Bug: As I sketch an open circle, the radius indicator in upper right has a fixed value of 10.1349, not the actual radius.
Bug: As I sketch a large open circle, when I reach 180 degrees i.e. a semi circle, the radius jumps down to smaller size rather than following pen.
Bug: Sketch an open circle, then double tap to reveal handles. Drag one end to join the other. The circle disappears. When the drag is released, a closed circle appears.
I understand the issue here. Because open circles are defined by three points on the circumference, there is no unique solution when only two points on the circumference are specified. But I guess some sort of reasonable behavior is needed.
I'm quite amazed by what I can do with your implementation of constraints.