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.
Tasks 2.1 + 2.2 + 2.3 of the safe-shutdown plan — the reversible
quiesce-without-restart machinery NAS drives during a lifecycle action (D4a).
These ship together because the endpoint, the control channel, and the gateway
state machine are one coherent slice.
2.2 — control channel (gateway/drain_control.py, new):
The dashboard has no HTTP path into a running gateway (guardrails: "there is NO
external control channel into a running gateway"); restart/drain is driven only
by markers the gateway reacts to. So begin/cancel-drain writes/removes a
presence-based marker .drain_request.json (HERMES_HOME-scoped, atomic write,
never-raises read; a corrupt marker reads as present-contentless → fail-safe
toward quiescing). This is Q-B option A.
2.2 — gateway state machine (gateway/run.py):
- _external_drain_active flag, DISTINCT from the shutdown _draining flag: this
one does NOT exit the process and is fully reversible.
- _enter_external_drain / _exit_external_drain: idempotent transitions that
flip gateway_state→draining / →running via _update_runtime_status (preserving
the live active_agents count). exit refuses to revert to running during a
real shutdown or after the loop stops (shutdown wins).
- _drain_control_watcher: 1s background task (modelled on _handoff_watcher)
reconciling accept-state with the marker; honours a marker that survived a
restart on its first tick. Registered alongside the other watchers in start.
- New-turn accept gate in _handle_message, placed BEFORE the session-slot
claim: when draining, refuse to START a new turn (so active_agents can only
fall → no TOCTOU race), while in-flight turns finish untouched. Internal/
system events (restart-recovery replays, bg-process completions) bypass it.
2.1 — endpoint (hermes_cli/web_server.py):
POST /api/gateway/drain {action: drain|cancel}. Authenticated by the Task-2.0a
token seam (the drain plugin registered this exact path as a token route);
attributes the request to the verified token principal. Begin writes the
marker, cancel removes it — the gateway process owns the actual transition.
Force-override (D6) is NOT here; it maps onto the existing immediate
/api/gateway/restart force path.
Tests (mocked — necessary-not-sufficient; the HARD live gate Q-B is next):
- tests/gateway/test_external_drain_control.py — marker contract (write/clear/
read/corrupt/atomic), state machine (enter/exit/idempotency/shutdown-wins/
loop-stopped), watcher reconcile-enter-then-exit, new-turn refusal, and
in-flight-not-interrupted. 15 tests.
- tests/hermes_cli/test_web_server.py — /api/gateway/drain begin/default-begin/
cancel/cancel-idempotent/bad-action-400. 6 tests.
- dashboard.drain_auth config section already added in 2.0b commit.
All touched suites green: 301 (gateway+auth) + 9 (web_server endpoints) passed.
Intentionally deferred:
- HARD live-validation gate (Q-B): real isolated `hermes gateway run`, drive a
real begin-drain marker, prove the 5-point checklist a–e.
- Spec-doc status flip + Phase-2 PR.
Build status: external-drain, restart-drain, status, dashboard-auth, drain-plugin,
token-auth, and web_server-endpoint suites green.
