I was in meetings for over three hours today. My constitution can't handle that.
Anyway, I started trying to really figure out how to work with Poetry's existing test libraries. I basically discovered that my first attempt at implementing "dev-mode" was probably pretty wrong. The interfaces and documentation, I haven't seen any reason to doubt them yet, but the changes I made to the core are likely to interact poorly with *checks notes* nearly everything.
With that in mind, I'm going to have to try again, because there's just no way this first attempt is right. No time for that now, because I'm tired.