In a set that echoed but didn’t quite mirror her well-regarded showing at Lollapalooza last month, she opened with “Rock Music,” the lead track from her two-week-old album, “Music Fashion Film.” Charli is leaning hard into her rock era, with conspicuous attention paid to her guitarist on the stage’s twin screens. Charli XCX is leaning hard into her rock era. Early in the day, this reporter met Morgan Le, an Outside Lands attendee from Oregon who might have been the Brat Final Boss. “It just kind of happened, and ‘Brat’ came out.