v1.12.3: stale-stream banner with Retry/Discard

When an assistant message sits status='streaming' with no token activity
for 60+ seconds, the chat shows a banner above the input offering Retry
or Discard. Both clear the stale row via a new backend endpoint
POST /api/chats/:id/discard_stale that updates status='failed' and
publishes chat_status='idle'.

Closes the UX gap that caused the 2026-05-21 debugging spiral —
slow streams and dead streams now look different to the user.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/server/src/routes/chats.ts

@@ -18,6 +18,12 @@ const ForkBody = z.object({
   name: z.string().min(1).max(200).optional(),
 });
 
+const DiscardStaleBody = z.object({
+  message_id: z.string().uuid(),
+});
+
+const STALE_MIN_AGE_SECONDS = 60;
+
 export function registerChatRoutes(
   app: FastifyInstance,
   sql: Sql,
@@ -320,6 +326,73 @@ export function registerChatRoutes(
     }
   );
 
+  // v1.12.3: explicit recovery from a stuck-streaming assistant row. The
+  // frontend gates this behind a 60s no-token-activity timer; the server
+  // re-checks the age and current status for safety. Non-streaming rows
+  // return 409 (frontend race; idempotent retry is fine).
+  app.post<{ Params: { id: string } }>(
+    '/api/chats/:id/discard_stale',
+    async (req, reply) => {
+      const parsed = DiscardStaleBody.safeParse(req.body ?? {});
+      if (!parsed.success) {
+        reply.code(400);
+        return { error: 'invalid body', details: parsed.error.flatten() };
+      }
+      const rows = await sql<{
+        id: string;
+        session_id: string;
+        chat_id: string;
+        status: string;
+        age_seconds: number;
+      }[]>`
+        SELECT id, session_id, chat_id, status,
+               EXTRACT(EPOCH FROM (clock_timestamp() - created_at))::int AS age_seconds
+        FROM messages
+        WHERE id = ${parsed.data.message_id} AND chat_id = ${req.params.id}
+      `;
+      if (rows.length === 0) {
+        reply.code(404);
+        return { error: 'message not found in chat' };
+      }
+      const msg = rows[0]!;
+      if (msg.status !== 'streaming') {
+        reply.code(409);
+        return { error: 'message is no longer streaming', current_status: msg.status };
+      }
+      if (msg.age_seconds < STALE_MIN_AGE_SECONDS) {
+        reply.code(409);
+        return { error: 'message is not stale yet', age_seconds: msg.age_seconds };
+      }
+      const updated = await sql<Message[]>`
+        UPDATE messages
+        SET status = 'failed',
+            content = COALESCE(content, ''),
+            finished_at = clock_timestamp()
+        WHERE id = ${msg.id} AND status = 'streaming'
+        RETURNING id, session_id, chat_id, role, content, kind, tool_calls, tool_results,
+                  status, last_seq, tokens_used, ctx_used, ctx_max, started_at, finished_at,
+                  created_at, metadata, summary, tail_start_id, compacted_at
+      `;
+      if (updated.length === 0) {
+        // Race: the row flipped out of 'streaming' between our SELECT and UPDATE.
+        reply.code(409);
+        return { error: 'message status changed mid-request' };
+      }
+      broker.publishUser('default', {
+        type: 'chat_status',
+        chat_id: msg.chat_id,
+        status: 'idle',
+        at: new Date().toISOString(),
+      });
+      broker.publish(msg.session_id, {
+        type: 'message_complete',
+        message_id: msg.id,
+        chat_id: msg.chat_id,
+      });
+      return updated[0];
+    }
+  );
+
   app.get<{ Params: { id: string } }>(
     '/api/chats/:id/messages',
     async (req, reply) => {

apps/web/src/api/client.ts

@@ -180,6 +180,11 @@ export const api = {
       request<{ ok: true }>(`/api/chats/${chatId}/compact`, { method: 'POST' }),
     stop: (chatId: string) =>
       request<{ stopped: boolean }>(`/api/chats/${chatId}/stop`, { method: 'POST' }),
+    discardStale: (chatId: string, messageId: string) =>
+      request<Message>(`/api/chats/${chatId}/discard_stale`, {
+        method: 'POST',
+        body: JSON.stringify({ message_id: messageId }),
+      }),
     forceSend: (chatId: string, content: string) =>
       request<{ user_message_id: string; assistant_message_id: string }>(
         `/api/chats/${chatId}/force_send`,

