await;
+    (status, serde_json::from_str(&body).unwrap_or(Value::Null))
+}
+
+fn post_chat(body: Value) -> Request<Body> {
+    Request::builder()
+        .method("POST")
+        .uri("/v1/chat/completions")
+        .header("content-type", "application/json")
+        .body(Body::from(body.to_string()))
+        .unwrap()
+}
+
+#[tokio::test]
+async fn health_and_models_describe_every_provider() {
+    let harness = harness();
+
+    let (status, health) = get_json(&harness.app, "/health").await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(health["status"], "ok");
+    assert_eq!(health["providers"].as_array().unwrap().len(), 2);
+
+    let (status, models) = get_json(&harness.app, "/v1/models").await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(models["object"], "list");
+    let ids: Vec<String> = models["data"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .map(|entry| entry["id"].as_str().unwrap().to_string())
+        .collect();
+    assert!(ids.contains(&"chatgpt".to_string()));
+    assert!(ids.contains(&"chatgpt/gpt-4o".to_string()));
+    assert!(ids.contains(&"claude/claude-sonnet-4".to_string()));
+}
+
+#[tokio::test]
+async fn a_chat_completion_returns_the_openai_shape_and_a_conversation_id() {
+    let harness = harness();
+    let (status, headers, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hello"}],
+        })),
+    )
+    .await;
+
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["object"], "chat.completion");
+    assert_eq!(value["model"], "chatgpt");
+    assert_eq!(value["choices"][0]["message"]["role"], "assistant");
+    assert_eq!(value["choices"][0]["finish_reason"], "stop");
+    let content = value["choices"][0]["message"]["content"].as_str().unwrap();
+    assert!(!content.is_empty());
+    assert!(value["usage"]["total_tokens"].as_u64().unwrap() >= 1);
+    assert!(value["id"].as_str().unwrap().starts_with("chatcmpl-"));
+
+    let conversation = headers
+        .get("x-conversation-id")
+        .unwrap()
+        .to_str()
+        .unwrap()
+        .to_string();
+    assert!(conversation.starts_with("fp-"), "{conversation}");
+    assert!(headers.get("x-trace-id").is_some());
+
+    // The thread mapping was persisted for the next turn.
+    let record = harness
+        .store
+        .get(&conversation)
+        .await
+        .expect("thread recorded");
+    assert_eq!(record.provider, "chatgpt");
+    assert!(record.web_url.is_some());
+}
+
+#[tokio::test]
+async fn the_same_conversation_is_reused_when_the_header_is_repeated() {
+    let harness = harness();
+    let request = |text: &str| {
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [
+                {"role": "user", "content": "opening"},
+                {"role": "assistant", "content": "answer"},
+                {"role": "user", "content": text},
+            ],
+        }))
+    };
+
+    let (_, headers, _) = send(&harness.app, request("second")).await;
+    let conversation = headers
+        .get("x-conversation-id")
+        .unwrap()
+        .to_str()
+        .unwrap()
+        .to_string();
+
+    let (status, _, _) = send(&harness.app, request("third")).await;
+    assert_eq!(status, StatusCode::OK);
+    let record = harness.store.get(&conversation).await.unwrap();
+    assert_eq!(
+        record.turns, 2,
+        "the second call must reuse the stored thread"
+    );
+}
+
+#[tokio::test]
+async fn streaming_emits_sse_chunks_and_terminates_with_done() {
+    let harness = harness();
+    let (status, headers, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hello"}],
+            "stream": true,
+        })),
+    )
+    .await;
+
+    assert_eq!(status, StatusCode::OK);
+    let content_type = headers.get("content-type").unwrap().to_str().unwrap();
+    assert!(
+        content_type.starts_with("text/event-stream"),
+        "{content_type}"
+    );
+    assert!(body.contains("chat.completion.chunk"), "{body}");
+    assert!(body.contains(r#""role":"assistant""#), "{body}");
+    assert!(body.contains("data: [DONE]"), "{body}");
+
+    let deltas: String = body
+        .lines()
+        .filter_map(|line| line.strip_prefix("data: "))
+        .filter(|payload| *payload != "[DONE]")
+        .filter_map(|payload| serde_json::from_str::<Value>(payload).ok())
+        .filter_map(|chunk| {
+            chunk["choices"][0]["delta"]["content"]
+                .as_str()
+                .map(str::to_string)
+        })
+        .collect();
+    assert!(!deltas.is_empty());
+    assert!(deltas.contains("mock backend"), "{deltas}");
+}
+
+#[tokio::test]
+async fn the_conversation_header_wins_over_the_fingerprint() {
+    let harness = harness();
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/chat/completions")
+        .header("content-type", "application/json")
+        .header("x-conversation-id", "client-thread-42")
+        .body(Body::from(
+            json!({"model": "chatgpt", "messages": [{"role": "user", "content": "hi"}]})
+                .to_string(),
+        ))
+        .unwrap();
+
+    let (status, headers, _) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(
+        headers.get("x-conversation-id").unwrap(),
+        "client-thread-42"
+    );
+    assert!(harness.store.get("client-thread-42").await.is_some());
+}
+
+#[tokio::test]
+async fn unsupported_parameters_are_rejected_with_a_clear_error() {
+    let harness = harness();
+
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hi"}],
+            "tools": [{"type": "function", "function": {"name": "f"}}],
+        })),
+    )
+    .await;
+    assert_eq!(status, StatusCode::BAD_REQUEST);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["error"]["code"], "unsupported_parameter");
+    assert_eq!(value["error"]["param"], "tools");
+    assert_eq!(value["error"]["type"], "invalid_request_error");
+
+    // n = 0 is a client mistake, unlike n > 1 which is now supported.
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hi"}],
+            "n": 0,
+        })),
+    )
+    .await;
+    assert_eq!(status, StatusCode::BAD_REQUEST);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["error"]["param"], "n");
+}
+
+#[tokio::test]
+async fn several_completions_come_back_as_several_choices() {
+    let harness = harness();
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hello"}],
+            "n": 3,
+        })),
+    )
+    .await;
+
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    let choices = value["choices"].as_array().unwrap();
+    assert_eq!(choices.len(), 3);
+    for (index, choice) in choices.iter().enumerate() {
+        assert_eq!(choice["index"], index as u64);
+        assert_eq!(choice["message"]["role"], "assistant");
+        assert_eq!(choice["finish_reason"], "stop");
+        assert!(!choice["message"]["content"].as_str().unwrap().is_empty());
+    }
+    assert!(value["usage"]["total_tokens"].as_u64().unwrap() >= 1);
+    let warnings = value["x_gateway_warnings"].as_array().unwrap();
+    assert!(
+        warnings.iter().any(|w| w
+            .as_str()
+            .unwrap()
+            .contains("independent web conversations")),
+        "{warnings:?}"
+    );
+}
+
+#[tokio::test]
+async fn n_is_clamped_to_the_configured_maximum() {
+    let mut config = GlobalConfig::default();
+    config.capture.max_variants = 2;
+    let harness = harness_with(config);
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hello"}],
+            "n": 9,
+        })),
+    )
+    .await;
+
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["choices"].as_array().unwrap().len(), 2);
+    let warnings = value["x_gateway_warnings"].as_array().unwrap();
+    assert!(
+        warnings
+            .iter()
+            .any(|w| w.as_str().unwrap().contains("clamped to 2")),
+        "{warnings:?}"
+    );
+}
+
+#[tokio::test]
+async fn streamed_choices_are_tagged_with_their_index() {
+    let harness = harness();
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hello"}],
+            "stream": true,
+            "n": 2,
+        })),
+    )
+    .await;
+
+    assert_eq!(status, StatusCode::OK);
+    let chunks: Vec<Value> = body
+        .lines()
+        .filter_map(|line| line.strip_prefix("data: "))
+        .filter(|payload| *payload != "[DONE]")
+        .filter_map(|payload| serde_json::from_str::<Value>(payload).ok())
+        .collect();
+    assert!(body.contains("data: [DONE]"), "{body}");
+
+    let indexes: Vec<u64> = chunks
+        .iter()
+        .flat_map(|chunk| chunk["choices"].as_array().cloned().unwrap_or_default())
+        .filter_map(|choice| choice["index"].as_u64())
+        .collect();
+    assert!(indexes.contains(&0), "{indexes:?}");
+    assert!(indexes.contains(&1), "{indexes:?}");
+
+    let stops = chunks
+        .iter()
+        .flat_map(|chunk| chunk["choices"].as_array().cloned().unwrap_or_default())
+        .filter(|choice| choice["finish_reason"] == "stop")
+        .count();
+    assert_eq!(stops, 2, "each choice must finish: {body}");
+}
+
+#[tokio::test]
+async fn an_account_can_be_selected_in_the_model_string() {
+    let harness = harness_with_accounts(GlobalConfig::default());
+
+    // The declared accounts show up in /v1/models and /health.
