Function create_mesh_shape 

pub fn create_mesh_shape(
    world: &mut World,
    body_id: BodyId,
    def: &ShapeDef,
    mesh: &MeshData,
    scale: Vec3,
) -> ShapeId

(b3CreateMeshShape)

The shape stores an owned clone of mesh (C keeps a borrowed pointer). Per-instance scale is sanitized via safe_scale.