Update scripts work now, although I don't really like the results very much. Gonna do some more thinking about exactly how to make it work and possibly make more data available to the decision scripts.
One thing I'm noticing is that lua is disturbingly slow in Debug mode. Possibly stripping some of my debug output will help, and of course Release is a very different beast which I will have to check out shortly. OTOH if it remains slow I'm going to have to seriously reconsider this whole design.
I've also managed to get collision-to-terrain working but it's a resource hog and slides irritatingly. Since the thing doesn't really have many collision objects, I might just do conform-to-surface instead. Also - picking! (Haven't hooked it to anything yet though.)