Add better timing info to chat sessions

[mjbvz]

Fixes #278567

Resubmission of #278858

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@bpasero

Matched files:

• src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsModel.ts
• src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsPicker.ts
• src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionsViewer.ts

[Copilot]

Pull request overview

This PR refactors chat session timing information to provide more granular tracking by replacing startTime/endTime with created, lastRequestStarted, and lastRequestEnded fields. The old fields are deprecated but maintained for backward compatibility.

Changes:

• Updated timing API to track session creation and individual request timing separately
• Deprecated old startTime and endTime fields in the public API
• Added backward compatibility for reading old cached sessions and external provider data

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
vscode.proposed.chatSessionsProvider.d.ts	Added new timing fields (created, lastRequestStarted, lastRequestEnded) and deprecated old fields (startTime, endTime)
chatService.ts	Updated IChatSessionTiming interface with new fields and comprehensive documentation
chatModel.ts	Updated timing getter to compute new timing fields from request data
chatSessionStore.ts	Updated session metadata to use new timing structure
chatSessionsService.ts	Changed to use IChatSessionTiming type directly
chatServiceImpl.ts	Added fallback logic for old data migration
agentSessionsModel.ts	Updated model to handle new timing fields with backward compatibility for cached sessions
extHostChatSessions.ts	Added backward compatibility layer to convert old API usage to new format
agentSessionsViewer.ts	Updated viewer to use new timing fields with proper fallback chain
agentSessionsPicker.ts	Updated picker to use new timing fields
localAgentSessionsProvider.test.ts	Updated tests with new timing structure and helper function
agentSessionsDataSource.test.ts	Updated tests to use new timing fields
agentSessionViewModel.test.ts	Updated tests with new timing structure