aha -- I think I found what triggered it since I did it again and it stalled
probably identically (didn't have remote console :-/):  I have ran

DISPLAY=:0 0install run -c http://gfxmonk.net/dist/0install/shellshape.xml
--replace

to try shellshape and whenever it finished downloading, it did smth which
triggered the bug, and screens went blank.  Probably it is a different,
although possibly related, issue since during original stalls I still have smth
on the screens.  In this case they just go down into suspend mode etc.  Do you
think I should file a separate report on this one?