feat(copilotcli): Perf impromvent by lazy loading chat session items

[DonJayamanne]

Co-authored-by: Copilot copilot@github.com

Fixes #309466

[github-actions]

⚠️ API Proposal Version Change Detected

The following proposed API files have version changes: vscode.proposed.chatSessionsProvider.d.ts

API proposal version changes should only be used when maintaining compatibility is not possible. Consider keeping the version as is and maintaining backward compatibility.

Any version changes must be adopted by the consuming extensions before the next insiders for the extension to work.

---

If the version change is required, comment /api-proposal-change-required to unblock this check and acknowledge that you will update any critical consuming extensions (Copilot Chat).

[github-actions]

Screenshot Changes

Base: 92c0a0f6 Current: 465382f8

Changed (1)

chat/aiCustomizations/aiCustomizationManagementEditor/McpBrowseMode/Light

Before	After

[Copilot]

Pull request overview

This PR introduces lazy resolution of chat session item details so expensive fields (notably git diff–derived changes) are only computed when a session item becomes visible, reducing startup/UI stalls when many sessions exist.

Changes:

• Adds a proposed API hook to lazily resolve ChatSessionItem details (resolveChatSessionItem) and wires it through ext host ↔ main thread plumbing.
• Updates the Agents/Sessions UI to trigger lazy resolution when rendering visible items.
• Implements lazy-loading in Copilot CLI session providers, guarded by a new advanced setting, and adds a lightweight “has cached changes” check in the worktree service.

Show a summary per file

File	Description
src/vscode-dts/vscode.proposed.chatSessionsProvider.d.ts	Proposed API: adds resolveChatSessionItem hook (provider + controller) and bumps proposal version.
src/vs/workbench/contrib/chat/test/common/mockChatSessionsService.ts	Updates mock service to implement the new resolveSessionItem API.
src/vs/workbench/contrib/chat/common/chatSessionsService.ts	Extends IChatSessionsService / controller contracts to support item resolution.
src/vs/workbench/contrib/chat/browser/chatSessions/chatSessions.contribution.ts	Implements resolveSessionItem in the workbench chat sessions service.
src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsViewer.ts	Triggers lazy resolve when items render in the session list UI.
src/vs/workbench/api/test/browser/mainThreadChatSessions.test.ts	Adjusts controller registration to the new signature.
src/vs/workbench/api/common/extHostChatSessions.ts	Adds $resolveChatSessionItem and bridges deprecated provider resolve hook via controller surface.
src/vs/workbench/api/common/extHost.protocol.ts	Ext host protocol changes: supportsResolve param + resolve RPC.
src/vs/workbench/api/browser/mainThreadChatSessions.ts	Main thread controller: adds resolve RPC invocation + per-resource resolve cache.
extensions/copilot/src/platform/configuration/common/configurationService.ts	Adds advanced setting key for lazy-loading session items.
extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts	Defers building changes eagerly; adds resolve hook to fill in changes lazily.
extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessions.ts	Same lazy-change strategy for controller-based CLI sessions.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionWorktreeServiceImpl.ts	Adds hasWorktreeChanges to detect cached changes quickly.
extensions/copilot/src/extension/chatSessions/common/chatSessionWorktreeService.ts	Extends interface with hasWorktreeChanges.
extensions/copilot/package.nls.json	Adds localized description for the new lazy-load setting.
extensions/copilot/package.json	Contributes the new advanced setting to VS Code configuration.

Copilot's findings

• Files reviewed: 15/16 changed files
• Comments generated: 3

[DonJayamanne]

address the code review comments

[DonJayamanne]

@copilot address the review comentsm

[Copilot]

@copilot address the review comentsm

Renamed the NLS key from github.copilot.config.lazyLoadSessionItem.enabled to github.copilot.config.cli.lazyLoadSessionItem.enabled in c03da85a, updating both package.nls.json and the markdownDescription reference in package.json. All other review comments were addressed in prior commits (renames + tests in 65ca61b7).

[Copilot]

Copilot's findings

Comments suppressed due to low confidence (1)

extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessions.ts:446

• originalRef for workspace changes no longer falls back to repositoryProperties.baseCommit when mergeBaseCommit is unavailable. That can make diff URIs point at HEAD and show incorrect/unstable comparisons. Consider restoring the previous fallback (mergeBaseCommit ?? baseCommit ?? 'HEAD') so workspace diffs remain anchored even when merge-base computation fails or hasn't been recorded yet.

				const originalRef = repositoryProperties?.mergeBaseCommit ?? 'HEAD';

• Files reviewed: 8/8 changed files
• Comments generated: 4