Thanks, Werner.

The 'noimage' approach is one means of RECOVERY that I've used.
What I was searching for here is a means of PREVENTION.

What with the cost of USBs coming down, there's not much
justification anymore for 2 Gb installs like I've championed up to now.

My favorite current configuration is a 16 Gb USB with 2 GB partition
and the remainder formatted ext3 with kn-recombine on it.
I can just as well shift downloads to that partition and not run
into the 'disasters' anymore.

Cheers.