Add start() to Transport interface

src/shared/transport.ts

@@ -4,6 +4,13 @@ import { JSONRPCMessage } from "../types.js";
  * Describes the minimal contract for a MCP transport that a client or server can communicate over.
  */
 export interface Transport {
+  /**
+   * Starts processing messages on the transport, including any connection steps that might need to be taken.
+   *
+   * This method should only be called after callbacks are installed, or else messages may be lost.
+   */
+  start(): Promise<void>;
+
   /**
    * Sends a JSON-RPC message (request or response).
    */