fix(app): keep hidden chats current through brief switches

packages/app/src/timeline/viewed-timeline-sync.test.ts

@@ -174,6 +174,10 @@ class TimelineWorld {
   }
 }
 
+test("keeps hidden agents subscribed for thirty seconds", () => {
+  expect(VIEWED_TIMELINE_UNSUBSCRIBE_GRACE_MS).toBe(30_000);
+});
+
 test("uses a tail fetch when a live cursor is not authoritative", async () => {
   const world = new TimelineWorld();
   world.setLiveCursor("agent-a", 9);

packages/app/src/timeline/viewed-timeline-sync.ts

@@ -42,7 +42,7 @@ export interface ViewedTimelineSync extends ViewedTimelineUiBridge {
 }
 
 const RETRY_DELAY_MS = 1_000;
-export const VIEWED_TIMELINE_UNSUBSCRIBE_GRACE_MS = 5_000;
+export const VIEWED_TIMELINE_UNSUBSCRIBE_GRACE_MS = 30_000;
 
 type CatchUpStatus = "running" | "complete" | "error";