import type { RequestHeaderBag } from '../types';
/**
 * Reads the HTTP request headers off the `extra` (v1) / `ctx` (v2) object the
 * MCP SDK hands a request handler, and returns them as a plain object with
 * lowercase keys. Returns `undefined` when the request did not come over HTTP —
 * stdio and in-memory transports carry no headers at all.
 *
 * The two SDK majors put them in different places and in different shapes: v1
 * attaches a plain object at `extra.requestInfo.headers`, while v2 attaches the
 * WHATWG `Request` at `ctx.http.req`, whose `headers` is a `Headers` instance
 * that only answers to `.get()`. A v1-shaped read returns `undefined` on v2,
 * which is why this exists.
 *
 * Normalisation is **by shape, not by source**: a framework is free to hand us a
 * plain object where the SDK hands `Headers`, so both fields are checked for
 * both shapes. `Headers` is duck-typed on `.entries` rather than `instanceof` —
 * workerd and other edge runtimes are a different realm and would fail the
 * identity check on a perfectly good object.
 *
 * Exported from the package for host callbacks. `identify`, `intentFallback`,
 * `eventProperties` and `beforeSend` receive the SDK's `extra` unchanged — we
 * deliberately do not synthesise a v1 shape on v2, because a fabricated
 * `requestInfo` is a convincing partial lie about a shape the SDK removed on
 * purpose. So a host that reads headers reads them through this instead:
 *
 * ```ts
 * import { getRequestHeaders } from '@posthog/mcp'
 *
 * identify: async (request, extra) => {
 *   const auth = getRequestHeaders(extra)?.['authorization']
 *   // ...
 * }
 * ```
 */
export declare function getRequestHeaders(extra: unknown): RequestHeaderBag | undefined;
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