The script helper's `reclaim` answered `absent` the moment the marker file
was missing, before the checkout lock was looked at, and the Desktop gate
(update-marker-gate.ts liveMarkerProbe) returned "nothing runs" for a
missing marker without asking the helper at all. An update that holds the
checkout lock before it publishes its marker, or after it retired it (the
CLI paths of the stacked PRs do both), therefore let the Desktop boot a
backend into a checkout still being written.
- marker.sh marker_op_reclaim_locked / marker-claim.ps1 Invoke-MarkerOp:
no marker -> `held` when the checkout lock (owner byte + lease bytes on
Windows) is held, else `absent`, under the same marker lock.
- update-marker-gate.ts (gate-lane file, additive): a missing marker is also
routed through the helper; only its positive `held` keeps the gate shut
(blocked screen, Retry, Start anyway as for a dead marker). Any other
answer, `error` included, proceeds as before, so a broken script never
blocks a markerless boot.
The gate test "a live owner never reaches the helper; an absent marker
neither" pinned the missing check for the absent half; that half is now the
new "no marker: only held keeps the gate shut" case.
Review 5411223284 (open thread: update-marker-gate.ts ~193 / helper absent).
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