feat(acp): add session resume support (#18043)

Co-authored-by: Jack Wotherspoon <jackwoth@google.com>

packages/cli/src/ui/hooks/useSessionBrowser.test.ts

@@ -24,7 +24,14 @@ import { coreEvents } from '@google/gemini-cli-core';
 // Mock modules
 vi.mock('fs/promises');
 vi.mock('path');
-vi.mock('../../utils/sessionUtils.js');
+vi.mock('../../utils/sessionUtils.js', async (importOriginal) => {
+  const actual =
+    await importOriginal<typeof import('../../utils/sessionUtils.js')>();
+  return {
+    ...actual,
+    getSessionFiles: vi.fn(),
+  };
+});
 
 const MOCKED_PROJECT_TEMP_DIR = '/test/project/temp';
 const MOCKED_CHATS_DIR = '/test/project/temp/chats';

packages/cli/src/ui/hooks/useSessionBrowser.ts

@@ -13,11 +13,12 @@ import type {
   ConversationRecord,
   ResumedSessionData,
 } from '@google/gemini-cli-core';
-import type { Part } from '@google/genai';
+import { coreEvents } from '@google/gemini-cli-core';
-import { partListUnionToString, coreEvents } from '@google/gemini-cli-core';
-import { checkExhaustive } from '../../utils/checks.js';
 import type { SessionInfo } from '../../utils/sessionUtils.js';
-import { MessageType, ToolCallStatus } from '../types.js';
+import { convertSessionToHistoryFormats } from '../../utils/sessionUtils.js';
+import type { Part } from '@google/genai';
+
+export { convertSessionToHistoryFormats };
 
 export const useSessionBrowser = (
   config: Config,
@@ -112,190 +113,3 @@ export const useSessionBrowser = (
     ),
   };
 };
-
-/**
- * Converts session/conversation data into UI history and Gemini client history formats.
- */
-export function convertSessionToHistoryFormats(
-  messages: ConversationRecord['messages'],
-): {
-  uiHistory: HistoryItemWithoutId[];
-  clientHistory: Array<{ role: 'user' | 'model'; parts: Part[] }>;
-} {
-  const uiHistory: HistoryItemWithoutId[] = [];
-
-  for (const msg of messages) {
-    // Add the message only if it has content
-    const displayContentString = msg.displayContent
-      ? partListUnionToString(msg.displayContent)
-      : undefined;
-    const contentString = partListUnionToString(msg.content);
-    const uiText = displayContentString || contentString;
-
-    if (uiText.trim()) {
-      let messageType: MessageType;
-      switch (msg.type) {
-        case 'user':
-          messageType = MessageType.USER;
-          break;
-        case 'info':
-          messageType = MessageType.INFO;
-          break;
-        case 'error':
-          messageType = MessageType.ERROR;
-          break;
-        case 'warning':
-          messageType = MessageType.WARNING;
-          break;
-        case 'gemini':
-          messageType = MessageType.GEMINI;
-          break;
-        default:
-          checkExhaustive(msg);
-          messageType = MessageType.GEMINI;
-          break;
-      }
-
-      uiHistory.push({
-        type: messageType,
-        text: uiText,
-      });
-    }
-
-    // Add tool calls if present
-    if (
-      msg.type !== 'user' &&
-      'toolCalls' in msg &&
-      msg.toolCalls &&
-      msg.toolCalls.length > 0
-    ) {
-      uiHistory.push({
-        type: 'tool_group',
-        tools: msg.toolCalls.map((tool) => ({
-          callId: tool.id,
-          name: tool.displayName || tool.name,
-          description: tool.description || '',
-          renderOutputAsMarkdown: tool.renderOutputAsMarkdown ?? true,
-          status:
-            tool.status === 'success'
-              ? ToolCallStatus.Success
-              : ToolCallStatus.Error,
-          resultDisplay: tool.resultDisplay,
-          confirmationDetails: undefined,
-        })),
-      });
-    }
-  }
-
-  // Convert to Gemini client history format
-  const clientHistory: Array<{ role: 'user' | 'model'; parts: Part[] }> = [];
-
-  for (const msg of messages) {
-    // Skip system/error messages and user slash commands
-    if (msg.type === 'info' || msg.type === 'error' || msg.type === 'warning') {
-      continue;
-    }
-
-    if (msg.type === 'user') {
-      // Skip user slash commands
-      const contentString = partListUnionToString(msg.content);
-      if (
-        contentString.trim().startsWith('/') ||
-        contentString.trim().startsWith('?')
-      ) {
-        continue;
-      }
-
-      // Add regular user message
-      clientHistory.push({
-        role: 'user',
-        parts: Array.isArray(msg.content)
-          ? (msg.content as Part[])
-          : [{ text: contentString }],
-      });
-    } else if (msg.type === 'gemini') {
-      // Handle Gemini messages with potential tool calls
-      const hasToolCalls = msg.toolCalls && msg.toolCalls.length > 0;
-
-      if (hasToolCalls) {
-        // Create model message with function calls
-        const modelParts: Part[] = [];
-
-        // Add text content if present
-        const contentString = partListUnionToString(msg.content);
-        if (msg.content && contentString.trim()) {
-          modelParts.push({ text: contentString });
-        }
-
-        // Add function calls
-        for (const toolCall of msg.toolCalls!) {
-          modelParts.push({
-            functionCall: {
-              name: toolCall.name,
-              args: toolCall.args,
-              ...(toolCall.id && { id: toolCall.id }),
-            },
-          });
-        }
-
-        clientHistory.push({
-          role: 'model',
-          parts: modelParts,
-        });
-
-        // Create single function response message with all tool call responses
-        const functionResponseParts: Part[] = [];
-        for (const toolCall of msg.toolCalls!) {
-          if (toolCall.result) {
-            // Convert PartListUnion result to function response format
-            let responseData: Part;
-
-            if (typeof toolCall.result === 'string') {
-              responseData = {
-                functionResponse: {
-                  id: toolCall.id,
-                  name: toolCall.name,
-                  response: {
-                    output: toolCall.result,
-                  },
-                },
-              };
-            } else if (Array.isArray(toolCall.result)) {
-              // toolCall.result is an array containing properly formatted
-              // function responses
-              functionResponseParts.push(...(toolCall.result as Part[]));
-              continue;
-            } else {
-              // Fallback for non-array results
-              responseData = toolCall.result;
-            }
-
-            functionResponseParts.push(responseData);
-          }
-        }
-
-        // Only add user message if we have function responses
-        if (functionResponseParts.length > 0) {
-          clientHistory.push({
-            role: 'user',
-            parts: functionResponseParts,
-          });
-        }
-      } else {
-        // Regular Gemini message without tool calls
-        const contentString = partListUnionToString(msg.content);
-        if (msg.content && contentString.trim()) {
-          clientHistory.push({
-            role: 'model',
-            parts: [{ text: contentString }],
-          });
-        }
-      }
-    }
-  }
-
-  return {
-    uiHistory,
-    clientHistory,
-  };
-}

