6 files changed, 1161 insertions, 1 deletions

diff --git a/packages/cli/src/acp/acp.ts b/packages/cli/src/acp/acp.ts
new file mode 100644
index 00000000..1fbdf7a8
--- /dev/null
+++ b/packages/cli/src/acp/acp.ts
@@ -0,0 +1,464 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* ACP defines a schema for a simple (experimental) JSON-RPC protocol that allows GUI applications to interact with agents. */
+
+import { Icon } from '@google/gemini-cli-core';
+import { WritableStream, ReadableStream } from 'node:stream/web';
+
+export class ClientConnection implements Client {
+  #connection: Connection<Agent>;
+
+  constructor(
+    agent: (client: Client) => Agent,
+    input: WritableStream<Uint8Array>,
+    output: ReadableStream<Uint8Array>,
+  ) {
+    this.#connection = new Connection(agent(this), input, output);
+  }
+
+  /**
+   * Streams part of an assistant response to the client
+   */
+  async streamAssistantMessageChunk(
+    params: StreamAssistantMessageChunkParams,
+  ): Promise<void> {
+    await this.#connection.sendRequest('streamAssistantMessageChunk', params);
+  }
+
+  /**
+   * Request confirmation before running a tool
+   *
+   * When allowed, the client returns a [`ToolCallId`] which can be used
+   * to update the tool call's `status` and `content` as it runs.
+   */
+  requestToolCallConfirmation(
+    params: RequestToolCallConfirmationParams,
+  ): Promise<RequestToolCallConfirmationResponse> {
+    return this.#connection.sendRequest('requestToolCallConfirmation', params);
+  }
+
+  /**
+   * pushToolCall allows the agent to start a tool call
+   * when it does not need to request permission to do so.
+   *
+   * The returned id can be used to update the UI for the tool
+   * call as needed.
+   */
+  pushToolCall(params: PushToolCallParams): Promise<PushToolCallResponse> {
+    return this.#connection.sendRequest('pushToolCall', params);
+  }
+
+  /**
+   * updateToolCall allows the agent to update the content and status of the tool call.
+   *
+   * The new content replaces what is currently displayed in the UI.
+   *
+   * The [`ToolCallId`] is included in the response of
+   * `pushToolCall` or `requestToolCallConfirmation` respectively.
+   */
+  async updateToolCall(params: UpdateToolCallParams): Promise<void> {
+    await this.#connection.sendRequest('updateToolCall', params);
+  }
+}
+
+type AnyMessage = AnyRequest | AnyResponse;
+
+type AnyRequest = {
+  id: number;
+  method: string;
+  params?: unknown;
+};
+
+type AnyResponse = { jsonrpc: '2.0'; id: number } & Result<unknown>;
+
+type Result<T> =
+  | {
+      result: T;
+    }
+  | {
+      error: ErrorResponse;
+    };
+
+type ErrorResponse = {
+  code: number;
+  message: string;
+  data?: { details?: string };
+};
+
+type PendingResponse = {
+  resolve: (response: unknown) => void;
+  reject: (error: ErrorResponse) => void;
+};
+
+class Connection<D> {
+  #pendingResponses: Map<number, PendingResponse> = new Map();
+  #nextRequestId: number = 0;
+  #delegate: D;
+  #peerInput: WritableStream<Uint8Array>;
+  #writeQueue: Promise<void> = Promise.resolve();
+  #textEncoder: TextEncoder;
+
+  constructor(
+    delegate: D,
+    peerInput: WritableStream<Uint8Array>,
+    peerOutput: ReadableStream<Uint8Array>,
+  ) {
+    this.#peerInput = peerInput;
+    this.#textEncoder = new TextEncoder();
+
+    this.#delegate = delegate;
+    this.#receive(peerOutput);
+  }
+
+  async #receive(output: ReadableStream<Uint8Array>) {
+    let content = '';
+    const decoder = new TextDecoder();
+    for await (const chunk of output) {
+      content += decoder.decode(chunk, { stream: true });
+      const lines = content.split('\n');
+      content = lines.pop() || '';
+
+      for (const line of lines) {
+        const trimmedLine = line.trim();
+
+        if (trimmedLine) {
+          const message = JSON.parse(trimmedLine);
+          this.#processMessage(message);
+        }
+      }
+    }
+  }
+
+  async #processMessage(message: AnyMessage) {
+    if ('method' in message) {
+      const response = await this.#tryCallDelegateMethod(
+        message.method,
+        message.params,
+      );
+
+      await this.#sendMessage({
+        jsonrpc: '2.0',
+        id: message.id,
+        ...response,
+      });
+    } else {
+      this.#handleResponse(message);
+    }
+  }
+
+  async #tryCallDelegateMethod(
+    method: string,
+    params?: unknown,
+  ): Promise<Result<unknown>> {
+    const methodName = method as keyof D;
+    if (typeof this.#delegate[methodName] !== 'function') {
+      return RequestError.methodNotFound(method).toResult();
+    }
+
+    try {
+      const result = await this.#delegate[methodName](params);
+      return { result: result ?? null };
+    } catch (error: unknown) {
+      if (error instanceof RequestError) {
+        return error.toResult();
+      }
+
+      let details;
+
+      if (error instanceof Error) {
+        details = error.message;
+      } else if (
