fix(core): await MCP initialization in non-interactive mode (#17390)

packages/core/src/config/config.test.ts

@@ -274,10 +274,11 @@ describe('Server Config (config.ts)', () => {
       );
     });
 
-    it('should not await MCP initialization', async () => {
+    it('should await MCP initialization in non-interactive mode', async () => {
       const config = new Config({
         ...baseParams,
         checkpointing: false,
+        // interactive defaults to false
       });
 
       const { McpClientManager } = await import(
@@ -295,7 +296,33 @@ describe('Server Config (config.ts)', () => {
 
       await config.initialize();
 
-      // Should return immediately, before MCP finishes (50ms delay)
+      // Should wait for MCP to finish
+      expect(mcpStarted).toBe(true);
+    });
+
+    it('should not await MCP initialization in interactive mode', async () => {
+      const config = new Config({
+        ...baseParams,
+        checkpointing: false,
+        interactive: true,
+      });
+
+      const { McpClientManager } = await import(
+        '../tools/mcp-client-manager.js'
+      );
+      let mcpStarted = false;
+
+      (McpClientManager as unknown as Mock).mockImplementation(() => ({
+        startConfiguredMcpServers: vi.fn().mockImplementation(async () => {
+          await new Promise((resolve) => setTimeout(resolve, 50));
+          mcpStarted = true;
+        }),
+        getMcpInstructions: vi.fn(),
+      }));
+
+      await config.initialize();
+
+      // Should return immediately, before MCP finishes
       expect(mcpStarted).toBe(false);
 
       // Wait for it to eventually finish to avoid open handles

packages/core/src/config/config.ts

@@ -815,13 +815,21 @@ export class Config {
     );
     // We do not await this promise so that the CLI can start up even if
     // MCP servers are slow to connect.
-    Promise.all([
+    const mcpInitialization = Promise.allSettled([
       this.mcpClientManager.startConfiguredMcpServers(),
       this.getExtensionLoader().start(this),
-    ]).catch((error) => {
-      debugLogger.error('Error initializing MCP clients:', error);
+    ]).then((results) => {
+      for (const result of results) {
+        if (result.status === 'rejected') {
+          debugLogger.error('Error initializing MCP clients:', result.reason);
+        }
+      }
     });
 
+    if (!this.interactive) {
+      await mcpInitialization;
+    }
+
     if (this.skillsSupport) {
       this.getSkillManager().setAdminSettings(this.adminSkillsEnabled);
       if (this.adminSkillsEnabled) {