packages/cli/src/utils/sessionUtils.ts

@@ -16,6 +16,13 @@ import {
 import * as fs from 'node:fs/promises';
 import path from 'node:path';
 import { stripUnsafeCharacters } from '../ui/utils/textUtils.js';
+import type { Part } from '@google/genai';
+import { checkExhaustive } from './checks.js';
+import {
+  MessageType,
+  ToolCallStatus,
+  type HistoryItemWithoutId,
+} from '../ui/types.js';
 
 /**
  * Constant for the resume "latest" identifier.
@@ -514,3 +521,190 @@ export class SessionSelector {
     }
   }
 }
+
+/**
+ * Converts session/conversation data into UI history and Gemini client history formats.
+ */
+export function convertSessionToHistoryFormats(
+  messages: ConversationRecord['messages'],
+): {
+  uiHistory: HistoryItemWithoutId[];
+  clientHistory: Array<{ role: 'user' | 'model'; parts: Part[] }>;
+} {
+  const uiHistory: HistoryItemWithoutId[] = [];
+
+  for (const msg of messages) {
+    // Add the message only if it has content
+    const displayContentString = msg.displayContent
+      ? partListUnionToString(msg.displayContent)
+      : undefined;
+    const contentString = partListUnionToString(msg.content);
+    const uiText = displayContentString || contentString;
+
+    if (uiText.trim()) {
+      let messageType: MessageType;
+      switch (msg.type) {
+        case 'user':
+          messageType = MessageType.USER;
+          break;
+        case 'info':
+          messageType = MessageType.INFO;
+          break;
+        case 'error':
+          messageType = MessageType.ERROR;
+          break;
+        case 'warning':
+          messageType = MessageType.WARNING;
+          break;
+        case 'gemini':
+          messageType = MessageType.GEMINI;
+          break;
+        default:
+          checkExhaustive(msg);
+          messageType = MessageType.GEMINI;
+          break;
+      }
+
+      uiHistory.push({
+        type: messageType,
+        text: uiText,
+      });
+    }
+
+    // Add tool calls if present
+    if (
+      msg.type !== 'user' &&
+      'toolCalls' in msg &&
+      msg.toolCalls &&
+      msg.toolCalls.length > 0
+    ) {
+      uiHistory.push({
+        type: 'tool_group',
+        tools: msg.toolCalls.map((tool) => ({
+          callId: tool.id,
+          name: tool.displayName || tool.name,
+          description: tool.description || '',
+          renderOutputAsMarkdown: tool.renderOutputAsMarkdown ?? true,
+          status:
+            tool.status === 'success'
+              ? ToolCallStatus.Success
+              : ToolCallStatus.Error,
+          resultDisplay: tool.resultDisplay,
+          confirmationDetails: undefined,
+        })),
+      });
+    }
+  }
+
+  // Convert to Gemini client history format
+  const clientHistory: Array<{ role: 'user' | 'model'; parts: Part[] }> = [];
+
+  for (const msg of messages) {
+    // Skip system/error messages and user slash commands
+    if (msg.type === 'info' || msg.type === 'error' || msg.type === 'warning') {
+      continue;
+    }
+
+    if (msg.type === 'user') {
+      // Skip user slash commands
+      const contentString = partListUnionToString(msg.content);
+      if (
+        contentString.trim().startsWith('/') ||
+        contentString.trim().startsWith('?')
+      ) {
+        continue;
+      }
+
+      // Add regular user message
+      clientHistory.push({
+        role: 'user',
+        parts: Array.isArray(msg.content)
+          ? (msg.content as Part[])
+          : [{ text: contentString }],
+      });
+    } else if (msg.type === 'gemini') {
+      // Handle Gemini messages with potential tool calls
+      const hasToolCalls = msg.toolCalls && msg.toolCalls.length > 0;
+
+      if (hasToolCalls) {
+        // Create model message with function calls
+        const modelParts: Part[] = [];
+
+        // Add text content if present
+        const contentString = partListUnionToString(msg.content);
+        if (msg.content && contentString.trim()) {
+          modelParts.push({ text: contentString });
+        }
+
+        // Add function calls
+        for (const toolCall of msg.toolCalls!) {
+          modelParts.push({
+            functionCall: {
+              name: toolCall.name,
+              args: toolCall.args,
+              ...(toolCall.id && { id: toolCall.id }),
+            },
+          });
+        }
+
+        clientHistory.push({
+          role: 'model',
+          parts: modelParts,
+        });
+
+        // Create single function response message with all tool call responses
+        const functionResponseParts: Part[] = [];
+        for (const toolCall of msg.toolCalls!) {
+          if (toolCall.result) {
+            // Convert PartListUnion result to function response format
+            let responseData: Part;
+
+            if (typeof toolCall.result === 'string') {
+              responseData = {
+                functionResponse: {
+                  id: toolCall.id,
+                  name: toolCall.name,
+                  response: {
+                    output: toolCall.result,
+                  },
+                },
+              };
+            } else if (Array.isArray(toolCall.result)) {
+              // toolCall.result is an array containing properly formatted
+              // function responses
+              functionResponseParts.push(...(toolCall.result as Part[]));
+              continue;
+            } else {
+              // Fallback for non-array results
+              responseData = toolCall.result;
+            }
+
+            functionResponseParts.push(responseData);
+          }
+        }
+
+        // Only add user message if we have function responses
+        if (functionResponseParts.length > 0) {
+          clientHistory.push({
+            role: 'user',
+            parts: functionResponseParts,
+          });
+        }
+      } else {
+        // Regular Gemini message without tool calls
+        const contentString = partListUnionToString(msg.content);
+        if (msg.content && contentString.trim()) {
+          clientHistory.push({
+            role: 'model',
+            parts: [{ text: contentString }],
+          });
+        }
+      }
+    }
+  }
+
+  return {
+    uiHistory,
+    clientHistory,
+  };
+}