+    let (_, models) = get_json(&harness.app, "/v1/models").await;
+    let ids: Vec<String> = models["data"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .map(|entry| entry["id"].as_str().unwrap().to_string())
+        .collect();
+    assert!(ids.contains(&"chatgpt@perso".to_string()), "{ids:?}");
+    assert!(ids.contains(&"chatgpt@pro".to_string()), "{ids:?}");
+
+    let (_, health) = get_json(&harness.app, "/health").await;
+    let chatgpt = health["providers"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .find(|provider| provider["name"] == "chatgpt")
+        .unwrap();
+    assert_eq!(chatgpt["accounts"].as_array().unwrap().len(), 2);
+
+    // By account id, and by e-mail address.
+    for model in ["chatgpt@pro", "chatgpt@brunocharest.bc@gmail.com"] {
+        let (status, _, body) = send(
+            &harness.app,
+            post_chat(json!({
+                "model": model,
+                "messages": [{"role": "user", "content": "hello"}],
+            })),
+        )
+        .await;
+        assert_eq!(status, StatusCode::OK, "{body}");
+        let value: Value = serde_json::from_str(&body).unwrap();
+        assert_eq!(value["model"], model);
+    }
+}
+
+#[tokio::test]
+async fn an_unknown_account_is_a_404_listing_the_known_ones() {
+    let harness = harness_with_accounts(GlobalConfig::default());
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt@nobody",
+            "messages": [{"role": "user", "content": "hello"}],
+        })),
+    )
+    .await;
+
+    assert_eq!(status, StatusCode::NOT_FOUND);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["error"]["code"], "account_not_found");
+    let message = value["error"]["message"].as_str().unwrap();
+    assert!(message.contains("no account 'nobody'"), "{message}");
+    assert!(message.contains("perso"), "{message}");
+    assert!(
+        !message.contains("does not match any configured provider"),
+        "the message must name the account problem: {message}"
+    );
+}
+
+#[tokio::test]
+async fn two_accounts_never_share_a_thread() {
+    let harness = harness_with_accounts(GlobalConfig::default());
+    let request = |model: &str| {
+        post_chat(json!({
+            "model": model,
+            "messages": [{"role": "user", "content": "hello"}],
+        }))
+    };
+
+    let (_, first, _) = send(&harness.app, request("chatgpt@perso")).await;
+    let (_, second, _) = send(&harness.app, request("chatgpt@pro")).await;
+    let first = first
+        .get("x-conversation-id")
+        .unwrap()
+        .to_str()
+        .unwrap()
+        .to_string();
+    let second = second
+        .get("x-conversation-id")
+        .unwrap()
+        .to_str()
+        .unwrap()
+        .to_string();
+    assert_ne!(first, second, "the account is part of the thread identity");
+}
+
+#[tokio::test]
+async fn an_unknown_model_is_a_404() {
+    let harness = harness();
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "gemini",
+            "messages": [{"role": "user", "content": "hi"}],
+        })),
+    )
+    .await;
+    assert_eq!(status, StatusCode::NOT_FOUND);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["error"]["code"], "model_not_found");
+    assert!(value["error"]["message"]
+        .as_str()
+        .unwrap()
+        .contains("chatgpt"));
+}
+
+#[tokio::test]
+async fn ignored_parameters_are_reported_in_the_response() {
+    let harness = harness();
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hi"}],
+            "temperature": 0.1,
+            "max_tokens": 10,
+        })),
+    )
+    .await;
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    let warnings = value["x_gateway_warnings"].as_array().unwrap();
+    assert!(warnings
+        .iter()
+        .any(|w| w.as_str().unwrap().contains("temperature")));
+    assert!(warnings
+        .iter()
+        .any(|w| w.as_str().unwrap().contains("max_tokens")));
+}
+
+#[tokio::test]
+async fn warnings_can_be_switched_off() {
+    let mut config = GlobalConfig::default();
+    config.server.include_warnings = false;
+    let harness = harness_with(config);
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hi"}],
+            "top_p": 0.5,
+        })),
+    )
+    .await;
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert!(value.get("x_gateway_warnings").is_none());
+}
+
+#[tokio::test]
+async fn the_legacy_completions_endpoint_is_supported() {
+    let harness = harness();
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/completions")
+        .header("content-type", "application/json")
+        .body(Body::from(
+            json!({"model": "chatgpt", "prompt": "say ok"}).to_string(),
+        ))
+        .unwrap();
+    let (status, headers, body) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["object"], "text_completion");
+    assert!(!value["choices"][0]["text"].as_str().unwrap().is_empty());
+    assert!(headers.get("x-conversation-id").is_some());
+
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/completions")
+        .header("content-type", "application/json")
+        .body(Body::from(
+            json!({"model": "chatgpt", "prompt": "say ok", "stream": true}).to_string(),
+        ))
+        .unwrap();
+    let (status, _, body) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::BAD_REQUEST);
+    assert!(body.contains("unsupported_parameter"));
+}
+
+#[tokio::test]
+async fn provider_status_and_validation_are_exposed() {
+    let harness = harness();
+
+    let (status, body) = get_json(&harness.app, "/v1/providers/chatgpt/status").await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(body["state"], "available");
+    assert_eq!(body["provider"], "chatgpt");
+
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/providers/chatgpt/validate")
+        .body(Body::empty())
+        .unwrap();
+    let (status, _, body) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["ok"], true);
+    assert_eq!(value["status"], "ok");
+    assert!(!value["steps"].as_array().unwrap().is_empty());
+
+    let (status, body) = get_json(&harness.app, "/v1/providers/nope/status").await;
+    assert_eq!(status, StatusCode::NOT_FOUND);
+    assert_eq!(body["error"]["code"], "model_not_found");
+}
+
+#[tokio::test]
+async fn provider_status_and_validation_can_name_an_account() {
+    let harness = harness_with_accounts(GlobalConfig::default());
+
+    // A named account is probed, and the answer says which one.
+    let (status, body) = get_json(&harness.app, "/v1/providers/chatgpt@pro/status").await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(body["state"], "available");
+    assert_eq!(body["provider"], "chatgpt@pro");
+
+    // The bare provider name means "its default account", and says so rather
+    // than leaving the caller to guess which profile answered.
+    let (status, body) = get_json(&harness.app, "/v1/providers/chatgpt/status").await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(body["provider"], "chatgpt@perso");
+
+    let (status, body) = post_account_validate(&harness, "chatgpt@pro").await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(body["ok"], true);
+    assert_eq!(body["provider"], "chatgpt@pro");
+
+    // The status route keeps working for a provider that declares no account.
+    let (status, body) = get_json(&harness.app, "/v1/providers/claude/status").await;
+    assert_eq!(status, StatusCode::OK);
+    assert_eq!(body["provider"], "claude");
+}
+
+#[tokio::test]
+async fn an_unknown_account_is_a_404_on_the_status_routes() {
+    let harness = harness_with_accounts(GlobalConfig::default());
+
+    let (status, body) = get_json(&harness.app, "/v1/providers/chatgpt@nobody/status").await;
+    assert_eq!(status, StatusCode::NOT_FOUND);
+    assert_eq!(body["error"]["code"], "account_not_found");
+    assert!(body["error"]["message"].as_str().unwrap().contains("perso"));
+
+    let (status, body) = post_account_validate(&harness, "chatgpt@nobody").await;
+    assert_eq!(status, StatusCode::NOT_FOUND);
+    assert_eq!(body["error"]["code"], "account_not_found");
+
+    // A provider that declares no account refuses a named one instead of
+    // silently probing its only profile.
