diff --git a/frontend/js/ai-fab.js b/frontend/js/ai-fab.js
new file mode 100644
index 0000000..382ab83
--- /dev/null
+++ b/frontend/js/ai-fab.js
@@ -0,0 +1,79 @@
+// ObsiGate — Floating Action Button (FAB) to open/close the BooksLM AI sidebar.
+// Always visible in the bottom-right corner; hides while BooksLM is open.
+import booksLM from './bookslm.js';
+import { state } from './state.js';
+import { showToast, TabManager } from './ui.js';
+import { t } from './i18n.js';
+import { safeCreateIcons } from './utils.js';
+
+let _fab = null;
+
+// Mirror palette.js getCurrentFile(): prefer the active tab, then fall back to state.
+function getCurrentFile() {
+  const id = TabManager._activeTabId;
+  if (id) {
+    const tab = TabManager._tabs.find((x) => x.id === id);
+    if (tab) return { vault: tab.vault, path: tab.path };
+  }
+  if (state.currentVault && state.currentPath) return { vault: state.currentVault, path: state.currentPath };
+  return null;
+}
+
+// The BooksLM panel is considered visible when it has `.open` without `.hidden`
+// (the header toggle collapses it off-screen via `.hidden`).
+function isBooksLmVisible() {
+  const panel = document.querySelector('.bookslm-panel');
+  return !!(panel && panel.classList.contains('open') && !panel.classList.contains('hidden'));
+}
+
+function syncVisibility() {
+  if (!_fab) return;
+  const visible = isBooksLmVisible();
+  _fab.hidden = visible;
+  const label = visible ? t('fab.close') : t('fab.open');
+  _fab.title = label;
+  _fab.setAttribute('aria-label', label);
+}
+
+async function onClick() {
+  const f = getCurrentFile();
+  if (!f) {
+    showToast(t('toast.no_open_file'), 'error');
+    return;
+  }
+
+  const sameDir = booksLM._isOpen && booksLM._vault === f.vault && booksLM._directory === f.path;
+  if (sameDir) {
+    // Already open for this directory: re-show a collapsed panel, or close it.
+    const panel = document.querySelector('.bookslm-panel');
+    if (panel && panel.classList.contains('hidden')) {
+      booksLM._toggleSidebar();
+    } else {
+      booksLM.close();
+    }
+    return;
+  }
+
+  await booksLM.open(f.vault, f.path);
+}
+
+export function initAIFab() {
+  if (_fab) return;
+
+  const btn = document.createElement('button');
+  btn.type = 'button';
+  btn.id = 'ai-fab';
+  btn.className = 'ai-fab';
+  btn.innerHTML = '<i data-lucide="bot" style="width:24px;height:24px"></i>';
+  document.body.appendChild(btn);
+  _fab = btn;
+
+  btn.addEventListener('click', onClick);
+  document.addEventListener('bookslm:opened', syncVisibility);
+  document.addEventListener('bookslm:closed', syncVisibility);
+
+  if (typeof safeCreateIcons === 'function') safeCreateIcons();
+  syncVisibility();
+}
+
+export default initAIFab;
diff --git a/frontend/js/app.js b/frontend/js/app.js
index 582c790..8b0998b 100644
--- a/frontend/js/app.js
+++ b/frontend/js/app.js
@@ -5,6 +5,8 @@
 import * as UI from './ui.js';
 import * as Utils from './utils.js';
 import { initI18n, t } from './i18n.js';
+import { state } from './state.js';
+import { initAIFab } from './ai-fab.js';
 
