A hive key becomes a certificate subject and a directory name, but only the
reserved-name and fragment guards looked at it, so `a/b` or `../x` evaluated
and misbehaved later. Assert at eval time that every key is 1-63 characters
of [a-z0-9-], the rule `Ident` applies in hive-types, and name the offending
keys in the message.
Her review: too much text, and an assertion helper instead of that much code
where the file should just say "this option cannot contain that".
`lib/name-guards.nix` gets `mustNotEqual` / `mustNotContain`; both call sites in
swarm-otel become four fields each — the option, the names, the list, and the
sentence explaining the failure. The message plumbing (find every offender,
quote them, name the list) is one shape shared by both.
Offenders are printed after their label rather than before it, because no
English verb agrees with both one name and five.
Converted the pre-existing equality assertion too. Leaving one hand-rolled
beside one helper-built is the worse of the two outcomes, and it is the same
guard.
Verified by evaluating both guards directly rather than only parsing: clean
rosters pass, `foo-agent`/`beehive` fail containment, `swarm` fails equality,
and `forgeworks`/`operator-hq` still pass — the control that keeps the two
lists from being merged.