+        typeof error === 'object' &&
+        error != null &&
+        'message' in error &&
+        typeof error.message === 'string'
+      ) {
+        details = error.message;
+      }
+
+      return RequestError.internalError(details).toResult();
+    }
+  }
+
+  #handleResponse(response: AnyResponse) {
+    const pendingResponse = this.#pendingResponses.get(response.id);
+    if (pendingResponse) {
+      if ('result' in response) {
+        pendingResponse.resolve(response.result);
+      } else if ('error' in response) {
+        pendingResponse.reject(response.error);
+      }
+      this.#pendingResponses.delete(response.id);
+    }
+  }
+
+  async sendRequest<Req, Resp>(method: string, params?: Req): Promise<Resp> {
+    const id = this.#nextRequestId++;
+    const responsePromise = new Promise((resolve, reject) => {
+      this.#pendingResponses.set(id, { resolve, reject });
+    });
+    await this.#sendMessage({ jsonrpc: '2.0', id, method, params });
+    return responsePromise as Promise<Resp>;
+  }
+
+  async #sendMessage(json: AnyMessage) {
+    const content = JSON.stringify(json) + '\n';
+    this.#writeQueue = this.#writeQueue
+      .then(async () => {
+        const writer = this.#peerInput.getWriter();
+        try {
+          await writer.write(this.#textEncoder.encode(content));
+        } finally {
+          writer.releaseLock();
+        }
+      })
+      .catch((error) => {
+        // Continue processing writes on error
+        console.error('ACP write error:', error);
+      });
+    return this.#writeQueue;
+  }
+}
+
+export class RequestError extends Error {
+  data?: { details?: string };
+
+  constructor(
+    public code: number,
+    message: string,
+    details?: string,
+  ) {
+    super(message);
+    this.name = 'RequestError';
+    if (details) {
+      this.data = { details };
+    }
+  }
+
+  static parseError(details?: string): RequestError {
+    return new RequestError(-32700, 'Parse error', details);
+  }
+
+  static invalidRequest(details?: string): RequestError {
+    return new RequestError(-32600, 'Invalid request', details);
+  }
+
+  static methodNotFound(details?: string): RequestError {
+    return new RequestError(-32601, 'Method not found', details);
+  }
+
+  static invalidParams(details?: string): RequestError {
+    return new RequestError(-32602, 'Invalid params', details);
+  }
+
+  static internalError(details?: string): RequestError {
+    return new RequestError(-32603, 'Internal error', details);
+  }
+
+  toResult<T>(): Result<T> {
+    return {
+      error: {
+        code: this.code,
+        message: this.message,
+        data: this.data,
+      },
+    };
+  }
+}
+
+// Protocol types
+
+export const LATEST_PROTOCOL_VERSION = '0.0.9';
+
+export type AssistantMessageChunk =
+  | {
+      text: string;
+    }
+  | {
+      thought: string;
+    };
+
+export type ToolCallConfirmation =
+  | {
+      description?: string | null;
+      type: 'edit';
+    }
+  | {
+      description?: string | null;
+      type: 'execute';
+      command: string;
+      rootCommand: string;
+    }
+  | {
+      description?: string | null;
+      type: 'mcp';
+      serverName: string;
+      toolDisplayName: string;
+      toolName: string;
+    }
+  | {
+      description?: string | null;
+      type: 'fetch';
+      urls: string[];
+    }
+  | {
+      description: string;
+      type: 'other';
+    };
+
+export type ToolCallContent =
+  | {
+      type: 'markdown';
+      markdown: string;
+    }
+  | {
+      type: 'diff';
+      newText: string;
+      oldText: string | null;
+      path: string;
+    };
+
+export type ToolCallStatus = 'running' | 'finished' | 'error';
+
+export type ToolCallId = number;
+
+export type ToolCallConfirmationOutcome =
+  | 'allow'
+  | 'alwaysAllow'
+  | 'alwaysAllowMcpServer'
+  | 'alwaysAllowTool'
+  | 'reject'
+  | 'cancel';
+
+/**
+ * A part in a user message
+ */
+export type UserMessageChunk =
+  | {
+      text: string;
+    }
+  | {
+      path: string;
+    };
+
+export interface StreamAssistantMessageChunkParams {
+  chunk: AssistantMessageChunk;
+}
+
+export interface RequestToolCallConfirmationParams {
+  confirmation: ToolCallConfirmation;
+  content?: ToolCallContent | null;
+  icon: Icon;
+  label: string;
+  locations?: ToolCallLocation[];
+}
+
+export interface ToolCallLocation {
+  line?: number | null;
+  path: string;
+}
+
+export interface PushToolCallParams {
+  content?: ToolCallContent | null;
+  icon: Icon;
+  label: string;
+  locations?: ToolCallLocation[];
+}
+
+export interface UpdateToolCallParams {
+  content: ToolCallContent | null;
+  status: ToolCallStatus;
+  toolCallId: ToolCallId;
+}
+
+export interface RequestToolCallConfirmationResponse {
+  id: ToolCallId;
+  outcome: ToolCallConfirmationOutcome;
+}
+
+export interface PushToolCallResponse {
+  id: ToolCallId;
+}
+
+export interface InitializeParams {
+  /**
+   * The version of the protocol that the client supports.
