scenario:

• zoom in or out
• focus cursor in a large box of text that overflows viewport both above and below
• position cursor near bottom, hit down arrow repeatedly. cursor should remain in viewport, with the viewport panning as necessary.
• position cursor near top, hit up arrow repeatedly. cursor should remain in viewport, with the viewport panning as necessary.

Again, I don't really understand when I'm supposed to scale coordinates vs not. But at least we have a manual test pinned down now, and it passes.