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/link/protocol.go

@@ -184,6 +184,15 @@ type Report struct {
 	// leaves the one it has: a rule written around a link with no name is a rule set that does not
 	// load, and that is a machine filtering nothing while its unit reports success.
 	Outward []string `json:"outward,omitempty"`
+
+	// Host is the version of the host that produced this report (novox/hq ADR 0141).
+	//
+	// **The machine has sent this since 0141 and this struct did not have it**, so it was
+	// unmarshalled into nothing and the mesh could not say which host any machine runs
+	// (novox/hq 04-ISSUES/087). A host refuses a declaration carrying a field it does not know, and
+	// refuses it whole — which is right, and makes every new field a flag day that the mesh could
+	// not see coming.
+	Host string `json:"host,omitempty"`
 	// Reachable is what can be reached on the machine now: every listening socket and every
 	// published container port. Only an adopted node reports it; it is what converging previews.
 	Reachable []Reach `json:"reachable,omitempty"`