HONG KONG—For months now, I’ve been told that Hong Kong’s protests would end soon. They’ll end when school starts, I heard during the summer. School did start, but the protests wore on, only now I saw high-school students in crisp school uniforms joining the protesters’ ranks. Next, the mask ban of early October was supposed to slow protesters down, but the very first day after that ban, I watched streams of protesters in masks and helmets make their way to their usual haunts on Hong Kong Island. The government shut down many of the subway lines that day, a practice...