feat(claude): implement workspace folder service for tracking file changes in chat sessions

extensions/copilot/src/extension/chatSessions/claude/AGENTS.md

@@ -214,6 +214,8 @@ In multi-root and empty workspaces, a folder picker option appears in the chat s
 ### Key Files
 
 - **`common/claudeFolderInfo.ts`**: `ClaudeFolderInfo` interface
+- **`../../chatSessions/common/claudeWorkspaceFolderService.ts`**: `IClaudeWorkspaceFolderService` interface — computes git diff changes for session items
+- **`../../chatSessions/vscode-node/claudeWorkspaceFolderServiceImpl.ts`**: Implementation — diffs the session's branch against its base branch, caches results, and maps changes to `ChatSessionChangedFile[]` for display in the Sessions view
 - **`../../chatSessions/vscode-node/claudeChatSessionContentProvider.ts`**: Folder resolution, picker options, and handler integration
 - **`../../chatSessions/vscode-node/folderRepositoryManagerImpl.ts`**: `FolderRepositoryManager` (abstract base) with `ClaudeFolderRepositoryManager` subclass — the Claude subclass does not depend on `ICopilotCLISessionService` (CopilotCLI has its own subclass `CopilotCLIFolderRepositoryManager`)
 - **`node/claudeCodeAgent.ts`**: Consumes `ClaudeFolderInfo` in `ClaudeCodeSession._startSession()`

extensions/copilot/src/extension/chatSessions/claude/CLAUDE_SESSION_USER_GUIDE.md

@@ -225,6 +225,7 @@ Each session in the list displays:
 | **Blue dot** | Indicates an unread or recently active session |
 | **Status icon** | Shows whether the session is completed, in progress, needs input, or failed |
 | **Folder badge** | In multi-root or empty workspaces, shows which folder the session ran in |
+| **Change stats** | Shows lines added and removed (e.g., `+584 -17`) — a quick summary of the session's code impact, computed by diffing the session's branch against its base branch |
 
 Sessions are sorted by recency — the most recent session appears at the top. In the dedicated sidebar, they're also grouped by time period.
 

extensions/copilot/src/extension/chatSessions/common/claudeWorkspaceFolderService.ts

@@ -0,0 +1,26 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import type * as vscode from 'vscode';
+import { createServiceIdentifier } from '../../../util/common/services';
+
+export const IClaudeWorkspaceFolderService = createServiceIdentifier<IClaudeWorkspaceFolderService>('IClaudeWorkspaceFolderService');
+
+/**
+ * Service for computing and caching workspace file changes for Claude chat sessions.
+ */
+export interface IClaudeWorkspaceFolderService {
+	readonly _serviceBrand: undefined;
+	/**
+	 * Computes file changes for a workspace directory by diffing the current branch against a base branch.
+	 * Results are cached per unique (cwd, gitBranch, gitBaseBranch) combination.
+	 *
+	 * @param cwd The working directory of the session.
+	 * @param gitBranch The current git branch name, or `undefined` if unknown.
+	 * @param gitBaseBranch The base branch to diff against, or `undefined` to diff against HEAD.
+	 * @param forceRefresh When `true`, bypasses the cache and recomputes changes.
+	 */
+	getWorkspaceChanges(cwd: string, gitBranch: string | undefined, gitBaseBranch: string | undefined, forceRefresh?: boolean): Promise<vscode.ChatSessionChangedFile[]>;
+}

