B0's run job, its input verb and judged-by move from mesh-sdk's go/delivery
into the Delivery domain's contracts, with B0's JSON names: the part
build-step carries StepAsk.run and the defs RunJob, RunProgram, RunHead,
RunInput and RunAnswer beside compose (the lead's ruling on Q1), and a
step's result the run's exit, output and said.
Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i