How the instruments work
Circle: center, then a point on its rim. Line or Segment: two points. Midpoint: two points. Perpendicular / Parallel: two baseline points, then the point to pass through. Transfer compass: center, then two endpoints of the radius.
Intersections appear automatically. Only given and derived points can be used. Exact constructions win; guessing positions cannot.
Keyboard: C circle, S segment, L line, M midpoint, P perpendicular, R parallel, T transfer. Arrow keys cycle points; Enter selects. Escape cancels. U undo, H hint.