+    let (status, body) = get_json(&harness.app, "/v1/providers/claude@perso/status").await;
+    assert_eq!(status, StatusCode::NOT_FOUND);
+    assert_eq!(body["error"]["code"], "account_not_found");
+}
+
+/// POST /v1/providers/{owner}/validate and parse the JSON body.
+async fn post_account_validate(harness: &Harness, owner: &str) -> (StatusCode, Value) {
+    let request = Request::builder()
+        .method("POST")
+        .uri(format!("/v1/providers/{owner}/validate"))
+        .body(Body::empty())
+        .unwrap();
+    let (status, _, body) = send(&harness.app, request).await;
+    (status, serde_json::from_str(&body).unwrap_or(Value::Null))
+}
+
+#[tokio::test]
+async fn reload_reports_the_configuration_diff() {
+    let harness = harness();
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/admin/reload")
+        .body(Body::empty())
+        .unwrap();
+    let (status, _, body) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::OK);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["config"], "reloaded");
+}
+
+#[tokio::test]
+async fn an_api_key_protects_the_v1_routes_only() {
+    let mut config = GlobalConfig::default();
+    config.server.api_key = "s3cret".to_string();
+    let harness = harness_with(config);
+
+    let (status, _, body) = send(
+        &harness.app,
+        post_chat(json!({
+            "model": "chatgpt",
+            "messages": [{"role": "user", "content": "hi"}],
+        })),
+    )
+    .await;
+    assert_eq!(status, StatusCode::UNAUTHORIZED);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["error"]["code"], "invalid_api_key");
+
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/chat/completions")
+        .header("content-type", "application/json")
+        .header("authorization", "Bearer s3cret")
+        .body(Body::from(
+            json!({"model": "chatgpt", "messages": [{"role": "user", "content": "hi"}]})
+                .to_string(),
+        ))
+        .unwrap();
+    let (status, _, _) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::OK);
+
+    // /health stays open so that monitors and the dashboard can reach it.
+    let (status, _) = get_json(&harness.app, "/health").await;
+    assert_eq!(status, StatusCode::OK);
+}
+
+#[tokio::test]
+async fn a_malformed_body_is_a_400_with_the_openai_error_shape() {
+    let harness = harness();
+    let request = Request::builder()
+        .method("POST")
+        .uri("/v1/chat/completions")
+        .header("content-type", "application/json")
+        .body(Body::from("{not json"))
+        .unwrap();
+    let (status, _, body) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::BAD_REQUEST);
+    let value: Value = serde_json::from_str(&body).unwrap();
+    assert_eq!(value["error"]["code"], "invalid_request");
+}
+
+#[tokio::test]
+async fn the_dashboard_is_served_and_exposes_metrics() {
+    let harness = harness();
+    let request = Request::builder()
+        .uri("/dashboard")
+        .body(Body::empty())
+        .unwrap();
+    let (status, _, body) = send(&harness.app, request).await;
+    assert_eq!(status, StatusCode::OK);
+    assert!(body.contains("llm-gateway"));
+
+    let (status, metrics) = get_json(&harness.app, "/metrics").await;
+    assert_eq!(status, StatusCode::OK);
+    assert!(metrics["requests_total"].is_number());
+
+    // The screenshot policy is only reachable through the configuration.
+    let config = harness.state.config();
+    assert_eq!(config.debug.screenshots, ScreenshotMode::OnError);
+}
diff --git a/tests/e2e_browser.rs b/tests/e2e_browser.rs
new file mode 100644
index 0000000..a39ff7d
--- /dev/null
+++ b/tests/e2e_browser.rs
@@ -0,0 +1,898 @@
+//! Browser end-to-end tests against the local ChatGPT fixture page.
+//!
+//! They need a real Chromium-based browser and are therefore ignored by default:
+//!
+//!     cargo test --test e2e_browser -- --ignored --test-threads=1
+//!
+//! The fixture is a static HTML file that imitates the real page (editor, send
+//! button, streaming indicator, login form, captcha, error banner), so the whole
+//! capture pipeline can be exercised without a network or a login.
+
+use std::path::PathBuf;
+use std::sync::Arc;
+use std::time::Duration;
+
+use llm_bridge::browser::{external_launch, resolve_executable, Session};
+use llm_bridge::config::{GlobalConfig, ScreenshotMode};
+use llm_bridge::error::GatewayError;
+use llm_bridge::paths::Layout;
+use llm_bridge::providers::config::ProviderConfig;
+use llm_bridge::providers::{
+    Attachment, AttachmentKind, LlmProvider, ProviderRegistry, TurnOutcome, TurnRequest,
+    WebUiProvider,
+};
+use llm_bridge::selftest;
+use tokio::time::timeout;
+
+/// Install a tracing subscriber once so the tests are diagnosable.
+fn init_logs() {
+    static ONCE: std::sync::Once = std::sync::Once::new();
+    ONCE.call_once(|| {
+        let filter = std::env::var("RUST_LOG").unwrap_or_else(|_| "info".to_string());
+        let _ = tracing_subscriber::fmt()
+            .with_env_filter(filter)
+            .with_test_writer()
+            .try_init();
+    });
+}
+
+/// Absolute file:// URL of the fixture, optionally with a query string.
+fn fixture_url(query: &str) -> String {
+    let path = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("tests")
+        .join("fixtures")
+        .join("chatgpt_mock.html");
+    let path = path.to_string_lossy().replace('\\', "/");
+    let url = format!("file:///{path}");
+    if query.is_empty() {
+        url
+    } else {
+        format!("{url}?{query}")
+    }
+}
+
+/// Provider configuration pointing at the fixture.
+fn provider_toml(base: &str) -> String {
+    format!(
+        r##"
+[provider]
+name = "fixture"
+display_name = "ChatGPT fixture"
+web_url = "{base}"
+new_conversation_url = "{base}"
+conversation_url_pattern = "#c=([0-9a-zA-Z-]{{8,}})"
+default_models = ["fixture-1"]
+enabled = true
+
+[selectors]
+input_field = "div#prompt-textarea"
+send_button = "button[data-testid='send-button']"
+response_container = "div[data-message-author-role='assistant']"
+streaming_indicator = "button[data-testid='stop-button']"
+file_input = "input[type='file']"
+new_chat_button = "a[data-testid='create-new-chat-button']"
+login_page_indicator = "form[action*='login']"
+captcha_indicator = "div#challenge-form"
+error_banner = "[data-testid='error-message'], div[role='alert']"
+attachment_indicator = "div[data-testid='attachment-chip']"
+copy_button = "button[data-testid='copy-button']"
+
+[login]
+url_patterns = ["login=1"]
+
+[rate_limit]
+text_patterns = ["too many requests"]
+
+[timeouts]
+page_load = 20
+response_generation = 15
+response_timeout = 30
+
+[input]
+poll_interval_ms = 100
+quiet_ms = 500
+
+[options]
+supports_images = true
+supports_streaming = true
+supports_new_chat = true
+"##
+    )
+}
+
+struct Harness {
+    registry: Arc<ProviderRegistry>,
+    provider: Arc<WebUiProvider>,
+    _tmp: tempfile::TempDir,
+}
+
+/// Boot a registry with a single fixture provider, or None when no browser exists.
+async fn harness(toml: &str) -> Option<Harness> {
+    harness_with(toml, |_| {}).await
+}
+
+/// Same, with a chance to tweak the global configuration.
+async fn harness_with(toml: &str, configure: impl FnOnce(&mut GlobalConfig)) -> Option<Harness> {
+    init_logs();
+    let chrome = resolve_executable(None, std::env::var("CHROME").ok())?;
+    let tmp = tempfile::tempdir().expect("temp dir");
+    let layout = Layout::rooted_at(tmp.path().join("state"));
+    layout.ensure().expect("layout");
+    // Only the fixture provider may be registered: the state directory is
+    // materialised with the providers shipped in the build.
