The responder has had an agent arm since the principal was minted, but
no deployment ever passed `--agent-publish-subject`, and an empty list
is a refusal by design: `Policy::permissions` returns `None` rather than
a grant that can do nothing, so every agent was turned away at CONNECT.
The subject itself is the one this thread settled on, `$SWARM.term`
namespaced per hive.
The value has to reach the responder with a literal dollar. systemd
substitutes `$NAME` in `ExecStart` whether or not the word is quoted,
so a single dollar expands `SWARM` — unset, therefore empty — and the
responder is handed `.term.{hive}.>`. That grant validates (it carries
the `{hive}` placeholder), is accepted, and matches nothing any agent
publishes to, so the failure surfaces as an authorization violation far
from its cause. `$$` in the unit text is the escape for one dollar.
The module-eval case reads the rendered unit rather than the module
source, because the single-dollar version renders perfectly well; the
doubled dollar is the only thing that distinguishes them before deploy.
The grant is per-hive, not per-agent: an agent's identity names its
hive, so any agent in a hive can publish as another. That is the
tradeoff ruled acceptable for now, tracked separately for tightening.
Refs #3805
767a863cf1