Cherry-picked from PR #94595 (author: Futahua) onto current main, with the
maintainer-review revision points folded in during the rebase:
- the lease engages UNCONDITIONALLY: try_acquire_active_session no longer
returns a disabled no-op lease when max_concurrent_sessions is unset;
the concurrency cap stays an orthogonal, optional policy checked second
- ownership uncertainty fails CLOSED (SESSION_COORDINATION_UNAVAILABLE)
instead of degrading to an untracked go-ahead: a corrupt/unreadable
registry must not be collapsed into 'no owner exists' (review blocker 2)
- the ownership admission sits at the _run_prompt_submit chokepoint that
EVERY fresh turn source crosses, and crash auto-continue acquires (or
bails) BEFORE emitting message.start — closing the #94778 bypass where
backend B's auto-continue ran a duplicate turn while backend A was live
(review blocker 1)
- the TUI gateway claim helper fails closed on claim exceptions for every
surface, not just desktop
- CLI and messaging-gateway call sites pass live_session_id metadata so
the (pid, live id) re-entrancy identity protects them from self-fencing
on a leaked lease
Co-authored-by: teknium1 <teknium1@users.noreply.github.com>
Futahua