/**
 * Zoe Middleware — Rate Limiting
 *
 * Token bucket rate limiter per key. Throws on limit exceeded.
 */
import type { PipelineContext, Middleware } from "../middleware.js";
export interface RateLimitOptions {
    /** Maximum requests allowed per window */
    maxRequests: number;
    /** Window duration in milliseconds */
    windowMs: number;
    /** Extract a key from context for per-key limiting (default: "global") */
    keyExtractor?: (ctx: PipelineContext) => string;
}
/**
 * Create a rate limiting middleware using a token bucket algorithm.
 *
 * @example
 * ```ts
 * const mw = rateLimitMiddleware({
 *   maxRequests: 60,
 *   windowMs: 60_000,
 *   keyExtractor: (ctx) => ctx.metadata.userId as string,
 * });
 * ```
 */
export declare function rateLimitMiddleware(options: RateLimitOptions): Middleware;