Function start_run 

pub(crate) fn start_run(
    inner: &Arc<Inner>,
    set: &mut JoinSet<()>,
    runs: &mut HashMap<Id, Run>,
    name: &str,
    generation: u64,
    token: CancellationToken,
    restart: Option<&str>,
)

Spawn one run of name, unless a newer run has replaced it. restart carries the death’s reason when this is a restart.