fix: increase stream idle timeout from 90s to 5 minutes

The 90s stream-idle timer was firing during legitimate long-running
agent turns (browser navigation, complex tool chains). Backend already
sends heartbeats every 30s to keep the connection alive, so the idle
timer just needs to be generous enough for edge cases where heartbeats
are delayed.

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

Author: Juan Roldan

packages/frontend/src/hooks/useAgentSocket.ts

@@ -47,7 +47,7 @@ type ChunkHandler = (chunk: StreamChunk) => void;
 
 const RECONNECT_MIN_MS = 1000;
 const RECONNECT_MAX_MS = 10000;
-const STREAM_TIMEOUT_MS = 90000; // 90s without chunks = stale
+const STREAM_TIMEOUT_MS = 300000; // 5min without chunks = stale
 
 export function useAgentSocket(
   agentId: string | undefined,
@@ -73,7 +73,7 @@ export function useAgentSocket(
       // No chunks for 90s — force done
       const handler = handlerRef.current;
       if (handler) {
-        handler({ type: 'error', message: 'Stream timeout — no response for 90s' });
+        handler({ type: 'error', message: 'Stream timeout — no response for 5 minutes' });
         handler({ type: 'done', sessionId: '' });
         handlerRef.current = null;
       }