Fixing a gate that sags because the post is solid but the frame is racked

The gate latch no longer lines up. The hinge post feels solid and doesn't visibly move, but measuring the gate diagonals shows the wooden frame has shifted out of square. Tightening hinge screws only lifts one corner temporarily. I'm considering a diagonal brace or an adjustable anti-sag cable, though I don't want to pull it out of shape in the opposite direction. Which reinforcement works best once the frame has already racked?