fix(cli): don't crash startup when the output-language file is unwritable (#10453)

packages/cli/src/i18n/languageUtils.test.ts

@@ -517,6 +517,15 @@ Always use formal tone.
       expect(() => initializeLlmOutputLanguage('auto')).not.toThrow();
     });
 
+    it('should not throw when the rule file cannot be created', () => {
+      vi.mocked(fs.existsSync).mockReturnValue(false);
+      vi.mocked(fs.mkdirSync).mockImplementation(() => {
+        throw new Error('EACCES: permission denied');
+      });
+
+      expect(() => initializeLlmOutputLanguage()).not.toThrow();
+    });
+
     it('should normalize Chinese locale and create Chinese rule file', () => {
       vi.mocked(fs.existsSync).mockReturnValue(false);
 

packages/cli/src/i18n/languageUtils.ts

@@ -319,5 +319,10 @@ export function initializeLlmOutputLanguage(outputLanguage?: string): void {
 
   // File doesn't exist or has invalid content, create it with configured language behavior
   const resolved = resolveOutputLanguageOrPreserveAuto(outputLanguage);
-  writeOutputLanguageFile(resolved);
+  try {
+    writeOutputLanguageFile(resolved);
+  } catch {
+    // Creation is best-effort, like the migration above: the rule file is
+    // advisory, so an unwritable global dir must not crash startup.
+  }
 }