Discussion summary:
- clean is supposed to remove the products of build
- build_ext is a subcommand of build
- build_ext with the inplace option writes files that are not removed by clean
- removing .pyc files is out of scope (they’re products of normal Python behavior, not related to distutils)
→ I’m reclassifying this as a distutils2 feature request concerning the products of build_ext --inplace.

I’m not sure whether we should remove those products when the --all option is given to clean, or add a new option that we could enable by default.