We speculated earlier this week that James Taylor might join Taylor Swift on stage at one of her two sold-out shows this weekend at Gillette Stadium. (They performed “Fire and Rain” together at Tanglewood a few years ago.) Well, that isn’t happening — and we know why. JT is planning to make a surprise appearance at the Newport Folk Festival. His camp wouldn’t comment Thursday, but we’re told that Taylor, whose new CD, “Before This World,” hit No. 1 on the Billboard 200, will play a 30-minute set starting at 3:40 p.m. Saturday. (On the schedule, he’s listed as “David B. Thompson.”) Old-timers will recall that Taylor first played Newport in July 1969, debuting some of the songs from his album “Sweet Baby James.” But the show was cut short by the on-stage announcement that Neil Armstrong and Buzz Aldrin had landed on the moon. So Saturday’s show is a bit of unfinished business. Taylor (and Bonnie Raitt) play Fenway Park on Aug. 6.