+   * This should be the latest version supported by the client.
+   */
+  protocolVersion: string;
+}
+
+export interface SendUserMessageParams {
+  chunks: UserMessageChunk[];
+}
+
+export interface InitializeResponse {
+  /**
+   * Indicates whether the agent is authenticated and
+   * ready to handle requests.
+   */
+  isAuthenticated: boolean;
+  /**
+   * The version of the protocol that the agent supports.
+   * If the agent supports the requested version, it should respond with the same version.
+   * Otherwise, the agent should respond with the latest version it supports.
+   */
+  protocolVersion: string;
+}
+
+export interface Error {
+  code: number;
+  data?: unknown;
+  message: string;
+}
+
+export interface Client {
+  streamAssistantMessageChunk(
+    params: StreamAssistantMessageChunkParams,
+  ): Promise<void>;
+
+  requestToolCallConfirmation(
+    params: RequestToolCallConfirmationParams,
+  ): Promise<RequestToolCallConfirmationResponse>;
+
+  pushToolCall(params: PushToolCallParams): Promise<PushToolCallResponse>;
+
+  updateToolCall(params: UpdateToolCallParams): Promise<void>;
+}
+
+export interface Agent {
+  /**
+   * Initializes the agent's state. It should be called before any other method,
+   * and no other methods should be called until it has completed.
+   *
+   * If the agent is not authenticated, then the client should prompt the user to authenticate,
+   * and then call the `authenticate` method.
+   * Otherwise the client can send other messages to the agent.
+   */
+  initialize(params: InitializeParams): Promise<InitializeResponse>;
+
+  /**
+   * Begins the authentication process.
+   *
+   * This method should only be called if `initialize` indicates the user isn't already authenticated.
+   * The Promise MUST not resolve until authentication is complete.
+   */
+  authenticate(): Promise<void>;
+
+  /**
+   * Allows the user to send a message to the agent.
+   * This method should complete after the agent is finished, during
+   * which time the agent may update the client by calling
+   * streamAssistantMessageChunk and other methods.
+   */
+  sendUserMessage(params: SendUserMessageParams): Promise<void>;
+
+  /**
+   * Cancels the current generation.
+   */
+  cancelSendMessage(): Promise<void>;
+}
diff --git a/packages/cli/src/acp/acpPeer.ts b/packages/cli/src/acp/acpPeer.ts
new file mode 100644
index 00000000..90952b7f
--- /dev/null
+++ b/packages/cli/src/acp/acpPeer.ts
@@ -0,0 +1,674 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { WritableStream, ReadableStream } from 'node:stream/web';
+
+import {
+  AuthType,
+  Config,
+  GeminiChat,
+  ToolRegistry,
+  logToolCall,
+  ToolResult,
+  convertToFunctionResponse,
+  ToolCallConfirmationDetails,
+  ToolConfirmationOutcome,
+  clearCachedCredentialFile,
+  isNodeError,
+  getErrorMessage,
+  isWithinRoot,
+  getErrorStatus,
+} from '@google/gemini-cli-core';
+import * as acp from './acp.js';
+import { Agent } from './acp.js';
+import { Readable, Writable } from 'node:stream';
+import { Content, Part, FunctionCall, PartListUnion } from '@google/genai';
+import { LoadedSettings, SettingScope } from '../config/settings.js';
+import * as fs from 'fs/promises';
+import * as path from 'path';
+
+export async function runAcpPeer(config: Config, settings: LoadedSettings) {
+  const stdout = Writable.toWeb(process.stdout) as WritableStream;
+  const stdin = Readable.toWeb(process.stdin) as ReadableStream<Uint8Array>;
+
+  // Stdout is used to send messages to the client, so console.log/console.info
+  // messages to stderr so that they don't interfere with ACP.
