chore(desktop): release v0.21.9

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/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@chat-app/desktop",
-  "version": "0.21.6",
+  "version": "0.21.9",
   "private": true,
   "description": "Electron desktop client (Windows / macOS / Linux)",
   "type": "module",

apps/desktop/src/components/MessageList.tsx

@@ -2,14 +2,17 @@ import { useVirtualizer } from '@tanstack/react-virtual';
 import {
   forwardRef,
   useCallback,
+  useEffect,
   useImperativeHandle,
   useLayoutEffect,
   useRef,
   useState,
+  type MutableRefObject,
   type ReactNode,
+  type RefObject,
 } 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 {
@@ -51,6 +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);
@@ -71,39 +81,81 @@ 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) return;
+    programmaticRef.current = performance.now();
+    el.scrollTop = el.scrollHeight;
+  }, []);
 
-  // Deferred reveal: when ready, anchor (before paint) then reveal.
+  // Re-pin to the true bottom whenever the content (or viewport) resizes while
+  // sticking. ResizeObserver fires after layout / before paint, so as rows measure
+  // 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
+  // getTotalSize effect lagged a frame, letting onScroll wrongly flip atBottom).
+  useEffect(() => {
+    const el = scrollElRef.current;
+    if (!el) return;
+    const ro = new ResizeObserver(() => {
+      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 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;
+    const rowIdx = Math.max(
+      0,
+      Math.min(initialAnchor.type === 'row' ? initialAnchor.index : 0, rows.length - 1),
+    );
+    if (initialAnchor.type === 'bottom') {
+      stickRef.current = true;
+      atBottomRef.current = true;
+      pinToBottom();
+    } else {
+      stickRef.current = false;
+      atBottomRef.current = false;
+      virtualizer.scrollToIndex(rowIdx, { align: 'start' });
+    }
     onAtBottomChange?.(atBottomRef.current);
-    requestAnimationFrame(() => setRevealed(true));
+    let prevSH = -1;
+    const settle = (attempts: number): void => {
+      const e = scrollElRef.current;
+      if (!e) {
+        setRevealed(true);
+        return;
+      }
+      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: when content grows and we were at the bottom, re-pin.
-  useLayoutEffect(() => {
-    if (!revealed) return;
-    if (atBottomRef.current) {
-      virtualizer.scrollToIndex(rows.length - 1, { align: 'end' });
-    }
-    // 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.
@@ -122,8 +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);
@@ -137,8 +194,9 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
     ref,
     () => ({
       scrollToBottom: () => {
+        stickRef.current = true;
         atBottomRef.current = true;
-        virtualizer.scrollToIndex(rows.length - 1, { align: 'end' });
+        pinToBottom();
       },
       scrollToRow: (index, align = 'center') => {
         virtualizer.scrollToIndex(index, { align });
@@ -151,11 +209,19 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
   const items = virtualizer.getVirtualItems();
 
   return (
+    <>
+      <ScrollDebugOverlay
+        scrollElRef={scrollElRef}
+        getTotal={() => virtualizer.getTotalSize()}
+        atBottomRef={atBottomRef}
+        revealed={revealed}
+        ready={ready}
+      />
       <div
         ref={scrollElRef}
         onScroll={handleScroll}
-      className="h-full overflow-y-auto"
-      style={{ opacity: revealed ? 1 : 0, position: 'relative' }}
+        className="min-h-0 flex-1 overflow-y-auto"
+        style={{ opacity: revealed ? 1 : 0, position: 'relative', overflowAnchor: 'none' }}
       >
       <div style={{ height: virtualizer.getTotalSize(), position: 'relative', width: '100%' }}>
         {items.map((vi) => (
@@ -178,5 +244,57 @@ export const MessageList = forwardRef<MessageListHandle, MessageListProps>(funct
         {/* 12px bottom breathing space (matches the old Virtuoso Footer). */}
         <div style={{ height: 12 }} />
       </div>
+    </>
   );
 });
+
+interface ScrollDebugOverlayProps {
+  scrollElRef: RefObject<HTMLDivElement>;
+  getTotal: () => number;
+  atBottomRef: MutableRefObject<boolean>;
+  revealed: boolean;
+  ready: boolean;
+}
+
+// TEMP on-screen debug readout — remove after the chat-switch scroll bug is fixed.
+function ScrollDebugOverlay({
+  scrollElRef,
+  getTotal,
+  atBottomRef,
+  revealed,
+  ready,
+}: ScrollDebugOverlayProps) {
+  const [, force] = useState(0);
+  useEffect(() => {
+    let raf = 0;
+    const loop = () => {
+      force((n) => (n + 1) % 1_000_000);
+      raf = requestAnimationFrame(loop);
+    };
+    raf = requestAnimationFrame(loop);
+    return () => cancelAnimationFrame(raf);
+  }, []);
+  const el = scrollElRef.current;
+  const sh = el?.scrollHeight ?? 0;
+  const ch = el?.clientHeight ?? 0;
+  const st = el ? Math.round(el.scrollTop) : 0;
+  return (
+    <div
+      style={{
+        position: 'fixed',
+        top: 8,
+        right: 8,
+        zIndex: 99999,
+        background: 'rgba(0,0,0,0.82)',
+        color: '#19ff8a',
+        font: '11px/1.4 monospace',
+        padding: '6px 9px',
+        borderRadius: 5,
+        pointerEvents: 'none',
+        whiteSpace: 'pre',
+      }}
+    >
+      {`scrollHeight=${sh}  clientHeight=${ch}\nscrollTop=${st}\ntotalSize=${Math.round(getTotal())}\nSCROLLABLE=${sh > ch + 4 ? 'YES' : 'NO'}\natBottom=${atBottomRef.current}  revealed=${revealed}  ready=${ready}`}
+    </div>
+  );
+}