fix(core): create new McpClient on restart to apply updated config (#20126)

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

@@ -264,6 +264,40 @@ describe('McpClientManager', () => {
         'No MCP server registered with the name "non-existent"',
       );
     });
+
+    it('should create a new McpClient with updated config on restart', async () => {
+      const originalConfig = { command: 'node', args: ['--port', '8000'] };
+      const updatedConfig = { command: 'node', args: ['--port', '9000'] };
+
+      mockConfig.getMcpServers.mockReturnValue({
+        'test-server': originalConfig,
+      });
+
+      // Track McpClient constructor calls
+      const constructorCalls: unknown[][] = [];
+      vi.mocked(McpClient).mockImplementation((...args: unknown[]) => {
+        constructorCalls.push(args);
+        return mockedMcpClient;
+      });
+      mockedMcpClient.getServerConfig.mockReturnValue(originalConfig);
+
+      const manager = new McpClientManager('0.0.1', toolRegistry, mockConfig);
+      await manager.startConfiguredMcpServers();
+
+      // First call should use the original config
+      expect(constructorCalls).toHaveLength(1);
+      expect(constructorCalls[0][1]).toBe(originalConfig);
+
+      // Simulate config file change and hot-reload
+      mockConfig.getMcpServers.mockReturnValue({
+        'test-server': updatedConfig,
+      });
+      await manager.startConfiguredMcpServers();
+
+      // A NEW McpClient should have been constructed with the updated config
+      expect(constructorCalls).toHaveLength(2);
+      expect(constructorCalls[1][1]).toBe(updatedConfig);
+    });
   });
 
   describe('getMcpInstructions', () => {

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

@@ -221,30 +221,27 @@ export class McpClientManager {
       (async () => {
         try {
           if (existing) {
+            this.clients.delete(name);
             await existing.disconnect();
           }
 
-          const client =
+          const client = new McpClient(
-            existing ??
+            name,
-            new McpClient(
+            config,
-              name,
+            this.toolRegistry,
-              config,
+            this.cliConfig.getPromptRegistry(),
-              this.toolRegistry,
+            this.cliConfig.getResourceRegistry(),
-              this.cliConfig.getPromptRegistry(),
+            this.cliConfig.getWorkspaceContext(),
-              this.cliConfig.getResourceRegistry(),
+            this.cliConfig,
-              this.cliConfig.getWorkspaceContext(),
+            this.cliConfig.getDebugMode(),
-              this.cliConfig,
+            this.clientVersion,
-              this.cliConfig.getDebugMode(),
+            async () => {
-              this.clientVersion,
+              debugLogger.log('Tools changed, updating Gemini context...');
-              async () => {
+              await this.scheduleMcpContextRefresh();
-                debugLogger.log('Tools changed, updating Gemini context...');
+            },
-                await this.scheduleMcpContextRefresh();
+          );
-              },
+          this.clients.set(name, client);
-            );
+          this.eventEmitter?.emit('mcp-client-update', this.clients);
-          if (!existing) {
-            this.clients.set(name, client);
-            this.eventEmitter?.emit('mcp-client-update', this.clients);
-          }
           try {
             await client.connect();
             await client.discover(this.cliConfig);