fix(patch): cherry-pick 0135b03 to release/v0.33.0-preview.2-pr-21171 [CONFLICTS] (#21336)

Co-authored-by: Shreya Keshive <shreyakeshive@google.com>

packages/cli/src/acp/fileSystemService.ts

@@ -0,0 +1,47 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { FileSystemService } from '@google/gemini-cli-core';
+import type * as acp from '@agentclientprotocol/sdk';
+
+/**
+ * ACP client-based implementation of FileSystemService
+ */
+export class AcpFileSystemService implements FileSystemService {
+  constructor(
+    private readonly connection: acp.AgentSideConnection,
+    private readonly sessionId: string,
+    private readonly capabilities: acp.FileSystemCapability,
+    private readonly fallback: FileSystemService,
+  ) {}
+
+  async readTextFile(filePath: string): Promise<string> {
+    if (!this.capabilities.readTextFile) {
+      return this.fallback.readTextFile(filePath);
+    }
+
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
+    const response = await this.connection.readTextFile({
+      path: filePath,
+      sessionId: this.sessionId,
+    });
+
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-return
+    return response.content;
+  }
+
+  async writeTextFile(filePath: string, content: string): Promise<void> {
+    if (!this.capabilities.writeTextFile) {
+      return this.fallback.writeTextFile(filePath, content);
+    }
+
+    await this.connection.writeTextFile({
+      path: filePath,
+      content,
+      sessionId: this.sessionId,
+    });
+  }
+}