-- A send records the build of each module it carried (novox/hq issue 259, ADR 0221).
--
-- A named push ends by sending every other machine whose declaration differs from what it was last
-- sent (ADR 0083). Read from the declaration's digest alone, a module whose upgrade policy records
-- rather than rolls out, or whose plan sends one machine first (ADR 0218), made every machine running
-- it differ, so `push <one machine>` sent all of them the build the policy was holding back. Which
-- build of each module a machine was last sent is what tells a held upgrade from a consequence of the
-- push, and it is not in a digest.
--
-- Module name to the commit its build was made from — the module's `built_from` when the declaration
-- was composed, empty for a module the mesh holds without a source. NULL for a machine last sent
-- before this was kept, or sent a declaration by hand: what it carried is not known, and the push
-- treats such a machine as held until it is pushed by name.
alter table node add column sent_builds jsonb;