Add half-space tracking for all compound constraints with branch
ambiguity: Planar, Revolute, Concentric, Cylindrical, Slider, Screw,
Universal, PointInPlane, and LineInPlane. Previously only
DistancePointPoint, Parallel, Angle, and Perpendicular were tracked,
so the Newton-Raphson solver could converge to the wrong branch for
compound constraints — causing parts to drift through plane
constraints while honoring revolute joints.
Add quaternion continuity enforcement in drag_step(): after solving,
each non-dragged body's quaternion is checked against its pre-step
value and negated if in the opposite hemisphere (standard SLERP
short-arc correction). This prevents the C++ validateNewPlacements()
from rejecting valid solutions as 'flipped orientation' due to the
quaternion double-cover ambiguity (q and -q encode the same rotation
but measure as ~340° apart).
c2ebcc3169