fix: handle SDK keep_alive messages to prevent idle timeout during long operations (#163)

The stream idle timer (330s) fires during long-running Claude Code tool
executions because the SDK's keep_alive heartbeat messages are silently
dropped. This causes a false "Stream idle timeout" error even though
Claude is still actively working.

Root cause: claude-client.ts only handles 6 SDK message types in its
switch statement and has no default case, so keep_alive messages from
the SDK are never forwarded to the frontend. The idle timer in
stream-session-manager.ts never gets reset by markActive().

Fix: thread keep_alive through the existing 3-layer event pipeline:
- claude-client.ts: forward keep_alive as SSE event (via default case)
- useSSEStream.ts: add onKeepAlive callback to SSECallbacks interface
- stream-session-manager.ts: call markActive() on keep_alive to reset
  the idle timer

No visible UI change — keep_alive only resets the timer silently.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/hooks/useSSEStream.ts

@@ -24,6 +24,7 @@ export interface SSECallbacks {
   onToolTimeout: (toolName: string, elapsedSeconds: number) => void;
   onModeChanged: (mode: string) => void;
   onTaskUpdate: (sessionId: string) => void;
+  onKeepAlive: () => void;
   onError: (accumulated: string) => void;
 }
 
@@ -146,6 +147,11 @@ function handleSSEEvent(
       return accumulated;
     }
 
+    case 'keep_alive': {
+      callbacks.onKeepAlive();
+      return accumulated;
+    }
+
     case 'error': {
       const next = accumulated + '\n\n**Error:** ' + event.data;
       callbacks.onError(next);
@@ -232,6 +238,7 @@ export function useSSEStream() {
         onToolTimeout: (n, s) => callbacksRef.current?.onToolTimeout(n, s),
         onModeChanged: (m) => callbacksRef.current?.onModeChanged(m),
         onTaskUpdate: (s) => callbacksRef.current?.onTaskUpdate(s),
+        onKeepAlive: () => callbacksRef.current?.onKeepAlive(),
         onError: (a) => callbacksRef.current?.onError(a),
       };
 

src/lib/claude-client.ts

@@ -873,6 +873,13 @@ export function streamClaude(options: ClaudeStreamOptions): ReadableStream<strin
               }));
               break;
             }
+
+            default: {
+              if ((message as { type: string }).type === 'keep_alive') {
+                controller.enqueue(formatSSE({ type: 'keep_alive', data: '' }));
+              }
+              break;
+            }
           }
         }
 

src/lib/stream-session-manager.ts

@@ -311,6 +311,9 @@ async function runStream(stream: ActiveStream, params: StartStreamParams): Promi
         markActive();
         window.dispatchEvent(new CustomEvent('tasks-updated'));
       },
+      onKeepAlive: () => {
+        markActive();
+      },
       onError: (acc) => {
         markActive();
         stream.accumulatedText = acc;

src/types/index.ts

@@ -356,6 +356,7 @@ export type SSEEventType =
   | 'permission_request' // permission approval needed
   | 'mode_changed'       // SDK permission mode changed (e.g. plan → code)
   | 'task_update'        // SDK TodoWrite task sync
+  | 'keep_alive'         // SDK keep-alive heartbeat (resets idle timer)
   | 'done';              // stream complete
 
 export interface SSEEvent {