Guest environment (race-attempt runs)

uname -a (stock kernel, all attempts):
  DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026  root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC  x86_64
kernel config: X86_64_GENERIC, INVARIANTS (KKASSERTs active)
QEMU/KVM: qemu-system-x86_64 -enable-kvm -m 4096 -smp 6, virtio disk+net
tools: as in ../DF-2658/env.txt
cluster rig: 512MB vn-backed images, newfs_hammer2 -L <label>, 3-master
  same-clid clone clusters; hammer verified via `ps axlw | grep h2nod-<label>`
  census (>=3 sync threads), separate top-level mountpoints for the EBUSY
  merge mounts (mount(8) returns 64 for both merges and usage errors)
sysctl: vfs.hammer2.debug=1 (f) / 0x8000 (g,h,i), debug.debugger_on_panic=0
backlog detection: /var/log/messages (kern.msgbuf saturates under debug=1
  floods and `dmesg` fails with "Cannot allocate memory")