`services.hyperhive.domain` and `swarm.hives.<hiveName>.domain` were two
homes for one value with nothing asserting they agreed. The failure that
buys is the worst shape a config defect has: it evaluates cleanly, and
the symptom ("the other hives can't reach me") appears on a machine
other than the misconfigured one.
The directory is now the single source. `hives.<name>.domain` gains the
`<name>.<swarm.domain>` default -- a derivation from two values an
operator had to state explicitly, not a guess -- so a conventional swarm
is a list of names and a hive addressed by something else says so in the
one place every other hive reads. `services.hyperhive.domain` reads its
own entry; the direct formula is deleted rather than kept as a fallback,
which would have restored the second path (and, reading `swarm.domain`
itself, a second path that can disagree).
Setting it directly still wins, with a deprecation warning: nothing
breaks today, but a value written only there is invisible to the swarm.
The self-entry assertion now fires on an EMPTY directory too. Since
`swarm.domain` became required, every hive is in a swarm -- a swarm of
one is still a swarm -- and this host's address is read out of the
directory, so the entry is missing either way and the precise message
should be the one that fires.
Upgrading costs one line on hives that never listed themselves:
`services.hyperhive.swarm.hives.<hiveName> = { };`, no value.
Neither has a fallback worth having: a guessed swarm domain is a wrong
hostname that evaluates cleanly and deploys, which is worse than an
eval failure naming the one line an operator has to write. Upgrading
past this sets both, once.
Requiring them also makes the hive domain fully derived rather than
merely derivable — `<hiveName>.<swarm.domain>` now always resolves, so
an operator writes the swarm's address and this hive's label and never
writes the hive domain at all.
`hiveName` stops being display-only in the process: it is the leftmost
label of the domain the hive is addressed by, which the option text and
docs now say.
Each of the three required options asserts separately, so a missing one
names itself. A missing `swarm.domain` legitimately fails two of them —
its own, and `domain`, which can no longer derive — and nix reports all
failing assertions together, so the operator sees the whole set rather
than one at a time.
The required-domain assertion in hive-network.nix could not be reached:
`forge.<domain>` and `matrix.<domain>` are evaluated while the
assertion list is, so an unset domain threw `cannot coerce null to a
string` naming one of those options instead of printing the message
that says which option to set.
Both defaults now fall back to a name under the reserved `.invalid`
TLD, which the assertion refuses to let out the door.
Every hive in a swarm occupies its own sub-domain of the swarm's, so
the hive domain is derivable rather than something each hive restates.
`services.hyperhive.swarm.domain` is new and nullable; the hive's own
`domain` keeps its existing required-ness and its existing assertion,
and gains a default of `<hiveName>.<swarm.domain>`.
Deliberately a default and not a rename: an alias would reinterpret the
domains hives have already deployed, while a default only fills in the
ones that never set one. Same reason there is no new assertion — the
existing message just names the derivation, so this adds a way to stop
failing rather than a way to fail.
