> I'll definitely be doing more to make the C API as compatible with OpenBSD as possible.

One suggestion I might add, it would be worth trying to compile any of OpenBSD's privilege separated network daemons on Linux (w/ Cosmopolitan Libc, or others). While you may have intended to use this facility primarily for your own APE Binaries, I suspect you'll find that the despite your intentions to make this compatible with the C API definition of pledge(2), in practice, your implementation is incompatible with privsep/privdrop software, for which pledge was designed. It was never intended for application "sandboxing".