Function transcript_position 

pub(crate) async fn transcript_position(
    filestore: &Arc<FileStore>,
    global_store: &Option<Arc<FileStore>>,
    mstore: &Arc<Store>,
    block_id: &str,
) -> Option<(String, String, u64)>

Where block_id’s transcript stands, from the same source read_range reads it from (the block’s own output, or the agent’s global zone): its stream, generation and line count. None while it doesn’t exist or can’t be counted. For the viewer feed, which reads the tail through read_range.