The mesh knows which host runs a machine, and says who is behind another

novox/hq 04-ISSUES/087. A host refuses a declaration carrying a field it
does not know, and refuses it WHOLE — deliberately, because that keeps a
half-understood declaration off a machine. It makes every new declaration
field a flag day: hosts first, then the controller. The mesh had no record
of which host any machine ran, so that order was kept by somebody
remembering it, and a machine that refused for this reason reported a
failure with nothing saying why.

The machine has reported its host version since ADR 0141. The
controller's own copy of the report did not have the field, so it was
unmarshalled into nothing and thrown away on arrival. It has it now,
records it, and shows it in `node show` — "not reported" rather than
blank, because a machine that has not said is not a machine running
nothing.

Status says which machines run an older host than another machine does,
and which is newest. Deliberately disagreement rather than staleness:
nothing delivers a host version yet (ADR 0141, accepted and not built), so
the mesh holds no canonical current version and cannot honestly say a
machine is behind THE host. What it can say is that the oldest host in the
mesh is what the mesh may send.

A machine that has reported nothing is left out rather than called
behind. Versions compare as strings, which suits the timestamps and
commits this mesh uses and is wrong for a scheme where "10" sorts before
"9" — said in the code, at the place that would have to learn.

internal/inventory/migrations/0045-a-machine-says-which-host-runs-it.sql

@@ -0,0 +1,15 @@
+-- The version of the host running on a machine, as the machine reports it.
+--
+-- novox/hq 04-ISSUES/087. A host parses a declaration strictly: a field it does not know makes it
+-- refuse the whole declaration and apply nothing. That is deliberate — it keeps a half-understood
+-- declaration off a machine — and it makes every new field in a declaration a flag day, hosts before
+-- controller. The mesh had no record of which host a machine runs, so it could neither refuse to send
+-- a declaration a machine cannot parse nor say which machines were behind. The order was kept by
+-- somebody remembering it.
+--
+-- The machine has been reporting this since ADR 0141 and the control plane discarded it: the field was
+-- absent from the controller's own copy of the report, so it was unmarshalled into nothing.
+--
+-- Null for a machine that has not reported since this column existed, which is not the same as a
+-- machine running no host — so a reader is never told a version the mesh does not have.
+alter table node add column host_version text;