Transmission TIR for rough glass

In the OSL implementation, I am sure that I correctly understand how total internal reflection is handled. One possibility is that the fresnel term for specular takes care of that since it goes to 1 in the case of TIR, thus not issuing a transmission btdf at all. If that is the case, I have two questions

1. how do you handle rough glass, that should have a btdf that depends on 1 - fresnel(w_h)
2. how do you decide whether to "flip" eta depending on inside-out test