+  console.log = console.error;
+  console.info = console.error;
+  console.debug = console.error;
+
+  new acp.ClientConnection(
+    (client: acp.Client) => new GeminiAgent(config, settings, client),
+    stdout,
+    stdin,
+  );
+}
+
+class GeminiAgent implements Agent {
+  chat?: GeminiChat;
+  pendingSend?: AbortController;
+
+  constructor(
+    private config: Config,
+    private settings: LoadedSettings,
+    private client: acp.Client,
+  ) {}
+
+  async initialize(_: acp.InitializeParams): Promise<acp.InitializeResponse> {
+    let isAuthenticated = false;
+    if (this.settings.merged.selectedAuthType) {
+      try {
+        await this.config.refreshAuth(this.settings.merged.selectedAuthType);
+        isAuthenticated = true;
+      } catch (error) {
+        console.error('Failed to refresh auth:', error);
+      }
+    }
+    return { protocolVersion: acp.LATEST_PROTOCOL_VERSION, isAuthenticated };
+  }
+
+  async authenticate(): Promise<void> {
+    await clearCachedCredentialFile();
+    await this.config.refreshAuth(AuthType.LOGIN_WITH_GOOGLE);
+    this.settings.setValue(
+      SettingScope.User,
+      'selectedAuthType',
+      AuthType.LOGIN_WITH_GOOGLE,
+    );
+  }
+
+  async cancelSendMessage(): Promise<void> {
+    if (!this.pendingSend) {
+      throw new Error('Not currently generating');
+    }
+
+    this.pendingSend.abort();
+    delete this.pendingSend;
+  }
+
+  async sendUserMessage(params: acp.SendUserMessageParams): Promise<void> {
+    this.pendingSend?.abort();
+    const pendingSend = new AbortController();
+    this.pendingSend = pendingSend;
+
+    if (!this.chat) {
+      const geminiClient = this.config.getGeminiClient();
+      this.chat = await geminiClient.startChat();
+    }
+
+    const promptId = Math.random().toString(16).slice(2);
+    const chat = this.chat!;
+    const toolRegistry: ToolRegistry = await this.config.getToolRegistry();
+    const parts = await this.#resolveUserMessage(params, pendingSend.signal);
+
+    let nextMessage: Content | null = { role: 'user', parts };
+
+    while (nextMessage !== null) {
+      if (pendingSend.signal.aborted) {
+        chat.addHistory(nextMessage);
+        return;
+      }
+
+      const functionCalls: FunctionCall[] = [];
+
+      try {
+        const responseStream = await chat.sendMessageStream(
+          {
+            message: nextMessage?.parts ?? [],
+            config: {
+              abortSignal: pendingSend.signal,
+              tools: [
+                {
+                  functionDeclarations: toolRegistry.getFunctionDeclarations(),
+                },
+              ],
+            },
+          },
+          promptId,
+        );
+        nextMessage = null;
+
+        for await (const resp of responseStream) {
+          if (pendingSend.signal.aborted) {
+            return;
+          }
+
+          if (resp.candidates && resp.candidates.length > 0) {
+            const candidate = resp.candidates[0];
+            for (const part of candidate.content?.parts ?? []) {
+              if (!part.text) {
+                continue;
+              }
+
+              this.client.streamAssistantMessageChunk({
+                chunk: part.thought
+                  ? { thought: part.text }
+                  : { text: part.text },
+              });
+            }
+          }
+
+          if (resp.functionCalls) {
+            functionCalls.push(...resp.functionCalls);
+          }
+        }
+      } catch (error) {
+        if (getErrorStatus(error) === 429) {
+          throw new acp.RequestError(
+            429,
+            'Rate limit exceeded. Try again later.',
+          );
+        }
+
+        throw error;
+      }
+
+      if (functionCalls.length > 0) {
+        const toolResponseParts: Part[] = [];
+
+        for (const fc of functionCalls) {
+          const response = await this.#runTool(
+            pendingSend.signal,
+            promptId,
+            fc,
+          );
+
+          const parts = Array.isArray(response) ? response : [response];
+
+          for (const part of parts) {
+            if (typeof part === 'string') {
+              toolResponseParts.push({ text: part });
+            } else if (part) {
+              toolResponseParts.push(part);
+            }
+          }
+        }
+
+        nextMessage = { role: 'user', parts: toolResponseParts };
+      }
+    }
+  }
+
+  async #runTool(
+    abortSignal: AbortSignal,
+    promptId: string,
+    fc: FunctionCall,
+  ): Promise<PartListUnion> {
+    const callId = fc.id ?? `${fc.name}-${Date.now()}`;
+    const args = (fc.args ?? {}) as Record<string, unknown>;
+
+    const startTime = Date.now();
+
+    const errorResponse = (error: Error) => {
+      const durationMs = Date.now() - startTime;
+      logToolCall(this.config, {
+        'event.name': 'tool_call',
+        'event.timestamp': new Date().toISOString(),
