fix(desktop): MessageList sticks to bottom via ResizeObserver + scroll guard

Data from the on-screen overlay showed SCROLLABLE=YES but scrollTop=84/0 and atBottom=false: the initial pin happened before rows finished measuring, then a measurement reflow fired onScroll with the stale (top) scrollTop, flipping atBottom=false and disabling re-pinning, so the list never reached the bottom. Fix: a ResizeObserver re-pins to the true bottom as the content measures/grows; a programmatic-scroll guard makes onScroll ignore the scrolls we cause (so measurement reflows no longer flip the stick intent); overflow-anchor:none so the browser doesn't fight us; reveal waits for the height to settle. Overlay kept for one more verification pass.

apps/desktop/src/components/MessageList.tsx

@@ -54,6 +54,13 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
   const scrollElRef = useRef<HTMLDivElement>(null);
   const [revealed, setRevealed] = useState(false);
   const atBottomRef = useRef(true);
+  // Intent: keep the view pinned to the bottom? Only a genuine user scroll flips
+  // this — measurement reflows must not.
+  const stickRef = useRef(true);
+  // Guard: scroll events we cause (pin / measure re-pin) fire a tick after we set
+  // scrollTop. handleScroll ignores events within this window so a measurement
+  // reflow is never mistaken for the user scrolling up.
+  const programmaticRef = useRef(0);
   // Load-older preservation: remember the first row key + scrollHeight so a
   // prepend can be detected and the viewport restored.
   const prevFirstKeyRef = useRef<string | null>(null);
@@ -77,71 +84,78 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
   const pinToBottom = useCallback(() => {
     const el = scrollElRef.current;
     if (!el) return;
-    const before = el.scrollTop;
+    programmaticRef.current = performance.now();
     el.scrollTop = el.scrollHeight;
-    // eslint-disable-next-line no-console
-    console.log(
-      `[scroll] pin sh=${el.scrollHeight} ch=${el.clientHeight} top:${Math.round(before)}->${Math.round(el.scrollTop)}`,
-    );
   }, []);
 
-  // Deferred reveal: when ready, position at the anchor (before paint), let one
+  // Re-pin to the true bottom whenever the content (or viewport) resizes while
-  // measure cycle settle (just-rendered rows get their real heights), re-pin,
+  // sticking. ResizeObserver fires after layout / before paint, so as rows measure
-  // then reveal — so what appears is already final.
+  // and the list grows the bottom stays pinned with no stale frame — THIS is what
-  //
+  // carries the list to the bottom through the measure settle (the old
-  // For the bottom case we drive scrollTop = scrollHeight DIRECTLY rather than
+  // getTotalSize effect lagged a frame, letting onScroll wrongly flip atBottom).
-  // virtualizer.scrollToIndex: scrollToIndex depends on the virtualizer's own
+  useEffect(() => {
-  // layout effect having run first (effect ordering is not guaranteed) and on its
+    const el = scrollElRef.current;
-  // size estimates — when it lost that race the list stayed pinned at the TOP.
+    if (!el) return;
-  // Driving the DOM scrollTop is order-independent and always lands at the true
+    const ro = new ResizeObserver(() => {
-  // bottom; the stick-to-bottom effect re-pins as the heights settle.
+      const e = scrollElRef.current;
+      if (stickRef.current && e) {
+        programmaticRef.current = performance.now();
+        e.scrollTop = e.scrollHeight;
+      }
+    });
+    ro.observe(el);
+    const inner = el.firstElementChild;
+    if (inner) ro.observe(inner);
+    return () => ro.disconnect();
+  }, []);
+
+  // Deferred reveal: when ready, pin to the anchor and keep pinning each frame
+  // until the list height has SETTLED (rows measure over 1-2 frames and grow it),
+  // THEN reveal — so what appears is already at the final bottom, with no
+  // top-then-jump flicker. The ResizeObserver above keeps it pinned afterwards.
   useLayoutEffect(() => {
     if (!ready || revealed || rows.length === 0) return;
     const el = scrollElRef.current;
     if (!el) return;
-    // eslint-disable-next-line no-console
+    const rowIdx = Math.max(
-    console.log(
+      0,
-      `[scroll] reveal anchor=${initialAnchor.type} rows=${rows.length} total=${Math.round(virtualizer.getTotalSize())} sh=${el.scrollHeight} ch=${el.clientHeight}`,
+      Math.min(initialAnchor.type === 'row' ? initialAnchor.index : 0, rows.length - 1),
     );
     if (initialAnchor.type === 'bottom') {
-      pinToBottom();
+      stickRef.current = true;
       atBottomRef.current = true;
+      pinToBottom();
     } else {
-      virtualizer.scrollToIndex(Math.max(0, Math.min(initialAnchor.index, rows.length - 1)), {
+      stickRef.current = false;
-        align: 'start',
-      });
       atBottomRef.current = false;
+      virtualizer.scrollToIndex(rowIdx, { align: 'start' });
     }
     onAtBottomChange?.(atBottomRef.current);
-    requestAnimationFrame(() => {
+    let prevSH = -1;
-      if (atBottomRef.current) {
+    const settle = (attempts: number): void => {
-        pinToBottom();
+      const e = scrollElRef.current;
-      } else if (initialAnchor.type === 'row') {
+      if (!e) {
-        // Re-apply after the virtualizer's own layout effect has run + measured,
+        setRevealed(true);
-        // so the saved scrolled-up row lands accurately (same ordering caveat as
+        return;
-        // the bottom case, handled here by deferring a frame).
-        virtualizer.scrollToIndex(Math.max(0, Math.min(initialAnchor.index, rows.length - 1)), {
-          align: 'start',
-        });
       }
-      requestAnimationFrame(() => setRevealed(true));
+      if (stickRef.current) {
-    });
+        programmaticRef.current = performance.now();
+        e.scrollTop = e.scrollHeight;
+      } else {
+        virtualizer.scrollToIndex(rowIdx, { align: 'start' });
+      }
+      const sh = e.scrollHeight;
+      if (sh === prevSH || attempts <= 0) {
+        setRevealed(true);
+      } else {
+        prevSH = sh;
+        requestAnimationFrame(() => settle(attempts - 1));
+      }
+    };
+    requestAnimationFrame(() => settle(10));
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [ready, rows.length]);
 
