Opus ship-gate non-blocking observations (no MUST-FIX), applied to lower future-maintainer
risk on the crown-jewel profile-switch surface:
- clarified the belt-and-suspenders _sessionListSkeletonActive=false at the real-paint site
- added a FOUR-GUARD CONTRACT doc-comment at the top of switchToProfile naming the four
interacting state pieces (embargo / invalidation / skeleton-flag / _wsTreeGen + _switchGen)
so a future edit touching one without the others doesn't silently reopen a window.
Co-authored-by: rodboev <rodboev@users.noreply.github.com>