Question: does anyone know if there’s a gesture to invoke a new draft in @draftsapp? Triple tap or swipe in some way? I’m lazy and don’t want reach up to hit the “+” button.

No. You can put a new draft action in your action bar over the keyboard if it’s something you need often. actions.getdrafts.com/a/1Rc
That was my assumption. But great tip on the keyboard action. 🙌