The grants part writes its list as an object of its own bucket, sealed to the bus node's key, and names it in
user-list.sealed; the node-engine of the node holding mesh-broker is granted that one key and an object by name, the
grants part its bucket (the controller's copy carries the same grants, byte for byte, golden regenerated there).
A state may name its readers (announce, NamedReaders): mesh-vault.bus-accounts is read by mesh-grants alone.
