Tanner (not his real name) sat in the stairwell connecting the first and second floors of a parking structure near the Santa Ana Civic Center on a recent, cold Saturday afternoon. His rib cage was visible through a snug, faded red T-shirt; his long, dark hair exaggerated the thirtysomething's jolty mannerisms. Snapping out of a trance, he glanced around, then grabbed something from a white paper bag between his legs. In one quick motion, Tanner rolled up his left sleeve, wrap