import type { RequestKeyOptions } from '../types.ts';
/**
 * Request serializer for generating deduplication and cache keys.
 *
 * Serializes by request identity: method + URL path+search + payload + stable headers.
 * Used for policies that identify duplicate requests.
 *
 * Only includes stable, semantically-meaningful headers (Authorization, Accept,
 * Accept-Language, Content-Type, Accept-Encoding). Dynamic headers like timestamps,
 * HMAC signatures, and request IDs are excluded to prevent cache pollution.
 *
 * Header lookup is case-insensitive (keys are lowercased for comparison).
 *
 * Uses `url.pathname + url.search` which:
 * - Includes the full path and query parameters
 * - Excludes the hash fragment (which shouldn't affect request identity)
 * - Excludes the origin (handled by FetchEngine instance)
 *
 * @param ctx - Request key context
 * @returns A unique string key for the request
 *
 * @example
 * ```typescript
 * requestSerializer({
 *     method: 'GET',
 *     path: '/users/123',
 *     url: new URL('https://api.example.com/users/123?page=1'),
 *     payload: undefined,
 *     headers: {
 *         'Authorization': 'Bearer token',
 *         'X-Timestamp': '1234567890',  // Ignored (dynamic)
 *         'Accept': 'application/json'
 *     }
 * });
 * // Returns: 'GET|/users/123?page=1|undefined|{"accept":"application/json","authorization":"Bearer token"}'
 * ```
 */
export declare const requestSerializer: (ctx: RequestKeyOptions) => string;