I'm wondering if my issue all along was parallel script executions (I reproduced the error message locally with `pre-commit run -a`, and I think in my case that's what happened).
Adding the file size to errors for sanity checking, since part of what had me looking again was checksum mismatches, and actually the parallel execution offers a consistent story there (checksum mismatch due to file being modified by another download mid-stream).
Moves common script logic into utils.py (not a great name, but couldn't come up with better). This is in particular to make the buildifier.py script really trivial, allowing that pre-commit to be easily added. However, scripts have also been diverging on how we find bazel, so I'm trying to unify that.
The advantage of reimplementing buildifier's pre-commit is that (a) we can now run buildifier server-side, and (b) we can stop advising installing it manually. Then the only Linux-specific package manager is Cargo, which is only used for watchman, which is optional -- so stop highlighting Linux-specific package managers in the tool instructions.
Jon Meow