swarm: wire the agents' queue coordinates and credential through the modules

The host end: `HIVE_C0RE_AGENT_QUEUE_CREDENTIAL_DIR` tells the daemon
where the reader unit put the files, and a new
`deploy.hive-controller.queue.agentNatsUrl` says where the queue is as an
agent *container* reaches it. That address defaults to the bridge one and
never to loopback — `statusPublish.natsUrl` beside it is loopback and
correct, because hive-c0re shares the host netns and an agent does not.
Paired with the swarm's token endpoint, gated together, and forwarded by
`hive_c0re::meta` as both an env var and an agent option: the harness
reads the variable at runtime, its unit is built from the option.

The agent end: `nix/agent-modules/queue.nix` declares that option pair
and, when set, has the harness unit inherit the two credentials by name.
Bare-id `LoadCredential=` is the terse form documented for inheriting
what the service manager received, and is non-fatal when the credential
is absent — which a hive whose publisher has not run yet needs.

No `HIVE_AGENT_OIDC_CA_FILE`: the meta flake already embeds the hive CA
and the swarm root into each container's trust store at build time, and
reqwest's rustls backend verifies against it.

Refs #3805
This commit is contained in:
atlas 2026-09-12 22:41:46 +02:00 committed by atlas
commit 86652f051a
7 changed files with 290 additions and 0 deletions

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@ -168,6 +168,21 @@ reader runs before `hive-c0re.service` and is wanted (not required) by it, so
an agent container never renders ahead of the credential; an unreachable store
delays the daemon's start rather than failing it.
That credential still has one hop left, because the reader of it lives inside
an agent container. **It crosses as a systemd credential, not as a bind
mount**, and the mode decides that: the secret is `root:0600` and a harness
runs as its own unprivileged agent user, so a bind would deliver a file that
user can't open. `hive-c0re` stats the two files — the directory is `0755`, so
it needs no read access to either — and hands them to
`systemd-nspawn --load-credential` through `hive-priv`, which runs as root.
Inside, `hive-agent.service` names the same two ids in `LoadCredential=` and
reads them out of its own `$CREDENTIALS_DIRECTORY`, owned by the agent user
and by nobody else. `hive-c0re` never reads the bytes at any point: it runs as
`hive-core`, which is the reason a copy wasn't an option either. When the
files aren't there the daemon forwards nothing and says so in its journal, and
the harness logs that it has no queue — the same absent-and-legal state, twice,
rather than a container that refuses to start.
⚠️ **Service↔store mTLS is its own trust domain.** A credential you must
already hold to authenticate can't be fetched from the thing it authenticates
you to, so the store's identity can't come from an authority the store