Idea: Add an option to set the mode to fs::copy

comex:

But just to be clear, copyfile and fcopyfile are userland library functions, not syscalls, so they don't add any new abilities.

macOS doesn't expose syscalls as part of its stable interface. You may be right about their implementation today not providing the same behavior, but it's not generally true on macOS that a "userland library function" doesn't turn around to perform a syscall.