In theory, the system of free trade driving the world economy is supposed to provide a level playing field for all. In practice, countries have long complained that rivals unfairly dish out aid in the form of state-backed subsidies to boost favored companies — often as they do the same. Now that the pandemic has forced governments to mount huge rescue efforts for their economies, the fragile set of rules that aim to keep state support in check is under threat. State aid has also become a sticki