geo/DimensionPromote

A 2D geometry stores two numbers per point instead of three, so it cannot leave its plane. A 3D one stores three and can. This node moves geometry between the two.

**To 3D never fails.** The two coordinates are kept as they are, the object transform is kept as it is, and the new z is zero, so the result sits exactly where the 2D form did. From then on a point can be moved out of the plane, which is usually the reason to reach for it: draw flat, then lift.

**To 2D drops the z**, and the plane is always the object's own XY plane. So put the geometry where you want it first: a geo/Transform that rotates it onto its plane is the ordinary way, and whatever z is left over after that is thrown away. The node never FITS a plane to the points, because a fit would pick a plane you did not ask for.

Precision is left alone, so a 32 bit geometry stays 32 bit and a 64 bit CAD geometry stays 64 bit. Geometry that is already in the requested dimension passes through untouched, so the node is safe to leave in a network. A solid, a volume or a manifold keeps its points outside the position buffer: those pass through when going to 3D, and are refused when going to 2D.