HONG KONG, July 28 (Reuters Breakingviews) - China faces a long slog to artificial intelligence supremacy. It wants to be a leader in the field by 2030 and this month unveiled new rules governing the technology that are less onerous than expected. But closed online ecosystems, Beijing’s controls on internet content and U.S. curbs on semiconductor exports to the world’s second largest economy will hamper progress. There were high expectations of what the People's Republic could achieve with the technology seen as having the power to solve some of the most pressing challenges on the planet. “In the age of...