fix(activity): prevent monitoring turns from emitting working events

Monitoring turns should surface only via the 'monitoring' snapshot in
the live state, not as separate working events that would contradict
the snapshot signal.

src/renderer/src/components/activity/ActivityPrototypePage.test.ts

@@ -171,6 +171,9 @@ describe('buildActivityEvents', () => {
 
     expect(result.liveAgentByPaneKey[PANE_KEY].state).toBe('monitoring')
     expect(threads[0].currentAgentState).toBe('monitoring')
+    // A monitoring turn must not emit a `working` event that contradicts the live snapshot.
+    expect(result.events).toHaveLength(0)
+    expect(threads[0].latestEvent).toBeNull()
     expect(groups[0]).toMatchObject({
       key: 'monitoring',
       label: 'Monitoring background tasks',

src/renderer/src/components/activity/activity-pane-events.ts

@@ -97,8 +97,11 @@ export function buildPaneActivityEvents(args: PaneEventInputs): ActivityEvent[]
     )
   }
 
+  // Monitoring live turns surface only via the 'monitoring' snapshot, never as a working event.
   const currentState =
-    args.liveState !== null || isHistoricalActivityState(args.entry.state) ? args.entry.state : null
+    args.liveState === 'working' || isHistoricalActivityState(args.entry.state)
+      ? args.entry.state
+      : null
   if (currentState === null || args.entry.sessionBoundary === true) {
     return events
   }