packages/cli/src/zed-integration/acpResume.test.ts

@@ -0,0 +1,224 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {
+  describe,
+  it,
+  expect,
+  vi,
+  beforeEach,
+  type Mocked,
+  type Mock,
+} from 'vitest';
+import { GeminiAgent } from './zedIntegration.js';
+import * as acp from '@agentclientprotocol/sdk';
+import { AuthType, type Config } from '@google/gemini-cli-core';
+import { loadCliConfig, type CliArgs } from '../config/config.js';
+import {
+  SessionSelector,
+  convertSessionToHistoryFormats,
+} from '../utils/sessionUtils.js';
+import type { LoadedSettings } from '../config/settings.js';
+
+vi.mock('../config/config.js', () => ({
+  loadCliConfig: vi.fn(),
+}));
+
+vi.mock('../utils/sessionUtils.js', async (importOriginal) => {
+  const actual =
+    await importOriginal<typeof import('../utils/sessionUtils.js')>();
+  return {
+    ...actual,
+    SessionSelector: vi.fn(),
+    convertSessionToHistoryFormats: vi.fn(),
+  };
+});
+
+describe('GeminiAgent Session Resume', () => {
+  let mockConfig: Mocked<Config>;
+  let mockSettings: Mocked<LoadedSettings>;
+  let mockArgv: CliArgs;
+  let mockConnection: Mocked<acp.AgentSideConnection>;
+  let agent: GeminiAgent;
+
+  beforeEach(() => {
+    mockConfig = {
+      refreshAuth: vi.fn().mockResolvedValue(undefined),
+      initialize: vi.fn().mockResolvedValue(undefined),
+      getFileSystemService: vi.fn(),
+      setFileSystemService: vi.fn(),
+      getGeminiClient: vi.fn().mockReturnValue({
+        initialize: vi.fn().mockResolvedValue(undefined),
+        resumeChat: vi.fn().mockResolvedValue(undefined),
+        getChat: vi.fn().mockReturnValue({}),
+      }),
+      storage: {
+        getProjectTempDir: vi.fn().mockReturnValue('/tmp/project'),
+      },
+    } as unknown as Mocked<Config>;
+    mockSettings = {
+      merged: {
+        security: { auth: { selectedType: AuthType.LOGIN_WITH_GOOGLE } },
+        mcpServers: {},
+      },
+      setValue: vi.fn(),
+    } as unknown as Mocked<LoadedSettings>;
+    mockArgv = {} as unknown as CliArgs;
+    mockConnection = {
+      sessionUpdate: vi.fn().mockResolvedValue(undefined),
+    } as unknown as Mocked<acp.AgentSideConnection>;
+
+    (loadCliConfig as Mock).mockResolvedValue(mockConfig);
+
+    agent = new GeminiAgent(mockConfig, mockSettings, mockArgv, mockConnection);
+  });
+
+  it('should advertise loadSession capability', async () => {
+    const response = await agent.initialize({
+      protocolVersion: acp.PROTOCOL_VERSION,
+    });
+    expect(response.agentCapabilities?.loadSession).toBe(true);
+  });
+
+  it('should load a session, resume chat, and stream all message types', async () => {
+    const sessionId = 'existing-session-id';
+    const sessionData = {
+      sessionId,
+      messages: [
+        { type: 'user', content: [{ text: 'Hello' }] },
+        {
+          type: 'gemini',
+          content: [{ text: 'Hi there' }],
+          thoughts: [{ subject: 'Thinking', description: 'about greeting' }],
+          toolCalls: [
+            {
+              id: 'call-1',
+              name: 'test_tool',
+              displayName: 'Test Tool',
+              status: 'success',
+              resultDisplay: 'Tool output',
+            },
+          ],
+        },
+        {
+          type: 'gemini',
+          content: [{ text: 'Trying a write' }],
+          toolCalls: [
