The external-drain marker .drain_request.json is written under HERMES_HOME,
which on Hermes Cloud is a persistent Fly volume (/opt/data). A begin-drain
marker therefore SURVIVES the post-update machine restart. But the disruptive
lifecycle actions a drain protects (auto-update / image migrate / env edit /
profile change) all restart the machine — which is exactly the signal the drain
is over. The freshly-restarted gateway re-read the orphaned marker on its
startup reconcile and parked itself back in 'draining', refusing every new turn
indefinitely (NS-570: ~52 min until manually cleared).
Fix: stamp the marker with an identity of THIS container/VM instantiation
(kernel boot_id + PID 1 start time, read from /proc) and treat a marker whose
epoch differs from the current instantiation as absent. A deliberate restart →
new PID 1 → new epoch → stale marker ignored → gateway boots 'running'. A marker
written during the current instantiation (the live drain) still matches; an s6
respawn of just the gateway (PID 1/init unchanged) keeps the same epoch, so an
in-flight drain is still honoured (D4a reversibility preserved).
The staleness check is lenient and never fail-closed: a legacy marker with no
epoch, a corrupt/contentless marker, or an environment with no /proc (epoch
unavailable) all degrade to the original presence-only behaviour. NAS is
untouched — it only ever POSTs begin/cancel-drain over HTTP; the marker file is
purely gateway-internal IPC.
The fix is entirely within gateway/drain_control.py; the watcher and the
dashboard endpoint go through the same drain_requested()/write_drain_request()
chokepoints and need no functional change.
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