The transparent-screenshot test looked at one corner pixel, outside the
dot grid's inset, so leaving the dots in would have passed. It now
requires every pixel left of the map to be empty.

The capture shell no longer paints a background, so a video frame is
opaque only because the view paints its own backdrop. The sink test now
checks every still and transition frame stays opaque.

Both checks fail with their guard removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>