+            {
+              id: 'call-2',
+              name: 'write_file',
+              displayName: 'Write File',
+              status: 'error',
+              resultDisplay: 'Permission denied',
+            },
+          ],
+        },
+      ],
+    };
+
+    mockConfig.getToolRegistry = vi.fn().mockReturnValue({
+      getTool: vi.fn().mockReturnValue({ kind: 'read' }),
+    });
+
+    (SessionSelector as unknown as Mock).mockImplementation(() => ({
+      resolveSession: vi.fn().mockResolvedValue({
+        sessionData,
+        sessionPath: '/path/to/session.json',
+      }),
+    }));
+
+    const mockClientHistory = [
+      { role: 'user', parts: [{ text: 'Hello' }] },
+      { role: 'model', parts: [{ text: 'Hi there' }] },
+    ];
+    (convertSessionToHistoryFormats as unknown as Mock).mockReturnValue({
+      clientHistory: mockClientHistory,
+      uiHistory: [],
+    });
+
+    const response = await agent.loadSession({
+      sessionId,
+      cwd: '/tmp',
+      mcpServers: [],
+    });
+
+    expect(response).toEqual({});
+
+    // Verify resumeChat received the correct arguments
+    expect(mockConfig.getGeminiClient().resumeChat).toHaveBeenCalledWith(
+      mockClientHistory,
+      expect.objectContaining({
+        conversation: sessionData,
+        filePath: '/path/to/session.json',
+      }),
+    );
+
+    await vi.waitFor(() => {
+      // User message
+      expect(mockConnection.sessionUpdate).toHaveBeenCalledWith(
+        expect.objectContaining({
+          update: expect.objectContaining({
+            sessionUpdate: 'user_message_chunk',
+            content: expect.objectContaining({ text: 'Hello' }),
+          }),
+        }),
+      );
+
+      // Agent thought
+      expect(mockConnection.sessionUpdate).toHaveBeenCalledWith(
+        expect.objectContaining({
+          update: expect.objectContaining({
+            sessionUpdate: 'agent_thought_chunk',
+            content: expect.objectContaining({
+              text: '**Thinking**\nabout greeting',
+            }),
+          }),
+        }),
+      );
+
+      // Agent message
+      expect(mockConnection.sessionUpdate).toHaveBeenCalledWith(
+        expect.objectContaining({
+          update: expect.objectContaining({
+            sessionUpdate: 'agent_message_chunk',
+            content: expect.objectContaining({ text: 'Hi there' }),
+          }),
+        }),
+      );
+
+      // Successful tool call → 'completed'
+      expect(mockConnection.sessionUpdate).toHaveBeenCalledWith(
+        expect.objectContaining({
+          update: expect.objectContaining({
+            sessionUpdate: 'tool_call',
+            toolCallId: 'call-1',
+            status: 'completed',
+            title: 'Test Tool',
+            kind: 'read',
+            content: [
+              {
+                type: 'content',
+                content: { type: 'text', text: 'Tool output' },
+              },
+            ],
+          }),
+        }),
+      );
+
+      // Failed tool call → 'failed'
+      expect(mockConnection.sessionUpdate).toHaveBeenCalledWith(
+        expect.objectContaining({
+          update: expect.objectContaining({
+            sessionUpdate: 'tool_call',
+            toolCallId: 'call-2',
+            status: 'failed',
+            title: 'Write File',
+          }),
+        }),
+      );
+    });
+  });
+});

