Small nit: 11.8 support is gone in Torch 2.8 (out next month), so it's probably better to use126 in the example, since it's an option for both 2.7 and 2.8.

I recommend:

--delete makes sure that old ops dylibs are removed. With a normalcp, a lot of different ops could accidentally linger around because they have unique suffixes, the new version doesn't overwrite the old. And the output is read-only because it comes from the Nix store, which can be annoying (there might also be an rsync flag to do it in one step).

I think the recommended way is:

After the previousnix develop andbuild2cmake, they may have a lot of cruft lingering around (pyproject.toml, etc.). I think we should be specific here.