Fix validation run — patched kernel
  DragonFly dfbsd 6.5-DEVELOPMENT #1: Mon Sep  7 10:27:31 UTC 2026
  root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC  x86_64

$ /tmp/fn                  (unprivileged, patched kernel #1)
FIONREAD on O_RDWR fd = 5 (expected 5)                  <-- FIXED (was 0)
FIONREAD on O_RDONLY fd = 5 (control, expected 5)
VERDICT: not_reproduced
fn-rc=1
(rc=1 = "bug marker absent" = correct post-fix behavior)