CHENGDU, China — One day last summer, Pu Xiaolan was halfway through a shift inspecting iPad cases when she received a beige wooden chair with white stripes and a high, sturdy back. At first, Ms. Pu wondered if someone had made a mistake. But when her bosses walked by, they just nodded curtly. So Ms. Pu gently sat down and leaned back. Her body relaxed. The rumors were true. When Ms. Pu was hired