Loading kernel seems to fail at main-n279667-7ce07c41423d

Yesterday's update to

FreeBSD freebeast.catwhisker.org 15.0-PRERELEASE FreeBSD 15.0-PRERELEASE #305 main-n279644-20f0996700a8: Sat Aug 16 10:59:06 UTC 2025     root@freebeast.catwhisker.org:/common/S4/obj/usr/src/amd64.amd64/sys/GENERIC amd64 1500060 1500061

was uneventful.

After updating sources to main-n279667-7ce07c41423d this morning,
"buildworld" &c. was also uneventful, but the following reboot did not
actually complete:  it brought up the loader menu as normal, but seems
(because it's a bit hard to tell what's going on when the screen is
blank) to fail to load and transfer control from the loader to the
kernel.  Eventually, it appears to time out & (attempt a) reboot again;
absent human intervention, I expect the cycle would repeat indefinitely.

So far, I have seen this on a (headless) build machine and one
laptop (the other laptop is just finishing the installworld bit as
I type); each machine is amd64 using BIOS booting (not UEFI).  I tend to
keep the machines pretty much in lock-step, as far as daily updates
(FreeBSD sources & ports), though the headless build machine has a lot
fewer ports (and a lot more CPU & memory).  Oh: they each boot from &
use UFS, not ZFS.

Given a clue, I'm happy to experiment & report results.

Peace,
david
-- 
David H. Wolfskill                              david@catwhisker.org
Of course firing the statistician will force the statistics to conform!

See https://www.catwhisker.org/~david/publickey.gpg for my public key.