act_runner records the --instance URL it was registered with and reads the
forge address from .runner and nowhere else: the nix option reaches only
`register`, and upstream re-registers on a changed token or labels, never on
a changed URL. Our own precond short-circuits on .runner existing, and
runner_valid asks whether the runner id still exists -- which after a rename
it does. So changing swarm.forge.domain left the runner dialling a name its
container's derived extraHosts no longer resolves, with every check green.
The symptom is CI going quiet rather than anything failing.
Compare the persisted address against the configured base as part of the
same early return. A disagreement mints a fresh registration token, which
changes the token hash upstream already keys on, so upstream removes .runner
and re-registers against the current --instance. This module never writes or
deletes that file; the deletion stays with the script that owns registration.
The comparison is host-only and lenient on purpose. Both sides render from
one nix expression -- http://${swarm.forge.domain}, reaching the runner as
instances.hive.url and this daemon as HIVE_FORGE_URL -- so they cannot drift,
while scheme, port and trailing slash are exactly the cosmetic differences
that would otherwise re-register on every boot. Unreadable, missing or
unparseable input keeps the existing credentials, matching runner_valid's
treatment of a transport error: only a positive disagreement counts.
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