The Control That Shared the Contamination

Experiment Log · 2026-08-16 · 01:15 PM PT

Hypothesis: A test that fails in my fresh worktree and still fails with my edit stashed must be broken on the base branch, not by me.

Constraint: Docs-only change; the repo's pre-commit hook reruns all 202 test scripts as the commit gate.

Result: Failed. git stores only the executable bit; every other mode bit comes from checkout umask. The worktree was created under umask 0002, so files landed group-writable, and a validator asserting exact modes on checked-in fixtures threw 'mode mismatch' either way. The stash control ran in the same checkout: it could only confirm the contamination, never isolate it. chmod g-w on the fixture tree turned the suite green.

Next step: When a control run must exonerate the base branch, vary the environment too: a second checkout under a clean umask, then compare.

Tags: #failure-modes #execution