+    if let Ok(entries) = std::fs::read_dir(layout.providers_dir()) {
+        for entry in entries.flatten() {
+            std::fs::remove_file(entry.path()).ok();
+        }
+    }
+    std::fs::write(layout.provider_config("fixture"), toml).expect("provider config");
+
+    let mut config = GlobalConfig::default();
+    config.browser.headless = true;
+    config.browser.executable = chrome.to_string_lossy().to_string();
+    config.capture.poll_interval_ms = 100;
+    config.capture.quiet_ms = 500;
+    config.capture.response_timeout_s = 30;
+    config.debug.screenshots = ScreenshotMode::OnError;
+    config.debug.dir = tmp.path().join("debug").to_string_lossy().to_string();
+    configure(&mut config);
+
+    let registry = Arc::new(ProviderRegistry::new(layout, config));
+    registry.reload().await.expect("registry reload");
+    let provider = registry
+        .get("fixture")
+        .expect("fixture provider registered");
+    Some(Harness {
+        registry,
+        provider,
+        _tmp: tmp,
+    })
+}
+
+/// Run one turn and return the deltas plus the final result.
+async fn run_turn(
+    provider: &Arc<WebUiProvider>,
+    session: &Session,
+    prompt: &str,
+    reuse_url: Option<String>,
+    attachments: Vec<Attachment>,
+) -> (Vec<String>, Result<TurnOutcome, GatewayError>) {
+    let request = TurnRequest {
+        prompt: prompt.to_string(),
+        attachments,
+        replay_history: reuse_url.is_none(),
+        reuse_url,
+        probe: false,
+        trace_id: "e2e".to_string(),
+        wait_for_tab: None,
+    };
+
+    let mut stream = match provider.run_turn(session.clone(), request).await {
+        Ok(stream) => stream,
+        Err(err) => return (Vec::new(), Err(err)),
+    };
+
+    let mut deltas = Vec::new();
+    loop {
+        match stream.recv().await {
+            Some(llm_bridge::providers::TurnEvent::Delta(delta)) => deltas.push(delta),
+            Some(llm_bridge::providers::TurnEvent::Completed(outcome)) => {
+                return (deltas, Ok(outcome))
+            }
+            Some(llm_bridge::providers::TurnEvent::Failed(err)) => return (deltas, Err(err)),
+            None => {
+                return (
+                    deltas,
+                    Err(GatewayError::internal(
+                        "the turn ended without a terminal event",
+                    )),
+                )
+            }
+        }
+    }
+}
+
+/// Assert that the error carries the expected machine readable code.
+fn expect_code(result: Result<TurnOutcome, GatewayError>, code: &str) {
+    match result {
+        Ok(outcome) => panic!("expected {code}, got an answer: {}", outcome.text),
+        Err(err) => assert_eq!(err.code(), code, "unexpected error: {err}"),
+    }
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn fixture_full_pipeline() {
+    let Some(harness) = harness(&provider_toml(&fixture_url("conv=1"))).await else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    assert_eq!(
+        harness.registry.all().len(),
+        1,
+        "only the fixture provider is configured"
+    );
+    let session = harness.provider.session(None).await.expect("session");
+
+    let (deltas, result) = timeout(
+        Duration::from_secs(90),
+        run_turn(
+            &harness.provider,
+            &session,
+            "hello fixture",
+            None,
+            Vec::new(),
+        ),
+    )
+    .await
+    .expect("the first turn timed out");
+
+    let outcome = result.expect("the first turn failed");
+    assert!(
+        outcome.text.starts_with("Echo: hello fixture"),
+        "{}",
+        outcome.text
+    );
+    assert!(outcome.text.contains("fixture page"), "{}", outcome.text);
+    assert!(
+        deltas.len() >= 2,
+        "expected several streamed deltas, got {deltas:?}"
+    );
+    assert_eq!(deltas.concat().trim(), outcome.text.trim());
+    let web_id = outcome
+        .web_id
+        .clone()
+        .expect("the conversation id must be extracted");
+    assert!(
+        web_id.len() >= 8,
+        "suspicious conversation id {web_id:?} from {:?}",
+        outcome.web_url
+    );
+
+    // Continuing the thread reopens the same web conversation.
+    let reuse = outcome.web_url.clone().expect("web url");
+    let (_, second) = timeout(
+        Duration::from_secs(90),
+        run_turn(
+            &harness.provider,
+            &session,
+            "second question",
+            Some(reuse),
+            Vec::new(),
+        ),
+    )
+    .await
+    .expect("the second turn timed out");
+    let second = second.expect("the second turn failed");
+    assert!(
+        second.text.starts_with("Echo: second question"),
+        "{}",
+        second.text
+    );
+    assert_eq!(
+        second.web_id, outcome.web_id,
+        "the web conversation changed"
+    );
+
+    // The provider passes its own validation. The validation opens its own
+    // tab, so the one this test holds is released first.
+    drop(session);
+    let cfg = harness.provider.cfg();
+    let report = selftest::validate_provider(harness.provider.as_ref(), &cfg, None)
+        .await
+        .expect("validation");
+    assert!(report.ok, "selftest failed: {report:?}");
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn fixture_selftest_works_on_a_brand_new_session() {
+    let Some(harness) = harness(&provider_toml(&fixture_url(""))).await else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    let session = harness.provider.session(None).await.expect("session");
+
+    // This is what the CLI does: a session that never navigated anywhere yet.
+    let start_page = session
+        .page()
+        .url()
+        .await
+        .unwrap_or_default()
+        .unwrap_or_default();
+    assert!(
+        start_page.is_empty() || start_page == "about:blank",
+        "a new session should start on about:blank, got {start_page:?}"
+    );
+
+    // The selftest acquires its own tab: release this one first, otherwise a
+    // single-tab provider (max_tabs = 1) answers "busy" instead.
+    drop(session);
+    let cfg = harness.provider.cfg();
+    let report = selftest::validate_provider(harness.provider.as_ref(), &cfg, None)
+        .await
+        .expect("validation on a fresh session");
+    assert!(report.ok, "selftest on a fresh session failed: {report:?}");
+    assert_eq!(report.status, "ok");
+    // The check must be quick: it opens the page instead of waiting for a
+    // selector to appear on about:blank.
+    assert!(
+        report.duration_ms < 20_000,
+        "selftest took {} ms",
+        report.duration_ms
+    );
+    let probe_step = report
+        .steps
+        .iter()
+        .find(|step| step.step == "page_probe")
+        .expect("page_probe step");
+    assert!(probe_step.ok, "page_probe failed: {probe_step:?}");
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn fixture_reports_login_captcha_error_and_rate_limit() {
+    let Some(harness) = harness(&provider_toml(&fixture_url(""))).await else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    let session = harness.provider.session(None).await.expect("session");
+
+    let cases = [
+        ("login=1", "requires_login"),
+        ("captcha=1", "captcha_required"),
+        ("error=1", "upstream_error"),
+        ("ratelimit=1", "upstream_rate_limit"),
+    ];
+
+    for (query, code) in cases {
+        let url = fixture_url(query);
+        let (_, result) = timeout(
+            Duration::from_secs(60),
+            run_turn(&harness.provider, &session, "hello", Some(url), Vec::new()),
+        )
+        .await
+        .unwrap_or_else(|_| panic!("the {query} case timed out"));
+        expect_code(result, code);
+    }
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn fixture_timeouts_and_missing_selectors() {
+    // A page that never produces text trips the first-token budget.
+    let impatient = provider_toml(&fixture_url(""))
+        .replace("response_generation = 15", "response_generation = 3");
+    let Some(harness) = harness(&impatient).await else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    let session = harness.provider.session(None).await.expect("session");
+
+    let (_, result) = timeout(
+        Duration::from_secs(60),
+        run_turn(
+            &harness.provider,
+            &session,
+            "hello",
+            Some(fixture_url("empty=1")),
+            Vec::new(),
+        ),
+    )
+    .await
+    .expect("the empty case timed out");
+    expect_code(result, "upstream_timeout");
+
+    // A page whose editor appears late is waited for, not failed.
