The differential harness proof deliberately creates a run directory under the repository tmp/ scratch root, because proving the oracle ignores concurrent __pycache__ churn requires an in-repo location. Under xdist that directory appears and disappears inside an unrelated consumer window, so the verdict CLI no-write proof failed on a sibling worker action rather than on anything the CLI did. tmp/ is gitignored scratch, not repository content, and joins the existing runtime-directory exclusions for the same reason each of those was added. The in-repo write invariant remains asserted directly by the harness in-repo destination refusal test.