/**
 * Redis-backed distributed crawl frontier.
 *
 * Replaces the in-memory CrawlFrontier for horizontally-scaled crawler deployments.
 * Multiple crawler workers on different containers can share the same URL queue for
 * a given job — enabling 10x crawl throughput on large enterprise apps.
 *
 * Redis key namespace:  zeta:frontier:{jobId}
 *   LIST  zeta:frontier:{jobId}:queue   — BFS queue (LPUSH/RPOP)
 *   SET   zeta:frontier:{jobId}:visited — deduplication set
 *   EXPIRE                               — 24h TTL on all keys
 *
 * Graceful fallback: if REDIS_URL is not set, RedisCrawlFrontier silently falls
 * back to in-memory arrays so local development works without Redis.
 */
export declare class RedisCrawlFrontier {
    private readonly jobId;
    private redis;
    private queueKey;
    private visitedKey;
    private inMemoryQueue;
    private inMemoryVisited;
    private useRedis;
    constructor(jobId: string);
    init(): Promise<void>;
    /** Add a URL to the frontier. No-op if already visited. Returns true if added. */
    push(url: string): Promise<boolean>;
    /** Pop the next URL (FIFO/BFS). Returns null if queue empty. */
    shift(): Promise<string | null>;
    /** Check if a URL has already been visited/queued. */
    hasVisited(url: string): Promise<boolean>;
    /** Current queue length. */
    length(): Promise<number>;
    /** Total visited count. */
    visitedCount(): Promise<number>;
    /** Seed initial URLs (used at job start). */
    seed(urls: string[]): Promise<void>;
    /** Clean up all Redis keys for this frontier. Call at job completion. */
    cleanup(): Promise<void>;
    /** Stats for monitoring. */
    stats(): Promise<{
        backend: 'redis' | 'memory';
        queued: number;
        visited: number;
    }>;
}
/** Check if Redis is configured for distributed frontier. */
export declare function isRedisFrontierEnabled(): boolean;