-  // Stick-to-bottom: whenever content grows (new row OR a measured row got
-  // taller) and we were at the bottom, re-pin to the true bottom. Runs while
-  // hidden too, so the list stays pinned through the initial measure settle.
-  useLayoutEffect(() => {
-    // eslint-disable-next-line no-console
-    console.log(
-      `[scroll] stick? atBottom=${atBottomRef.current} total=${Math.round(virtualizer.getTotalSize())} revealed=${revealed}`,
-    );
-    if (!atBottomRef.current) return;
-    pinToBottom();
-    // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [rows.length, virtualizer.getTotalSize()]);
-
   // Load-older preservation: if rows were prepended (first key changed and the
   // user is near the top), restore scrollTop by the height delta so the viewport
   // stays put instead of jumping.
@@ -160,8 +174,13 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
   }, [rows]);
 
   const handleScroll = useCallback(() => {
+    // Ignore scroll events we triggered (pin / measure re-pin); they fire a tick
+    // after we set scrollTop. Only a genuine user scroll updates the stick intent —
+    // otherwise a measurement reflow wrongly flips atBottom and stops the pinning.
+    if (performance.now() - programmaticRef.current < 120) return;
     const m = readMetrics();
     const atBottom = isNearBottom(m, atBottomThreshold);
+    stickRef.current = atBottom;
     if (atBottom !== atBottomRef.current) {
       atBottomRef.current = atBottom;
       onAtBottomChange?.(atBottom);
@@ -175,6 +194,7 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
     ref,
     () => ({
       scrollToBottom: () => {
+        stickRef.current = true;
         atBottomRef.current = true;
         pinToBottom();
       },
@@ -201,7 +221,7 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
         ref={scrollElRef}
         onScroll={handleScroll}
         className="min-h-0 flex-1 overflow-y-auto"
-        style={{ opacity: revealed ? 1 : 0, position: 'relative' }}
+        style={{ opacity: revealed ? 1 : 0, position: 'relative', overflowAnchor: 'none' }}
       >
       <div style={{ height: virtualizer.getTotalSize(), position: 'relative', width: '100%' }}>
         {items.map((vi) => (