Christopher W. Richardson wrote:
> Which appears to indicate that no one became root anywhere near
> the time of the reboot (and a more thorough search of the log
> confirms that no one had done so within days, other than me).
> 
> What's the proper way to go about diagnosing this (oh, and please
> cc me, as I'm not on this list)?

I think you want to start by saving a core dump.  See swapctl(8),
panic(9), and savecore(8).  

If I had a machine routinely failing like that in under 24 hours, I'd
suspect the hardware....

HTH.

--jkl