fix(core): handle non-compliant mcpbridge responses from Xcode 26.3 (#18376)

packages/core/src/tools/mcp-client.ts

@@ -42,6 +42,7 @@ import { AuthProviderType } from '../config/config.js';
 import { GoogleCredentialProvider } from '../mcp/google-auth-provider.js';
 import { ServiceAccountImpersonationProvider } from '../mcp/sa-impersonation-provider.js';
 import { DiscoveredMCPTool } from './mcp-tool.js';
+import { XcodeMcpBridgeFixTransport } from './xcode-mcp-fix-transport.js';
 
 import type { CallableTool, FunctionCall, Part, Tool } from '@google/genai';
 import { basename } from 'node:path';
@@ -1905,7 +1906,7 @@ export async function createTransport(
   }
 
   if (mcpServerConfig.command) {
-    const transport = new StdioClientTransport({
+    let transport: Transport = new StdioClientTransport({
       command: mcpServerConfig.command,
       args: mcpServerConfig.args || [],
       env: sanitizeEnvironment(
@@ -1928,14 +1929,38 @@ export async function createTransport(
       cwd: mcpServerConfig.cwd,
       stderr: 'pipe',
     });
+
+    // Fix for Xcode 26.3 mcpbridge non-compliant responses
+    // It returns JSON in `content` instead of `structuredContent`
+    if (
+      mcpServerConfig.command === 'xcrun' &&
+      mcpServerConfig.args?.includes('mcpbridge')
+    ) {
+      transport = new XcodeMcpBridgeFixTransport(transport);
+    }
+
     if (debugMode) {
-      transport.stderr!.on('data', (data) => {
-        const stderrStr = data.toString().trim();
-        debugLogger.debug(
-          `[DEBUG] [MCP STDERR (${mcpServerName})]: `,
-          stderrStr,
-        );
-      });
+      // The `XcodeMcpBridgeFixTransport` wrapper hides the underlying `StdioClientTransport`,
+      // which exposes `stderr` for debug logging. We need to unwrap it to attach the listener.
+
+      const underlyingTransport =
+        transport instanceof XcodeMcpBridgeFixTransport
+          ? // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            (transport as any).transport
+          : transport;
+
+      if (
+        underlyingTransport instanceof StdioClientTransport &&
+        underlyingTransport.stderr
+      ) {
+        underlyingTransport.stderr.on('data', (data) => {
+          const stderrStr = data.toString().trim();
+          debugLogger.debug(
+            `[DEBUG] [MCP STDERR (${mcpServerName})]: `,
+            stderrStr,
+          );
+        });
+      }
     }
     return transport;
   }