[immibis]

Probably because Linux doesn't really have a good model for ad-hoc permission restrictions. It has enough bits to make a Docker container out of, but that's a full new system. You can't really restrict a subprocess to only write files under this directory.

[newsoftheday]

For plain Linux, chmod, chmod's sticky bit and setfacl provide extensive ad hoc permissions restricting. Your comment is 4 hours old, I'm surprised I'm the first person to help correct its inaccuracy.

[immibis]

How can those be used to restrict a certain subprocess to only write in a certain directory?

[godelski]

chown

[immibis]

how?

[godelski]

chgrp claude someDirectory

[immibis]

This doesn't meet the requirement. It doesn't restrict a certain subprocess to only write in a certain directory. You are just saying these things to quickly shut down the uncomfortable thought that Linux can't do something.