+        prompt_id: promptId,
+        function_name: fc.name ?? '',
+        function_args: args,
+        duration_ms: durationMs,
+        success: false,
+        error: error.message,
+      });
+
+      return [
+        {
+          functionResponse: {
+            id: callId,
+            name: fc.name ?? '',
+            response: { error: error.message },
+          },
+        },
+      ];
+    };
+
+    if (!fc.name) {
+      return errorResponse(new Error('Missing function name'));
+    }
+
+    const toolRegistry: ToolRegistry = await this.config.getToolRegistry();
+    const tool = toolRegistry.getTool(fc.name as string);
+
+    if (!tool) {
+      return errorResponse(
+        new Error(`Tool "${fc.name}" not found in registry.`),
+      );
+    }
+
+    let toolCallId;
+    const confirmationDetails = await tool.shouldConfirmExecute(
+      args,
+      abortSignal,
+    );
+    if (confirmationDetails) {
+      let content: acp.ToolCallContent | null = null;
+      if (confirmationDetails.type === 'edit') {
+        content = {
+          type: 'diff',
+          path: confirmationDetails.fileName,
+          oldText: confirmationDetails.originalContent,
+          newText: confirmationDetails.newContent,
+        };
+      }
+
+      const result = await this.client.requestToolCallConfirmation({
+        label: tool.getDescription(args),
+        icon: tool.icon,
+        content,
+        confirmation: toAcpToolCallConfirmation(confirmationDetails),
+        locations: tool.toolLocations(args),
+      });
+
+      await confirmationDetails.onConfirm(toToolCallOutcome(result.outcome));
+      switch (result.outcome) {
+        case 'reject':
+          return errorResponse(
+            new Error(`Tool "${fc.name}" not allowed to run by the user.`),
+          );
+
+        case 'cancel':
+          return errorResponse(
+            new Error(`Tool "${fc.name}" was canceled by the user.`),
+          );
+        case 'allow':
+        case 'alwaysAllow':
+        case 'alwaysAllowMcpServer':
+        case 'alwaysAllowTool':
+          break;
+        default: {
+          const resultOutcome: never = result.outcome;
+          throw new Error(`Unexpected: ${resultOutcome}`);
+        }
+      }
+
+      toolCallId = result.id;
+    } else {
+      const result = await this.client.pushToolCall({
+        icon: tool.icon,
+        label: tool.getDescription(args),
+        locations: tool.toolLocations(args),
+      });
+
+      toolCallId = result.id;
+    }
+
+    try {
+      const toolResult: ToolResult = await tool.execute(args, abortSignal);
+      const toolCallContent = toToolCallContent(toolResult);
+
+      await this.client.updateToolCall({
+        toolCallId,
+        status: 'finished',
+        content: toolCallContent,
+      });
+
+      const durationMs = Date.now() - startTime;
+      logToolCall(this.config, {
+        'event.name': 'tool_call',
+        'event.timestamp': new Date().toISOString(),
+        function_name: fc.name,
+        function_args: args,
+        duration_ms: durationMs,
+        success: true,
+        prompt_id: promptId,
+      });
+
+      return convertToFunctionResponse(fc.name, callId, toolResult.llmContent);
+    } catch (e) {
+      const error = e instanceof Error ? e : new Error(String(e));
+      await this.client.updateToolCall({
+        toolCallId,
+        status: 'error',
+        content: { type: 'markdown', markdown: error.message },
+      });
+
+      return errorResponse(error);
+    }
+  }
+
+  async #resolveUserMessage(
+    message: acp.SendUserMessageParams,
+    abortSignal: AbortSignal,
+  ): Promise<Part[]> {
+    const atPathCommandParts = message.chunks.filter((part) => 'path' in part);
+
+    if (atPathCommandParts.length === 0) {
+      return message.chunks.map((chunk) => {
+        if ('text' in chunk) {
+          return { text: chunk.text };
+        } else {
+          throw new Error('Unexpected chunk type');
+        }
+      });
+    }
+
+    // Get centralized file discovery service
+    const fileDiscovery = this.config.getFileService();
+    const respectGitIgnore = this.config.getFileFilteringRespectGitIgnore();
+
+    const pathSpecsToRead: string[] = [];
+    const atPathToResolvedSpecMap = new Map<string, string>();
+    const contentLabelsForDisplay: string[] = [];
+    const ignoredPaths: string[] = [];
+
+    const toolRegistry = await this.config.getToolRegistry();
+    const readManyFilesTool = toolRegistry.getTool('read_many_files');
+    const globTool = toolRegistry.getTool('glob');
+
+    if (!readManyFilesTool) {
+      throw new Error('Error: read_many_files tool not found.');
+    }
+
+    for (const atPathPart of atPathCommandParts) {
+      const pathName = atPathPart.path;
+
+      // Check if path should be ignored by git
+      if (fileDiscovery.shouldGitIgnoreFile(pathName)) {