packages/cli/src/zed-integration/zedIntegration.test.ts

@@ -129,7 +129,7 @@ describe('GeminiAgent', () => {
 
     expect(response.protocolVersion).toBe(acp.PROTOCOL_VERSION);
     expect(response.authMethods).toHaveLength(3);
-    expect(response.agentCapabilities?.loadSession).toBe(false);
+    expect(response.agentCapabilities?.loadSession).toBe(true);
   });
 
   it('should authenticate correctly', async () => {
@@ -273,6 +273,7 @@ describe('Session', () => {
     mockChat = {
       sendMessageStream: vi.fn(),
       addHistory: vi.fn(),
+      recordCompletedToolCalls: vi.fn(),
     } as unknown as Mocked<GeminiChat>;
     mockTool = {
       kind: 'native',
@@ -293,6 +294,7 @@ describe('Session', () => {
     } as unknown as Mocked<MessageBus>;
     mockConfig = {
       getModel: vi.fn().mockReturnValue('gemini-pro'),
+      getActiveModel: vi.fn().mockReturnValue('gemini-pro'),
       getPreviewFeatures: vi.fn().mockReturnValue({}),
       getToolRegistry: vi.fn().mockReturnValue(mockToolRegistry),
       getFileService: vi.fn().mockReturnValue({

