import type { Awaitable } from "./Awaitable";
/**
 * Assume Stream content is ordered plain json object, (class is not supported)
 * And new element always insert into head
 *
 * Set ttl in your store settings
 *
 * 1. cache whole list once upstream flushed
 * 2. Stop upstream and Continue with cached list once head matched
 *
 * This step should place at near the output end.
 */
export declare function cacheTails<T>(store: {
    has?: (key: string) => Awaitable<boolean>;
    get: (key: string) => Awaitable<T[] | undefined>;
    set: (key: string, chunks: T[]) => Awaitable<any>;
}, _options?: string | {
    /**
     * Key could step name,
     * or defaults to `new Error().stack` if you r lazy enough
     */
    key?: string;
}): {
    writable: WritableStream<any>;
    readable: ReadableStream<any>;
};