/**
 * Token bucket rate limiter with lazy refill on acquire.
 */
export declare class RateLimiter {
    private readonly rateDelta;
    private readonly rateLimit;
    private readonly now;
    private static readonly defaultNow;
    /** Remaining tokens in the current rate-limit window. */
    private tokens;
    /** Timestamp (ms) of the last token refill. */
    private lastRefill;
    /** Resolvers waiting for a token when the bucket is empty. */
    private waiters;
    /** Creates a rate limiter with the given burst size and window duration. */
    constructor(rateDelta: number, rateLimit: number, now?: () => number);
    /** Wait until a token is available, then consume one. */
    acquire(): Promise<void>;
    /** Wake waiters after the clock advances (for testing). */
    notify(): void;
    /** Refills tokens based on elapsed time and wakes waiting acquirers. */
    private refill;
}