feat(a2a): Introduce restore command for a2a server (#13015)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Shreya Keshive <shreyakeshive@google.com>

packages/a2a-server/src/agent/task.ts

@@ -27,6 +27,8 @@ import {
   type Config,
   type UserTierId,
   type AnsiOutput,
+  EDIT_TOOL_NAMES,
+  processRestorableToolCalls,
 } from '@google/gemini-cli-core';
 import type { RequestContext } from '@a2a-js/sdk/server';
 import { type ExecutionEventBus } from '@a2a-js/sdk/server';
@@ -40,7 +42,8 @@ import type {
 } from '@a2a-js/sdk';
 import { v4 as uuidv4 } from 'uuid';
 import { logger } from '../utils/logger.js';
-import * as fs from 'node:fs';
+import * as fs from 'node:fs/promises';
+import * as path from 'node:path';
 import { CoderAgentEvent } from '../types.js';
 import type {
   CoderAgentMessage,
@@ -511,7 +514,7 @@ export class Task {
     new_string: string,
   ): Promise<string> {
     try {
-      const currentContent = fs.readFileSync(file_path, 'utf8');
+      const currentContent = await fs.readFile(file_path, 'utf8');
       return this._applyReplacement(
         currentContent,
         old_string,
@@ -554,6 +557,44 @@ export class Task {
       return;
     }
 
+    // Set checkpoint file before any file modification tool executes
+    const restorableToolCalls = requests.filter((request) =>
+      EDIT_TOOL_NAMES.has(request.name),
+    );
+
+    if (restorableToolCalls.length > 0) {
+      const gitService = await this.config.getGitService();
+      if (gitService) {
+        const { checkpointsToWrite, toolCallToCheckpointMap, errors } =
+          await processRestorableToolCalls(
+            restorableToolCalls,
+            gitService,
+            this.geminiClient,
+          );
+
+        if (errors.length > 0) {
+          errors.forEach((error) => logger.error(error));
+        }
+
+        if (checkpointsToWrite.size > 0) {
+          const checkpointDir =
+            this.config.storage.getProjectTempCheckpointsDir();
+          await fs.mkdir(checkpointDir, { recursive: true });
+          for (const [fileName, content] of checkpointsToWrite) {
+            const filePath = path.join(checkpointDir, fileName);
+            await fs.writeFile(filePath, content);
+          }
+        }
+
+        for (const request of requests) {
+          const checkpoint = toolCallToCheckpointMap.get(request.callId);
+          if (checkpoint) {
+            request.checkpoint = checkpoint;
+          }
+        }
+      }
+    }
+
     const updatedRequests = await Promise.all(
       requests.map(async (request) => {
         if (