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
  (sys/kern/vfs_subr.c + sys/vfs/fifofs/fifo_vnops.c per fix.diff,
   built with: cd /usr/src && make -j6 nativekernel && make installkernel)

$ /tmp/leak_scm            (root, patched kernel #1)
baseline: 4 stream sockets
fifo-open (+2 expected): 6 stream sockets
fifo fd hidden in unix socket buffer; nobody owns it
umount -f /mnt/df3161b (takes ~13s while retries exhaust)...
umount rc=0
after umount -f + close (leak: stays +2): 4 stream sockets   <-- FIXED (was 6 pre-patch)
done

console during run:
  unmount(/mnt/df3161b): (0xfffff80116de7800): 1 namecache refs, 1 mount refs still present
  unmount(/mnt/df3161b): forcing unmount

regression (normal fifo semantics on patched kernel):
  read-ok:hello          (blocking reader/writer rendezvous)
  regwr / rdwr-ok        (O_RDWR read+write through fd 9)

build logs: BUILD-RC=0 (nativekernel), INSTALL-RC=0 (installkernel)