The container runtime's module must state the mesh's registry to the runtime it owns, so the
controller can stop writing that into the runtime's file (hq issue 190). ${seat:<seat>:reach}
answers host:port without a binding: nothing required, granted or minted, and the address is
one the mesh already composes into every reference it built. Only mesh-artifact-store is
answered; another seat is refused by name. Unanswered in a file written into as JSON, the empty
member is dropped, so the runtime is never told to trust "".