Conflict: sendfile.go (!linux build tag) was incorrectly modified to
include linuxSendfile and getSocketFd functions which already exist
in sendfile_linux.go.
Resolution: Keep HEAD version (simple fallback returning ENOTSUP) as
Linux implementation is properly separated in sendfile_linux.go.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
