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.
The grants part composes the bus's user list with the composer the controller uses (ADR 0547 §5), copied rather than
moved: the controller is not changed and keeps its own until it loses the lease. Left out: the bus client, the broker's
address from the environment and the client's two methods; the lease's two subjects are copied in.
One table test holds the copy to four meshes' lists and the server golden, written by the controller's own
internal/broker from the same fixtures (testdata/controller-user-lists.json).
jschoubben