California is once again at the center of a high-stakes debate over taxes, population trends and the future of the state’s economy, as a prominent tech investor warns that a new wave of residents could leave within the next year. The warning lands at a moment when official data shows modest population growth returning, even as moving companies and demographers track persistent outflows to other states. The question is not whether people are leaving, but whether policy choices in the coming months will turn a steady trickle into the kind of large-scale relocation that reshapes communities and tax bases. The...