halacha - What is the law with eating the third Shabbos meal when the first day of Pesach is Shabbos?

This year the first day of Pesach is Shabbos. There is an obligation to eat a third meal. It seem that there may be two issues: see here

Eating a third meal may take away the appetite for matzoh at the seder, and normally we do not allow matzoh to be eaten after noon before the (first) seder.

This problem is discussed widely when Erev Pesach falls on Shabbos (see eg this article from OU) but not so widely when the first day of Pesach is Shabbos.