For months earlier this year, Vietnamese officials tracking the operations of a Chinese oil-and-gas survey ship off their country’s coast in the South China Sea sent urgent communications to Beijing, demanding that the vessel leave Vietnam’s 200-nautical-mile exclusive economic zone. China’s response: Vietnam should stop drilling activities off its own southern coast, according to a Vietnamese official. There, a rig named Hakuryu-5 had begun work in May under a contract with Russian state-owned company Rosneft, which…