// reused, so we don't care about a Begin after an End.
	id := TaskID(ev.args[0])
	if _, ok := o.activeTasks[id]; ok {
		return curCtx, false, fmt.Errorf("task ID conflict: %d", id)
	}
	// Get the parent ID, but don't validate it. There's no guarantee
	// we actually have information on whether it's active.
	parentID := TaskID(ev.args[1])
	if parentID == BackgroundTask {