Sessions: deleting a session with a worktree should also delete the worktree

[copilot-swe-agent]

Description

Archiving a session that runs in an isolated git worktree correctly cleans up the worktree. In src/vs/platform/agentHost/node/agentSideEffects.ts:

case ActionType.SessionIsArchivedChanged: {
	// Host-owned worktree lifecycle (agents stay unaware): remove the
	// clean, branch-preserved worktree on archive and recreate it on
	// unarchive. Serialized per session inside the controller so it can't
	// interleave with a first-send worktree resolution.
	if (this._worktree) {
		const sessionUri = URI.parse(channel);
		const sessionId = AgentSession.id(channel);
		const worktreeOp = action.isArchived
			? this._worktree.cleanupWorktreeOnArchive(sessionUri, sessionId)
			: this._worktree.recreateWorktreeOnUnarchive(sessionUri, sessionId);
		...
	}
	...
}

cleanupWorktreeOnArchive / recreateWorktreeOnUnarchive live in src/vs/platform/agentHost/node/shared/worktreeIsolation.ts and only get called from the archive/unarchive side effect above.

However, deleting a session (ISessionsManagementService.deleteSession -> provider deleteSession/deleteSessions, e.g. baseAgentHostSessionsProvider.ts deleteSessions() -> connection.disposeSession(...) -> AgentService.disposeSession) never calls into the worktree cleanup path, so a session's worktree is left behind on disk after the session itself is deleted.

Suggested fix

When a session with an active worktree is deleted, remove its worktree the same way archiving does, e.g. by calling this._worktree.cleanupWorktreeOnArchive(...) (or an equivalent dedicated cleanup) from the session-deletion path in AgentService/agentSideEffects.ts before/while disposing the session, so no orphaned worktrees remain regardless of whether the user archives or deletes.

Context

Raised internally:

rob: How do automation sessions get archived, to clean up the worktree? Seems like they can only be deleted
Ben Villalobos: currently you can only delete from the view directly. A quick way to do it would be to click into the session itself and click archive from the controls at the top

does a worktree only get deleted on archive and not session deletion?
rob: Ah I see. It should be cleaned up on deletion too