+        ignoredPaths.push(pathName);
+        const reason = respectGitIgnore
+          ? 'git-ignored and will be skipped'
+          : 'ignored by custom patterns';
+        console.warn(`Path ${pathName} is ${reason}.`);
+        continue;
+      }
+
+      let currentPathSpec = pathName;
+      let resolvedSuccessfully = false;
+
+      try {
+        const absolutePath = path.resolve(this.config.getTargetDir(), pathName);
+        if (isWithinRoot(absolutePath, this.config.getTargetDir())) {
+          const stats = await fs.stat(absolutePath);
+          if (stats.isDirectory()) {
+            currentPathSpec = pathName.endsWith('/')
+              ? `${pathName}**`
+              : `${pathName}/**`;
+            this.#debug(
+              `Path ${pathName} resolved to directory, using glob: ${currentPathSpec}`,
+            );
+          } else {
+            this.#debug(
+              `Path ${pathName} resolved to file: ${currentPathSpec}`,
+            );
+          }
+          resolvedSuccessfully = true;
+        } else {
+          this.#debug(
+            `Path ${pathName} is outside the project directory. Skipping.`,
+          );
+        }
+      } catch (error) {
+        if (isNodeError(error) && error.code === 'ENOENT') {
+          if (this.config.getEnableRecursiveFileSearch() && globTool) {
+            this.#debug(
+              `Path ${pathName} not found directly, attempting glob search.`,
+            );
+            try {
+              const globResult = await globTool.execute(
+                {
+                  pattern: `**/*${pathName}*`,
+                  path: this.config.getTargetDir(),
+                },
+                abortSignal,
+              );
+              if (
+                globResult.llmContent &&
+                typeof globResult.llmContent === 'string' &&
+                !globResult.llmContent.startsWith('No files found') &&
+                !globResult.llmContent.startsWith('Error:')
+              ) {
+                const lines = globResult.llmContent.split('\n');
+                if (lines.length > 1 && lines[1]) {
+                  const firstMatchAbsolute = lines[1].trim();
+                  currentPathSpec = path.relative(
+                    this.config.getTargetDir(),
+                    firstMatchAbsolute,
+                  );
+                  this.#debug(
+                    `Glob search for ${pathName} found ${firstMatchAbsolute}, using relative path: ${currentPathSpec}`,
+                  );
+                  resolvedSuccessfully = true;
+                } else {
+                  this.#debug(
+                    `Glob search for '**/*${pathName}*' did not return a usable path. Path ${pathName} will be skipped.`,
+                  );
+                }
+              } else {
+                this.#debug(
+                  `Glob search for '**/*${pathName}*' found no files or an error. Path ${pathName} will be skipped.`,
+                );
+              }
+            } catch (globError) {
+              console.error(
+                `Error during glob search for ${pathName}: ${getErrorMessage(globError)}`,
+              );
+            }
+          } else {
+            this.#debug(
+              `Glob tool not found. Path ${pathName} will be skipped.`,
+            );
+          }
+        } else {
+          console.error(
+            `Error stating path ${pathName}. Path ${pathName} will be skipped.`,
+          );
+        }
+      }
+
+      if (resolvedSuccessfully) {
+        pathSpecsToRead.push(currentPathSpec);
+        atPathToResolvedSpecMap.set(pathName, currentPathSpec);
+        contentLabelsForDisplay.push(pathName);
+      }
+    }
+
+    // Construct the initial part of the query for the LLM
+    let initialQueryText = '';
+    for (let i = 0; i < message.chunks.length; i++) {
+      const chunk = message.chunks[i];
+      if ('text' in chunk) {
+        initialQueryText += chunk.text;
+      } else {
+        // type === 'atPath'
+        const resolvedSpec = atPathToResolvedSpecMap.get(chunk.path);
+        if (
+          i > 0 &&
+          initialQueryText.length > 0 &&
+          !initialQueryText.endsWith(' ') &&
+          resolvedSpec
+        ) {
+          // Add space if previous part was text and didn't end with space, or if previous was @path
+          const prevPart = message.chunks[i - 1];
+          if (
+            'text' in prevPart ||
+            ('path' in prevPart && atPathToResolvedSpecMap.has(prevPart.path))
+          ) {
+            initialQueryText += ' ';
+          }
+        }
+        if (resolvedSpec) {
+          initialQueryText += `@${resolvedSpec}`;
+        } else {
+          // If not resolved for reading (e.g. lone @ or invalid path that was skipped),
+          // add the original @-string back, ensuring spacing if it's not the first element.
