The agent-client verifiers keep their lab directory as the run's artifact record (receipt, transcripts, profiles, Evidence) and name it as artifacts in the receipt, so it is not a fixture root that release should remove. VerifierFixture.keepArtifacts allocates such a directory canonically, never removes it, and names it on stderr at allocation so a run that fails before its receipt still reports where its artifacts are. The 11 client verifiers use it, and the verifier-fixture-root baseline shrinks by 11 sites.