6 files changed, 425 insertions, 0 deletions
diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index d42fbbec..297178fd 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -25,6 +25,7 @@ import { WebSearchTool } from '../tools/web-search.js';
 import { GeminiClient } from '../core/client.js';
 import { GEMINI_CONFIG_DIR as GEMINI_DIR } from '../tools/memoryTool.js';
 import { FileDiscoveryService } from '../services/fileDiscoveryService.js';
+import { GitService } from '../services/gitService.js';
 import { initializeTelemetry } from '../telemetry/index.js';
 
 export enum ApprovalMode {
@@ -80,6 +81,7 @@ export interface ConfigParameters {
   fileFilteringRespectGitIgnore?: boolean;
   fileFilteringAllowBuildArtifacts?: boolean;
   enableModifyWithExternalEditors?: boolean;
+  checkpoint?: boolean;
 }
 
 export class Config {
@@ -111,6 +113,8 @@ export class Config {
   private readonly fileFilteringAllowBuildArtifacts: boolean;
   private readonly enableModifyWithExternalEditors: boolean;
   private fileDiscoveryService: FileDiscoveryService | null = null;
+  private gitService: GitService | undefined = undefined;
+  private readonly checkpoint: boolean;
 
   constructor(params: ConfigParameters) {
     this.sessionId = params.sessionId;
@@ -142,6 +146,7 @@ export class Config {
       params.fileFilteringAllowBuildArtifacts ?? false;
     this.enableModifyWithExternalEditors =
       params.enableModifyWithExternalEditors ?? false;
+    this.checkpoint = params.checkpoint ?? false;
 
     if (params.contextFileName) {
       setGeminiMdFilename(params.contextFileName);
@@ -182,6 +187,10 @@ export class Config {
     return this.targetDir;
   }
 
+  getProjectRoot(): string {
+    return this.targetDir;
+  }
+
   async getToolRegistry(): Promise<ToolRegistry> {
     return this.toolRegistry;
   }
@@ -265,6 +274,10 @@ export class Config {
     return this.geminiClient;
   }
 
+  getGeminiDir(): string {
+    return path.join(this.targetDir, GEMINI_DIR);
+  }
+
   getGeminiIgnorePatterns(): string[] {
     return this.geminiIgnorePatterns;
   }
@@ -281,6 +294,10 @@ export class Config {
     return this.enableModifyWithExternalEditors;
   }
 
+  getCheckpointEnabled(): boolean {
+    return this.checkpoint;
+  }
+
   async getFileService(): Promise<FileDiscoveryService> {
     if (!this.fileDiscoveryService) {
       this.fileDiscoveryService = new FileDiscoveryService(this.targetDir);
@@ -291,6 +308,14 @@ export class Config {
     }
     return this.fileDiscoveryService;
   }
+
+  async getGitService(): Promise<GitService> {
+    if (!this.gitService) {
+      this.gitService = new GitService(this.targetDir);
+      await this.gitService.initialize();
+    }
+    return this.gitService;
+  }
 }
 
 function findEnvFile(startDir: string): string | null {
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index 596ddcd7..4e4dc55e 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -77,6 +77,16 @@ export class GeminiClient {
     return this.chat;
   }
 
+  async getHistory(): Promise<Content[]> {
+    const chat = await this.chat;
+    return chat.getHistory();
+  }
+
+  async setHistory(history: Content[]): Promise<void> {
+    const chat = await this.chat;
+    chat.setHistory(history);
+  }
+
   private async getEnvironment(): Promise<Part[]> {
     const cwd = process.cwd();
     const today = new Date().toLocaleDateString(undefined, {
diff --git a/packages/core/src/core/geminiChat.ts b/packages/core/src/core/geminiChat.ts
index 2a81aca8..d15f9d1a 100644
--- a/packages/core/src/core/geminiChat.ts
+++ b/packages/core/src/core/geminiChat.ts
@@ -297,6 +297,9 @@ export class GeminiChat {
   addHistory(content: Content): void {
     this.history.push(content);
   }
+  setHistory(history: Content[]): void {
+    this.history = history;
+  }
 
   private async *processStreamResponse(
     streamResponse: AsyncGenerator<GenerateContentResponse>,
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 60959281..09ad1e92 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -29,6 +29,7 @@ export * from './utils/editor.js';
 
 // Export services
 export * from './services/fileDiscoveryService.js';
+export * from './services/gitService.js';
 
