Hm... well, maybe i have just somehow missed the section... but what happens if you get interupted while casting? Mage Cuffs (which are designed for that) are, i think, the most common cause for that... but also: If someone is faster than the mage and wishes to shoot him exactly when the mage tries to draw mana. What happens? (I know it is hard to do that when casting takes a bit less than a second)
My first instinct would be to have the mage roll a composure (Cha+Will) test with the sustained damage as threshold. But maybe that's just because i am crazy? Maybe Body+Will?
Oh and also the description of the mage cuffs state, that ANY magical activity activates them (Even surrounding activity not originating from the cuffed mage) BUT what is it with calling a spirit, or commanding it? How much connection through the astral plane do you need for that? I think summoning would be out, but i am unsure with calling and commanding. It clearly IS astral activity... but not very strong... maybe it just jumps straight through your aura into the meta planes?
Hm... anyone has some thought for me on that matter?