Function capture_loop_ext 

fn capture_loop_ext(
    conn: &Connection,
    queue: &mut EventQueue<CaptureState>,
    state: &mut CaptureState,
    output: &WlOutput,
    gbm: Option<&Device<File>>,
    wake: RawFd,
    index: usize,
    from_main: &Receiver<ToHost>,
    frames: &FrameSink,
    want: &mut Option<Want>,
) -> ExtOutcome

ext-image-copy-capture capture loop: one persistent session per output. The compositor holds each capture until the content actually changes, so a static screen costs nothing — the property copy_with_damage provides on the wlr path. Frames land in the same slot machinery and HostFrame shape as that path.