fix(assistant): #91 maintien de l'ancre en haut pendant le streaming, libération au scroll manuel

frontend/js/bookslm.js

@@ -122,6 +122,9 @@ class BooksLM {
     this._menuSeq = 0;
     // Timer that hides the "done" activity indicator after a short delay.
     this._activityHideTimer = null;
+    // True while the latest question should stay pinned to the top of the
+    // thread (cleared as soon as the user scrolls manually).
+    this._pinnedTurn = false;
     // Cache of every indexed path per vault, backing instant `@` filtering.
     this._pathCache = null;
     this._pathCacheVault = null;
@@ -887,6 +890,14 @@ class BooksLM {
       this._activatePath(path, kind);
     });
 
+    // A manual scroll releases the top-pinning of the latest question.
+    const messagesEl = panel.querySelector('.bookslm-messages');
+    if (messagesEl) {
+      const unpin = () => { this._pinnedTurn = false; };
+      messagesEl.addEventListener('wheel', unpin, { passive: true });
+      messagesEl.addEventListener('touchmove', unpin, { passive: true });
+    }
+
     // Close the session / command menus when clicking elsewhere in the panel.
     panel.addEventListener('click', (e) => {
       if (!e.target.closest('.bookslm-history-menu') && !e.target.closest('.bookslm-btn-history')) {
@@ -1793,16 +1804,20 @@ class BooksLM {
     }
 
     if (opts.anchor) this._anchorLatestUser();
+    else if (this._isLoading && this._pinnedTurn) this._anchorLatestUser({ instant: true });
     else container.scrollTop = prevTop;
   }
 
   /**
    * Scroll the messages window so the most recent user post sits at the very
    * top of the viewport (its `scroll-margin-top` keeps a breathing gap),
-   * reproducing Notion-AI's conversation anchoring.
+   * reproducing Notion-AI's conversation anchoring. The pin stays active
+   * while the answer streams, so the question never leaves the top — until
+   * the user scrolls manually (see the wheel/touch listeners in `_render()`).
    */
-  _anchorLatestUser() {
+  _anchorLatestUser(opts = {}) {
     if (!this._panel) return;
+    this._pinnedTurn = true;
     const container = this._panel.querySelector('.bookslm-messages');
     if (!container) return;
     const users = container.querySelectorAll('.bookslm-msg.user');
@@ -1810,9 +1825,10 @@ class BooksLM {
     // Fallback (admin notes with no user post): anchor the newest message.
     const el = users[users.length - 1] || all[all.length - 1] || container.firstElementChild;
     if (!el) return;
+    const behavior = opts.instant ? 'auto' : 'smooth';
     const apply = () => {
       try {
-        el.scrollIntoView({ behavior: 'smooth', block: 'start' });
+        el.scrollIntoView({ behavior, block: 'start' });
       } catch {
         const cRect = container.getBoundingClientRect();
         const eRect = el.getBoundingClientRect();