Rising tensions in the Middle East cast a fresh shadow over the opening of China’s largest trade fair, at a time when the impact of geopolitical shocks is being reflected in the nation’s trade figures. In conversations across sprawling exhibition halls after the Canton Fair opened its doors on Wednesday in China’s manufacturing hub of Guangzhou, domestic exporters and foreign buyers sounded each other out, trying to gauge how far those shocks might ripple through global trade. The threat of US...