"Question 1: I am invited to my S's school function. When it comes to posturing, do I attend and then excuse myself a bit early (since I did/do have plans afterward)?"
NO!!!! You go and enjoy the WHOLE thing...but be ready to bail out when it becomes difficult with an excuse...but milk it discreetly for all its worth....
"Question 2: I finally got my first chance to affirm something my wife said about her behavior and my behavior prior to bomb. Unfortunately, I said something more like "Yeah, I know I was doing X (not talking much)." It was more matter-of-fact than affirming her observation. Was that a blown opportunity to affirm and be constructive, or is my 'yeah I know' attitude close enough?"
It probably was a blown opportunity...but its gone, forget it!...just rehearse what you would say if the opportunity came up again...