Agent sessions: provide `inProgressTime` and `finishedOrFailedTime` from provider

[bpasero]

Usecase: show how long the current task is running (if in-progress) and when the last response finished.

Today we do tracking of these properties in-memory:

vscode/src/vs/workbench/contrib/chat/browser/agentSessions/agentSessionViewModel.ts

Lines 217 to 225 in 5942390

	// State + Timings
	// TODO@bpasero this is a workaround for not having precise timing info in sessions
	// yet: we only track the time when a transition changes because then we can say with
	// confidence that the time is correct by assuming `Date.now()`. A better approach would
	// be to get all this information directly from the session.
	const status = session.status ?? ChatSessionStatus.Completed;
	const state = this.mapSessionToState.get(session.resource);
	let inProgressTime = state?.inProgressTime;
	let finishedOrFailedTime = state?.finishedOrFailedTime;

We need to get this data from the provider to show it properly. This needs support for that info from the provider API.

//cc @mjbvz @osortega @rebornix @DonJayamanne

[bpasero]

This is provided for chat sessions in #278449 by Connor, but not yet wired into the local sessions provider.

[mjbvz]

This makes sense to me. May also be a good time to update the existing timing field names as I find them confusing. Here's what I'm thinking:

• createdTime — When the session was first created. If we prefer we could also call this firstRequestStartTime to track when the first request was made since some providers may only consider it a real session if a request has been made

• latestRequestStartTime? — The time when the most recent request began. If there is an ongoing request, this would be when that request started. Otherwise it would track the most recent request's start time. Would be undefined if no requests have been made

• latestRequestEndTime? — Time when the most recent request ended (either succeeded or failed). Would be undefined if there is an ongoing request

For the API, I also had a proposal that would make the time fields part of the state: #263696 The idea was to try to prevent invalid chat session states. We can revisit that if it still seems interesting

[bpasero]

@mjbvz I like this, maybe we can shorten it a bit considering that these properties are already in a timing section:

• created
• lastRequestCreated
• lastRequestEnded

And then we can synthesize:

• the startTime today is created
• the inProgressTime is Date.now() - lastRequestCreated
• the finishedOrFailedTime is lastRequestEnded - lastRequestCreated

I would also like to point out that these times should not be optional in the API!

[mjbvz]

Yes I like that. I'll go ahead and make that change