 // Export base tool definitions
 export * from './tools/tools.js';
diff --git a/packages/core/src/services/gitService.test.ts b/packages/core/src/services/gitService.test.ts
new file mode 100644
index 00000000..67c3c091
--- /dev/null
+++ b/packages/core/src/services/gitService.test.ts
@@ -0,0 +1,254 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { GitService, historyDirName } from './gitService.js';
+import * as path from 'path';
+import type * as FsPromisesModule from 'fs/promises';
+import type { ChildProcess } from 'node:child_process';
+
+const hoistedMockExec = vi.hoisted(() => vi.fn());
+vi.mock('node:child_process', () => ({
+  exec: hoistedMockExec,
+}));
+
+const hoistedMockMkdir = vi.hoisted(() => vi.fn());
+const hoistedMockReadFile = vi.hoisted(() => vi.fn());
+const hoistedMockWriteFile = vi.hoisted(() => vi.fn());
+
+vi.mock('fs/promises', async (importOriginal) => {
+  const actual = (await importOriginal()) as typeof FsPromisesModule;
+  return {
+    ...actual,
+    mkdir: hoistedMockMkdir,
+    readFile: hoistedMockReadFile,
+    writeFile: hoistedMockWriteFile,
+  };
+});
+
+const hoistedMockSimpleGit = vi.hoisted(() => vi.fn());
+const hoistedMockCheckIsRepo = vi.hoisted(() => vi.fn());
+const hoistedMockInit = vi.hoisted(() => vi.fn());
+const hoistedMockRaw = vi.hoisted(() => vi.fn());
+const hoistedMockAdd = vi.hoisted(() => vi.fn());
+const hoistedMockCommit = vi.hoisted(() => vi.fn());
+vi.mock('simple-git', () => ({
+  simpleGit: hoistedMockSimpleGit.mockImplementation(() => ({
+    checkIsRepo: hoistedMockCheckIsRepo,
+    init: hoistedMockInit,
+    raw: hoistedMockRaw,
+    add: hoistedMockAdd,
+    commit: hoistedMockCommit,
+  })),
+  CheckRepoActions: { IS_REPO_ROOT: 'is-repo-root' },
+}));
+
+const hoistedIsGitRepositoryMock = vi.hoisted(() => vi.fn());
+vi.mock('../utils/gitUtils.js', () => ({
+  isGitRepository: hoistedIsGitRepositoryMock,
+}));
+
+const hoistedMockIsNodeError = vi.hoisted(() => vi.fn());
+vi.mock('../utils/errors.js', () => ({
+  isNodeError: hoistedMockIsNodeError,
+}));
+
+describe('GitService', () => {
+  const mockProjectRoot = '/test/project';
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    hoistedIsGitRepositoryMock.mockReturnValue(true);
+    hoistedMockExec.mockImplementation((command, callback) => {
+      if (command === 'git --version') {
+        callback(null, 'git version 2.0.0');
+      } else {
+        callback(new Error('Command not mocked'));
+      }
+      return {};
+    });
+    hoistedMockMkdir.mockResolvedValue(undefined);
+    hoistedMockReadFile.mockResolvedValue('');
+    hoistedMockWriteFile.mockResolvedValue(undefined);
+    hoistedMockIsNodeError.mockImplementation((e) => e instanceof Error);
+
+    hoistedMockSimpleGit.mockImplementation(() => ({
+      checkIsRepo: hoistedMockCheckIsRepo,
+      init: hoistedMockInit,
+      raw: hoistedMockRaw,
+      add: hoistedMockAdd,
+      commit: hoistedMockCommit,
+    }));
+    hoistedMockCheckIsRepo.mockResolvedValue(false);
+    hoistedMockInit.mockResolvedValue(undefined);
+    hoistedMockRaw.mockResolvedValue('');
+    hoistedMockAdd.mockResolvedValue(undefined);
+    hoistedMockCommit.mockResolvedValue({
+      commit: 'initial',
+    });
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  describe('constructor', () => {
+    it('should successfully create an instance if projectRoot is a Git repository', () => {
+      expect(() => new GitService(mockProjectRoot)).not.toThrow();
+    });
+  });
+
+  describe('verifyGitAvailability', () => {
+    it('should resolve true if git --version command succeeds', async () => {
+      const service = new GitService(mockProjectRoot);
+      await expect(service.verifyGitAvailability()).resolves.toBe(true);
+    });
+
+    it('should resolve false if git --version command fails', async () => {
+      hoistedMockExec.mockImplementation((command, callback) => {
+        callback(new Error('git not found'));
+        return {} as ChildProcess;
+      });
+      const service = new GitService(mockProjectRoot);
+      await expect(service.verifyGitAvailability()).resolves.toBe(false);
+    });
+  });
+
+  describe('initialize', () => {
+    it('should throw an error if projectRoot is not a Git repository', async () => {
+      hoistedIsGitRepositoryMock.mockReturnValue(false);
+      const service = new GitService(mockProjectRoot);
+      await expect(service.initialize()).rejects.toThrow(
+        'GitService requires a Git repository',
+      );
+    });
+
