DF-2650 + DF-2649 fix-validation kernel build (guest /usr/src, patched with
combined.diff = DF-2649/fix.diff + DF-2650/fix.diff).

[provenance] The full build log lived in the guest at /tmp/fix_build.log;
the guest was subsequently wedged at db> by the intentional DF-2649
fix-regression run (still-panicking DF-0875 manifestation), so the log
could not be pulled in full afterwards.  Verbatim excerpts captured live
during the build follow; the completion markers and the resulting kernel's
observed behavior (fix_run.log) are the ground truth.

$ cd /usr/src && patch -p1 --dry-run < /tmp/combined.diff   -> applies cleanly
$ patch -p1 < /tmp/combined.diff                           -> GUEST_PATCHED
$ make nativekernel                                        -> (below)
$ make installkernel                                       -> FIXBUILD_DONE

--- excerpt 1 (mkdep over hammer2, note -DINVARIANTS) ---
CCVER=gcc80 CC=cc mkdep -f .depend -a -nostdinc -DINVARIANTS -D_KERNEL -DKLD_MODULE -I. -Idragonfly -I/usr/obj/usr/src/sys/X86_64_GENERIC -I/usr/obj/usr/src/sys/X86_64_GENERIC/include -Idragonfly/../include -I/usr/include -DHAVE_KERNEL_OPTION_HEADERS -std=gnu11 /usr/src/sys/vfs/hammer2/hammer2_vfsops.c /usr/src/sys/vfs/hammer2/hammer2_ondisk.c /usr/src/sys/vfs/hammer2/hammer2_chain.c /usr/src/sys/vfs/hammer2/hammer2_flush.c /usr/src/sys/vfs/hammer2/hammer2_freemap.c /usr/src/sys/vfs/hammer2/hammer2_ioctl.c /usr/src/sys/vfs/hammer2/hammer2_bulkfree.c /usr/src/sys/vfs/hammer2/hammer2_io.c [...]

--- excerpt 2 (the patched file compiles clean under -Werror) ---
cc -c -O2 -pipe -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wcast-qual -Wold-style-definition -Wmissing-include-dirs -Wno-pointer-sign -Winit-self -Wundef -Wno-unused-but-set-variable -std=gnu11 -g -nostdinc [...] -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h -Wold-style-declaration -fno-common -ffreestanding -fno-stack-protector -fno-strict-aliasing -fno-strict-overflow -fno-asynchronous-unwind-tables -fno-omit-frame-pointer -mcmodel=kernel -mno-red-zone -mno-mmx -mno-sse -msoft-float -mno-fp-ret-in-387 -mindirect-branch=thunk-inline /usr/src/sys/vfs/hammer2/hammer2_bulkfree.c -Werror

--- excerpt 3 (completion) ---
--------------------------------------------------------------
>>> Kernel build for X86_64_GENERIC completed
--------------------------------------------------------------
FIXBUILD_DONE

reboot -> DragonFly 6.5-DEVELOPMENT #0: Sun Aug 30 00:18:56 UTC 2026
root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC  (fixed kernel booted)