Why: after the lease write the assignments are frozen, so the part's union kept a module the catalogue takes off a node
with its account, grant, membership and user-list entry. The lease is read as the assigner reads it
(buscompose.LeaseHandedAway); before it, or with no placement on the bus, the union stands. The read stays declared until
the first change after the lease write, named in modules/assignments-readers with the assigner; a TestGrants row refuses
any other module.json that reads mesh-controller.assignments, as mesh-catalog's checks/placement does for the catalogue.
