Function stop 

pub async fn stop(
    state: &AppState,
    block_id: &str,
    graceful: bool,
    stop_background: Option<bool>,
) -> Result<TeardownReport, String>

Stop (agent.stop, FleetBulkStop, a deferred Stop action): Policy::stop. stop_background is the caller’s answer to “also stop its background tasks?”; None takes the user’s setting (SETTING_STOP_KEEPS_BACKGROUND). Errors with NOT_RUNNING when the block has no controller, as agent.stop always has.