packages/cli/src/zed-integration/zedIntegration.ts

@@ -10,6 +10,7 @@ import type {
   ToolResult,
   ToolCallConfirmationDetails,
   FilterFilesOptions,
+  ConversationRecord,
 } from '@google/gemini-cli-core';
 import {
   AuthType,
@@ -32,6 +33,7 @@ import {
   createWorkingStdio,
   startupProfiler,
   Kind,
+  partListUnionToString,
 } from '@google/gemini-cli-core';
 import * as acp from '@agentclientprotocol/sdk';
 import { AcpFileSystemService } from './fileSystemService.js';
@@ -47,6 +49,10 @@ import { randomUUID } from 'node:crypto';
 import type { CliArgs } from '../config/config.js';
 import { loadCliConfig } from '../config/config.js';
 import { runExitCleanup } from '../utils/cleanup.js';
+import {
+  SessionSelector,
+  convertSessionToHistoryFormats,
+} from '../utils/sessionUtils.js';
 
 export async function runZedIntegration(
   config: Config,
@@ -107,7 +113,7 @@ export class GeminiAgent {
       protocolVersion: acp.PROTOCOL_VERSION,
       authMethods,
       agentCapabilities: {
-        loadSession: false,
+        loadSession: true,
         promptCapabilities: {
           image: true,
           audio: true,
@@ -146,23 +152,11 @@ export class GeminiAgent {
     mcpServers,
   }: acp.NewSessionRequest): Promise<acp.NewSessionResponse> {
     const sessionId = randomUUID();
-    const config = await this.newSessionConfig(sessionId, cwd, mcpServers);
+    const config = await this.initializeSessionConfig(
-
+      sessionId,
-    let isAuthenticated = false;
+      cwd,
-    if (this.settings.merged.security.auth.selectedType) {
+      mcpServers,
-      try {
+    );
-        await config.refreshAuth(
-          this.settings.merged.security.auth.selectedType,
-        );
-        isAuthenticated = true;
-      } catch (e) {
-        debugLogger.error(`Authentication failed: ${e}`);
-      }
-    }
-
-    if (!isAuthenticated) {
-      throw acp.RequestError.authRequired();
-    }
 
     if (this.clientCapabilities?.fs) {
       const acpFileSystemService = new AcpFileSystemService(
@@ -184,6 +178,88 @@ export class GeminiAgent {
     };
   }
 
+  async loadSession({
+    sessionId,
+    cwd,
+    mcpServers,
+  }: acp.LoadSessionRequest): Promise<acp.LoadSessionResponse> {
+    const config = await this.initializeSessionConfig(
+      sessionId,
+      cwd,
+      mcpServers,
+    );
+
+    const sessionSelector = new SessionSelector(config);
+    const { sessionData, sessionPath } =
+      await sessionSelector.resolveSession(sessionId);
+
+    if (this.clientCapabilities?.fs) {
+      const acpFileSystemService = new AcpFileSystemService(
+        this.connection,
+        sessionId,
+        this.clientCapabilities.fs,
+        config.getFileSystemService(),
+      );
+      config.setFileSystemService(acpFileSystemService);
+    }
+
+    const { clientHistory } = convertSessionToHistoryFormats(
+      sessionData.messages,
+    );
+
+    const geminiClient = config.getGeminiClient();
+    await geminiClient.initialize();
+    await geminiClient.resumeChat(clientHistory, {
+      conversation: sessionData,
+      filePath: sessionPath,
+    });
+
+    const session = new Session(
+      sessionId,
+      geminiClient.getChat(),
+      config,
+      this.connection,
+    );
+    this.sessions.set(sessionId, session);
+
+    // Stream history back to client
+    // eslint-disable-next-line @typescript-eslint/no-floating-promises
+    session.streamHistory(sessionData.messages);
+
+    return {};
+  }
+
+  private async initializeSessionConfig(
+    sessionId: string,
+    cwd: string,
+    mcpServers: acp.McpServer[],
+  ): Promise<Config> {
+    const selectedAuthType = this.settings.merged.security.auth.selectedType;
+    if (!selectedAuthType) {
+      throw acp.RequestError.authRequired();
+    }
+
+    // 1. Create config WITHOUT initializing it (no MCP servers started yet)
+    const config = await this.newSessionConfig(sessionId, cwd, mcpServers);
+
+    // 2. Authenticate BEFORE initializing configuration or starting MCP servers.
+    // This satisfies the security requirement to verify the user before executing
+    // potentially unsafe server definitions.
+    try {
+      await config.refreshAuth(selectedAuthType);
+    } catch (e) {
+      debugLogger.error(`Authentication failed: ${e}`);
+      throw acp.RequestError.authRequired();
+    }
+
+    // 3. Now that we are authenticated, it is safe to initialize the config
+    // which starts the MCP servers and other heavy resources.
+    await config.initialize();
+    startupProfiler.flush(config);
+
+    return config;
+  }
+
   async newSessionConfig(
     sessionId: string,
     cwd: string,
@@ -228,8 +304,6 @@ export class GeminiAgent {
 
     const config = await loadCliConfig(settings, sessionId, this.argv, { cwd });
 
