/**
 * Rubric Protocol — Background Attestation Queue
 * Buffers attestation calls, submits in batches, retries on failure.
 * Survives process restart via optional JSON persistence.
 */
export interface QueueItem {
    id: string;
    endpoint: string;
    payload: Record<string, unknown>;
    headers: Record<string, string>;
    attempts: number;
    maxAttempts: number;
    nextRetryAt: number;
    enqueuedAt: number;
    failedPermanently?: boolean;
    lastError?: string;
}
export interface QueueConfig {
    flushInterval?: number;
    batchSize?: number;
    maxAttempts?: number;
    backoffBase?: number;
    persistPath?: string;
    onDeadLetter?: (item: QueueItem) => void;
    onSuccess?: (item: QueueItem, response: unknown) => void;
    onError?: (item: QueueItem, error: Error) => void;
}
export type QueueStats = {
    queued: number;
    inflight: number;
    deadLetters: number;
    totalSubmitted: number;
    totalFailed: number;
};
export declare class BackgroundQueue {
    private queue;
    private deadLetters;
    private inflight;
    private timer;
    private totalSubmitted;
    private totalFailed;
    private readonly config;
    constructor(config?: QueueConfig);
    enqueue(endpoint: string, payload: Record<string, unknown>, headers: Record<string, string>, options?: {
        maxAttempts?: number;
    }): string;
    start(): void;
    stop(): Promise<void>;
    stats(): QueueStats;
    flush(): Promise<void>;
    private _flush;
    private _submit;
    private _persist;
    private _loadFromDisk;
}
export declare function sleep(ms: number): Promise<void>;
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