feat: #61 Plugin system — backend API, sandboxed Web Worker, hooks wired to real app flow, user guide, 47+21 tests

docs/PLUGINS.md

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+# Plugin System — ObsiGate #61
+
+## Overview
+
+ObsiGate's plugin system enables extending the application with custom
+renderers, search filters, and editor actions — all sandboxed for security.
+
+Plugins run in a Web Worker sandbox and communicate with the main app via
+structured `postMessage`. No plugin can access the DOM, localStorage, or
+make network requests without explicit permission.
+
+## Quick Start
+
+### Installing a Plugin
+
+1. Go to **Settings > Plugins** in the sidebar
+2. Click **Install Plugin**
+3. Upload a `.zip` file or a directory containing:
+   - `plugin.json` — the manifest
+   - Your main JS file (entry point specified in `main`)
+
+### Creating a Plugin
+
+Use the **View Template** button in Settings > Plugins to get started.
+
+## Manifest (plugin.json)
+
+```json
+{
+  "name": "my-plugin",
+  "version": "1.0.0",
+  "description": "A brief description of what this plugin does",
+  "author": "your-name",
+  "main": "index.js",
+  "hooks": {
+    "onFileRender": "renderFile",
+    "onSearchFilter": "filterResults",
+    "onEditorAction": "handleAction"
+  },
+  "permissions": ["read_files"],
+  "min_obsigate_version": "2.1.0",
+  "license": "MIT",
+  "homepage": "https://example.com",
+  "repository": "https://github.com/user/plugin"
+}
+```
+
+### Required Fields
+
+| Field         | Type   | Description                                     |
+|---------------|--------|-------------------------------------------------|
+| `name`        | string | Lowercase alphanumeric + hyphens (e.g. `my-plugin`) |
+| `version`     | string | Semantic version (e.g. `1.0.0`, `1.0.0-beta.1`)   |
+| `description` | string | Brief description                                    |
+| `author`      | string | Author name                                          |
+| `main`        | string | Entry point file (relative to plugin root)            |
+
+### Optional Fields
+
+| Field                  | Type   | Default     | Description                              |
+|------------------------|--------|-------------|------------------------------------------|
+| `hooks`                | object | `{}`        | Map of hook name → handler function name |
+| `permissions`          | array  | `[]`        | Required permissions                     |
+| `min_obsigate_version` | string | `"2.1.0"`   | Minimum ObsiGate version                 |
+| `license`              | string | `"MIT"`     | License identifier                       |
+| `homepage`             | string | `null`      | Plugin homepage URL                      |
+| `repository`           | string | `null`      | Source repository URL                    |
+
+## Available Hooks
+
+| Hook              | When it fires                     | Handler signature              |
+|-------------------|-----------------------------------|--------------------------------|
+| `onFileRender`    | Before a file is rendered         | `(ctx) → transformed ctx`      |
+| `onSearchFilter`  | During search result filtering    | `(results) → filtered results` |
+| `onEditorAction`  | When editor action is triggered   | `(action, state) → result`     |
+| `onSidebarItem`   | Sidebar item is rendered          | `(item) → enhanced item`       |
+| `onFileCreate`    | After a file is created           | `(file) → void`                |
+| `onFileDelete`    | After a file is deleted           | `(file) → void`                |
+| `onVaultMount`    | When a vault is mounted           | `(vault) → void`               |
+
+## Permissions
+
+Plugins must declare the permissions they need. The sandbox enforces these
+restrictions at runtime.
