The subject and its payload live in `swarm-queue-client` for the reason
the knowledge event's already does: three crates have to agree on the
string, and the one that agrees hardest — the auth-callout responder,
which decides whether the publish is permitted at all — speaks neither
`jetstream` nor `kv`.
Swarm-wide rather than a `$SWARM.deploy.<hive>` family. That family
would look like isolation and provide none: this responder scopes
publish only, leaving `sub` unrestricted, so a hive could subscribe to
another's subject as easily as to its own. Until `sub` is scoped the
split costs a wider grant and buys nothing, so the addressing goes in
the payload and each hive filters on its own name.
Unlike the knowledge event the message is addressed, so it carries a
payload — a trigger, never the config. The hive already tracks the
agent's config repo; desired state on the wire would make this a second
source of truth for something git owns, and a hive that missed a
message would be wrong rather than late.
Both test arms mirrored from the knowledge event. The negative one
matters more here: a forged knowledge event makes a hive re-read a
repo, a forged deploy event makes it rebuild and restart a named agent.