A horn section does not care about borders. It never has. The notes drift across the line the same way the smell of street tacos drifts north and the freeway hum drifts south, because the line is a legal fact and not a musical one, and players on both sides have known that since long before anyone drew it. The festival stretches across both cities — free open-air concerts in downtown Tijuana and downtown San Diego, plus a ticketed headline night at the arts center in Escondido — which effectively turns the border region into one stage. Brian Blade headlines with his Fellowship Band, a group that moves between jazz, rock, folk and gospel without asking permission to cross anything. Mingus Dynasty plays the Charles Mingus book with Wayne Escoffery, Helen Sung and Boris Kozlov. The free shows are the heart of it: music in public, no velvet rope. Go stand on a sidewalk and hear something extraordinary for nothing.