 // Wire up AI toolbar toast (avoids circular import in utils.js)
 window._obsigateShowToast = UI.showToast;
@@ -99,6 +101,7 @@ async function init() {
   initMermaid();
   setupFocusMode();
   Utils.safeCreateIcons();
+  initAIFab();
 }
 
 document.addEventListener("DOMContentLoaded", () => {
@@ -111,15 +114,16 @@ document.addEventListener("DOMContentLoaded", () => {
     window.__OBSIGATE_BOOTED = true;
     if (typeof window.__obsigateBootReady === "function") window.__obsigateBootReady();
   }
-  // Show version in header
+  // Show version in header — always visible, fallback before the async fetch
+  const versionBadge = document.getElementById('version-badge');
+  if (versionBadge) {
+    versionBadge.textContent = window.__OBSIGATE_VERSION || state.APP_VERSION || 'dev';
+  }
   fetch('/api/health')
     .then(r => r.json())
     .then(d => {
       const badge = document.getElementById('version-badge');
-      if (badge && d.version) {
-        badge.textContent = d.version;
-        badge.style.display = 'inline-block';
-      }
+      if (badge && d.version) badge.textContent = d.version;
     })
     .catch(() => {});
 });
diff --git a/frontend/js/bookslm.js b/frontend/js/bookslm.js
index d2ec5b3..39caefb 100644
--- a/frontend/js/bookslm.js
+++ b/frontend/js/bookslm.js
@@ -44,14 +44,17 @@ class BooksLM {
     // Open with animation
     requestAnimationFrame(() => {
       this._panel.classList.add('open');
+      let hidden = false;
       // Apply persisted hidden state (user toggled off in a previous session)
       try {
         const savedHidden = localStorage.getItem('obsigate-bookslm-hidden');
         if (savedHidden === 'true') {
           this._panel.classList.add('hidden');
           this._updateToggleIcon();
+          hidden = true;
         }
       } catch { /* */ }
+      document.dispatchEvent(new CustomEvent(hidden ? 'bookslm:closed' : 'bookslm:opened', { detail: { vault, directory } }));
     });
     this._isOpen = true;
 
@@ -79,6 +82,7 @@ class BooksLM {
     if (!this._panel || !this._isOpen) return;
     this._panel.classList.remove('open');
     this._isOpen = false;
+    document.dispatchEvent(new CustomEvent('bookslm:closed'));
     // Abort any in-flight request
     if (this._abortCtrl) {
       this._abortCtrl.abort();
@@ -102,6 +106,7 @@ class BooksLM {
       localStorage.setItem('obsigate-bookslm-hidden', isHidden ? 'true' : 'false');
     } catch { /* */ }
     this._updateToggleIcon();
+    document.dispatchEvent(new CustomEvent(isHidden ? 'bookslm:closed' : 'bookslm:opened'));
   }
 
   /**
diff --git a/frontend/locales/en.json b/frontend/locales/en.json
index ee5ac4a..127644f 100644
--- a/frontend/locales/en.json
+++ b/frontend/locales/en.json
@@ -1599,5 +1599,7 @@
   "bookslm.context_too_large": "Directory too large — some files were truncated",
   "bookslm.source": "Source",
   "palette.bookslm_open": "BooksLM: Open for current directory",
-  "palette.bookslm_new": "BooksLM: New conversation"
+  "palette.bookslm_new": "BooksLM: New conversation",
+  "fab.open": "Open AI assistant",
+  "fab.close": "Close AI assistant"
 }
diff --git a/frontend/locales/fr.json b/frontend/locales/fr.json
index 84b7839..fd5e234 100644
--- a/frontend/locales/fr.json
+++ b/frontend/locales/fr.json
@@ -1599,5 +1599,7 @@
   "bookslm.context_too_large": "Répertoire trop volumineux — certains fichiers ont été tronqués",
   "bookslm.source": "Source",
   "palette.bookslm_open": "BooksLM: Ouvrir pour le répertoire courant",
-  "palette.bookslm_new": "BooksLM: Nouvelle conversation"
+  "palette.bookslm_new": "BooksLM: Nouvelle conversation",
+  "fab.open": "Ouvrir l'assistant AI",
+  "fab.close": "Fermer l'assistant AI"
 }
diff --git a/frontend/style.css b/frontend/style.css
index 18dcb1b..4f490a4 100644
--- a/frontend/style.css
+++ b/frontend/style.css
@@ -522,15 +522,16 @@ a:hover {
   background: color-mix(in srgb, var(--accent) 10%, transparent);
 }
 
