Charlie Sexton’s been a fixture of the Austin music scene for almost as long as Willie. Way back when—before Charlie’s high-profile stints as lead guitarist for Bob Dylan and Elvis Costello; before he produced Lucinda Williams’s exquisite 2001 album Essence; before he cofounded early nineties blues-rock supergroup the Arc Angels; and even before his mid-eighties moment as a new-wave heartthrob on MTV—he was known around town as Little Charlie, the self-taught guitar prodigy who’d first performed publicly in 1978, when he was invited onstage at the Continental Club at the tender age of nine.(Read a transcript of this episode below.)On this week’s One by Willie, Charlie goes deep into the weeds on one of Willie’s early-sixties Pamper demos, “I Let My Mind Wander,” a cut that…