A per-agent queue credential is minted at agent creation and nothing has
ever removed it. An agent declared destroyed loses its container and
keeps its credential: a bearer secret recovered from a snapshot or a
stale capture still authenticates as that agent, so the set of usable
credentials only grows.
Delete the path the mint published, on the one transition that ends an
agent's life. It mirrors step 3 of `mint_and_verify` and no other step:
the leaf, the ACL document and the cert role are what a hive uses to
collect an agent's secrets and are re-minted on every run of the mint.
Every version, not the newest. The mint rewrites the path when the
principal it names needs correcting, so KV v2's plain delete would leave
the identical secret readable at ?version=N. That is a separately-ACL'd
path, hence the second stanza in the controller's grant -- `delete` on
metadata discloses nothing, and `update` on the data path already lets
this principal destroy any agent credential's usability.
The destroy is not blocked by a failed revocation: the declaration is
already published and refusing the call would leave an operator with an
agent they cannot tear down. The failure is logged at error instead,
naming the agent, since a silent orphan is the fault being removed.
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