One host runs one multiplexing gateway, but the update pipeline still treated
the pull->restart obligation, enumerated units, recovery payloads and the
planned-restart notice as per-profile. Two profiles updating meant two outages
of the same process, and a served profile's channels were never told.
- hermes_cli/update_host_obligation.py: new host-scoped obligation record in
gateway.host_rendezvous.host_state_dir() (host-update-restart.json), plus the
unit->live-MainPID collapse rule. The legacy per-home marker stays readable
and clearable so an in-flight obligation is still discharged.
- update_cmd_fleet: arm/clear/read the host record; the catch-up restart is
idempotent per host (a completed restart onto the checkout SHA is never
repeated); leftover per-profile units resolving to one MainPID restart once.
- update_restart_recovery: payload profiles served by one host process are one
restart target, reported under "covered".
- gateway notices: owed targets and the online notice span every served
profile's home channels; the marker survives until each was reached.