Eric wrote:
> I don't know of any OS that supports NULs in filenames

HFS, HFS Plus, and Apple File System all support NULs in filenames.

HFS Plus volumes include a special special directory called the metadata directory, in the volume's root directory, called "\0\0\0\0HFS+ Private Data".

https://developer.apple.com/library/archive/technotes/tn/tn1150.html#HFSPlusNames

There are, I believe, Carbon APIs for checking for file names which do not rely on NUL-terminated strings (they use an array of Unicode characters with an explicit length), but I don't know enough about OS X APIs to know if they are current generation.