I'm treating my PR to mypy bazel integration as dead in the water. Abandoning that approach, this seems to work reasonably well as a replacement. It's actually a slightly newer version of mypy too -- the bazel integration was stuck on an old version.
Note I don't think we're losing much: we shouldn't be writing too much python.
I'm seeing if I can upstream thundergolfer/bazel-mypy-integration#43, but we can also point at my fork for the time being.
This should resolve conflicts with mypy treating imports as non-hermetic, creating inconsistent behavior if packages are/aren't installed locally.