Witchwarpers: Spontaneous or Prepared spellcasters?

[Pluralgrey]

Cannot find any text in Player Core suggesting which kind of spellcaster the Witchwarper is.
Mystic is only clarified in Chapter 7 "Spells" and not in the class description.

[Perses13]

They're spontaneous casters. You can tell because they have signature spells and their spellcasting text doesn't refer to preparing from their list.

While Paizo uses the term spontaneous casters in the general rules, I don't think I've ever actually seen a class in PF2 or SF2 actually say it is one in their class description.