Interface TypedEventBus<EventMap>

Subscribe to type. Returns an unsubscribe thunk that callers should store (e.g., in an EventGroup or a dispose() list).

replayLast: true causes the last emitted payload for type, if any, to fire immediately on subscription. Useful for late-binding panels that need the current value (e.g., FPS counter that wants to show something before the next frame).

Emit payload to every subscriber of type. No-op if no one is listening (events drop silently — that's the design).

Whether at least one listener is currently subscribed to type. Lets producers gate expensive work behind "anyone consuming?" (e.g. GPU picking only runs when a selection listener exists).

Drop all subscribers (or just those for type). Used by tests that share the singleton between cases. Production code should use the per-subscription unsubscribe instead.