/**
 * In-memory pre-send queue (best-effort ordering before delivery).
 */
export interface QueuedDelivery<T> {
    id: string;
    item: T;
    enqueuedAt: number;
}
export declare function createDeliveryQueue<T>(): {
    enqueue(item: T): string;
    dequeue(): QueuedDelivery<T> | undefined;
    size(): number;
};