Add /resume slash command to switch between previous sessions

packages/cli/src/services/BuiltinCommandLoader.ts

@@ -29,6 +29,7 @@ import { modelCommand } from '../ui/commands/modelCommand.js';
 import { permissionsCommand } from '../ui/commands/permissionsCommand.js';
 import { quitCommand } from '../ui/commands/quitCommand.js';
 import { restoreCommand } from '../ui/commands/restoreCommand.js';
+import { resumeCommand } from '../ui/commands/resumeCommand.js';
 import { settingsCommand } from '../ui/commands/settingsCommand.js';
 import { statsCommand } from '../ui/commands/statsCommand.js';
 import { summaryCommand } from '../ui/commands/summaryCommand.js';
@@ -76,6 +77,7 @@ export class BuiltinCommandLoader implements ICommandLoader {
       ...(this.config?.getFolderTrust() ? [permissionsCommand] : []),
       quitCommand,
       restoreCommand(this.config),
+      resumeCommand,
       statsCommand,
       summaryCommand,
       themeCommand,

packages/cli/src/ui/commands/resumeCommand.ts

@@ -0,0 +1,89 @@
+/**
+ * @license
+ * Copyright 2025 Qwen Code
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type {
+  SlashCommand,
+  SlashCommandActionReturn,
+  CommandContext,
+} from './types.js';
+import { CommandKind } from './types.js';
+import { t } from '../../i18n/index.js';
+import { showResumeSessionPicker } from '../components/ResumeSessionPicker.js';
+import {
+  SessionService,
+  buildApiHistoryFromConversation,
+  replayUiTelemetryFromConversation,
+  uiTelemetryService,
+} from '@qwen-code/qwen-code-core';
+import { buildResumedHistoryItems } from '../utils/resumeHistoryUtils.js';
+
+export const resumeCommand: SlashCommand = {
+  name: 'resume',
+  kind: CommandKind.BUILT_IN,
+  get description() {
+    return t('Resume a previous session');
+  },
+  action: async (
+    context: CommandContext,
+  ): Promise<void | SlashCommandActionReturn> => {
+    const { config } = context.services;
+
+    if (!config) {
+      return {
+        type: 'message',
+        messageType: 'error',
+        content: 'Config not available',
+      };
+    }
+
+    // Show the session picker
+    const cwd = config.getTargetDir();
+    const selectedSessionId = await showResumeSessionPicker(cwd);
+
+    if (!selectedSessionId) {
+      // User cancelled
+      return;
+    }
+
+    // Load the session data
+    const sessionService = new SessionService(cwd);
+    const sessionData = await sessionService.loadSession(selectedSessionId);
+
+    if (!sessionData) {
+      return {
+        type: 'message',
+        messageType: 'error',
+        content: `Could not load session: ${selectedSessionId}`,
+      };
+    }
+
+    // Reset and replay UI telemetry to restore metrics
+    uiTelemetryService.reset();
+    replayUiTelemetryFromConversation(sessionData.conversation);
+
+    // Build UI history items using existing utility
+    const uiHistoryWithIds = buildResumedHistoryItems(sessionData, config);
+    // Strip IDs for LoadHistoryActionReturn (IDs are re-assigned by loadHistory)
+    const uiHistory = uiHistoryWithIds.map(({ id: _id, ...rest }) => rest);
+
+    // Build API history for the LLM client
+    const clientHistory = buildApiHistoryFromConversation(
+      sessionData.conversation,
+    );
+
+    // Update session in config and context
+    config.startNewSession(selectedSessionId);
+    if (context.session.startNewSession) {
+      context.session.startNewSession(selectedSessionId);
+    }
+
+    return {
+      type: 'load_history',
+      history: uiHistory,
+      clientHistory,
+    };
+  },
+};