alt Hacker NewsThis is what I was going for with Treebeard[0]. It is sandbox-exec, worktrees, and COW/overlay filesystem. The overlay filesystem is nice, in that you have access to git-ignored files in the original directory without having to worry about those files being modified in the original (due to the COW semantics). Though, truthfully, I haven’t found myself using it much since getting it all working.
This approach is too complex for what is provided. You're better off just making a copy of the tree and simply using sandbox-exec. macFUSE is a shitshow.
The main issue I want to solve is unexpected writes to arbitrary paths should be allowed but ultimately discarded. macOS simply doesn't offer a way to namespace the filesystem in that way.