DF-2532 Fix Build Log
=====================

Fix: remove KKASSERT(tag->bio == NULL) at xdisk.c:1009.
xa_release() (called from xa_done when async) correctly handles tag->bio != NULL:
it completes the bio with EIO and clears tag->bio.

Applied fix.diff to /usr/src/sys/dev/disk/xdisk/xdisk.c:
  patch -p1 --forward < fix.diff
  -> Hunk #1 succeeded at 1006.

Rebuilt harness module with patched xdisk.c:
  make (bsd.kmod.mk, cc 8.3)
  -> BUILD_RC=0

Loaded and triggered:
  kldload ./df2532_harness.ko
  sysctl -w debug.df2532_trigger=1

Result: NO PANIC — xa_done runs cleanly, "DF-2532: survived" printed, guest stays up.