Function execute_turn 

pub async fn execute_turn<F, Fut>(
    agent: Arc<Mutex<Agent>>,
    prompt: String,
    cancel: CancellationToken,
    attribution: TurnAttribution,
    cost_context: Option<ToolLoopCostTrackingContext>,
    on_event: F,
) -> Result<TurnOutcome, TurnError>
where
    F: Fn(TurnEvent) -> Fut + Send + 'static,
    Fut: Future<Output = ()> + Send,