Installing the module that provides `artifact-store` requires something
that provides `artifact-store`: its image is mirrored in, mirroring
publishes to the store, and the builder refuses to run without one.
Never seen, because the lab always has a registry standing before the
mesh asks for one, and so does any mesh built on a machine that already
had one.
What it blocks is larger than a registry. The store holds images and
packed archives both — it is the module catalogue in artefact form — so
until it exists a mesh can run only what its bundle already carries.
The substrate record already answers it. It asks of each candidate
whether it can grant itself the thing it provides: the store cannot
create its own database, the broker cannot create its own virtual host,
and the registry cannot grant itself a repository. So the registry
module names its image and is never built.
With a limit worth saying out loud rather than discovering: a module
providing the store may not build artifacts of its own, a UI or a tool
server included, because there is nowhere to put them until it runs.
Such a registry is two modules.