+    let (_, result) = timeout(
+        Duration::from_secs(90),
+        run_turn(
+            &harness.provider,
+            &session,
+            "late editor",
+            Some(fixture_url("loading=1")),
+            Vec::new(),
+        ),
+    )
+    .await
+    .expect("the loading case timed out");
+    let outcome = result.expect("the late editor should still be driven");
+    assert!(
+        outcome.text.starts_with("Echo: late editor"),
+        "{}",
+        outcome.text
+    );
+
+    // A stale selector is reported as such.
+    let broken = provider_toml(&fixture_url(""))
+        .replace(
+            "input_field = \"div#prompt-textarea\"",
+            "input_field = \"div#this-does-not-exist\"",
+        )
+        .replace("page_load = 20", "page_load = 4");
+    harness
+        .provider
+        .replace_config(ProviderConfig::parse(&broken, "fixture.toml").expect("broken config"))
+        .await;
+    let (_, result) = timeout(
+        Duration::from_secs(60),
+        run_turn(&harness.provider, &session, "hello", None, Vec::new()),
+    )
+    .await
+    .expect("the broken selector case timed out");
+    expect_code(result, "selector_missing");
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn two_tabs_of_one_browser_answer_concurrently() {
+    let toml = provider_toml(&fixture_url("conv=1"));
+    let Some(harness) = harness_with(&toml, |config| {
+        config.browser.max_tabs = 2;
+    })
+    .await
+    else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    let first = harness.provider.session(None).await.expect("first tab");
+    let second = harness.provider.session(None).await.expect("second tab");
+    let url = fixture_url("conv=1");
+
+    let outcome = timeout(Duration::from_secs(30), async {
+        // Navigate both tabs at once...
+        let (a, b) = tokio::join!(
+            llm_bridge::browser::dom::goto(first.page(), &url, Duration::from_secs(10)),
+            llm_bridge::browser::dom::goto(second.page(), &url, Duration::from_secs(10)),
+        );
+        a.expect("the first tab did not navigate");
+        b.expect("the second tab did not navigate");
+
+        // ... then hammer both, the way the capture loop does.
+        for _ in 0..20 {
+            let (a, b) = tokio::join!(
+                first.page().evaluate_expression("document.title"),
+                second.page().evaluate_expression("document.title"),
+            );
+            a.expect("the first tab stopped answering");
+            b.expect("the second tab stopped answering");
+        }
+    })
+    .await;
+
+    assert!(
+        outcome.is_ok(),
+        "two tabs of one browser stopped answering: {outcome:?}"
+    );
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn two_tabs_serve_two_turns_in_parallel() {
+    let toml = provider_toml(&fixture_url("conv=1&delay=5000"));
+    let Some(harness) = harness_with(&toml, |config| {
+        config.browser.max_tabs = 2;
+    })
+    .await
+    else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+
+    // Two tabs of the same account can be leased at the same time.
+    let first = harness.provider.session(None).await.expect("first tab");
+    let second = harness.provider.session(None).await.expect("second tab");
+    assert_ne!(first.tab_slot(), second.tab_slot());
+    let stats = harness.provider.tab_stats();
+    assert_eq!(stats[0].1.max_tabs, 2);
+    assert_eq!(stats[0].1.busy, 2);
+
+    let started = std::time::Instant::now();
+    let (a, b) = tokio::join!(
+        run_turn(&harness.provider, &first, "first", None, Vec::new()),
+        run_turn(&harness.provider, &second, "second", None, Vec::new()),
+    );
+    let elapsed = started.elapsed();
+
+    let a = a.1.expect("the first turn failed");
+    let b = b.1.expect("the second turn failed");
+    assert!(a.text.contains("first"), "{}", a.text);
+    assert!(b.text.contains("second"), "{}", b.text);
+    // Each generation takes five seconds: serving them one after the other
+    // takes more than ten, two tabs take about six.
+    assert!(
+        elapsed < Duration::from_secs(9),
+        "two tabs did not run in parallel: {elapsed:?}"
+    );
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn a_busy_single_tab_account_refuses_a_second_request() {
+    let toml = provider_toml(&fixture_url("conv=1"));
+    let Some(harness) = harness_with(&toml, |config| {
+        config.browser.max_tabs = 1;
+        config.browser.busy_wait_s = 1;
+    })
+    .await
+    else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+
+    let held = harness.provider.session(None).await.expect("the only tab");
+    let started = std::time::Instant::now();
+    let err = harness
+        .provider
+        .session(None)
+        .await
+        .expect_err("the second request must not get a tab");
+    assert_eq!(err.code(), "provider_busy");
+    assert_eq!(err.http_status(), 429);
+    assert!(
+        started.elapsed() >= Duration::from_secs(1),
+        "the request did not wait for the configured budget"
+    );
+
+    drop(held);
+    assert!(harness.provider.session(None).await.is_ok());
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn each_account_has_its_own_browser_and_tab_pool() {
+    let mut toml = provider_toml(&fixture_url("conv=1&delay=3000"));
+    toml.push_str("\n[[accounts]]\nid = \"un\"\ndefault = true\n\n[[accounts]]\nid = \"deux\"\n");
+    let Some(harness) = harness(&toml).await else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+
+    let accounts = harness.provider.accounts();
+    assert_eq!(accounts.len(), 2);
+    assert_ne!(accounts[0].profile, accounts[1].profile);
+
+    // max_tabs is 1 for both accounts, yet one tab per account is available at
+    // the same time: the pools are per account, not per provider.
+    let one = harness
+        .provider
+        .session(Some("un"))
+        .await
+        .expect("account un");
+    let two = harness
+        .provider
+        .session(Some("deux"))
+        .await
+        .expect("account deux");
+    assert_eq!(one.account(), Some("un"));
+    assert_eq!(two.account(), Some("deux"));
+
+    let started = std::time::Instant::now();
+    let (a, b) = tokio::join!(
+        run_turn(&harness.provider, &one, "un", None, Vec::new()),
+        run_turn(&harness.provider, &two, "deux", None, Vec::new()),
+    );
+    let elapsed = started.elapsed();
+    assert!(a.1.is_ok(), "account un failed: {:?}", a.1.err());
+    assert!(b.1.is_ok(), "account deux failed: {:?}", b.1.err());
+    assert!(
+        elapsed < Duration::from_secs(6),
+        "the two accounts did not answer at the same time: {elapsed:?}"
+    );
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn fixture_returns_markdown_and_never_the_toolbar_text() {
+    let toml = provider_toml(&fixture_url("conv=1&rich=1"));
+    let Some(harness) = harness(&toml).await else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    let session = harness.provider.session(None).await.expect("session");
+
+    // Auto mode: the provider copy button first, the HTML conversion otherwise.
+    let (_, result) = timeout(
+        Duration::from_secs(90),
+        run_turn(&harness.provider, &session, "rich answer", None, Vec::new()),
+    )
+    .await
+    .expect("the rich turn timed out");
+    let outcome = result.expect("the rich turn failed");
+
+    assert!(
+        outcome.fidelity == "clipboard" || outcome.fidelity == "dom",
+        "unexpected fidelity {:?}: {}",
+        outcome.fidelity,
+        outcome.text
+    );
+    eprintln!("rich answer captured through the {} path", outcome.fidelity);
+
+    // Structure the plain text capture used to lose.
+    assert!(outcome.text.contains("## Answer"), "{}", outcome.text);
+    assert!(outcome.text.contains("- first point"), "{}", outcome.text);
+    assert!(outcome.text.contains("```rust"), "{}", outcome.text);
+    assert!(
+        outcome.text.contains("| Name | Value |"),
+        "{}",
+        outcome.text
+    );
+    assert!(outcome.text.contains("| alpha | 1 |"), "{}", outcome.text);
+    // The toolbar sits next to the answer, so its label is not answer text.
+    assert!(!outcome.text.contains("Copy"), "{}", outcome.text);
+
+    // Forcing the DOM conversion must give the same structure.
