perf(cli): cache loadSettings to reduce redundant disk I/O at startup

packages/cli/src/config/settings.test.ts

@@ -76,6 +76,7 @@ import {
   LoadedSettings,
   sanitizeEnvVar,
   createTestMergedSettings,
+  resetSettingsCacheForTesting,
 } from './settings.js';
 import {
   FatalConfigError,
@@ -174,6 +175,7 @@ describe('Settings Loading and Merging', () => {
 
   beforeEach(() => {
     vi.resetAllMocks();
+    resetSettingsCacheForTesting();
 
     mockFsExistsSync = vi.mocked(fs.existsSync);
     mockFsMkdirSync = vi.mocked(fs.mkdirSync);
@@ -1541,6 +1543,53 @@ describe('Settings Loading and Merging', () => {
         isWorkspaceHomeDirSpy.mockRestore();
       }
     });
+
+    describe('caching', () => {
+      it('should cache loadSettings results', () => {
+        const mockedRead = vi.mocked(fs.readFileSync);
+        mockedRead.mockClear();
+        mockedRead.mockReturnValue('{}');
+        (mockFsExistsSync as Mock).mockReturnValue(true);
+
+        const settings1 = loadSettings(MOCK_WORKSPACE_DIR);
+        const settings2 = loadSettings(MOCK_WORKSPACE_DIR);
+
+        expect(mockedRead).toHaveBeenCalledTimes(5); // system, systemDefaults, user, workspace, and potentially an env file
+        expect(settings1).toBe(settings2);
+      });
+
+      it('should use separate cache for different workspace directories', () => {
+        const mockedRead = vi.mocked(fs.readFileSync);
+        mockedRead.mockClear();
+        mockedRead.mockReturnValue('{}');
+        (mockFsExistsSync as Mock).mockReturnValue(true);
+
+        const workspace1 = '/mock/workspace1';
+        const workspace2 = '/mock/workspace2';
+
+        const settings1 = loadSettings(workspace1);
+        const settings2 = loadSettings(workspace2);
+
+        expect(mockedRead).toHaveBeenCalledTimes(10); // 5 for each workspace
+        expect(settings1).not.toBe(settings2);
+      });
+
+      it('should clear cache when saveSettings is called', () => {
+        const mockedRead = vi.mocked(fs.readFileSync);
+        mockedRead.mockClear();
+        mockedRead.mockReturnValue('{}');
+        (mockFsExistsSync as Mock).mockReturnValue(true);
+
+        const settings1 = loadSettings(MOCK_WORKSPACE_DIR);
+        expect(mockedRead).toHaveBeenCalledTimes(5);
+
+        saveSettings(settings1.user);
+
+        const settings2 = loadSettings(MOCK_WORKSPACE_DIR);
+        expect(mockedRead).toHaveBeenCalledTimes(10); // Should have re-read from disk
+        expect(settings1).not.toBe(settings2);
+      });
+    });
   });
 
   describe('excludedProjectEnvVars integration', () => {

packages/cli/src/config/settings.ts

@@ -18,6 +18,7 @@ import {
   coreEvents,
   homedir,
   type AdminControlsSettings,
+  createCache,
 } from '@google/gemini-cli-core';
 import stripJsonComments from 'strip-json-comments';
 import { DefaultLight } from '../ui/themes/builtin/light/default-light.js';
@@ -615,13 +616,37 @@ export function loadEnvironment(
   }
 }
 
+// Cache to store the results of loadSettings to avoid redundant disk I/O.
+const settingsCache = createCache<string, LoadedSettings>({
+  storage: 'map',
+  defaultTtl: 5000, // 5 seconds
+});
+
+/**
+ * Resets the settings cache. Used exclusively for test isolation.
+ * @internal
+ */
+export function resetSettingsCacheForTesting() {
+  settingsCache.clear();
+}
+
 /**
  * Loads settings from user and workspace directories.
  * Project settings override user settings.
  */
 export function loadSettings(
   workspaceDir: string = process.cwd(),
 ): LoadedSettings {
+  const normalizedWorkspaceDir = path.resolve(workspaceDir);
+  return settingsCache.getOrCreate(normalizedWorkspaceDir, () =>
+    _doLoadSettings(normalizedWorkspaceDir),
+  );
+}
+
+/**
+ * Internal implementation of the settings loading logic.
+ */
+function _doLoadSettings(workspaceDir: string): LoadedSettings {
   let systemSettings: Settings = {};
   let systemDefaultSettings: Settings = {};
   let userSettings: Settings = {};
@@ -1029,6 +1054,8 @@ export function migrateDeprecatedSettings(
 }
 
 export function saveSettings(settingsFile: SettingsFile): void {
+  // Clear settings cache to ensure next load gets the updated file on disk.
+  settingsCache.clear();
   try {
     // Ensure the directory exists
     const dirPath = path.dirname(settingsFile.path);