Have you ever shipped a pytest suite that looked literate on your laptop and then went illiterate on the server? I spent two days chasing a collector crash that never reproduced on my Mac. I had pinned the same CPython minor and the same requirements lock, which made the gap feel insulting. The tests were not flaky in the usual sense, and the assertion logic itself was boringly deterministic. The process died while printing a failure I had decorated with a checkmark. POSIX C locale still owns a ...