OK, I did a factory reset for the third time. Floor is now working OK,
but still just blackness from pass-through cameras. I glad you had more
luck than me, and I hope the folks at Oculus will come up with a fix
that works for everyone sometime soon....
Oh well - as K-Brownie-FDT said above, the cameras are still working,
it's just they're not show images when you breach the guardian, and
while it's annoying, I can still play games and use the controllers. I
guess I'll wait and keep my fingers cross...