During active sessions, every domain event triggered a full
syncSnapshot (IPC fetch + state rebuild + React re-render cascade) and
sometimes a provider query invalidation. Events fire in rapid bursts
during AI turns.

Replace per-event processing with a throttle-first pattern: schedule a
flush on the first event, absorb subsequent events within a 100ms
window, then sync once. Provider query invalidation is batched via a
flag. Since syncSnapshot fetches the complete snapshot, no events are
lost by skipping intermediate syncs.