test(cli): add tests for builtin extension collisions and migration

packages/cli/extensions-dir/my-extension/gemini-extension.json

@@ -0,0 +1 @@
+{ "name": "my-extension", "version": "1.0.0", "mcpServers": {} }

packages/cli/src/config/extension-manager.test.ts

@@ -22,6 +22,7 @@ import {
   getRealPath,
   type CustomTheme,
   IntegrityDataStatus,
+  coreEvents,
 } from '@google/gemini-cli-core';
 
 const mockHomedir = vi.hoisted(() => vi.fn(() => '/tmp/mock-home'));
@@ -697,4 +698,97 @@ describe('ExtensionManager', () => {
       );
     });
   });
+
+  describe('Builtin Extensions', () => {
+    let builtinExtensionsDir: string;
+
+    beforeEach(() => {
+      builtinExtensionsDir = fs.mkdtempSync(
+        path.join(tempHomeDir, 'gemini-cli-test-builtin-'),
+      );
+    });
+
+    it('should warn and prefer builtin when names collide', async () => {
+      // 1. Create a manual extension named 'test-ext'
+      createExtension({
+        extensionsDir: userExtensionsDir,
+        name: 'test-ext',
+        version: '1.0.0-manual',
+      });
+
+      // 2. Create a builtin extension named 'test-ext'
+      createExtension({
+        extensionsDir: builtinExtensionsDir,
+        name: 'test-ext',
+        version: '1.0.0-builtin',
+      });
+
+      const emitSpy = vi.spyOn(coreEvents, 'emitFeedback');
+
+      // Create a FRESH manager to ensure loadExtensions actually runs
+      const manager = new ExtensionManager({
+        settings: createTestMergedSettings(),
+        workspaceDir: tempWorkspaceDir,
+        requestConsent: vi.fn().mockResolvedValue(true),
+        requestSetting: null,
+      });
+
+      const extensions = await manager.loadExtensions(builtinExtensionsDir);
+
+      // Verify builtin took precedence
+      const testExt = extensions.find((e) => e.name === 'test-ext');
+      expect(testExt).toBeDefined();
+      expect(testExt?.version).toBe('1.0.0-builtin');
+
+      // Verify warning was shown
+      expect(emitSpy).toHaveBeenCalledWith(
+        'warning',
+        expect.stringContaining('Extension "test-ext" is now built-in'),
+      );
+    });
+
+    it('should warn when legacy conductor is found while loading sdd builtin', async () => {
+      // 1. Create a manual extension named 'conductor'
+      createExtension({
+        extensionsDir: userExtensionsDir,
+        name: 'conductor',
+        version: '0.1.0',
+      });
+
+      // 2. Create a builtin extension named 'sdd'
+      createExtension({
+        extensionsDir: builtinExtensionsDir,
+        name: 'sdd',
+        version: '1.0.0',
+      });
+
+      const emitSpy = vi.spyOn(coreEvents, 'emitFeedback');
+
+      // Create a FRESH manager
+      const manager = new ExtensionManager({
+        settings: createTestMergedSettings(),
+        workspaceDir: tempWorkspaceDir,
+        requestConsent: vi.fn().mockResolvedValue(true),
+        requestSetting: null,
+      });
+
+      const extensions = await manager.loadExtensions(builtinExtensionsDir);
+
+      // Verify both are loaded (logic currently loads both but warns)
+      expect(extensions.find((e) => e.name === 'conductor')).toBeDefined();
+      expect(extensions.find((e) => e.name === 'sdd')).toBeDefined();
+
+      // Verify warning was shown
+      expect(emitSpy).toHaveBeenCalledWith(
+        'warning',
+        expect.stringContaining(
+          'The "conductor" extension has been renamed to "sdd"',
+        ),
+      );
+      expect(emitSpy).toHaveBeenCalledWith(
+        'warning',
+        expect.stringContaining('.gemini/specs/'),
+      );
+    });
+  });
 });

packages/cli/src/config/extension-manager.ts

@@ -604,7 +604,7 @@ Would you like to attempt to install via "git clone" instead?`,
   /**
    * Loads all installed extensions, should only be called once.
    */
-  async loadExtensions(): Promise<GeminiCLIExtension[]> {
+  async loadExtensions(builtinDir?: string): Promise<GeminiCLIExtension[]> {
     if (this.loadedExtensions) {
       throw new Error('Extensions already loaded, only load extensions once.');
     }
@@ -637,26 +637,30 @@ Would you like to attempt to install via "git clone" instead?`,
           (ext): ext is GeminiCLIExtension => ext !== null,
         );
 
-        let builtinExtensionsDir = path.join(
+        let builtinExtensionsDir = builtinDir;
-          path.dirname(fileURLToPath(import.meta.url)),
+        if (!builtinExtensionsDir) {
-          'extensions',
-          'builtin',
-        );
-        if (!fs.existsSync(builtinExtensionsDir)) {
           builtinExtensionsDir = path.join(
             path.dirname(fileURLToPath(import.meta.url)),
-            '..',
-            '..',
-            '..',
-            '..',
-            'core',
-            'src',
             'extensions',
             'builtin',
           );
+          if (!fs.existsSync(builtinExtensionsDir)) {
+            builtinExtensionsDir = path.join(
+              path.dirname(fileURLToPath(import.meta.url)),
+              '..',
+              '..',
+              '..',
+              '..',
+              'core',
+              'src',
+              'extensions',
+              'builtin',
+            );
+          }
         }
 
-        if (!process.env['VITEST'] && fs.existsSync(builtinExtensionsDir)) {
+        const loadBuiltins = builtinDir || !process.env['VITEST'];
+        if (loadBuiltins && fs.existsSync(builtinExtensionsDir)) {
           const builtinSubdirs =
             await fs.promises.readdir(builtinExtensionsDir);
           const builtinPromises = builtinSubdirs.map((subdir) => {