"2d" does not select a second API — see the module header and plan P5-3.
It selects a plane constraint over the same 3D-typed API: positions live in
the world XY plane (z = 0), rotation is about +Z only, and §30's overlap
queries degrade to their planar forms (overlapSphere is a circle,
overlapBox a rectangle) exactly as §21 requires.
Which dimensional model a world simulates (§21).
"2d"does not select a second API — see the module header and plan P5-3. It selects a plane constraint over the same 3D-typed API: positions live in the world XY plane (z = 0), rotation is about+Zonly, and §30's overlap queries degrade to their planar forms (overlapSphereis a circle,overlapBoxa rectangle) exactly as §21 requires.