A full / made every check on shanks end 'store never became ready' with the reason erased by --rm.
Builds now remove their local image tag, narrowed source and context clone; a build or check
refuses under 20 GiB free on / and the workspace, saying so; the throwaway store is no longer
started with --rm and a store that does not come up reports its exit code and last 20 log lines.
