Function make_fallback_user_texture_view 

pub(crate) fn make_fallback_user_texture_view(
    device: &Device,
    queue: &Queue,
) -> TextureView

1×1 opaque white texture for unfilled user-texture slots. Returns just the view — the underlying texture is created on the spot and kept alive by the view’s refcounted handle. Sampling it produces vec4(1, 1, 1, 1) so any tex2D(sampler_user_N_texture, uv) * X degrades to X.