feat(compat): export InMemoryTransport from public API surface

.changeset/export-inmemory-transport.md

@@ -0,0 +1,6 @@
+---
+'@modelcontextprotocol/server': patch
+'@modelcontextprotocol/client': patch
+---
+
+Export `InMemoryTransport` for in-process testing.

packages/core/src/exports/public/index.ts

@@ -70,6 +70,7 @@
 // Transport types (NOT normalizeHeaders)
 export type { FetchLike, Transport, TransportSendOptions } from '../../shared/transport.js';
 export { createFetchWithInit } from '../../shared/transport.js';
+export { InMemoryTransport } from '../../util/inMemory.js';
 
 // URI Template
 export type { Variables } from '../../shared/uriTemplate.js';

packages/core/src/util/inMemory.ts

@@ -9,6 +9,9 @@ interface QueuedMessage {
 
 /**
  * In-memory transport for creating clients and servers that talk to each other within the same process.
+ *
+ * Intended for testing and development. For production in-process connections, use
+ * `StreamableHTTPClientTransport` against a local server URL.
  */
 export class InMemoryTransport implements Transport {
     private _otherTransport?: InMemoryTransport;