Pinning a decision rather than changing behaviour, because I was one
edit away from reversing it and left no reason on the field.
The sibling `matrix::Credential::homeserver` is an `Option`, which reads
like the house style to copy. It is not: that field is optional because
it was added to objects already in the store, and KV2 keeps those
versions forever. This path has never been written, so there is nothing
to stay compatible with.
Making it optional would also defeat the field. The id rides with the
secret so a reader never has to spell `hive-<name>-agent` itself, and
the only thing a reader holding `None` can do is exactly that. An object
without an id is not a usable credential, so failing to decode is the
behaviour we want.
Refs #3853
The agreement half of delivering the agent queue principal's client secret
through the store. No producer yet, so nothing writes this path — the unit
that does lands in the same PR, with the write grant it needs.
queue.rs is the sibling matrix.rs prescribes for a second kind of secret
rather than another field on a shared struct. Keyed per HIVE, not per agent:
the queue identity is minted once per hive at deploy time and says which hive
an agent belongs to, never which agent.
The client id rides with the secret for matrix.rs's stated reason — a
credential has to be reconstructable from the store alone, and deriving
`hive-<name>-agent` on the reading side is the split spelling the authelia
module warns denies every agent as a timeout.
policy.rs's render() takes the hive name now and emits a second, narrow
stanza for that hive's own path. The agent stanza is untouched: an agent's
path does not name its hive, so narrowing it still needs the enumeration
docs/trust-boundary/security.md rejects. A hive path does name its principal,
so scoping it costs nothing and drifts nowhere.
every_hive_gets_a_byte_identical_document is replaced rather than deleted.
Its surviving half is that the text is a function of the deploy-time name
alone, so a re-emission cannot drift; the new arms are that one hive's
document cannot reach another's path, and that a name which could close the
stanza is refused — live again now that a name reaches the document text.
Refs #3853
