{# A backdrop (docs/backgrounds.md): the scene the page's `#backdrop-data` names (written just before this include) drawn by the engine, Rust compiled to WebAssembly. The viewer's choice (Settings › Appearance) is a cookie; unset, a touch-only device or Save-Data gets a still sky. Any failure leaves no backdrop and nothing else changed. A sky with `live` polls `/sky/arrivals` for what happened since and adds it. #}