fix: ensure transport is closed when connection initialization fails during client connect

Author: sid293

packages/client/src/client/client.ts

@@ -490,17 +490,17 @@ export class Client extends Protocol<ClientContext> {
      * ```
      */
     override async connect(transport: Transport, options?: RequestOptions): Promise<void> {
-        await super.connect(transport);
-        // When transport sessionId is already set this means we are trying to reconnect.
-        // Restore the protocol version negotiated during the original initialize handshake
-        // so HTTP transports include the required mcp-protocol-version header, but skip re-init.
-        if (transport.sessionId !== undefined) {
-            if (this._negotiatedProtocolVersion !== undefined && transport.setProtocolVersion) {
-                transport.setProtocolVersion(this._negotiatedProtocolVersion);
-            }
-            return;
-        }
         try {
+            await super.connect(transport);
+            // When transport sessionId is already set this means we are trying to reconnect.
+            // Restore the protocol version negotiated during the original initialize handshake
+            // so HTTP transports include the required mcp-protocol-version header, but skip re-init.
+            if (transport.sessionId !== undefined) {
+                if (this._negotiatedProtocolVersion !== undefined && transport.setProtocolVersion) {
+                    transport.setProtocolVersion(this._negotiatedProtocolVersion);
+                }
+                return;
+            }
             const result = await this._requestWithSchema(
                 {
                     method: 'initialize',

test/integration/test/client/client.test.ts

@@ -217,6 +217,33 @@ test('should reject unsupported protocol version', async () => {
     expect(clientTransport.close).toHaveBeenCalled();
 });
 
+/***
+ * Test: Connection Initialization Failure Cleanup
+ */
+test('should close transport and clean up if connection initialization fails', async () => {
+    const clientTransport: Transport = {
+        start: vi.fn().mockRejectedValue(new Error('Transport start failed')),
+        close: vi.fn().mockResolvedValue(undefined),
+        send: vi.fn().mockResolvedValue(undefined)
+    };
+
+    const client = new Client(
+        {
+            name: 'test client',
+            version: '1.0'
+        },
+        {
+            capabilities: {}
+        }
+    );
+
+    await expect(client.connect(clientTransport)).rejects.toThrow('Transport start failed');
+
+    // The transport.close() method should be called to clean up resources
+    // because the client.connect() method caught the error and called this.close()
+    expect(clientTransport.close).toHaveBeenCalled();
+});
+
 /***
  * Test: Connect New Client to Old Supported Server Version
  */