Besides the procedures to "create" and close file descriptors, they
are only needed to make a port. Why not combine open-file and
fd->*port in one? All other procedures either take pathname or a port.

That removes file descriptors completely from the srfi. Future srfis
may need fds again (especially process management) but we could wait
until then to introduce necessary procedures to either extract/dup fd
from a port, or open an fd without going through ports. Adding back
later is easier than removing or changing existing behavior.

That removes port-internal-fd, which looks like a hack to me. And also
remove (for now) the risk of accidentally closing an fd that belongs
to some port.
--
Duy