My opponent cast a card draw spell with card selection at the end of my turn, tapping them out. I was given priority to cast my own spell. I waited to allow them to draw and priority automatically passed through to their next main phase. As a result I was unable to resolve my spell while they were tapped out and recorded a match loss when they countered my card draw at the end of their next turn.

You must give me priority when I have an instant or I might as well go and install hearthstone.