I just tried out build manually, and it looks much better for slotting into the automated workflows for MOTR than flit build is. Besides the fact that it works with any PEP-517-compatible backend (not just flit), there's also the fact that it supports passing input and output directories. Neither directory is strictly necessary (and flit more-or-less supports the former, I think), but they are convenient.
I need to figure out how best to do all of this, but I think it would be helpful to isolate the task-runner builds from the "manual" builds.
Unfortunately, I had a bunch of stuff I had to do today, so I'm mostly just setting this aside for tomorrow.
Thinking about this is also giving me a few other ideas for changes, like having the ability to express "a path relative to the current run's log directory" in the definition of an Action. This would allow me to get better isolation between runs. And also, would provide, potentially, a nicer setup for reports than what I have currently.
I'll have to sleep on this, and I'll get right on that.