import { type ContextPlugin } from "@nifrajs/core/server";
export interface RequestIdOptions {
    /** Header read for an inbound id (trace propagation) + echoed on the response. Default `"x-request-id"`. */
    readonly header?: string;
    /** Generate an id when the inbound header is absent. Default `crypto.randomUUID()`. */
    readonly generate?: () => string;
}
/**
 * A {@link defineContextPlugin} plugin that gives every request a stable id: it reuses an inbound
 * `x-request-id` (or generates one), exposes it on the handler context as **`c.requestId`** (typed,
 * threaded by `derive`), and echoes it on EVERY response leaving the app - handler-returned raw
 * `Response`s and redirects, `onRequest` short-circuits (an auth 401, an admission 429), and
 * framework-generated 404/405/422/timeout responses included. Core deliberately does not merge
 * `c.set.headers` onto a handler-returned `Response`, so the echo lives in an app-global
 * `onResponse` hook (paired with the derive through a `WeakMap` keyed on the request) with a node
 * twin, keeping the Node adapter on its direct writer with no request-walk cost. Idempotent -
 * applying it twice is a no-op.
 *
 * ```ts
 * app.use(requestId())          // c.requestId available downstream; X-Request-Id on responses
 * ```
 */
export declare function requestId(options?: RequestIdOptions): ContextPlugin<{
    requestId: string;
}>;
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