export interface PersistentCacheOptions {
    max?: number;
    ttl?: number;
    persistence?: boolean;
    directory?: string;
    maxFileBytes?: number;
}
/**
 * Bounded in-memory TTL/LRU cache for browser and workerd builds.
 *
 * This adapter intentionally has no persistence, process hooks, timers, or
 * shared global registry. Its public surface matches the Node persistent
 * cache so the email engine can select it at bundle time without changing
 * callers.
 */
export declare class PersistentCache<T extends {}> {
    private readonly cache;
    private readonly expirations;
    private readonly max;
    private readonly ttl;
    constructor(name: string, options?: PersistentCacheOptions);
    /** Get a value and promote it to the most-recently-used position. */
    get(key: string): T | undefined;
    /** Set a value with the default TTL or a per-entry override. */
    set(key: string, value: T, ttlMs?: number): void;
    /** Check existence without changing LRU order. */
    has(key: string): boolean;
    delete(key: string): boolean;
    clear(): void;
    get size(): number;
    /** There is no backing store to flush in a web runtime. */
    flush(): boolean;
    /** Detaches no lifecycle hooks; the in-memory cache remains usable. */
    dispose(): boolean;
    private purgeExpired;
    private pushExpiry;
    private popExpiry;
    /** Bound stale heap tokens left behind by overwrites and LRU eviction. */
    private compactExpirationsIfNeeded;
}