Review hardening (the finding's ordering premise did not hold — see the
PR thread — but its failure-path kernel did): onBoundary cleared the
pending intent BEFORE appending the mode/set, so a backend rejecting
that one write lost the switch forever while the picker kept showing it
optimistically. The intent is now cleared only after the append lands;
a failed flush stays parked and the next healthy boundary converges the
log with the picker. The containment test extends to pin the re-park
and the retry.
The bridge's re-notify keeps deriving from the logged event's value —
now documented in place: the service holds ONE coalesced pending slot
(every flush reads the latest selection, so a stale flush cannot
exist), and for any other writer the logged value is the truth the
picker should track, in log order.