`swarm-bao.nix` declared the store's half of the mTLS pair as options —
`serverCertFile`, `serverKeyFile`, `clientCaFile` — and left the reader's
half as a literal inside `glue-bao-tls.nix`, which only runs where
`deploy.bao.enable` is set. A hive that did not host the store therefore
could not read from it and could not be pointed at a certificate even
when one had been placed by hand.
Adds `clientCertFile`, `clientKeyFile` and `serverCaFile` beside their
three server siblings, `mkDefault`ed by the glue to the leaf it already
mints, and moves `glue-matrix-bao-token.nix` onto them. Its gate becomes
"this host holds an identity" rather than "the store is a neighbour",
and the unit ordering that names store-local units is now conditional --
`Requires=` on an absent unit fails the job.
`serverCaFile` is separate from `clientCaFile` on purpose: one is the
store choosing which readers to trust, the other a reader choosing which
store to trust. Self-signing collapses them to one file, which is a
property of that deployment and not of the pairing.
Closes#3855.
694abf4439