-- A failed unit is never silent (novox/hq issue 315).
--
-- Beside the state of every long-running resource and its networking, each machine's node-engine states
-- its service managers: running, degraded or unknown, and every failed unit no module places — a mount of
-- the machine's own table, a unit a removed package left behind. A module's failed unit is among the
-- resources, as that module's. Kept with the machine's newest statement, replaced with it, so `node show`
-- and a controller started again read the same word. Null for a machine whose node-engine is older than
-- this reading: its units are not known — never healthy, never a reason to raise anything.
alter table node_health add column units jsonb;