Note: this is me reply to myself (which I concede is a little lame and maybe I shouldn't've.)
I forgot my favorite question of this type, which, BTW, a couple of doctors I consulted did not seem to be able to answer: how many micrograms in .05 milligrams?
In other words, my hypothesis is that the way to identify the "programming gear" is to test knowledge of some really simple "formal system" such as arithmetic or metric-system prefixes that one would expect adults with a practical command of the simple formal system to be well-rehearsed in.
People on this board have talked about programming as a gear in your brain that, to a first approximation, you have or you don't. I'm wondering if there's some well put-together resource you can direct someone with zero experience and just a web-browser to and say "if you're having fun an hour from now, you have the gear, good luck" -- maybe something on Khan academy?
(I learned to program a long time ago, and I started with BASIC program listings in my math textbook -- I don't actually know what the optimal onramps are now.)