Interface ExternalUpgradeRequest

The minimal request shape TwilioWebhookServer.receiveExternalUpgrade needs to complete a WebSocket handshake: ws's own handleUpgrade reads only .headers and .method on the no-verifyClient path this server uses (it never touches .socket, .url beyond what this class itself parses). A REAL http.IncomingMessage cannot travel across a process boundary — only the raw net.Socket handle can (via ChildProcess.send(msg, socket)) — so a host platform that accepts the upgrade in a separate process reconstructs this minimal shape from the request line + headers it read before handing the socket off.