Type Alias: AsyncCancelableEvent

AsyncCancelableEvent = "beforeEntryMove" | "beforeEntryResize" | "beforeEntryEdit"

S3.5: the only two event names whose handler may veto asynchronously, by returning a Promise<void | false> instead of resolving false synchronously — EventBus<GanttEventMap, AsyncCancelableEvent> is what actually grants that return shape at on/off/emit's call sites (data/event-bus.ts's TAsyncKeys). Every other event (grid width, selection) stays sync-only: plans/02 §3's async-veto path is scoped to a data gesture's own before-event, not every veto.