-/* Version badge in header */
+/* Version badge in header — always visible */
 .version-badge {
-  display: none;
-  font-size: 10px;
-  color: var(--text-muted);
-  padding: 2px 8px;
+  display: inline-block;
+  font-size: 11px;
+  color: var(--text-secondary);
+  font-weight: 500;
+  padding: 3px 10px;
   border-radius: 10px;
-  background: color-mix(in srgb, var(--text-muted) 8%, transparent);
-  border: 1px solid color-mix(in srgb, var(--text-muted) 15%, transparent);
+  background: color-mix(in srgb, var(--text-secondary) 10%, transparent);
+  border: 1px solid color-mix(in srgb, var(--text-secondary) 20%, transparent);
   font-family: var(--font-mono, monospace);
   white-space: nowrap;
   cursor: default;
@@ -9077,3 +9078,33 @@ body.popup-mode .content-area {
 @media (max-width: 768px) {
   .bookslm-panel { width: 100%; }
 }
+
+/* ── AI Floating Action Button ───────────────────────── */
+.ai-fab {
+  position: fixed;
+  bottom: 24px;
+  right: 24px;
+  width: 52px;
+  height: 52px;
+  border-radius: 50%;
+  background: var(--accent);
+  color: #fff;
+  border: none;
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 99;
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
+  transition: transform 200ms ease, opacity 200ms ease;
+  padding: 0;
+}
+.ai-fab:hover {
+  transform: scale(1.08);
+}
+.ai-fab:active {
+  transform: scale(0.96);
+}
+.ai-fab[hidden] {
+  display: none;
+}
diff --git a/tests/frontend/unit.test.mjs b/tests/frontend/unit.test.mjs
index a56be78..744db7d 100644
--- a/tests/frontend/unit.test.mjs
+++ b/tests/frontend/unit.test.mjs
@@ -187,6 +187,25 @@ function testAdminModuleSyntax() {
   console.log('  ✓ admin.js parses without syntax errors');
 }
 
+// ── Test ai-fab.js (FAB — Floating Action Button) ─────────────────────────
+const AIFAB_PATH = join(JS_DIR, 'ai-fab.js');
+
+function testAIFabModuleExists() {
+  const content = readFileSync(AIFAB_PATH, 'utf-8');
+  assert.ok(content.length > 0, 'ai-fab.js must be a non-empty file');
+  assert.ok(/from\s+['"]\.\/bookslm\.js['"]/.test(content), 'ai-fab.js must import from ./bookslm.js');
+  assert.ok(/from\s+['"]\.\/state\.js['"]/.test(content), 'ai-fab.js must import from ./state.js');
+  assert.ok(/from\s+['"]\.\/i18n\.js['"]/.test(content), 'ai-fab.js must import from ./i18n.js');
+  console.log('  ✓ ai-fab.js exists and imports the expected modules');
+}
+
+function testAIFabModuleExports() {
+  const content = readFileSync(AIFAB_PATH, 'utf-8');
+  const exported = _collectExportedNames(content);
+  assert.ok(exported.has('initAIFab'), 'ai-fab.js must export initAIFab');
+  console.log('  ✓ ai-fab.js exports initAIFab');
+}
+
 // ── Run all tests ──────────────────────────────────────────────────────────
 async function main() {
   let passed = 0, failed = 0;
@@ -199,6 +218,8 @@ async function main() {
     ['admin module exists', testAdminModuleExists],
     ['admin module exports', testAdminModuleExports],
     ['admin module syntax', testAdminModuleSyntax],
+    ['ai-fab module exists', testAIFabModuleExists],
+    ['ai-fab module exports', testAIFabModuleExports],
   ];
 
   for (const [name, fn] of tests) {