Function forward_take_progress 

async fn forward_take_progress(
    updates: UpdateFanout,
    key: SessionSlot,
    generation: u64,
    initiator: Option<u64>,
    progress: Option<Receiver<WindowProgress>>,
)

Forward a take’s progress steps as updates while it runs. Steps arrive while the recording is still open (segments settling, no total) and again after the stop (total known); the task ends when the take’s segmenter closes the stream.