The edit you asked for, and the edit you got
Image models do not paint over one region and leave the rest alone; they regenerate the frame and re-render the whole scene around your instruction. That is why a request to remove a cable can also move a chair, rewrite the label on a box, or turn a reflection into something the room does not contain.
The wipe makes that drift visible. Two versions in the same coordinates, revealing one over the other, turn every difference into a flicker at the divider. Nothing needs to be remembered or listed: the change announces itself as you drag.