+    it('should throw an error if Git is not available', async () => {
+      hoistedMockExec.mockImplementation((command, callback) => {
+        callback(new Error('git not found'));
+        return {} as ChildProcess;
+      });
+      const service = new GitService(mockProjectRoot);
+      await expect(service.initialize()).rejects.toThrow(
+        'GitService requires Git to be installed',
+      );
+    });
+  });
+
+  it('should call setupHiddenGitRepository if Git is available', async () => {
+    const service = new GitService(mockProjectRoot);
+    const setupSpy = vi
+      .spyOn(service, 'setupHiddenGitRepository')
+      .mockResolvedValue(undefined);
+
+    await service.initialize();
+    expect(setupSpy).toHaveBeenCalled();
+  });
+
+  describe('setupHiddenGitRepository', () => {
+    const historyDir = path.join(mockProjectRoot, historyDirName);
+    const repoDir = path.join(historyDir, 'repository');
+    const hiddenGitIgnorePath = path.join(repoDir, '.gitignore');
+    const visibleGitIgnorePath = path.join(mockProjectRoot, '.gitignore');
+
+    it('should create history and repository directories', async () => {
+      const service = new GitService(mockProjectRoot);
+      await service.setupHiddenGitRepository();
+      expect(hoistedMockMkdir).toHaveBeenCalledWith(repoDir, {
+        recursive: true,
+      });
+    });
+
+    it('should initialize git repo in historyDir if not already initialized', async () => {
+      hoistedMockCheckIsRepo.mockResolvedValue(false);
+      const service = new GitService(mockProjectRoot);
+      await service.setupHiddenGitRepository();
+      expect(hoistedMockSimpleGit).toHaveBeenCalledWith(repoDir);
+      expect(hoistedMockInit).toHaveBeenCalled();
+    });
+
+    it('should not initialize git repo if already initialized', async () => {
+      hoistedMockCheckIsRepo.mockResolvedValue(true);
+      const service = new GitService(mockProjectRoot);
+      await service.setupHiddenGitRepository();
+      expect(hoistedMockInit).not.toHaveBeenCalled();
+    });
+
+    it('should copy .gitignore from projectRoot if it exists', async () => {
+      const gitignoreContent = `node_modules/\n.env`;
+      hoistedMockReadFile.mockImplementation(async (filePath) => {
+        if (filePath === visibleGitIgnorePath) {
+          return gitignoreContent;
+        }
+        return '';
+      });
+      const service = new GitService(mockProjectRoot);
+      await service.setupHiddenGitRepository();
+      expect(hoistedMockReadFile).toHaveBeenCalledWith(
+        visibleGitIgnorePath,
+        'utf-8',
+      );
+      expect(hoistedMockWriteFile).toHaveBeenCalledWith(
+        hiddenGitIgnorePath,
+        gitignoreContent,
+      );
+    });
+
+    it('should throw an error if reading projectRoot .gitignore fails with other errors', async () => {
+      const readError = new Error('Read permission denied');
+      hoistedMockReadFile.mockImplementation(async (filePath) => {
+        if (filePath === visibleGitIgnorePath) {
+          throw readError;
+        }
+        return '';
+      });
+      hoistedMockIsNodeError.mockImplementation(
+        (e: unknown): e is NodeJS.ErrnoException =>
+          e === readError &&
+          e instanceof Error &&
+          (e as NodeJS.ErrnoException).code !== 'ENOENT',
+      );
+
+      const service = new GitService(mockProjectRoot);
+      await expect(service.setupHiddenGitRepository()).rejects.toThrow(
+        'Read permission denied',
+      );
+    });
+
+    it('should add historyDirName to projectRoot .gitignore if not present', async () => {
+      const initialGitignoreContent = 'node_modules/';
+      hoistedMockReadFile.mockImplementation(async (filePath) => {
+        if (filePath === visibleGitIgnorePath) {
+          return initialGitignoreContent;
+        }
+        return '';
+      });
+      const service = new GitService(mockProjectRoot);
+      await service.setupHiddenGitRepository();
+      const expectedContent = `${initialGitignoreContent}\n# Gemini CLI history directory\n${historyDirName}\n`;
+      expect(hoistedMockWriteFile).toHaveBeenCalledWith(
+        visibleGitIgnorePath,
+        expectedContent,
+      );
+    });
+
+    it('should make an initial commit if no commits exist in history repo', async () => {
+      hoistedMockRaw.mockResolvedValue('');
+      const service = new GitService(mockProjectRoot);
+      await service.setupHiddenGitRepository();
+      expect(hoistedMockAdd).toHaveBeenCalledWith(hiddenGitIgnorePath);
