Every tech company needs a good origin story. The startup garage, the dorm room and the hacker house are firmly embedded in American tech mythology. For hacker-entrepreneurs in Mexico, the border with the U.S. looms large. A subset of them hope to one day cross it and pitch their big idea to venture capitalists in Silicon Valley. One way there is to work the hackathon circuit in Mexico. That’s the subject of MIT anthropologist Héctor Beltrán’s new book “Code Work.” Beltrán details how coders gain currency in the field by participating in hackathons. Mexican politicians get something out of them too. The events are frequently sponsored by the government, with big promises of funding and support. But the prize, all too often, is a handshake and photo-op with a public official, and maybe a thank-you letter, but no real investment.