A circle's drop check adds the anchor of its box, in drawing units, to
its saved position, in world units, and removes the circle when the sum
is off the map. With the box at 110 m that sum lands 130 units past the
circle's real centre, so a circle near the top or left of the map
vanished on a short drag. The anchor is now converted to world units
first.

Abilities, agents, images and rectangles make the same unit mix in their
checks; their anchors are small enough that it has not shown, and they
are left for their own change.

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