extensions/copilot/src/extension/chatSessions/vscode-node/chatSessions.ts

@@ -38,6 +38,7 @@ import { ClaudeSlashCommandService, IClaudeSlashCommandService } from '../claude
 import { IAgentSessionsWorkspace } from '../common/agentSessionsWorkspace';
 import { IChatSessionMetadataStore } from '../common/chatSessionMetadataStore';
 import { IChatSessionWorkspaceFolderService } from '../common/chatSessionWorkspaceFolderService';
+import { IClaudeWorkspaceFolderService } from '../common/claudeWorkspaceFolderService';
 import { IChatSessionWorktreeCheckpointService } from '../common/chatSessionWorktreeCheckpointService';
 import { IChatSessionWorktreeService } from '../common/chatSessionWorktreeService';
 import { IChatFolderMruService, IFolderRepositoryManager } from '../common/folderRepositoryManager';
@@ -61,6 +62,7 @@ import { UserQuestionHandler } from './askUserQuestionHandler';
 import { ChatSessionMetadataStore } from './chatSessionMetadataStoreImpl';
 import { ChatSessionRepositoryTracker } from './chatSessionRepositoryTracker';
 import { ChatSessionWorkspaceFolderService } from './chatSessionWorkspaceFolderServiceImpl';
+import { ClaudeWorkspaceFolderService } from './claudeWorkspaceFolderServiceImpl';
 import { ChatSessionWorktreeCheckpointService } from './chatSessionWorktreeCheckpointServiceImpl';
 import { ChatSessionWorktreeService } from './chatSessionWorktreeServiceImpl';
 import { ClaudeChatSessionContentProvider } from './claudeChatSessionContentProvider';
@@ -142,6 +144,7 @@ export class ChatSessionsContrib extends Disposable implements IExtensionContrib
 				[IChatSessionWorktreeService, new SyncDescriptor(ChatSessionWorktreeService)],
 				[IChatSessionWorktreeCheckpointService, new SyncDescriptor(ChatSessionWorktreeCheckpointService)],
 				[IChatSessionWorkspaceFolderService, new SyncDescriptor(ChatSessionWorkspaceFolderService)],
+				[IClaudeWorkspaceFolderService, new SyncDescriptor(ClaudeWorkspaceFolderService)],
 				[IFolderRepositoryManager, new SyncDescriptor(ClaudeFolderRepositoryManager)],
 				[IChatFolderMruService, new SyncDescriptor(ClaudeCodeFolderMruService)],
 				[IClaudeRuntimeDataService, new SyncDescriptor(ClaudeRuntimeDataService)],

extensions/copilot/src/extension/chatSessions/vscode-node/claudeChatSessionContentProvider.ts

@@ -18,6 +18,7 @@ import { autorun, derived, IObservable, ISettableObservable, observableFromEvent
 import { basename } from '../../../util/vs/base/common/resources';
 import { URI } from '../../../util/vs/base/common/uri';
 import { generateUuid } from '../../../util/vs/base/common/uuid';
+import { IInstantiationService } from '../../../util/vs/platform/instantiation/common/instantiation';
 import { ClaudeFolderInfo } from '../claude/common/claudeFolderInfo';
 import { ClaudeSessionUri } from '../claude/common/claudeSessionUri';
 import { ClaudeAgentManager } from '../claude/node/claudeCodeAgent';
@@ -29,6 +30,7 @@ import { IClaudeCodeSessionService } from '../claude/node/sessionParser/claudeCo
 import { IClaudeCodeSessionInfo } from '../claude/node/sessionParser/claudeSessionSchema';
 import { IClaudeSlashCommandService } from '../claude/vscode-node/claudeSlashCommandService';
 import { IChatFolderMruService } from '../common/folderRepositoryManager';
+import { IClaudeWorkspaceFolderService } from '../common/claudeWorkspaceFolderService';
 import { buildChatHistory } from './chatHistoryBuilder';
 import { ClaudeSessionOptionBuilder, buildPermissionModeItems, FOLDER_OPTION_ID, isPermissionMode, PERMISSION_MODE_OPTION_ID } from './claudeSessionOptionBuilder';
 import { toWorkspaceFolderOptionItem } from './sessionOptionGroupBuilder';
@@ -60,21 +62,11 @@ export class ClaudeChatSessionContentProvider extends Disposable implements vsco
 		@IClaudeCodeSessionService private readonly sessionService: IClaudeCodeSessionService,
 		@IClaudeSessionStateService private readonly sessionStateService: IClaudeSessionStateService,
 		@IClaudeSlashCommandService private readonly slashCommandService: IClaudeSlashCommandService,
-		@IConfigurationService configurationService: IConfigurationService,
 		@IClaudeCodeModels private readonly claudeModels: IClaudeCodeModels,
-		@IChatFolderMruService folderMruService: IChatFolderMruService,
-		@IWorkspaceService workspaceService: IWorkspaceService,
-		@INativeEnvService envService: INativeEnvService,
-		@IGitService gitService: IGitService,
-		@IClaudeCodeSdkService sdkService: IClaudeCodeSdkService,
-		@ILogService logService: ILogService,
+		@IInstantiationService instantiationService: IInstantiationService
 	) {
 		super();
-		this._controller = this._register(new ClaudeChatSessionItemController(
-			sessionService, sessionStateService, configurationService,
-			folderMruService, workspaceService, envService,
-			gitService, sdkService, logService,
-		));
+		this._controller = this._register(instantiationService.createInstance(ClaudeChatSessionItemController));
 	}
 