+
+| Permission            | Description                                      |
+|-----------------------|--------------------------------------------------|
+| `read_files`          | Read file contents from the vault                 |
+| `write_files`         | Write/create files in the vault                   |
+| `read_vault_metadata` | Access vault configuration and metadata           |
+| `network_request`     | Make HTTP requests to external services           |
+| `ui_notify`           | Show toast notifications in the UI                |
+| `access_clipboard`    | Read/write to the system clipboard                |
+
+## Security Model
+
+### Sandbox Architecture
+
+```
+┌─────────────────────────────────┐
+│  Main App (browser context)     │
+│                                 │
+│  PluginManager                  │
+│    ├── install/uninstall        │
+│    ├── enable/disable           │
+│    └── hook dispatch            │
+│         │ postMessage (C3)      │
+│         ▼                       │
+│  ┌─────────────────────────┐    │
+│  │  Web Worker Sandbox     │    │
+│  │  (no DOM, no localStorage│   │
+│  │   no network by default) │   │
+│  │                          │   │
+│  │  Plugin code executes    │   │
+│  │  here with structured    │   │
+│  │  message passing only    │   │
+│  └─────────────────────────┘    │
+└─────────────────────────────────┘
+```
+
+### Security Guarantees
+
+- **C1**: Manifest validation (name format, semver, allowed hooks/permissions)
+- **C2**: Vault isolation — plugins are scoped to a single vault
+- **C3**: Web Worker sandbox — no DOM, no `localStorage`, no `importScripts`
+- **C4**: ZIP validation — path traversal, file count, size limits
+- **C5**: Directory validation — manifest + entry point presence
+- **C6**: Permission enforcement at sandbox boundary
+
+### Limits
+
+- Max 50 plugins per vault
+- Max 500 KB per plugin file
+- Max 100 files per plugin ZIP
+- No dynamic `import()` or `eval()`
+
+## Plugin Storage
+
+Plugins are installed under `<vault>/.obsigate-plugins/<plugin-name>/`:
+```
+.obsigate-plugins/
+  my-plugin/
+    plugin.json      # manifest
+    index.js         # entry point
+    .disabled        # marker file (created when disabled)
+```
+
+## API Reference
+
+### Backend Endpoints
+
+| Method | Endpoint                        | Auth    | Description              |
+|--------|---------------------------------|---------|--------------------------|
+| GET    | `/api/plugins`                  | require_auth | List installed plugins |
+| POST   | `/api/plugins/install`          | require_admin | Install from ZIP      |
+| DELETE | `/api/plugins/{name}`           | require_admin | Uninstall plugin      |
+| POST   | `/api/plugins/{name}/enable`    | require_admin | Enable plugin         |
+| POST   | `/api/plugins/{name}/disable`   | require_admin | Disable plugin        |
+| GET    | `/api/plugins/{name}/code/{file}` | require_auth | Get plugin code     |
+| GET    | `/api/plugins/{name}/hooks`     | require_auth | Get plugin hooks     |
+| GET    | `/api/plugins/template`         | require_auth | Get plugin template  |
+
+### Frontend Module (`plugins.js`)
+
+```javascript
+import { PluginManager } from './plugins.js';
+
+// Install
+await PluginManager.installPlugin(manifest, code);
+
+// Enable/Disable
+await PluginManager.enablePlugin('my-plugin');
+await PluginManager.disablePlugin('my-plugin');
+
+// Uninstall
+await PluginManager.uninstallPlugin('my-plugin');
+
+// Get code for sandbox
+const code = await PluginManager.getPluginCode('my-plugin', 'index.js');
+
+// List
+const plugins = await PluginManager.getCachedPlugins();
+```
+
+## Creating Your First Plugin
+
+1. Create a directory with `plugin.json`:
+
+```json
+{
+  "name": "hello-world",
+  "version": "1.0.0",
+  "description": "My first ObsiGate plugin",
+  "author": "you",
+  "main": "index.js",
+  "hooks": {
+    "onFileRender": "render"
+  },
+  "permissions": ["read_files", "ui_notify"]
+}
+```
+
+2. Create `index.js`:
+
+```javascript
+export function render(ctx) {
+  // Add a custom header to rendered markdown
+  if (ctx.content && ctx.path.endsWith('.md')) {
+    ctx.content = `> 📝 Plugin: hello-world\n\n${ctx.content}`;
+  }
+  return ctx;
+}
+```
+
+3. Zip the directory and install via Settings > Plugins > Install Plugin.