I made a 90-degree prism out of glass with index of refraction of 1.5, which is high enough to produce total internal reflection at 45 degrees. I've done this before with no problem, but suddenly the light seems to just disappear. As far as I can tell the normals are all pointing outward.
So I put a mirror (glossy BDSF) next to it, and it's not reflecting either.
I expect to see two roughy square spots on the green object, but there is no trace of reflection.
I'm sure this is something obvious. I don't use Blender often enough to instinctively set everything correctly, but it seems like the defaults should be set up to allow this simple test to work.
What have I done wrong?
I'm attaching the blend file as well.
Left: Prism material, Right: Mirror material.