Function build_render_app 

pub fn build_render_app(
    ctx: &WgpuContext,
    width: u32,
    height: u32,
    oit_layers: usize,
) -> SubApp

Create an independent render runtime with the shared frame, viewport, and OIT infrastructure installed.

Item plugins install their own extraction and GPU systems on top. Extraction systems can read the current EvaluatedFrame resource during RenderSchedule::Extract. Plugins configure the render world directly; no logic world is created.