/**
 * Prunes *.expired.json tombstones older than retentionDays*2.
 * Keeps recent expiry signal (default 4 days) while bounding history readdir cost.
 */
export declare function pruneExpiredTombstones(historyDir: string, retentionDays: number, getActive: () => ReadonlySet<string>, isHashFn: (value: string) => boolean, isLive?: (sessionHash: string) => Promise<boolean>): Promise<void>;