Add TTFT watchdog to detect and surface LLM stalls

When llama-server is queue-backed it accepts the connection but never
produces tokens; after ~60s Caddy drops the connection and the frontend
clears loading state with no response and no error shown to the user.

Backend: replace the async-for event loop with an explicit __anext__()
iterator wrapped in asyncio.wait_for(). A 30s timeout (TTFT_TIMEOUT_SECONDS)
applies only in the window between on_chat_model_start and the first content
token — tool calls are excluded. On timeout, emits a stalled error event and
logs it rather than waiting for the proxy to kill the connection.

Frontend: separates stall errors from generic errors; shows a "Simba didn't
respond in time. Retry" pill that re-sends the original query.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

raggr-frontend/src/api/conversationService.ts

@@ -6,7 +6,7 @@ export type SSEEvent =
   | { type: "tool_end"; tool: string }
   | { type: "content"; delta: string }
   | { type: "response"; message: string }
-  | { type: "error"; message: string };
+  | { type: "error"; message: string; stalled?: boolean };
 
 export type SSEEventCallback = (event: SSEEvent) => void;
 

raggr-frontend/src/components/ChatScreen.tsx

@@ -61,6 +61,8 @@ export const ChatScreen = ({ setAuthenticated, isAdmin }: ChatScreenProps) => {
     stopGeneration,
     error,
     clearError,
+    stalled,
+    retryStalled,
   } = useChat({
     createConversation,
     refreshConversations,
@@ -273,6 +275,20 @@ export const ChatScreen = ({ setAuthenticated, isAdmin }: ChatScreenProps) => {
                   </div>
                 )}
 
+                {stalled && (
+                  <div className="flex justify-center message-enter">
+                    <div className="inline-flex items-center gap-2 px-3 py-1.5 rounded-full bg-red-50 border border-red-200 text-xs text-red-600">
+                      <span>Simba didn&apos;t respond in time.</span>
+                      <button
+                        onClick={retryStalled}
+                        className="font-medium underline underline-offset-2 hover:text-red-800 transition-colors cursor-pointer"
+                      >
+                        Retry
+                      </button>
+                    </div>
+                  </div>
+                )}
+
                 <div ref={messagesEndRef} />
               </div>
             </div>

raggr-frontend/src/hooks/useChat.ts

@@ -51,9 +51,12 @@ export function useChat({
   const [messagesLoading, setMessagesLoading] = useState(false);
   const [pendingImage, setPendingImage] = useState<File | null>(null);
   const [error, setError] = useState<string | null>(null);
+  const [stalled, setStalled] = useState(false);
   const [streaming, setStreaming] = useState(false);
   const [thinking, setThinking] = useState(false);
 
+  const stalledQueryRef = useRef<string | null>(null);
+
   const isMountedRef = useRef(true);
   // True once tokens for the current assistant reply have started arriving, so
   // new content appends to the live bubble instead of creating another one.
@@ -144,6 +147,8 @@ export function useChat({
       const imageFile = pendingImage;
 
       setError(null);
+      setStalled(false);
+      stalledQueryRef.current = null;
       streamingActiveRef.current = false;
       setStreaming(false);
       updateMessages((prev) => prev.concat([{ text: query, speaker: "user" }]));
@@ -239,7 +244,11 @@ export function useChat({
               }
             } else if (event.type === "error") {
               console.error("Stream error:", event.message);
-              if (isMountedRef.current) {
+              if (!isMountedRef.current) return;
+              if (event.stalled) {
+                stalledQueryRef.current = query;
+                setStalled(true);
+              } else {
                 setError("Simba ran into a problem answering that.");
               }
             }
@@ -293,6 +302,14 @@ export function useChat({
 
   const clearError = useCallback(() => setError(null), []);
 
+  const retryStalled = useCallback(() => {
+    const q = stalledQueryRef.current;
+    if (!q) return;
+    setStalled(false);
+    stalledQueryRef.current = null;
+    sendMessage(q, false);
+  }, [sendMessage]);
+
   return {
     messages,
     setMessages: updateMessages,
@@ -306,5 +323,7 @@ export function useChat({
     stopGeneration,
     error,
     clearError,
+    stalled,
+    retryStalled,
   };
 }