Leyline of Singularity changes the properties of permanents, whereas Sisay tutors for permanent cards. Permanent cards only become permanents when they're on the battlefield, so the Leyline doesn't have any effect on cards that aren't on the battlefield regardless whether or not they would become permanents when they're on the battlefield.
July 14, 2019 11:54 a.m.
The short way to remember is this:
It's a permanent on the battlefield.
It's a spell on the stack.
Everywhere else it's a card.