When the gateway's home refuses a new .accepted receipt, mark_stop_accepted
stamps the kept request itself with accepted=true; that stamp is then the
only durable trace that this draining incarnation accepted the update's
stop. _read_live_pid_marker unlinked every expired marker, so a second
signal past the request TTL (another Ctrl+C / SIGTERM, which calls the
consumer again) or a planned-stop watcher probe in the same home deleted
it, and recovery then retired the restart debt of a gateway that was still
draining.
An expired stamped request still matches nobody (no PID-reuse grief), but
the TTL cleanup no longer unlinks it.
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