Experimental implementation of PEP 638 on CPython 3.14.2, and what it showed about the spec

I built an experimental implementation of PEP 638 on top of CPython v3.14.2, plus a Pyodide build so it can be tried in a browser. I am posting it here because the PEP still says “Reference Implementation: None as yet”, and because implementing it turned up several places where the text needs a decision. Disclosure: the patch was written with heavy AI assistance (Claude). I am not proposing it for merging. It is a prototype meant to make the discussion concrete. Patch: GitHub - sadaszewski/py...