 	// #region Chat Participant Handler
@@ -134,9 +126,9 @@ export class ClaudeChatSessionContentProvider extends Disposable implements vsco
 			});
 
 			const prompt = request.prompt;
-			this._controller.updateItemStatus(effectiveSessionId, vscode.ChatSessionStatus.InProgress, prompt);
+			await this._controller.updateItemStatus(effectiveSessionId, vscode.ChatSessionStatus.InProgress, prompt);
 			const result = await this.claudeAgentManager.handleRequest(effectiveSessionId, request, context, stream, token, isNewSession, yieldRequested);
-			this._controller.updateItemStatus(effectiveSessionId, vscode.ChatSessionStatus.Completed, prompt);
+			await this._controller.updateItemStatus(effectiveSessionId, vscode.ChatSessionStatus.Completed, prompt);
 
 			// Clear usage handler after request completes
 			this.sessionStateService.setUsageHandlerForSession(effectiveSessionId, undefined);
@@ -217,6 +209,7 @@ export class ClaudeChatSessionItemController extends Disposable {
 		@IGitService private readonly _gitService: IGitService,
 		@IClaudeCodeSdkService private readonly _sdkService: IClaudeCodeSdkService,
 		@ILogService private readonly _logService: ILogService,
+		@IClaudeWorkspaceFolderService private readonly _claudeWorkspaceFolderService: IClaudeWorkspaceFolderService,
 	) {
 		super();
 		this._optionBuilder = new ClaudeSessionOptionBuilder(_configurationService, folderMruService, _workspaceService);
@@ -642,7 +635,7 @@ export class ClaudeChatSessionItemController extends Disposable {
 		if (!item) {
 			const session = await this._claudeCodeSessionService.getSession(resource, CancellationToken.None);
 			if (session) {
-				item = this._createClaudeChatSessionItem(session);
+				item = await this._createClaudeChatSessionItem(session);
 			} else {
 				const newlyCreatedSessionInfo: IClaudeCodeSessionInfo = {
 					id: sessionId,
@@ -651,7 +644,7 @@ export class ClaudeChatSessionItemController extends Disposable {
 					lastRequestEnded: Date.now(),
 					folderName: undefined
 				};
-				item = this._createClaudeChatSessionItem(newlyCreatedSessionInfo);
+				item = await this._createClaudeChatSessionItem(newlyCreatedSessionInfo);
 			}
 
 			this._controller.items.add(item);
@@ -676,18 +669,37 @@ export class ClaudeChatSessionItemController extends Disposable {
 				} else {
 					item.timing = { ...item.timing, lastRequestEnded: Date.now() };
 				}
+				const session = await this._claudeCodeSessionService.getSession(resource, CancellationToken.None);
+				if (session?.cwd) {
+					item.changes = await this._claudeWorkspaceFolderService.getWorkspaceChanges(
+						session.cwd,
+						session.gitBranch,
+						undefined,
+						true,
+					);
+				}
 			}
 		}
 	}
 
 	private async _refreshItems(token: vscode.CancellationToken): Promise<void> {
 		const sessions = await this._claudeCodeSessionService.getAllSessions(token);
-		const items = sessions.map(session => this._createClaudeChatSessionItem(session));
+		const results = await Promise.allSettled(sessions.map(session => this._createClaudeChatSessionItem(session)));
+		const items: vscode.ChatSessionItem[] = [];
+		for (let i = 0; i < results.length; i++) {
+			const result = results[i];
+			if (result.status === 'fulfilled') {
+				items.push(result.value);
+			} else {
+				const session = sessions[i];
+				this._logService.warn(`Failed to create Claude chat session item for ${session.id} (${session.label}) ${result.reason}`);
+			}
+		}
 		items.push(...this._inProgressItems.values());
 		this._controller.items.replace(items);
 	}
 
-	private _createClaudeChatSessionItem(session: IClaudeCodeSessionInfo): vscode.ChatSessionItem {
+	private async _createClaudeChatSessionItem(session: IClaudeCodeSessionInfo): Promise<vscode.ChatSessionItem> {
 		let badge: vscode.MarkdownString | undefined;
 		if (session.folderName && this._showBadge) {
 			badge = new vscode.MarkdownString(`$(folder) ${session.folderName}`);
@@ -704,8 +716,12 @@ export class ClaudeChatSessionItemController extends Disposable {
 		};
 		item.iconPath = new vscode.ThemeIcon('claude');
 		if (session.cwd) {
-			// Agents app needs this to decide the working directory for the session
 			item.metadata = { workingDirectoryPath: session.cwd };
+			item.changes = await this._claudeWorkspaceFolderService.getWorkspaceChanges(
+				session.cwd,
+				session.gitBranch,
+				undefined,
+			);
 		}
 		return item;
 	}