Function shape_set_mesh 

pub fn shape_set_mesh(
    world: &mut World,
    shape_id: ShapeId,
    mesh: &MeshData,
    scale: Vec3,
)

(b3Shape_SetMesh)

Retypes the shape to a mesh, swapping in mesh (an owned clone, as create_mesh_shape does — C keeps a borrowed pointer) at the sanitized scale, then destroys the shape’s contacts and rebuilds the broad-phase proxy. Like C, this does no mass update: mesh shapes carry no mass, and the C source only calls b3ResetProxy.