+    let forced = provider_toml(&fixture_url("conv=1&rich=1")).replace(
+        "poll_interval_ms = 100",
+        "poll_interval_ms = 100\nmarkdown = \"dom\"",
+    );
+    harness
+        .provider
+        .replace_config(ProviderConfig::parse(&forced, "fixture.toml").expect("forced config"))
+        .await;
+
+    let (_, result) = timeout(
+        Duration::from_secs(90),
+        run_turn(&harness.provider, &session, "dom answer", None, Vec::new()),
+    )
+    .await
+    .expect("the forced DOM turn timed out");
+    let forced_outcome = result.expect("the forced DOM turn failed");
+    assert_eq!(forced_outcome.fidelity, "dom");
+    assert!(
+        forced_outcome.text.contains("## Answer"),
+        "{}",
+        forced_outcome.text
+    );
+    assert!(
+        forced_outcome.text.contains("```rust"),
+        "{}",
+        forced_outcome.text
+    );
+    assert!(
+        forced_outcome.text.contains("| alpha | 1 |"),
+        "{}",
+        forced_outcome.text
+    );
+    assert!(
+        !forced_outcome.text.contains("Copy"),
+        "{}",
+        forced_outcome.text
+    );
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn fixture_handles_rewrites_and_attachments() {
+    let Some(harness) = harness(&provider_toml(&fixture_url(""))).await else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    let session = harness.provider.session(None).await.expect("session");
+
+    // A mid-stream rewrite must not corrupt the final answer.
+    let (_, result) = timeout(
+        Duration::from_secs(90),
+        run_turn(
+            &harness.provider,
+            &session,
+            "rewrite please",
+            Some(fixture_url("rewrite=1")),
+            Vec::new(),
+        ),
+    )
+    .await
+    .expect("the rewrite case timed out");
+    let outcome = result.expect("the rewrite case failed");
+    assert!(
+        outcome.text.starts_with("Echo: rewrite please"),
+        "{}",
+        outcome.text
+    );
+    assert!(!outcome.text.contains("Draft answer"), "{}", outcome.text);
+
+    // Attachments are pushed into the file input and acknowledged by the page.
+    let dir = std::env::temp_dir().join("llm-gateway-e2e");
+    std::fs::create_dir_all(&dir).expect("temp dir");
+    let image = dir.join("pixel.png");
+    std::fs::write(&image, b"\x89PNG\r\n\x1a\n").expect("write png");
+
+    let (_, result) = timeout(
+        Duration::from_secs(90),
+        run_turn(
+            &harness.provider,
+            &session,
+            "with an image",
+            None,
+            vec![Attachment {
+                path: image,
+                mime: "image/png".to_string(),
+                kind: AttachmentKind::Image,
+            }],
+        ),
+    )
+    .await
+    .expect("the attachment case timed out");
+    let outcome = result.expect("the attachment case failed");
+    assert!(outcome.text.contains("pixel.png"), "{}", outcome.text);
+
+    harness.provider.shutdown().await.expect("shutdown");
+}
+
+/// Wait until something accepts TCP connections on a port.
+async fn wait_for_port(port: u16, budget: Duration) -> bool {
+    let deadline = std::time::Instant::now() + budget;
+    while std::time::Instant::now() < deadline {
+        if std::net::TcpStream::connect(("127.0.0.1", port)).is_ok() {
+            return true;
+        }
+        tokio::time::sleep(Duration::from_millis(200)).await;
+    }
+    false
+}
+
+/// Wait until the browser is really up: its debugging endpoint answers and the
+/// page we asked it to open is loaded.
+async fn wait_for_ready_browser(port: u16, expected_url: &str, budget: Duration) -> bool {
+    let client = reqwest::Client::new();
+    let endpoint = format!("http://127.0.0.1:{port}/json/list");
+    let deadline = std::time::Instant::now() + budget;
+    while std::time::Instant::now() < deadline {
+        if let Ok(response) = client.get(&endpoint).send().await {
+            if let Ok(targets) = response.json::<Vec<serde_json::Value>>().await {
+                let ready = targets.iter().any(|target| {
+                    target["type"] == "page"
+                        && target["url"]
+                            .as_str()
+                            .is_some_and(|url| url.contains(expected_url))
+                });
+                if ready {
+                    return true;
+                }
+            }
+        }
+        tokio::time::sleep(Duration::from_millis(250)).await;
+    }
+    false
+}
+
+/// Kills and reaps a browser process the test started, on every path.
+struct BrowserProcess {
+    child: std::process::Child,
+}
+
+impl BrowserProcess {
+    fn spawn(launch: &llm_bridge::browser::ExternalLaunch) -> Self {
+        Self {
+            child: launch.spawn().expect("spawning the browser"),
+        }
+    }
+
+    fn is_running(&mut self) -> bool {
+        self.child.try_wait().ok().flatten().is_none()
+    }
+}
+
+impl Drop for BrowserProcess {
+    fn drop(&mut self) {
+        let _ = self.child.kill();
+        let _ = self.child.wait();
+    }
+}
+
+/// Ask the OS for a free port.
+fn free_port() -> u16 {
+    let listener = std::net::TcpListener::bind("127.0.0.1:0").expect("bind an ephemeral port");
+    listener.local_addr().expect("local address").port()
+}
+
+#[tokio::test]
+#[ignore = "requires a real Chromium-based browser"]
+async fn attach_mode_uses_a_browser_the_user_started() {
+    init_logs();
+    let Some(chrome) = resolve_executable(None, std::env::var("CHROME").ok()) else {
+        eprintln!("no browser found, skipping");
+        return;
+    };
+    let tmp = tempfile::tempdir().expect("temp dir");
+    let profile = tmp.path().join("attached-profile");
+    let port = free_port();
+
+    // The user starts the browser: no automation switch, no user agent spoofing.
+    let launch = external_launch(Some(&chrome), &profile, &fixture_url("conv=1"), Some(port));
+    assert!(!launch.command_line().contains("enable-automation"));
+    let mut browser = BrowserProcess::spawn(&launch);
+    if !wait_for_port(port, Duration::from_secs(30)).await {
+        panic!("the browser never opened its debugging port");
+    }
+    // Attaching to a browser that is still starting up races with Chrome
+    // creating its first tab: wait until the page is really there.
+    if !wait_for_ready_browser(port, "chatgpt_mock.html", Duration::from_secs(30)).await {
+        panic!("the browser never finished opening the fixture page");
+    }
+
+    let Some(harness) = harness_with(&provider_toml(&fixture_url("conv=1")), |config| {
+        config.browser.attach = true;
+        config.browser.debug_port = port;
+    })
+    .await
+    else {
+        return;
+    };
+
+    let session = harness
+        .provider
+        .session(None)
+        .await
+        .expect("attach to the running browser");
+
+    // The gateway reuses a tab the browser exposes to us, and otherwise opens
+    // one of its own in that same browser: either way the session, the cookies
+    // and the window belong to the user and are never closed by the gateway.
+    let url = session
+        .page()
+        .url()
+        .await
+        .unwrap_or_default()
+        .unwrap_or_default();
+    assert!(
+        !url.starts_with("devtools://"),
+        "unexpected page attached: {url:?}"
+    );
+
+    let (deltas, result) = timeout(
+        Duration::from_secs(90),
+        run_turn(
+            &harness.provider,
+            &session,
+            "attached hello",
+            None,
+            Vec::new(),
+        ),
+    )
+    .await
+    .expect("the attached turn timed out");
+    let outcome = result.expect("the attached turn failed");
+    assert!(
+        outcome.text.starts_with("Echo: attached hello"),
+        "{}",
+        outcome.text
+    );
+    assert!(
+        deltas.len() >= 2,
+        "expected streamed deltas, got {deltas:?}"
+    );
+
+    // Shutting the gateway down must leave the user's browser alone.
+    harness.provider.shutdown().await.expect("shutdown");
+    tokio::time::sleep(Duration::from_millis(500)).await;
+    assert!(
+        browser.is_running(),
+        "attach mode must not close the browser it connected to"
+    );
+}
+
+#[test]
+fn the_fixture_configuration_is_valid() {
+    let cfg = ProviderConfig::parse(&provider_toml(&fixture_url("")), "fixture.toml").unwrap();
+    assert!(cfg.is_usable(), "{:?}", cfg.problems);
+    assert!(cfg.capabilities().supports_images);
+    assert_eq!(cfg.file.timeouts.response_generation, 15);
+}
diff --git a/tests/fixtures/chatgpt_mock.html b/tests/fixtures/chatgpt_mock.html
new file mode 100644
index 0000000..836bfed
--- /dev/null
+++ b/tests/fixtures/chatgpt_mock.html
@@ -0,0 +1,387 @@
+<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8" />
+<title>ChatGPT fixture</title>
+<!--
+  Local fake of the ChatGPT web UI used by the browser end-to-end tests.
