Hi. I've been debating how to respond to the shall vs must thing. The short answer is that there are reasons why you might prefer shall, but I find that I'd rather say "must is good enough," than try and come up with an articulate presentation of the energy which would conclude by saying that if must still seemed like the right choice go with it.
So, I'm fine with s/shall/must. Sent mostly to give Charles some support so things don't stall.