Function surface_failure 

fn surface_failure(
    block_id: &str,
    failure: &AgentFailure,
    broker: Option<&Broker>,
    mstore: &Option<Arc<Store>>,
    event_bus: &Option<Arc<EventBus>>,
)

Record failure as the block’s agent:last_failure, then publish it as agent-failure on block:<id> (persisted for replay) when there is a broker.