Bare mesh-builder@sha256:... is only resolvable for a module with a build
section — the mesh's own build step rewrites the reference to a real
registry path as part of resolving build.artifacts. builder is handed
over, not built, so nothing ever rewrites it: pushed as written, docker
read it literally and tried Docker Hub. Took the live node's mesh-builder
down for the length of one push-and-fix (docker: pull access denied for
mesh-builder, repository does not exist). novox.internal:5100, not the
literal external IP docker inspect showed live, for the same reason
addresses generally don't get hardcoded in this catalogue.