Carry actual flow state and freeze callback round identity

Local review candidate only. Explicitly selected inherited prerequisites and prior repair patches; unrelated WIP and independent MQ fixes are excluded. No push or deployment authorized.

src/main/java/com/yunhai/flowcenter/engine/FlowEvent.java

@@ -69,6 +69,15 @@ public class FlowEvent {
     private final String operatorName;
     /** 事件明细（result/opinion/rejectNode/task.created 的 n/m 等），可为空 */
     private final Map<String, Object> data;
+    private Map<String, Object> roundIdentity;
+
+    public void captureRoundIdentity(Integer round, String requestToken) {
+        if (roundIdentity != null) return;
+        Map<String, Object> identity = new HashMap<>();
+        identity.put("applyRound", round);
+        identity.put("requestToken", requestToken);
+        roundIdentity = java.util.Collections.unmodifiableMap(identity);
+    }
 
     public static FlowEvent of(Type type, Long instanceId) {
         return new FlowEvent(type, instanceId, null, null, null, new HashMap<>());