Behind the Magic of "Harry Potter" Onstage

“Harry Potter and the Cursed Child,” the two-part play that won a record-breaking number of awards in England, opened this month in San Francisco. The Curran theater is taken over by shifting staircases, invisibility cloaks and items that float with the flick of a wand. Forum talks with Andrew Evans, the magic and illusions lead from the Curran Theater production, about creating onstage magic for an audience accustomed to special effects on the big screen. We’ll also check in with the actors playing Harry Potter and his son, Albus.