after trivial update, 15.0 ARM64 system no longer boots

hi lists,

i have a FreeBSD 15.0/arm64 system, an RPi4, which was previously
running 15.0 with pkgbase.  i rebuilt main on my pkg server and updated
the RPi with 'pkg update', which only included ~2 commits neither of
which seemed like they had anything to do with booting, but after the
update, the system no longer boots.

the problem seems to be a hang during kernel initialisation:

https://www.le-fay.org/tmp/30d/9fE0NG.jpeg

i am not really an expert on either ARM64 in general or on the RPi
hardware in particular.  could anyone suggest how i could debug this
problem, e.g. to get more information about why the system won't finish
booting?

	thanks, lexi.