When a 23-year-old Sam Altman took the stage at Apple Inc.’s annual developer conference in 2008, he gushed about being able to use the company’s new App Store to promote his software, a friend-locating service called Loopt. “We think this is a new era of mobile, and we’re thrilled to be part of it,” Altman said.Now, 16 years later, Apple is calling upon the entrepreneur again — but with a twist. This time, the company needs his help as much as he needs Apple....