Ben Platt, Molly Gordon and Amy Sedaris have signed up to lead the cast of “Theater Camp,” a feature adaptation of Nick Lieberman’s 2020 short film of the same name.“Booksmart” and “Shiva Baby” star Gordon will make her directorial debut alongside Lieberman, who has helmed a number of video shorts and music videos for Platt, the award-winning star of “Dear Evan Hansen.” Gordon, Lieberman, Platt and co-star Noah Galvin (“Booksmart”), who wrote the short film together, will write the screenplay. The foursome will partner with composer Mark Sonnenblick (“Lyle, Lyle, Crocodile”) on original music.Set in upstate New York, the film revolves around the eccentric staff of a rundown theater camp that threatens to fall apart when its beloved founder falls into a coma right before the start of the summer session.