The machine has reported its host version since ADR 0141, whose own
comment says why it must: without it nothing can say a machine is behind.
The controller's copy of the report did not have the field, so it
unmarshalled into nothing and was thrown away on arrival. Two structs
describe one message and only the sending side had it.
node show names it per machine, "not reported" where the mesh has not been
told. status names every machine running an older host than another does,
and which is newest.
Disagreement rather than staleness, deliberately: nothing delivers a host
version yet, so the mesh holds no canonical current one and "behind" has
no fixed point. What it can say is that the oldest host in the mesh is
what the mesh may send.
Two refusals to guess: a machine that reported nothing is not called
behind, and versions compare as strings — right for the timestamps this
mesh uses, wrong for a scheme where 10 sorts before 9, said at the place
that would have to learn.
107 gains the note that this is what makes its new field safe to consider,
and that one machine of four is behind today, so it is not free yet.
