DF-2584 fix A/B — PATCHED kernel (fix.diff: limit 16 + deferral list)
Guest: DragonFly 6.5-DEVELOPMENT #1: Wed Oct 14 11:01:17 UTC 2026 (nativekernel
rebuild of X86_64_GENERIC with fix.diff applied in /usr/src)
Image: h2c60.img — the SAME image that double-faults the stock kernel.

$ sh /root/run2584.sh /root/h2c60.img
MOUNT-OK
-rw-rw-rw-  1 root  wheel  32768 Oct 14 09:14 /mnt/h2/f
stat: inum=1024 size=32768
--- overwriting /f (32KB, same block size) ---
32768 bytes transferred in 0.000531 secs
--- sync (expect panic: hammer2: flush depth limit) ---
SYNC-SURVIVED (no panic)
UMOUNT-OK

vs baseline stock kernel on the same image+commands: Fatal double fault
during sync (panic.txt).  Bad behavior eliminated; guest stayed healthy.
(Persistence caveat for this crafted chain: run.persist60.log, VERDICT.md #4.)

Intermediate fix iteration (for the record): variant with
hammer2_chain_setflush(parent) at deferral time livelocked the flush
(pagedaemon "Continuous paging for 1 minutes" x many, sync never returned);
final fix.diff drops that call.