svos-dev found the failure neither Beszel nor Uptime Kuma can see, and
measured it: a config change on 09-19 made svos.service refuse to boot, the
RUNNING process predated the change and kept serving, and the service sat one
restart from dark for three days. Every uptime probe was green and correct --
the thing was up. The signal that catches this is failed-START, not down.
A count after that conversation: 13 running user units on nh3-dev, ZERO with
an OnFailure hook. Including althing-po-herald, whose silent failure cuts
infra-ops's own mail delivery -- a blind spot in the notification path every
other alarm on this fleet depends on.
One template, one drop-in, 12 units hooked (dbus excluded as systemd's own
plumbing). Not noise: OnFailure does not fire on a clean restart or a
deliberate stop, and with Restart=on-failure a crash-loop yields one message
per episode rather than one per attempt.
⚠ %i, NEVER %I -- and the acceptance test is the only reason this is right.
%I unescapes the instance name and systemd escaping maps "-" to "/", so the
first run delivered a message for "onfailure/selftest.service", a unit that
does not exist, with a spool path that tried to create directories.
althing-po-herald.service would have arrived as althing/po/herald.service.
It "worked" -- mail was delivered -- which is exactly the kind of success that
is not one. The referring unit passes %n raw, so literal %i is correct.
⚠ The notifier never reports itself, guarded twice on purpose: the template
carries no OnFailure, and the script bails on its own instance name. A
notification loop is the one bug that pages you forever.
Delivery is spool-first. postbox has no outbox, and an alarm for moments
nobody is watching must survive the post office being one of the things that
is down. If the herald itself fails, the message still REACHES the post office
(postbox talks to it directly; the herald only delivers inbound pokes) -- not
pushed, but stored for the next read.
Acceptance-tested twice against a unit that exits 42: once to catch the %I
bug, once to confirm the fix. Test unit removed.
