fix(chat): a finished turn ends without a Stop hook; Stop no longer flickers

Claude Code skips the Stop hook in roughly one turn in fifteen (only the
prompt-suggestion helper's SubagentStop arrives), so the main agent stayed
"working" until the idle Notification a minute later and the chat kept
showing Stop on a finished answer. The transcript's turn_duration entry is
now an end of turn too: one newer than the session's last prompt, read
while main still works with no tool open, lands it in Waiting like Stop.

The chat's Stop button now drops to Send only after every busy signal has
been quiet for 2.5 s (Stop pressed still drops at once), so a spinner line
that comes and goes while the CLI redraws no longer flips it back and forth,
and only the newest "working" read is applied.

client/src/components/run/PaneChat.tsx

@@ -124,6 +124,11 @@ const isSettable = (m: unknown): m is PermissionMode => MODES.some(([v]) => v ==
 const OUTPUT_FETCH_MS = 1000;
 /** A tool with no known busy line counts as at work this long after its pane last drew. */
 const OUTPUT_BUSY_MS = 2000;
+/** How long Stop stays up after every busy signal dropped: the screen's busy
+ *  line comes and goes while the CLI redraws, and without a hold the button
+ *  flickered between Stop and Send mid-turn. An explicit end (Stop pressed)
+ *  is not held. */
+const BUSY_HOLD_MS = 2500;
 const SIDE_KEY = "agenthub.chat.panelWidth";
 const clampSide = (f: number) => Math.round(Math.min(0.7, Math.max(0.2, f)) * 100) / 100;
 const outlineKey = (sessionId: string) => `agenthub.chat.panel.${sessionId}`;
@@ -140,6 +145,23 @@ const storedSide = () => {
  *  older; every Claude model since (Sonnet/Opus 4.6+, the 5 family) has 1M
  *  (LiteLLM's list, 2026-10). Null for another vendor's model. */
 // ponytail: a fixed rule, not a table; read LiteLLM's max_input_tokens if a new 200K model ships.
+/** `value`, except that a drop to false shows only once it has lasted
+ *  `holdMs`; a change of `release` (Stop pressed) lets it drop at once. */
+export function useHeldTrue(value: boolean, holdMs: number, release: unknown): boolean {
+  const [held, setHeld] = useState(value);
+  const released = useRef(release);
+  useEffect(() => {
+    if (value) return setHeld(true);
+    if (released.current !== release) {
+      released.current = release;
+      return setHeld(false);
+    }
+    const timer = window.setTimeout(() => setHeld(false), holdMs);
+    return () => window.clearTimeout(timer);
+  }, [value, holdMs, release]);
+  return value || held;
+}
+
 export function contextWindow(model: string | null): number | null {
   // A Codex/omp chat reports its own window (ContextMeter's `window`).
   if (!model?.startsWith("claude-")) return null;
@@ -622,13 +644,18 @@ export const PaneChat = memo(function PaneChat({
   const [waiting, setWaiting] = useState(false);
   // Stop presses, for the conversation's live line (issue #74).
   const [stops, setStops] = useState(0);
-  const readWorking = useCallback(
-    () =>
+  // Reads overlap (every throttled transcript change starts one); only the
+  // newest may land, or a slow older answer put back a state already left.
+  const readSeq = useRef(0);
+  const readWorking = useCallback(() => {
+    const seq = ++readSeq.current;
+    return (
       api.agents
         .list({ session_id: sessionId, status: "working" })
         // With session_id the server answers every agent of the session, its
         // status filter ignored: check the status here.
         .then((r) => {
+          if (seq !== readSeq.current) return;
           const main = r.agents.filter((a) => a.type === "main");
           // A fresh start, resume or `/clear` leaves main "working" at an
           // empty prompt (SessionStart's flag) until the first prompt.
@@ -637,9 +664,9 @@ export const PaneChat = memo(function PaneChat({
           );
           setWaiting(main.some((a) => agentAwaitingReason(a) === "notification"));
         })
-        .catch(() => {}),
-    [sessionId]
-  );
+        .catch(() => {})
+    );
+  }, [sessionId]);
   useEffect(() => {
     void readWorking();
   }, [readWorking]);
@@ -714,7 +741,7 @@ export const PaneChat = memo(function PaneChat({
     }, 700);
     return () => window.clearInterval(timer);
   }, [runId, onScreen]);
-  const busy = working || screenBusy;
+  const busy = useHeldTrue(working || screenBusy, BUSY_HOLD_MS, stops);
   const asking = waiting || menu !== null;
   // Gone until the pane redraws: no second press on a stale menu.
   const choose = (index: number) => {

client/src/components/run/__tests__/PaneChat.test.tsx

@@ -215,6 +215,10 @@ describe("PaneChat — Stop", () => {
       await act(async () => {
         await vi.advanceTimersByTimeAsync(5000);
       });
+      // Send comes back once nothing has said busy for BUSY_HOLD_MS.
+      await act(async () => {
+        await vi.advanceTimersByTimeAsync(2600);
+      });
       await waitFor(() => expect(screen.queryByTestId("pane-chat-stop")).toBeNull());
     } finally {
       vi.useRealTimers();
@@ -233,6 +237,10 @@ describe("PaneChat — Stop", () => {
       await act(async () => {
         await vi.advanceTimersByTimeAsync(800);
       });
+      // Send comes back once nothing has said busy for BUSY_HOLD_MS.
+      await act(async () => {
+        await vi.advanceTimersByTimeAsync(2600);
+      });
       await waitFor(() => expect(screen.queryByTestId("pane-chat-stop")).toBeNull());
     } finally {
       vi.useRealTimers();
@@ -240,6 +248,32 @@ describe("PaneChat — Stop", () => {
     }
   });
 
+  it("does not flicker to Send when the busy line drops out for a moment", async () => {
+    vi.useFakeTimers({ shouldAdvanceTime: true });
+    vi.mocked(readRunBusy).mockReturnValue(true);
+    try {
+      renderChat();
+      expect(await screen.findByTestId("pane-chat-stop")).toBeInTheDocument();
+      // A redraw: the spinner line is gone for a poll or two.
+      vi.mocked(readRunBusy).mockReturnValue(false);
+      await act(async () => {
+        await vi.advanceTimersByTimeAsync(1500);
+      });
+      await act(async () => {
+        await vi.advanceTimersByTimeAsync(50);
+      });
+      expect(screen.getByTestId("pane-chat-stop")).toBeInTheDocument();
+      vi.mocked(readRunBusy).mockReturnValue(true);
+      await act(async () => {
+        await vi.advanceTimersByTimeAsync(800);
+      });
+      expect(screen.getByTestId("pane-chat-stop")).toBeInTheDocument();
+    } finally {
+      vi.useRealTimers();
+      vi.mocked(readRunBusy).mockReturnValue(false);
+    }
+  });
+
   it("counts a tool with no known busy line as working while its pane draws", async () => {
     vi.useFakeTimers({ shouldAdvanceTime: true });
     vi.mocked(readRunBusy).mockReturnValue(null);
@@ -261,6 +295,10 @@ describe("PaneChat — Stop", () => {
       await act(async () => {
         await vi.advanceTimersByTimeAsync(2800);
       });
+      // Send comes back once nothing has said busy for BUSY_HOLD_MS.
+      await act(async () => {
+        await vi.advanceTimersByTimeAsync(2600);
+      });
       await waitFor(() => expect(screen.queryByTestId("pane-chat-stop")).toBeNull());
     } finally {
       vi.useRealTimers();