- Add ai-session-store unit tests for upsert/get round-trips, active filtering, stale recovery, cleanup, thinking debounce, and update/delete events
- Add persistence and resume-history integration tests for planning, subtask, and mission interview sessions across SQLite reload and cancellation flows
- Add reconnect and cross-tab lock tests covering SSE Last-Event-ID replay, keep-alive ping touches, optimistic lock conflicts, stale lock expiry, and lock release on tab close
- Expand useBackgroundSessions hook tests for SSE-driven updates/deletes, project-scoped fetch/stream behavior, counts, dismiss, and refresh state handling
- Add a shared AiSessionSync store with BroadcastChannel + storage fallback, ownership locks, heartbeats, and stale-tab detection
- Merge cross-tab session snapshots into useBackgroundSessions with timestamp guards and rebroadcast SSE updates to peers
- Update background session UI and planning/mission/subtask modals to show active-tab lock status and only allow takeover when ownership is stale
- Add hook tests covering sync store messaging/fallback behavior and background session cross-tab merge flows
