Harden scaffold validation and rerun sentinels #2

Job	Run time
smoke-runtime (sg-only, configs/registry_smoke_matrix.json)	14m 56s
contract-audit	1m 37s
smoke-runtime (baseline, configs/registry_smoke_matrix.json)	14m 12s
smoke-runtime (artifact-only, configs/registry_smoke_artifact_matrix.json)	12m 15s
	43m 0s

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