`credential.rs` calls `SecretStore::from_env`, and nothing set `BAO_*` for
this unit — only `swarm-bao-matrix-token` had them. Fixing that alone would
not have been enough: hive-c0re runs as hive-core, and glue-bao-tls mints the
client key `0600` inside a `0700` directory, so the daemon cannot read the
file even when it is named.
Both halves go through LoadCredential, which this unit already uses for the
swarm-status client secret: root reads the identity at unit start, hive-core
sees it under `%d`, and no second on-disk copy exists.
The gate is the identity, never `deploy.bao.enable` — a hive that reads a
store on another machine holds a certificate and runs no store. Four
module-eval cases: the co-located and off-host presence arms, the absence arm
for a hive with no identity, and a presence/absence pair for the optional CA.
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