// Sponza miss (runs in SHADE). Primary miss → two-stop sky gradient.
// Shadow miss → the sun is unoccluded, so add the pending direct term.
fn miss_main(ray: RayDesc, payload: ptr<function, Payload>) {
    if ((*payload).shadowRay == 1u) {
        rtAccumulate((*payload).color);
        return;
    }
    let t = clamp(ray.direction.y * 0.5 + 0.5, 0.0, 1.0);
    let sky    = vec3<f32>(0.45, 0.65, 0.95);
    let zenith = vec3<f32>(0.95, 0.85, 0.65);
    rtAccumulate(mix(sky, zenith, t));
}