Rashid Assad, owner of Roy’s Taco Hut, on San Antonio’s West Side, likes to talk about the variety of flour tortillas. A former tortilleria owner and Monterrey, Mexico, native, he waxes poetic about their brown spots, as unique as a tiger’s stripes; their distinctive, flaky layers; and the merits of different sizes and thicknesses. Roy’s excels at its flour tortillas—a smidge thinner than the typical mattress-thick San Antonio–style ones—which are the perfect vehicles for the taqueria’s traditional and offbeat tacos. Despite the fact that Roy’s is on its third owner (Roy Avila, who opened the shop in 1978, retired in 2010), the menu and decor haven’t changed much over the last forty-some years. Classic rock and folk tunes by the Beatles, Bob Dylan, and Jimi Hendrix…