+          if (
+            i > 0 &&
+            initialQueryText.length > 0 &&
+            !initialQueryText.endsWith(' ') &&
+            !chunk.path.startsWith(' ')
+          ) {
+            initialQueryText += ' ';
+          }
+          initialQueryText += `@${chunk.path}`;
+        }
+      }
+    }
+    initialQueryText = initialQueryText.trim();
+
+    // Inform user about ignored paths
+    if (ignoredPaths.length > 0) {
+      const ignoreType = respectGitIgnore ? 'git-ignored' : 'custom-ignored';
+      this.#debug(
+        `Ignored ${ignoredPaths.length} ${ignoreType} files: ${ignoredPaths.join(', ')}`,
+      );
+    }
+
+    // Fallback for lone "@" or completely invalid @-commands resulting in empty initialQueryText
+    if (pathSpecsToRead.length === 0) {
+      console.warn('No valid file paths found in @ commands to read.');
+      return [{ text: initialQueryText }];
+    }
+
+    const processedQueryParts: Part[] = [{ text: initialQueryText }];
+
+    const toolArgs = {
+      paths: pathSpecsToRead,
+      respectGitIgnore, // Use configuration setting
+    };
+
+    const toolCall = await this.client.pushToolCall({
+      icon: readManyFilesTool.icon,
+      label: readManyFilesTool.getDescription(toolArgs),
+    });
+    try {
+      const result = await readManyFilesTool.execute(toolArgs, abortSignal);
+      const content = toToolCallContent(result) || {
+        type: 'markdown',
+        markdown: `Successfully read: ${contentLabelsForDisplay.join(', ')}`,
+      };
+      await this.client.updateToolCall({
+        toolCallId: toolCall.id,
+        status: 'finished',
+        content,
+      });
+
+      if (Array.isArray(result.llmContent)) {
+        const fileContentRegex = /^--- (.*?) ---\n\n([\s\S]*?)\n\n$/;
+        processedQueryParts.push({
+          text: '\n--- Content from referenced files ---',
+        });
+        for (const part of result.llmContent) {
+          if (typeof part === 'string') {
+            const match = fileContentRegex.exec(part);
+            if (match) {
+              const filePathSpecInContent = match[1]; // This is a resolved pathSpec
+              const fileActualContent = match[2].trim();
+              processedQueryParts.push({
+                text: `\nContent from @${filePathSpecInContent}:\n`,
+              });
+              processedQueryParts.push({ text: fileActualContent });
+            } else {
+              processedQueryParts.push({ text: part });
+            }
+          } else {
+            // part is a Part object.
+            processedQueryParts.push(part);
+          }
+        }
+        processedQueryParts.push({ text: '\n--- End of content ---' });
+      } else {
+        console.warn(
+          'read_many_files tool returned no content or empty content.',
+        );
+      }
+
+      return processedQueryParts;
+    } catch (error: unknown) {
+      await this.client.updateToolCall({
+        toolCallId: toolCall.id,
+        status: 'error',
+        content: {
+          type: 'markdown',
+          markdown: `Error reading files (${contentLabelsForDisplay.join(', ')}): ${getErrorMessage(error)}`,
+        },
+      });
+      throw error;
+    }
+  }
+
+  #debug(msg: string) {
+    if (this.config.getDebugMode()) {
+      console.warn(msg);
+    }
+  }
+}
+
+function toToolCallContent(toolResult: ToolResult): acp.ToolCallContent | null {
+  if (toolResult.returnDisplay) {
+    if (typeof toolResult.returnDisplay === 'string') {
+      return {
+        type: 'markdown',
+        markdown: toolResult.returnDisplay,
+      };
+    } else {
+      return {
+        type: 'diff',
+        path: toolResult.returnDisplay.fileName,
+        oldText: toolResult.returnDisplay.originalContent,
+        newText: toolResult.returnDisplay.newContent,
+      };
+    }
+  } else {
+    return null;
+  }
+}
+
+function toAcpToolCallConfirmation(
+  confirmationDetails: ToolCallConfirmationDetails,
+): acp.ToolCallConfirmation {
+  switch (confirmationDetails.type) {
+    case 'edit':
+      return { type: 'edit' };
+    case 'exec':
+      return {
+        type: 'execute',
+        rootCommand: confirmationDetails.rootCommand,
+        command: confirmationDetails.command,
+      };
+    case 'mcp':
+      return {
+        type: 'mcp',
+        serverName: confirmationDetails.serverName,
+        toolName: confirmationDetails.toolName,
+        toolDisplayName: confirmationDetails.toolDisplayName,
+      };
+    case 'info':
+      return {
+        type: 'fetch',
+        urls: confirmationDetails.urls || [],
+        description: confirmationDetails.urls?.length
+          ? null
+          : confirmationDetails.prompt,
+      };
+    default: {
+      const unreachable: never = confirmationDetails;
+      throw new Error(`Unexpected: ${unreachable}`);
+    }
+  }
+}
+
+function toToolCallOutcome(
+  outcome: acp.ToolCallConfirmationOutcome,
+): ToolConfirmationOutcome {
+  switch (outcome) {
