fix(desktop): MessageList anchors via direct scrollTop + flex-1 height

scrollToIndex raced the virtualizer's own layout effect and depended on size estimates, leaving the list pinned at the top on open (and flickering as it settled). Drive scrollTop = scrollHeight directly for the bottom case (order-independent, true bottom) and re-pin on measure; switch the scroll root from h-full to flex-1 min-h-0 so it always has a bounded, scrollable height.

apps/desktop/src/components/MessageList.tsx

@@ -9,7 +9,7 @@ import {
   type ReactNode,
 } from 'react';
 
-import { isNearBottom, isNearTop, type Anchor } from '../lib/scrollController';
+import { isNearBottom, isNearTop } from '../lib/scrollController';
 import type { VirtuosoRow } from '../pages/ConversationPage';
 
 export interface MessageListHandle {
@@ -71,36 +71,57 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
       : { scrollTop: 0, scrollHeight: 0, clientHeight: 0 };
   }, []);
 
-  const applyAnchor = useCallback(
-    (anchor: Anchor) => {
-      virtualizer.scrollToIndex(anchor.index, { align: anchor.align });
-      // Re-apply next frame: dynamic measurement settles after first paint, so a
-      // single scrollToIndex can land a few px off. Still hidden here → invisible.
-      requestAnimationFrame(() => virtualizer.scrollToIndex(anchor.index, { align: anchor.align }));
-    },
-    [virtualizer],
-  );
+  const pinToBottom = useCallback(() => {
+    const el = scrollElRef.current;
+    if (el) el.scrollTop = el.scrollHeight;
+  }, []);
 
-  // Deferred reveal: when ready, anchor (before paint) then reveal.
+  // Deferred reveal: when ready, position at the anchor (before paint), let one
+  // measure cycle settle (just-rendered rows get their real heights), re-pin,
+  // then reveal — so what appears is already final.
+  //
+  // For the bottom case we drive scrollTop = scrollHeight DIRECTLY rather than
+  // virtualizer.scrollToIndex: scrollToIndex depends on the virtualizer's own
+  // layout effect having run first (effect ordering is not guaranteed) and on its
+  // size estimates — when it lost that race the list stayed pinned at the TOP.
+  // Driving the DOM scrollTop is order-independent and always lands at the true
+  // bottom; the stick-to-bottom effect re-pins as the heights settle.
   useLayoutEffect(() => {
     if (!ready || revealed || rows.length === 0) return;
-    const anchor: Anchor =
-      initialAnchor.type === 'bottom'
-        ? { index: rows.length - 1, align: 'end' }
-        : { index: Math.max(0, Math.min(initialAnchor.index, rows.length - 1)), align: 'start' };
-    applyAnchor(anchor);
-    atBottomRef.current = initialAnchor.type === 'bottom';
+    const el = scrollElRef.current;
+    if (!el) return;
+    if (initialAnchor.type === 'bottom') {
+      pinToBottom();
+      atBottomRef.current = true;
+    } else {
+      virtualizer.scrollToIndex(Math.max(0, Math.min(initialAnchor.index, rows.length - 1)), {
+        align: 'start',
+      });
+      atBottomRef.current = false;
+    }
     onAtBottomChange?.(atBottomRef.current);
+    requestAnimationFrame(() => {
+      if (atBottomRef.current) {
+        pinToBottom();
+      } else if (initialAnchor.type === 'row') {
+        // Re-apply after the virtualizer's own layout effect has run + measured,
+        // so the saved scrolled-up row lands accurately (same ordering caveat as
+        // 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));
+    });
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [ready, rows.length]);
 
-  // Stick-to-bottom: when content grows and we were at the bottom, re-pin.
+  // 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(() => {
-    if (!revealed) return;
-    if (atBottomRef.current) {
-      virtualizer.scrollToIndex(rows.length - 1, { align: 'end' });
-    }
+    if (!atBottomRef.current) return;
+    pinToBottom();
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [rows.length, virtualizer.getTotalSize()]);
 
@@ -138,7 +159,7 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
     () => ({
       scrollToBottom: () => {
         atBottomRef.current = true;
-        virtualizer.scrollToIndex(rows.length - 1, { align: 'end' });
+        pinToBottom();
       },
       scrollToRow: (index, align = 'center') => {
         virtualizer.scrollToIndex(index, { align });
@@ -154,7 +175,7 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
     <div
       ref={scrollElRef}
       onScroll={handleScroll}
-      className="h-full overflow-y-auto"
+      className="min-h-0 flex-1 overflow-y-auto"
       style={{ opacity: revealed ? 1 : 0, position: 'relative' }}
     >
       <div style={{ height: virtualizer.getTotalSize(), position: 'relative', width: '100%' }}>