Review follow-up (#78574): the aborted-restart handler only flagged the fleet
stale when the post-failure survivor probe was None or non-empty. A positive
empty probe was treated as proof-of-safety — but `[]` is only safe when
nothing was running before the phase. If a gateway was discovered, stopped
(SIGTERM/drain), and its replacement never came back, the probe is empty at
exactly that unsafe moment and the update reported success — the fail-open
contract this fix exists to close.
Snapshot the pre-restart gateway PIDs before any stop/drain and route the
handler decision through a pure _restart_phase_failure_is_incomplete() helper
that fails closed on an empty survivor set whenever a gateway existed
pre-restart (or the pre-state could not be read). Add decision-level regression
tests covering the stopped-without-replacement gap, unknown pre-state, and the
truly-no-gateway positive control.
The gateway auto-restart phase in `hermes update` was wrapped in a blanket
`except Exception` that only logged at debug level. When the phase raised
early — e.g. importing `hermes_cli.gateway` from the freshly pulled checkout
inside a process that already loaded pre-update modules — every drain and
restart line vanished from the update output, the update printed
"Update complete!" and exited 0, and the still-running gateway kept serving
pre-update modules against replaced source files. The next Telegram turn died
with `ImportError: cannot import name 'is_trivial_prompt'`.
The handler now probes for surviving gateway processes and, unless it can
positively prove none are running, prints the cause plus a manual recovery
command and marks the fleet restart incomplete — which exits nonzero and
writes the gateway-mode exit-code marker, matching the existing
failed-or-stale-unit path.
Fixes#78574
PRATHAMESH75