This got superseeded by the "super knife" in421823e34e14 years ago it seems, it cannot be executed atm. (and even if reactivated, it crashes in multiple places). Stumbled over this while checking on usages of #BM_custom_loop_normals_to_vector_layer / #BM_custom_loop_normals_from_vector_layer (to add this to more tools), and apparently this outdated piece of code got an update in93c8955a72:) -- work on adding this to our "real" Knife is upcoming in another PR... Pull Request: https://projects.blender.org/blender/blender/pulls/124970