fix(engine): stop coal_feeder before starting distributor on acc_time trigger

When accumulated_run_sec reaches acc_time_sec, the coal feeder must be stopped
before entering DistributorRunning state. Previously the feeder was left running
while the distributor also ran, which is incorrect per the control spec.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/control/engine.rs

@@ -291,10 +291,31 @@ async fn tick_state_machine(
                 return;
             }
 
-            // Check AccTime — trigger distributor
+            // Check AccTime — stop feeder then trigger distributor
             if unit.acc_time_sec > 0
                 && runtime.accumulated_run_sec >= unit.acc_time_sec as i64 * 1000
             {
+                let monitor = state
+                    .connection_manager
+                    .get_point_monitor_data_read_guard()
+                    .await;
+                if let Some((pid, vt)) =
+                    feeder_roles.and_then(|r| find_cmd(r, "stop_cmd", &monitor))
+                {
+                    drop(monitor);
+                    if let Err(e) =
+                        send_pulse_command(&state.connection_manager, pid, vt.as_ref(), 300).await
+                    {
+                        tracing::warn!("Engine: stop coal_feeder before distributor failed: {}", e);
+                        return;
+                    }
+                    if state.config.simulate_plc {
+                        if let Some(eq_id) = feeder_eq_id {
+                            crate::control::command::simulate_run_feedback(state, eq_id, false)
+                                .await;
+                        }
+                    }
+                }
                 runtime.state = UnitRuntimeState::DistributorRunning;
                 runtime.distributor_run_elapsed_sec = 0;
             }