Amazon is beginning to add Massachusetts-made robots. In October, the company divulged for the first time that it has deployed more than 1,300 robotic warehouse workers from Kiva Systems in North Reading, a company Amazon bought last year for $775 million. But as Kiva ramps up production of its robotic systems for its new parent — the number on order from Amazon may be as high as 18,000, according to one trade publication, — the big question is what happens to Kiva’s early customers. Major retailers such as Staples, Walgreens, The Gap, Office Depot, and Crate & Barrel installed Kiva’s technology in their warehouses. And now, they must grapple not only with possible shortages of Kiva bots, but also whether to do business with a direct competitor.