+
+  The Rust driver opens this file with a file:// URL and drives it over CDP:
+  it inserts text through Input.insertText / execCommand / key events, clicks
+  button[data-testid=send-button], then polls the DOM until the answer settles.
+
+  DOM contract (selectors live in the test provider TOML):
+    - editor               div#prompt-textarea.ProseMirror[contenteditable=true]
+    - send button          button[data-testid=send-button]   (disabled while empty)
+    - answer containers    div[data-message-author-role=assistant]  (one per answer)
+                           the text lives in div.answer-body inside it, and the
+                           toolbar (with the copy button) is a sibling of the
+                           answer node, exactly like the real page: the capture
+                           must not pick the word "Copy" up as answer text
+    - answer toolbar       div.message-toolbar > button[data-testid=copy-button]
+                           copies the answer as Markdown, like the real UI
+    - streaming indicator  button[data-testid=stop-button]    (only while generating)
+    - file input           input[type=file]                   (hidden)
+    - attachment chips     div[data-testid=attachment-chip]
+    - new chat             a[data-testid=create-new-chat-button]
+    - login mode           form[action="/auth/login"]
+    - captcha mode         div#challenge-form
+    - error mode           div[role=alert]
+
+  Query parameters:
+    conv=1        after the first send, set location.hash to #c=<uuid> and keep it
+    login=1       render the sign-in form instead of the editor
+    captcha=1     render a bot challenge
+    error=1       render an error banner; sending produces no answer
+    ratelimit=1   the page text contains "too many requests"; sending produces no answer
+    empty=1       sending shows the stop button but never writes any text
+    delay=<ms>    minimum generation time (default 1200)
+    loading=1     the editor only appears after 3 seconds
+    rewrite=1     the answer is rewritten mid-stream before settling
+    rich=1        the answer is rendered as rich HTML (heading, list, code
+                  block, table) and the copy button copies it as Markdown
+-->
+<style>
+  body { font: 15px/1.5 system-ui, sans-serif; margin: 0; background: #212121; color: #ececec; }
+  header { padding: 10px 16px; border-bottom: 1px solid #3a3a3a; display: flex; gap: 12px; }
+  #messages { padding: 16px; height: 320px; overflow: auto; }
+  .msg { max-width: 70%; margin: 8px 0; padding: 8px 12px; border-radius: 10px; white-space: pre-wrap; }
+  [data-message-author-role="user"] { background: #2f2f2f; margin-left: auto; }
+  [data-message-author-role="assistant"] { background: #303030; }
+  footer { padding: 12px 16px; border-top: 1px solid #3a3a3a; }
+  #prompt-textarea { min-height: 48px; padding: 10px; background: #303030; border-radius: 12px;
+                     border: 1px solid #4a4a4a; outline: none; }
+  #prompt-textarea:focus { border-color: #7aa2f7; }
+  button { font: inherit; padding: 6px 12px; border-radius: 8px; border: 1px solid #4a4a4a;
+           background: #303030; color: #ececec; cursor: pointer; }
+  button[disabled] { opacity: .45; cursor: default; }
+  #attachments { display: flex; gap: 6px; flex-wrap: wrap; margin-bottom: 8px; }
+  [data-testid="attachment-chip"] { background: #3a3a3a; border-radius: 6px; padding: 2px 8px; font-size: 13px; }
+  .message-toolbar { display: flex; gap: 6px; margin: 2px 0 10px; }
+  .message-toolbar button { font-size: 12px; padding: 2px 8px; }
+  .answer-body table { border-collapse: collapse; margin: 6px 0; }
+  .answer-body th, .answer-body td { border: 1px solid #555; padding: 2px 8px; }
+  .answer-body pre { background: #1b1b1b; padding: 8px; border-radius: 6px; overflow: auto; }
+  #toolbar { display: flex; justify-content: space-between; align-items: center; margin-top: 8px; }
+  .banner { margin: 12px 16px; padding: 10px 12px; border-radius: 8px; background: #4a2020; }
+  #challenge-form { margin: 24px 16px; padding: 20px; background: #3a3a3a; border-radius: 10px; }
+  form { margin: 40px auto; width: 320px; padding: 24px; background: #2a2a2a; border-radius: 12px; }
+  input[type="email"], input[type="password"] { width: 100%; padding: 8px; margin: 4px 0 12px;
+                                                background: #303030; border: 1px solid #4a4a4a;
+                                                border-radius: 8px; color: inherit; }
+</style>
+</head>
+<body>
+<div id="app"></div>
+<script>
+(function () {
+  "use strict";
+
+  var params = new URLSearchParams(location.search);
+  var mode = function (name) { return params.get(name) === "1"; };
+
+  var state = {
+    generating: false,
+    token: 0,
+    attachments: [],
+    conversation: null,
+    answerCount: 0
+  };
+
+  // A reopened conversation keeps its identifier so that the driver can prove
+  // that it is continuing the same web thread.
+  var hashMatch = /#c=([0-9a-zA-Z-]+)/.exec(location.hash);
+  if (hashMatch) { state.conversation = hashMatch[1]; }
+
+  function answer(prompt) {
+    var trimmed = prompt.trim();
+    var text;
+    if (trimmed.toLowerCase().indexOf("ok") !== -1) {
+      text = "ok";
+    } else {
+      text = "Echo: " + trimmed + " — this answer was generated by the local ChatGPT fixture page.";
+    }
+    if (state.attachments.length) {
+      text = text + " (attached: " + state.attachments.join(", ") + ")";
+    }
+    return text;
+  }
+
+  function escapeHtml(value) {
+    return String(value)
+      .replace(/&/g, "&amp;")
+      .replace(/</g, "&lt;")
+      .replace(/>/g, "&gt;");
+  }
+
+  // The rich rendering of one answer: a heading, a list, a fenced code block
+  // and a table, i.e. exactly the constructs a plain innerText capture loses.
+  function richHtml(prompt) {
+    return (
+      "<h2>Answer</h2>" +
+      "<p>Echo: <strong>" + escapeHtml(prompt.trim()) + "</strong></p>" +
+      "<ul><li>first point</li><li>second point</li></ul>" +
+      '<pre><code class="language-rust">fn main() {\n    println!("hi");\n}</code></pre>' +
+      "<table><thead><tr><th>Name</th><th>Value</th></tr></thead>" +
+      "<tbody><tr><td>alpha</td><td>1</td></tr><tr><td>beta</td><td>2</td></tr></tbody></table>"
+    );
+  }
+
+  // What the real copy button puts in the clipboard: the Markdown rendering.
+  function richMarkdown(prompt) {
+    return (
+      "## Answer\n\n" +
+      "Echo: **" + prompt.trim() + "**\n\n" +
+      "- first point\n" +
+      "- second point\n\n" +
+      "```rust\n" +
+      'fn main() {\n    println!("hi");\n}\n' +
+      "```\n\n" +
+      "| Name | Value |\n" +
+      "| --- | --- |\n" +
+      "| alpha | 1 |\n" +
+      "| beta | 2 |\n"
+    );
+  }
+
+  // Give one assistant message the toolbar the real page shows next to it.
+  // The copy button is a sibling of the answer node, not a child, so a capture
+  // that reads the whole turn would pick the word "Copy" up as answer text.
+  function attachToolbar(turn, prompt) {
+    var toolbar = document.createElement("div");
+    toolbar.className = "message-toolbar";
+    var copy = document.createElement("button");
+    copy.setAttribute("data-testid", "copy-button");
+    copy.setAttribute("aria-label", "Copy");
+    copy.textContent = "Copy";
+    copy.addEventListener("click", function (event) {
+      event.preventDefault();
+      var markdown = richMarkdown(prompt);
+      if (navigator.clipboard && navigator.clipboard.writeText) {
+        navigator.clipboard.writeText(markdown)["catch"](function () {});
+      }
+    });
+    toolbar.appendChild(copy);
+    turn.appendChild(toolbar);
+  }
+
+  // Give one assistant message the toolbar the real page shows next to it.
