Update session replacement logic to ensure active session wrapper reflects committed session

[DonJayamanne]

Fixes #318883

[DonJayamanne]

@sandy081 @benibenj Not sure whether the changes are correct
Tagging you as this reverts the chagnes you have made
I"m not confident of this new change not breaking anything else,

@lszomoru tagging you as you might have a better fix/ideas

[Copilot]

Pull request overview

This PR fixes session replacement handling in the Agents window so that when a provider replaces an “untitled” session with its committed form without changing the session id, the active session wrapper is rebuilt to point at the committed ISession object. This addresses issue #318883 where UI surfaces (e.g. “Branch Changes”) could stay empty until navigating away/back because they were still observing the stale session instance.

Changes:

• Route provider onDidReplaceSession handling through VisibleSessions.updateSession(from, to) to rebuild the wrapper even when from.sessionId === to.sessionId.
• Add a regression test asserting that same-id replacement updates both activeSession and visibleSessions wrappers.

Show a summary per file

File	Description
src/vs/sessions/services/sessions/browser/sessionsManagementService.ts	Uses VisibleSessions.updateSession during session replacement so the active/visible wrappers reflect the committed session object even when ids don’t change.
src/vs/sessions/services/sessions/test/browser/sessionsManagementService.test.ts	Adds a regression test covering same-id replacement updating the active session wrapper and visible sessions wrapper.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0