centerAt returns early while the window is hidden, and nothing replays the last
position when it comes back, so re-opening the magnifier showed whatever region
the cursor was over when it was closed - with current pixels, which makes it
look like a live view of the wrong place. Remember the position while hidden and
apply it on show.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>