Retention so a reader can ask what a hive last said without anyone
keeping a second copy. The container is ephemeral = false, so the store
survives a restart with no bind mount, and losing it degrades to the
true answer (nothing known) rather than a stale one.
The per-account grant is the part that is easy to miss: the server
option gives the SERVER JetStream, and an account gets it only from its
own. Measured against a running 2.14.1 with this exact two-account
shape - global-only makes kv operations fail 10039 while the server
starts cleanly and logs Starting JetStream, so no rendering check can
see it. Deliberately not granted to the callout account: the responder
mints credentials and has no business holding stream state.