+    case 'allow':
+      return ToolConfirmationOutcome.ProceedOnce;
+    case 'alwaysAllow':
+      return ToolConfirmationOutcome.ProceedAlways;
+    case 'alwaysAllowMcpServer':
+      return ToolConfirmationOutcome.ProceedAlwaysServer;
+    case 'alwaysAllowTool':
+      return ToolConfirmationOutcome.ProceedAlwaysTool;
+    case 'reject':
+    case 'cancel':
+      return ToolConfirmationOutcome.Cancel;
+    default: {
+      const unreachable: never = outcome;
+      throw new Error(`Unexpected: ${unreachable}`);
+    }
+  }
+}
diff --git a/packages/cli/src/config/config.ts b/packages/cli/src/config/config.ts
index f76d6c60..543801f0 100644
--- a/packages/cli/src/config/config.ts
+++ b/packages/cli/src/config/config.ts
@@ -54,6 +54,7 @@ export interface CliArgs {
   telemetryOtlpEndpoint: string | undefined;
   telemetryLogPrompts: boolean | undefined;
   allowedMcpServerNames: string[] | undefined;
+  experimentalAcp: boolean | undefined;
   extensions: string[] | undefined;
   listExtensions: boolean | undefined;
   ideMode: boolean | undefined;
@@ -162,6 +163,10 @@ export async function parseArguments(): Promise<CliArgs> {
       description: 'Enables checkpointing of file edits',
       default: false,
     })
+    .option('experimental-acp', {
+      type: 'boolean',
+      description: 'Starts the agent in ACP mode',
+    })
     .option('allowed-mcp-server-names', {
       type: 'array',
       string: true,
@@ -396,6 +401,7 @@ export async function loadCliConfig(
     model: argv.model!,
     extensionContextFilePaths,
     maxSessionTurns: settings.maxSessionTurns ?? -1,
+    experimentalAcp: argv.experimentalAcp || false,
     listExtensions: argv.listExtensions || false,
     activeExtensions: activeExtensions.map((e) => ({
       name: e.config.name,
diff --git a/packages/cli/src/gemini.tsx b/packages/cli/src/gemini.tsx
index f0d3f401..71e69952 100644
--- a/packages/cli/src/gemini.tsx
+++ b/packages/cli/src/gemini.tsx
@@ -84,6 +84,7 @@ async function relaunchWithAdditionalArgs(additionalArgs: string[]) {
   await new Promise((resolve) => child.on('close', resolve));
   process.exit(0);
 }
+import { runAcpPeer } from './acp/acpPeer.js';
 
 export async function main() {
   const workspaceRoot = process.cwd();
@@ -189,6 +190,10 @@ export async function main() {
     await getOauthClient(settings.merged.selectedAuthType, config);
   }
 
+  if (config.getExperimentalAcp()) {
+    return runAcpPeer(config, settings);
+  }
+
   let input = config.getQuestion();
   const startupWarnings = [
     ...(await getStartupWarnings()),
diff --git a/packages/cli/src/ui/components/messages/ToolMessage.test.tsx b/packages/cli/src/ui/components/messages/ToolMessage.test.tsx
index 7b9de92e..c9bed003 100644
--- a/packages/cli/src/ui/components/messages/ToolMessage.test.tsx
+++ b/packages/cli/src/ui/components/messages/ToolMessage.test.tsx
@@ -152,6 +152,8 @@ describe('<ToolMessage />', () => {
     const diffResult = {
       fileDiff: '--- a/file.txt\n+++ b/file.txt\n@@ -1 +1 @@\n-old\n+new',
       fileName: 'file.txt',
+      originalContent: 'old',
+      newContent: 'new',
     };
     const { lastFrame } = renderWithContext(
       <ToolMessage {...baseProps} resultDisplay={diffResult} />,
diff --git a/packages/cli/src/ui/hooks/useToolScheduler.test.ts b/packages/cli/src/ui/hooks/useToolScheduler.test.ts
index e9354ee9..81ea1f77 100644
--- a/packages/cli/src/ui/hooks/useToolScheduler.test.ts
+++ b/packages/cli/src/ui/hooks/useToolScheduler.test.ts
@@ -23,7 +23,8 @@ import {
   ToolCallResponseInfo,
   ToolCall, // Import from core
   Status as ToolCallStatusType,
-  ApprovalMode, // Import from core
+  ApprovalMode,
+  Icon,
 } from '@google/gemini-cli-core';
 import {
   HistoryItemWithoutId,
@@ -56,6 +57,8 @@ const mockTool: Tool = {
   name: 'mockTool',
   displayName: 'Mock Tool',
   description: 'A mock tool for testing',
+  icon: Icon.Hammer,
+  toolLocations: vi.fn(),
   isOutputMarkdown: false,
   canUpdateOutput: false,
   schema: {},
@@ -85,6 +88,8 @@ const mockToolRequiresConfirmation: Tool = {
       onConfirm: mockOnUserConfirmForToolConfirmation,
       fileName: 'mockToolRequiresConfirmation.ts',
       fileDiff: 'Mock tool requires confirmation',
+      originalContent: 'Original content',
+      newContent: 'New content',
     }),
   ),
 };
@@ -807,6 +812,8 @@ describe('mapToDisplay', () => {
     isOutputMarkdown: false,
     canUpdateOutput: false,
     schema: {},
+    icon: Icon.Hammer,
+    toolLocations: vi.fn(),
     validateToolParams: vi.fn(),
     execute: vi.fn(),
     shouldConfirmExecute: vi.fn(),
@@ -885,6 +892,8 @@ describe('mapToDisplay', () => {
           toolDisplayName: 'Test Tool Display',
           fileName: 'test.ts',
           fileDiff: 'Test diff',
+          originalContent: 'Original content',
+          newContent: 'New content',
         } as ToolCallConfirmationDetails,
       },
       expectedStatus: ToolCallStatus.Confirming,