Swiss policymakers are preparing to introduce their first foreign-investment screening system for security-critical industries, signalling a break from the open-door stance that has long underpinned the country’s prosperity. In May 2014, barely anyone noticed the takeover of a Swiss developer of experimental aviation engines by a rice cooker maker in China. The buyout of Mistral Engines by Guangdong Elecpro was just one of several by the Chinese firm under a plan to “obtain advanced foreign technology” and move into producing drones and helicopters. A much bigger deal came three years later, when state-owned ChemChina paid $43 billion (CHF34.5 billion) , the country’s biggest overseas acquisition, for Switzerland’s agrochemical giant Syngenta. This time there was concern, particularly in some US farming states, that handing China a big chunk of the world market for seeds threatened food security. Yet the plan went ahead with approval from regulators in both the United States and …