Not sure if ``numerary`` will help, but I thought I'd put it on the radar

[posita]

I don't know if you saw, but I pulled out a lot of my number typing work-arounds into their own package called numerary. If this journey lines up with your own, numerary could be an intermediary solution until python/mypy#3186 is fixed. (Alternatively, the techniques used therein might provide inspiration if you can't take a dependency.) Happy to consult here, if helpful.