A sibling unit rather than more script in swarm-bao-controller-policy, because
that unit's name is an operator-facing string: docs/getting-started/setup.md
tells a reader to run `systemctl status swarm-bao-controller-policy`. Widening
it to two principals makes the name wrong; renaming it makes the instruction
wrong.
`after` and not `requires`. The controller's unit creates the KV and cert-auth
mounts this one writes into, so the ordering is real — but a failed oneshot
still counts as finished, so `requires` would neither wait for its success nor
re-run this unit when the sibling's own retry eventually lands. Ordering plus
this unit's `Restart=on-failure` is what converges.
Four module-eval cases, because the unit arrived with every claim about it in
prose and the suite still reporting the same count: the grant is write-only and
reaches the hive prefix alone (pinned as the whole capability list, since an
added capability is what a presence check misses, with negative arms for the
agent prefix, the bare swarm prefix and the policy path); it is ordered after
the unit that creates the mounts; it renders on the host; and the control, that
it does not render inside the store's container.
Refs #3853
98f2a94d82