Have you ever shipped broken sdists with missing files or possibly dirty sdists
with files that shouldn't have been there? Have you noticed that standards
compliant tools aren't making the same sdist that flit build is? Is hatchling
adding .DSStore files when you ship from your macOS? No matter what
build-backend you use, check-sdist can help!

Check-sdist builds an sdist and compares the contents with your Git repository
contents. It can even temporarily inject common junk files (like pycache files
or OS specific files) and help verify that those aren't getting bundled into
your sdist. If you are getting files you didn't expect or missing files you did
expect, consult your build backend's docs to see how to include or exclude
files.