+  // The copy button is a sibling of the answer node, not a child, so a capture
+  // that reads the whole turn would pick the word "Copy" up as answer text.
+  function attachToolbar(turn, prompt) {
+    var toolbar = document.createElement("div");
+    toolbar.className = "message-toolbar";
+    var copy = document.createElement("button");
+    copy.setAttribute("data-testid", "copy-button");
+    copy.setAttribute("aria-label", "Copy");
+    copy.textContent = "Copy";
+    copy.addEventListener("click", function (event) {
+      event.preventDefault();
+      var markdown = richMarkdown(prompt);
+      if (navigator.clipboard && navigator.clipboard.writeText) {
+        navigator.clipboard.writeText(markdown)["catch"](function () {});
+      }
+    });
+    toolbar.appendChild(copy);
+    turn.appendChild(toolbar);
+  }
+
+  function render() {
+    var app = document.getElementById("app");
+    if (mode("login")) {
+      app.innerHTML =
+        '<form action="/auth/login" method="post">' +
+        '<h2>Sign in (fixture)</h2>' +
+        '<label>Email<input type="email" name="email" /></label>' +
+        '<label>Password<input type="password" name="password" /></label>' +
+        '<button type="submit">Continue</button>' +
+        '</form>';
+      return;
+    }
+
+    var banner = "";
+    if (mode("error")) {
+      banner = '<div role="alert">Something went wrong. Please try again.</div>';
+    }
+    if (mode("ratelimit")) {
+      banner += '<div class="banner">Too many requests right now, please try again later.</div>';
+    }
+    var challenge = mode("captcha") ? '<div id="challenge-form">Verify you are human</div>' : "";
+
+    app.innerHTML =
+      '<header><a data-testid="create-new-chat-button" href="#">New chat</a><span>ChatGPT fixture</span></header>' +
+      banner + challenge +
+      '<div id="messages"></div>' +
+      '<footer>' +
+      '<div id="attachments"></div>' +
+      '<div id="prompt-textarea" class="ProseMirror" contenteditable="true"></div>' +
+      '<div id="toolbar">' +
+      '<input type="file" multiple hidden />' +
+      '<button data-testid="send-button" disabled>Send</button>' +
+      '</div>' +
+      '</footer>';
+
+    var editor = document.getElementById("prompt-textarea");
+    var send = document.querySelector("[data-testid='send-button']");
+    var fileInput = document.querySelector("input[type='file']");
+
+    function refresh() { send.disabled = editor.innerText.trim().length === 0 || state.generating; }
+    editor.addEventListener("input", refresh);
+    editor.addEventListener("keyup", refresh);
+    editor.addEventListener("blur", refresh);
+    window.setInterval(refresh, 100);
+
+    editor.addEventListener("keydown", function (event) {
+      if (event.key === "Enter" && !event.shiftKey) {
+        event.preventDefault();
+        submit();
+      }
+    });
+
+    send.addEventListener("click", function (event) { event.preventDefault(); submit(); });
+
+    fileInput.addEventListener("change", function () {
+      var strip = document.getElementById("attachments");
+      for (var i = 0; i < fileInput.files.length; i += 1) {
+        var file = fileInput.files[i];
+        state.attachments.push(file.name);
+        var chip = document.createElement("div");
+        chip.setAttribute("data-testid", "attachment-chip");
+        chip.textContent = file.name;
+        strip.appendChild(chip);
+      }
+    });
+
+    var newChat = document.querySelector("[data-testid='create-new-chat-button']");
+    newChat.addEventListener("click", function (event) {
+      event.preventDefault();
+      state.token += 1;
+      state.generating = false;
+      state.answerCount = 0;
+      state.attachments = [];
+      document.getElementById("messages").innerHTML = "";
+      document.getElementById("attachments").innerHTML = "";
+      if (state.conversation) { history.replaceState(null, "", location.pathname + location.search); }
+      state.conversation = null;
+      editor.innerText = "";
+      refresh();
+    });
+
+    refresh();
+  }
+
+  function stopButton() { return document.querySelector("[data-testid='stop-button']"); }
+
+  function setStopButton(visible) {
+    var existing = stopButton();
+    if (visible && !existing) {
+      var button = document.createElement("button");
+      button.setAttribute("data-testid", "stop-button");
+      button.textContent = "Stop";
+      button.addEventListener("click", function () { state.token += 1; state.generating = false; setStopButton(false); });
+      document.getElementById("toolbar").appendChild(button);
+    } else if (!visible && existing) {
+      existing.remove();
+    }
+  }
+
+  function submit() {
+    var editor = document.getElementById("prompt-textarea");
+    var prompt = editor.innerText;
+    if (!prompt.trim() || state.generating) { return; }
+
+    var messages = document.getElementById("messages");
+    var user = document.createElement("div");
+    user.setAttribute("data-message-author-role", "user");
+    user.textContent = prompt;
+    messages.appendChild(user);
+
+    editor.innerText = "";
+    editor.dispatchEvent(new Event("input", { bubbles: true }));
+
+    if (mode("conv") && !state.conversation) {
+      state.conversation = (crypto.randomUUID ? crypto.randomUUID() : String(Date.now()));
+      location.hash = "#c=" + state.conversation;
+    }
+
+    if (mode("login") || mode("captcha")) { return; }
+    if (mode("error") || mode("ratelimit")) { return; }
+
+    state.generating = true;
+    state.token += 1;
+    var token = state.token;
+    setStopButton(true);
+
+    // The page wraps one exchange in a "turn" element, like the real UI: the
+    // answer node holds the text only, and the toolbar is its sibling.
+    var turn = document.createElement("div");
+    turn.className = "turn";
+    turn.setAttribute("data-testid", "conversation-turn");
+    var node = document.createElement("div");
+    node.setAttribute("data-message-author-role", "assistant");
+    var body = document.createElement("div");
+    body.className = "answer-body";
+    node.appendChild(body);
+    turn.appendChild(node);
+    messages.appendChild(turn);
+    state.answerCount += 1;
+    if (mode("rich")) {
+      attachToolbar(turn, prompt);
+    }
+
+    var full = answer(prompt);
+    var draft = mode("rewrite") ? "Draft answer being rewritten" : null;
+    var delay = parseInt(params.get("delay") || "1200", 10);
+    var steps = 22;
+    var written = "";
+
+    if (mode("empty")) {
+      window.setTimeout(function () {
+        if (token !== state.token) { return; }
+        state.generating = false;
+        setStopButton(false);
+      }, delay);
+      return;
+    }
+
+    var index = 0;
+    var timer = window.setInterval(function () {
+      if (token !== state.token) { window.clearInterval(timer); return; }
+      index += 1;
+      var target = full;
+      if (draft && index * 2 < steps) { target = draft; }
+      else if (draft && index === Math.floor(steps / 2) + 1) { written = ""; }
+      var chars = Math.ceil(target.length * (index / steps));
+      written = target.slice(0, chars);
+      body.innerText = written;
+      if (index >= steps) {
+        window.clearInterval(timer);
+        // The settled answer is rendered: the rich modes turn it into HTML,
+        // which is what a plain text capture cannot represent.
+        try {
+          if (mode("rich")) {
+            body.innerHTML = richHtml(prompt);
+          } else {
+            body.innerText = full;
+          }
+        } catch (e) {
+          body.innerText = full;
+        }
+        state.generating = false;
+        setStopButton(false);
+        var send = document.querySelector("[data-testid='send-button']");
+        if (send) { send.disabled = document.getElementById("prompt-textarea").innerText.trim().length === 0; }
+      }
+    }, Math.max(20, Math.floor(delay / steps)));
+  }
+
+  window.fixtureState = state;
+  if (mode("loading")) {
+    window.setTimeout(render, 3000);
+  } else {
+    render();
+  }
+})();
+</script>
+</body>
+</html>