Earlier, when I posted resolv.conf, I spotted what might be a problem:
Network Manager was active, even though I'd turned it off long ago.
Using the GUI tool, I turned it off again. This morning's updates
included some kmod-nvidia stuff and later I found that one of my games
(Plants vs Zombies, under Wine) wasn't loading, so I tried logging out
and back in. Alas, X wouldn't start, forcing a reboot. (Only a little
under 4 days of uptime, so no great loss.) Everything came up properly,
I have DNS without playing games and Network Manager didn't activate.
Now, the only question remaining is, what turned it back on in the first
place, and that's not exactly urgent.