Agent chat: closing the queue at the latest row keeps the last row on the composer

webviews/src/agent-session/acpmux/App.tsx

@@ -1792,6 +1792,7 @@ export function VirtualTranscript({
   needsYou,
   dock,
   queueWithdrawn,
+  queueIds,
   focusComposer,
   openAt,
   onAnchor,
@@ -1823,6 +1824,9 @@ export function VirtualTranscript({
   /// Prompts withdrawn from the queue (snapshot `queueWithdrawn`): no row comes for one whose card
   /// leaves the stack, so the view keeps no room for it.
   queueWithdrawn?: readonly string[];
+  /// IDs from the queue snapshot: a folded prompt has no card in the DOM, but remains queued and
+  /// must not be recorded as withdrawn when the fold changes.
+  queueIds?: readonly string[];
   /// Where a keyboard Jump to latest leaves focus, since the button hides (inert) once there.
   focusComposer?: () => void;
   onToggleActivity: (id: string) => void;
@@ -1921,14 +1925,35 @@ export function VirtualTranscript({
   withdrawn.current = withdrawnSet;
   const dockRef = useRef(dock);
   dockRef.current = dock;
+  const queueSession = useRef(sessionId);
+  queueSession.current = sessionId;
+  /// The chat and the stack `queuedIds` were noted in.
+  const notedIn = useRef<{ sessionId?: string; dock?: HTMLElement | null }>({});
   /// Notes the stack's queued prompts; called first by each size observer (the stack's, and the
-  /// view's, for a stack laid out under the transcript), so the render a size change makes knows.
+  /// view's, for a stack laid out under the transcript), so the render a size change makes knows,
+  /// and by each change of the queue (below). A prompt the queue's fold hides (ComposerQueue
+  /// `data-folded-ids`) is still queued: closing the fold is not its card leaving, and no room is
+  /// kept under the last row for a prompt that stays queued (Leo 2026-10-21: the queue closed left a
+  /// hole over the stack, then the rows dropped).
   const noteQueue = useCallback(() => {
-    const now = new Set(
-      [...(dockRef.current?.querySelectorAll<HTMLElement>(".acpmux-queued") ?? [])].map(
-        (card) => card.dataset.promptId ?? "",
+    const dock = dockRef.current;
+    const now = new Set([
+      ...[...(dock?.querySelectorAll<HTMLElement>(".acpmux-queued") ?? [])].map((card) => card.dataset.promptId ?? ""),
+      ...[...(dock?.querySelectorAll<HTMLElement>("[data-folded-ids]") ?? [])].flatMap((list) =>
+        (list.dataset.foldedIds ?? "").split(" "),
       ),
-    );
+      ...(queueIds ?? []),
+    ]);
+    // Another chat's queue, or another stack, starts over: the last one's prompts never left this
+    // one, and no room is held for them (#24182: switched to a chat with its own queue, the last
+    // chat's prompts read as cards that left, and a prompt withdrawn later kept room as a sent one).
+    if (notedIn.current.sessionId !== queueSession.current || notedIn.current.dock !== dock) {
+      notedIn.current = { sessionId: queueSession.current, dock };
+      queuedIds.current = now;
+      heldFor.current.clear();
+      queueLeft.current = false;
+      return;
+    }
     const left = [...queuedIds.current].filter((id) => !now.has(id));
     queuedIds.current = now;
     if (!left.length) return;
@@ -1937,7 +1962,7 @@ export function VirtualTranscript({
     queueLeft.current = true;
     // Only the size change of this frame is the card leaving.
     requestAnimationFrame(() => requestAnimationFrame(() => (queueLeft.current = false)));
-  }, []);
+  }, [queueIds]);
   useLayoutEffect(() => {
     if (!dock) {
       setDockSpace(0);
@@ -1973,6 +1998,11 @@ export function VirtualTranscript({
     setDockCard(card(space));
     return () => observer.disconnect();
   }, [dock, noteQueue]);
+  // And each time the queue changes, in the commit that draws it. A change that leaves the stack's
+  // size as it was (a prompt the fold hides, or one an opened list's cap cuts off, run by another
+  // client) runs neither observer: still noted as queued, the next resize took it for a card that
+  // left then, and kept room above the stack for FLOOR_HOLD_MS that then glided away (#24182).
+  useLayoutEffect(() => noteQueue(), [sessionId, queueIds, noteQueue]);
   const [width, setWidth] = useState(() => lastTranscriptBox.width);
   // The column's cap (layout.json `chatWidth`): a new one measures every row again.
   const chatWidth = useChatWidth();
@@ -3955,6 +3985,7 @@ function AcpmuxPane() {
       ),
     [clientSnapshot, switchView, catalog],
   );
+  const queueIds = useMemo(() => snapshot.queue.map((entry) => entry.id), [snapshot.queue]);
   // Another chat ends the replay: coming back to this one opens it live.
   if (replaying && snapshot.sessionId !== replaying) setReplaying(undefined);
   // A /btw failure belongs to its chat: another chat drops it.
@@ -7551,6 +7582,7 @@ function AcpmuxPane() {
                                                   // Quick Chat's panel stacks its composer below the transcript.
                                                   dock={quick ? undefined : dock}
                                                   queueWithdrawn={snapshot.queueWithdrawn}
+                                                  queueIds={quick ? undefined : queueIds}
                                                   find={quick ? undefined : find}
                                                   sessionId={
                                                     childRows

webviews/src/agent-session/acpmux/ComposerQueue.tsx

@@ -573,6 +573,16 @@ export function ComposerQueue({
         ref={list}
         className="ui-glass ui-glass-floats acpmux-composer-queue"
         data-unfolded={foldable && !folded ? "" : undefined}
+        // The prompts the fold hides, still queued: the transcript keeps no room for them as it
+        // does for a card that leaves (VirtualTranscript `noteQueue`).
+        data-folded-ids={
+          folded
+            ? shown
+                .slice(visible.length)
+                .map((entry) => entry.id)
+                .join(" ")
+            : undefined
+        }
         // A row that takes focus from the keyboard (keys, a move, ↑ from the prompt) scrolls in whole.
         onFocus={(event) => {
           const row = (event.target as HTMLElement).closest("li");