Function prepare_layer_composites 

pub fn prepare_layer_composites(
    commands: Commands<'_, '_>,
    extracted: Res<'_, ExtractedUiLayers>,
    store: ResMut<'_, LayerTextureStore>,
    pipeline: Option<Res<'_, LayerCompositePipeline>>,
    pipeline_cache: Res<'_, PipelineCache>,
    render_device: Res<'_, RenderDevice>,
    render_queue: Res<'_, RenderQueue>,
    meta: ResMut<'_, LayerCompositeMeta>,
    uniforms_meta: ResMut<'_, CompositeUniformsMeta>,
    filter_meta: Res<'_, LayerFilterMeta>,
    backdrop_meta: Res<'_, BackdropMeta>,
    phases: ResMut<'_, ViewSortedRenderPhases<TransparentUi>>,
)

Builds composite-quad vertices + bind groups and stamps LayerCompositeBatch onto the quad entities, writing each quad’s vertex range back into its phase item.