Function build_tick_request 

pub fn build_tick_request(
    kind: &str,
    job_id: &str,
    agent_id: &str,
    cursor: Option<&[u8]>,
    config: Value,
    now: DateTime<Utc>,
    interval_hint: Duration,
) -> TickRequest

Build the JSON-RPC tick request from runner inputs. Pure fn so the caller (or a future test harness) can exercise the wire shape without a broker.