apps/web/src/components/StaleStreamBanner.tsx

@@ -0,0 +1,34 @@
+interface Props {
+  onRetry: () => void;
+  onDiscard: () => void;
+}
+
+// v1.12.3: shown when an assistant message has been 'streaming' for 60+
+// seconds without new tokens. Lives above ChatInput in ChatPane. Retry
+// discards the stuck row then resends the last user message; Discard just
+// clears the row and drops the dot to idle.
+export function StaleStreamBanner({ onRetry, onDiscard }: Props) {
+  return (
+    <div className="border border-amber-500/30 bg-amber-500/5 rounded-md p-3 mb-2 mx-4 flex items-center justify-between gap-2">
+      <span className="text-sm text-muted-foreground">
+        Previous response didn't complete.
+      </span>
+      <div className="flex gap-2">
+        <button
+          type="button"
+          onClick={onRetry}
+          className="text-xs px-2 py-1 rounded border border-border hover:bg-accent max-md:min-h-[44px] max-md:px-3"
+        >
+          Retry
+        </button>
+        <button
+          type="button"
+          onClick={onDiscard}
+          className="text-xs px-2 py-1 rounded border border-border hover:bg-accent max-md:min-h-[44px] max-md:px-3"
+        >
+          Discard
+        </button>
+      </div>
+    </div>
+  );
+}

apps/web/src/components/panes/ChatPane.tsx

@@ -5,6 +5,7 @@ import { api } from '@/api/client';
 import { useSessionStream } from '@/hooks/useSessionStream';
 import { MessageList } from '@/components/MessageList';
 import { ChatInput } from '@/components/ChatInput';
+import { StaleStreamBanner } from '@/components/StaleStreamBanner';
 import {
   DropdownMenu,
   DropdownMenuContent,
@@ -44,6 +45,38 @@ export function ChatPane({ sessionId, chatId, projectId, agentId, onAgentChange,
 
   const chatMessages = stream.messages.filter((m) => m.chat_id === chatId);
   const streaming = chatMessages.some((m) => m.status === 'streaming');
+
+  // v1.12.3: stale-stream detection. Watches the (at most one) streaming
+  // assistant row. If its content length doesn't grow for STALE_THRESHOLD_MS,
+  // assume the upstream call is dead and surface the recovery banner. We use
+  // content length as the activity signal because every token delta extends
+  // it; last_seq isn't currently bumped per delta.
+  const STALE_THRESHOLD_MS = 60_000;
+  const streamingMsg = chatMessages.find((m) => m.status === 'streaming' && m.role === 'assistant');
+  const streamingId = streamingMsg?.id ?? null;
+  const streamingLen = streamingMsg?.content.length ?? 0;
+  const lastActivityRef = useRef<{ id: string; len: number; at: number } | null>(null);
+  const [stale, setStale] = useState(false);
+  useEffect(() => {
+    if (!streamingId) {
+      lastActivityRef.current = null;
+      setStale(false);
+      return;
+    }
+    const prev = lastActivityRef.current;
+    if (!prev || prev.id !== streamingId || prev.len !== streamingLen) {
+      lastActivityRef.current = { id: streamingId, len: streamingLen, at: Date.now() };
+      setStale(false);
+    }
+    const interval = setInterval(() => {
+      const a = lastActivityRef.current;
+      if (!a) return;
+      if (Date.now() - a.at >= STALE_THRESHOLD_MS) {
+        setStale(true);
+      }
+    }, 5_000);
+    return () => clearInterval(interval);
+  }, [streamingId, streamingLen]);
   // v1.11.5: per-chat model context limit comes from chat.model_context_limit
   // populated by GET /api/sessions/:id/chats. Threaded into ChatInput so
   // ContextBar can render a zero-state before the first assistant message.
@@ -87,6 +120,45 @@ export function ChatPane({ sessionId, chatId, projectId, agentId, onAgentChange,
     }
   }
 
+  const handleDiscardStale = useCallback(async () => {
+    if (!streamingId) return;
+    try {
+      await api.chats.discardStale(chatId, streamingId);
+      setStale(false);
+      lastActivityRef.current = null;
+    } catch (err) {
+      // 409 (race) is benign — the row already terminated some other way.
+      const msg = err instanceof Error ? err.message : 'discard failed';
+      if (!msg.includes('409')) toast.error(msg);
+      setStale(false);
+    }
+  }, [chatId, streamingId]);
+
+  const handleRetryStale = useCallback(async () => {
+    if (!streamingId) return;
+    const lastUser = [...chatMessages].reverse().find((m) => m.role === 'user' && m.kind === 'message');
+    if (!lastUser) {
+      toast.error('no prior user message to retry');
+      return;
+    }
+    try {
+      await api.chats.discardStale(chatId, streamingId);
+    } catch (err) {
+      const msg = err instanceof Error ? err.message : 'discard failed';
+      if (!msg.includes('409')) {
+        toast.error(msg);
+        return;
+      }
+    }
+    setStale(false);
+    lastActivityRef.current = null;
+    try {
+      await api.messages.send(chatId, lastUser.content);
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : 'retry send failed');
+    }
+  }, [chatId, streamingId, chatMessages]);
+
   const handleForceSend = useCallback(async (content: string) => {
     const trimmed = content.trim();
     if (!trimmed) return;
@@ -187,6 +259,13 @@ export function ChatPane({ sessionId, chatId, projectId, agentId, onAgentChange,
         </div>
       )}
 
+      {stale && streamingId && (
+        <StaleStreamBanner
+          onRetry={() => void handleRetryStale()}
+          onDiscard={() => void handleDiscardStale()}
+        />
+      )}
+
       <ChatInput
         disabled={false}
         projectId={projectId}