Reset coordinator state when the last subscriber leaves, clear pending debounce timers on close, and keep coordinated EventSource construction owned by the coordinator while fallback subscriptions keep their local factories.
Prune stale election candidates as generations advance, reset coordination availability on explicit close, and keep fallback subscribers tracked so coordinator shutdown can clean them up consistently.
Stop coordinated election and leadership work when BroadcastChannel posting fails, so tabs degrade cleanly to per-subscriber fallback without stale resync or heartbeat side effects. Expand election coverage for the edge cases called out in the coordination plan.
Elect a single browser tab to own the global attach stream and broadcast run events to sibling tabs. Keep the existing per-tab EventSource path as the fallback when cross-tab coordination is unavailable.
