Fix live activity timer

backend/api/server.py

@@ -485,6 +485,7 @@ class RunManager:
                 'current_stage': record.current_stage,
                 'started_at': record.started_at,
                 'updated_at': record.updated_at,
+                'elapsed_ms': max(0, int((time.time() - record.started_at) * 1000)),
                 'pending_prompt': record.pending_prompt,
                 'error': record.error,
                 'events': [dict(event) for event in record.events],
@@ -1612,7 +1613,10 @@ def create_app(state: AgentState) -> FastAPI:
                 merged['events'] = stored_snapshot.get('events')
             if memory_snapshot.get('current_stage'):
                 merged['current_stage'] = memory_snapshot.get('current_stage')
-            if stored_snapshot.get('elapsed_ms') is not None:
+            if (
+                memory_snapshot.get('status') not in ACTIVE_RUN_STATUSES
+                and stored_snapshot.get('elapsed_ms') is not None
+            ):
                 merged['elapsed_ms'] = stored_snapshot.get('elapsed_ms')
             if stored_snapshot.get('finished_at') is not None:
                 merged['finished_at'] = stored_snapshot.get('finished_at')

frontend/app/components/assistant-ui/thread.tsx

@@ -2014,6 +2014,7 @@ const ActivityChainSummary: FC<{
 	});
 	const initialStartedAtMs =
 		metadataRunStartedAtMs ?? contentRunStartedAtMs ?? messageCreatedAtMs;
+	const liveStartedAtRef = useRef<number | null>(initialStartedAtMs);
 	const [elapsedMs, setElapsedMs] = useState<number | null>(() => {
 		if (storedElapsedMs !== null) return storedElapsedMs;
 		if (initialStartedAtMs !== null) {
@@ -2041,11 +2042,14 @@ const ActivityChainSummary: FC<{
 			setElapsedMs(storedElapsedMs);
 			return;
 		}
-		const startedAt =
-			metadataRunStartedAtMs ??
-			contentRunStartedAtMs ??
-			messageCreatedAtMs ??
-			(storedElapsedMs === null ? null : Date.now() - storedElapsedMs);
+		const explicitStartedAt =
+			metadataRunStartedAtMs ?? contentRunStartedAtMs ?? messageCreatedAtMs;
+		if (explicitStartedAt !== null) {
+			liveStartedAtRef.current = explicitStartedAt;
+		} else if (liveStartedAtRef.current === null && storedElapsedMs !== null) {
+			liveStartedAtRef.current = Date.now() - storedElapsedMs;
+		}
+		const startedAt = liveStartedAtRef.current;
 		if (startedAt === null) {
 			setElapsedMs(storedElapsedMs);
 			return;