DF-2504 fix validation run — PATCHED kernel
"DragonFly 6.5-DEVELOPMENT #1: Thu Oct 15 23:37:29 UTC 2026"
(fix.diff applied to /usr/src/sys/dev/disk/nata/atapi-cd.c;
 kernel rebuilt + installed + booted; exact same PoC binary as baseline)

$ /root/dfrig4/poc_setblocksize /dev/acd0 2352
== DF-2504 PoC ==
open(/dev/acd0, O_RDONLY) = fd 3
control: CDRIOCSETBLOCKSIZE(2352) ... ok
control: CDRIOCGETBLOCKSIZE -> 2352

$ /root/dfrig4/poc_setblocksize /dev/acd0
== DF-2504 PoC ==
open(/dev/acd0, O_RDONLY) = fd 3
firing CDRIOCSETBLOCKSIZE(0): atapi-cd.c:724 stores 0 into
    cdp->block_size, :951 rounddown(iomax=65534, 0) divides --
    FATAL TRAP expected
ioctl error: Invalid argument          <-- EINVAL, no divide, no trap
SURVIVED-PATCHED
(guest up throughout; vm.sh status => up)

Baseline (kernel #0, stock): same ioctl -> Fatal trap 18, integer
divide fault, Stopped at acd_set_ioparm+0x69: divl %ecx,%eax (panic.txt).
Result: baseline 1/1 panic; patched 0/1 -> fix validated.