+      expect(hoistedMockCommit).toHaveBeenCalledWith('Initial commit');
+    });
+
+    it('should not make an initial commit if commits already exist', async () => {
+      hoistedMockRaw.mockResolvedValue('test-commit');
+      const service = new GitService(mockProjectRoot);
+      await service.setupHiddenGitRepository();
+      expect(hoistedMockAdd).not.toHaveBeenCalled();
+      expect(hoistedMockCommit).not.toHaveBeenCalled();
+    });
+  });
+});
diff --git a/packages/core/src/services/gitService.ts b/packages/core/src/services/gitService.ts
new file mode 100644
index 00000000..8cd6b887
--- /dev/null
+++ b/packages/core/src/services/gitService.ts
@@ -0,0 +1,132 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as fs from 'fs/promises';
+import * as path from 'path';
+import { isNodeError } from '../utils/errors.js';
+import { isGitRepository } from '../utils/gitUtils.js';
+import { exec } from 'node:child_process';
+import { simpleGit, SimpleGit, CheckRepoActions } from 'simple-git';
+
+export const historyDirName = '.gemini_cli_history';
+
+export class GitService {
+  private projectRoot: string;
+
+  constructor(projectRoot: string) {
+    this.projectRoot = path.resolve(projectRoot);
+  }
+
+  async initialize(): Promise<void> {
+    if (!isGitRepository(this.projectRoot)) {
+      throw new Error('GitService requires a Git repository');
+    }
+    const gitAvailable = await this.verifyGitAvailability();
+    if (!gitAvailable) {
+      throw new Error('GitService requires Git to be installed');
+    }
+    this.setupHiddenGitRepository();
+  }
+
+  verifyGitAvailability(): Promise<boolean> {
+    return new Promise((resolve) => {
+      exec('git --version', (error) => {
+        if (error) {
+          resolve(false);
+        } else {
+          resolve(true);
+        }
+      });
+    });
+  }
+
+  /**
+   * Creates a hidden git repository in the project root.
+   * The Git repository is used to support checkpointing.
+   */
+  async setupHiddenGitRepository() {
+    const historyDir = path.join(this.projectRoot, historyDirName);
+    const repoDir = path.join(historyDir, 'repository');
+
+    await fs.mkdir(repoDir, { recursive: true });
+    const repoInstance: SimpleGit = simpleGit(repoDir);
+    const isRepoDefined = await repoInstance.checkIsRepo(
+      CheckRepoActions.IS_REPO_ROOT,
+    );
+    if (!isRepoDefined) {
+      await repoInstance.init();
+      try {
+        await repoInstance.raw([
+          'worktree',
+          'add',
+          this.projectRoot,
+          '--force',
+        ]);
+      } catch (error) {
+        console.log('Failed to add worktree:', error);
+      }
+    }
+
+    const visibileGitIgnorePath = path.join(this.projectRoot, '.gitignore');
+    const hiddenGitIgnorePath = path.join(repoDir, '.gitignore');
+
+    let visibileGitIgnoreContent = ``;
+    try {
+      visibileGitIgnoreContent = await fs.readFile(
+        visibileGitIgnorePath,
+        'utf-8',
+      );
+    } catch (error) {
+      if (isNodeError(error) && error.code !== 'ENOENT') {
+        throw error;
+      }
+    }
+
+    await fs.writeFile(hiddenGitIgnorePath, visibileGitIgnoreContent);
+
+    if (!visibileGitIgnoreContent.includes(historyDirName)) {
+      const updatedContent = `${visibileGitIgnoreContent}\n# Gemini CLI history directory\n${historyDirName}\n`;
+      await fs.writeFile(visibileGitIgnorePath, updatedContent);
+    }
+
+    const commit = await repoInstance.raw([
+      'rev-list',
+      '--all',
+      '--max-count=1',
+    ]);
+    if (!commit) {
+      await repoInstance.add(hiddenGitIgnorePath);
+
+      await repoInstance.commit('Initial commit');
+    }
+  }
+
+  private get hiddenGitRepository(): SimpleGit {
+    const historyDir = path.join(this.projectRoot, historyDirName);
+    const repoDir = path.join(historyDir, 'repository');
+    return simpleGit(this.projectRoot).env({
+      GIT_DIR: path.join(repoDir, '.git'),
+      GIT_WORK_TREE: this.projectRoot,
+    });
+  }
+
+  async getCurrentCommitHash(): Promise<string> {
+    const hash = await this.hiddenGitRepository.raw('rev-parse', 'HEAD');
+    return hash.trim();
+  }
+
+  async createFileSnapshot(message: string): Promise<string> {
+    const repo = this.hiddenGitRepository;
+    await repo.add('.');
+    const commitResult = await repo.commit(message);
+    return commitResult.commit;
+  }
+
+  async restoreProjectFromSnapshot(commitHash: string): Promise<void> {
+    const repo = this.hiddenGitRepository;
+    await repo.raw(['restore', '--source', commitHash, '.']);
+  }
+}