-    await config.initialize();
-    startupProfiler.flush(config);
     return config;
   }
 
@@ -269,6 +343,73 @@ export class Session {
     this.pendingPrompt = null;
   }
 
+  async streamHistory(messages: ConversationRecord['messages']): Promise<void> {
+    for (const msg of messages) {
+      const contentString = partListUnionToString(msg.content);
+
+      if (msg.type === 'user') {
+        if (contentString.trim()) {
+          await this.sendUpdate({
+            sessionUpdate: 'user_message_chunk',
+            content: { type: 'text', text: contentString },
+          });
+        }
+      } else if (msg.type === 'gemini') {
+        // Thoughts
+        if (msg.thoughts) {
+          for (const thought of msg.thoughts) {
+            const thoughtText = `**${thought.subject}**\n${thought.description}`;
+            await this.sendUpdate({
+              sessionUpdate: 'agent_thought_chunk',
+              content: { type: 'text', text: thoughtText },
+            });
+          }
+        }
+
+        // Message text
+        if (contentString.trim()) {
+          await this.sendUpdate({
+            sessionUpdate: 'agent_message_chunk',
+            content: { type: 'text', text: contentString },
+          });
+        }
+
+        // Tool calls
+        if (msg.toolCalls) {
+          for (const toolCall of msg.toolCalls) {
+            const toolCallContent: acp.ToolCallContent[] = [];
+            if (toolCall.resultDisplay) {
+              if (typeof toolCall.resultDisplay === 'string') {
+                toolCallContent.push({
+                  type: 'content',
+                  content: { type: 'text', text: toolCall.resultDisplay },
+                });
+              } else if ('fileName' in toolCall.resultDisplay) {
+                toolCallContent.push({
+                  type: 'diff',
+                  path: toolCall.resultDisplay.fileName,
+                  oldText: toolCall.resultDisplay.originalContent,
+                  newText: toolCall.resultDisplay.newContent,
+                });
+              }
+            }
+
+            const tool = this.config.getToolRegistry().getTool(toolCall.name);
+
+            await this.sendUpdate({
+              sessionUpdate: 'tool_call',
+              toolCallId: toolCall.id,
+              status: toolCall.status === 'success' ? 'completed' : 'failed',
+              title: toolCall.displayName || toolCall.name,
+              content: toolCallContent,
+              kind: tool ? toAcpToolKind(tool.kind) : 'other',
+            });
+          }
+        }
+      }
+    }
+  }
+
   async prompt(params: acp.PromptRequest): Promise<acp.PromptResponse> {
     this.pendingPrompt?.abort();
     const pendingSend = new AbortController();
@@ -533,6 +674,33 @@ export class Session {
         ),
       );
 
+      this.chat.recordCompletedToolCalls(this.config.getActiveModel(), [
+        {
+          status: 'success',
+          request: {
+            callId,
+            name: fc.name,
+            args,
+            isClientInitiated: false,
+            prompt_id: promptId,
+          },
+          tool,
+          invocation,
+          response: {
+            callId,
+            responseParts: convertToFunctionResponse(
+              fc.name,
+              callId,
+              toolResult.llmContent,
+              this.config.getActiveModel(),
+            ),
+            resultDisplay: toolResult.returnDisplay,
+            error: undefined,
+            errorType: undefined,
+          },
+        },
+      ]);
+
       return convertToFunctionResponse(
         fc.name,
         callId,
@@ -551,6 +719,35 @@ export class Session {
         ],
       });
 
+      this.chat.recordCompletedToolCalls(this.config.getActiveModel(), [
+        {
+          status: 'error',
+          request: {
+            callId,
+            name: fc.name,
+            args,
+            isClientInitiated: false,
+            prompt_id: promptId,
+          },
+          tool,
+          response: {
+            callId,
+            responseParts: [
+              {
+                functionResponse: {
+                  id: callId,
+                  name: fc.name ?? '',
+                  response: { error: error.message },
+                },
+              },
+            ],
+            resultDisplay: error.message,
+            error,
+            errorType: undefined,
+          },
+        },
+      ]);
+
       return errorResponse(error);
     }
   }