- A placeholder is `${secret:<name>}`, the name the module calls the credential (catalogue.SecretLocal): the local
name where it keeps several values of one provision, else the provision. The `<provision>.<local>` form goes.
- The engine finds the one key under `<node>.<module>.` of mesh-provisioner's `provisions` going by that name. That is
what node.<node> may read, by a watch to its caught-up mark; plans are not read.
- The reference's ID must be a credential name of that provision (provisions.VaultName). The vault's answer must carry
exactly that name and generation. Anything else refuses the write, naming both.
Pins mesh-sdk 66ff33d. Tests: rows in TestAWriteAndAnApplyOfTheSameFileSerialise (a local name, a name no provision
goes by, a reference to no credential of the provision, a mismatched answer).
jschoubben
cbe8528f91