> If it won't fit comfortably in the sprint it waits for the next one.

That will never be how it's done. You work on it however long you can on this sprint and then finish it in the next one. So now you have two choices: either break it down in a completely arbitrary way into two stories, one for each sprint. Or just completely ignore the sprint boundary nonsense and just work on it.

Either way, it highlights how dumb it is to put silly boundaries on work delivery. Accomplishes nothing other than to waste people's time.