[BUG] Desktop: archiving a child session also archives its parent session

Platform: macOS, Claude desktop app, Code tab

What happens: A session starts a child session with start_session. The child shows under the parent in the sidebar. When I archive the finished child, the app also archives the parent. The parent drops out of the active list. I have lost track of several sessions this way.

Expected: Archiving a child archives only the child. The parent stays active.

Evidence: In my session list, some parents are archived while their children are still active. This matches parents being archived as a side effect, not on purpose.

Settings: "Archive inactive sessions" is set to Never. These sessions had no PR, so "auto-archive on PR close" does not apply.

Workaround: Detach the child to the top level before archiving it, or unarchive the parent afterward.