fix(lastleg): read committed order command replays after lock waits

lastleg-service/src/main/java/com/baiyue/lastleg/service/LastlegOrderCommandService.java

@@ -21,6 +21,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 import jakarta.annotation.Resource;
 import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Isolation;
 import org.springframework.transaction.annotation.Transactional;
 import org.springframework.web.server.ResponseStatusException;
 
@@ -55,7 +56,9 @@ public class LastlegOrderCommandService {
     @Resource private InventoryCommandService inventory;
     @Resource private ObjectMapper objectMapper;
 
-    @Transactional
+    // Ownership is read before waiting for the order lock. Under MySQL repeatable
+    // read that snapshot can hide the preceding writer's idempotency record.
+    @Transactional(isolation = Isolation.READ_COMMITTED)
     public LastlegOrderCommandDtos.HoldResponse hold(String requestedCustomerId, long orderId,
                                                       String idempotencyKey,
                                                       LastlegOrderCommandDtos.HoldRequest request,
@@ -122,7 +125,7 @@ public class LastlegOrderCommandService {
         return response;
     }
 
-    @Transactional
+    @Transactional(isolation = Isolation.READ_COMMITTED)
     public LastlegOrderCommandDtos.ManualNodesResponse saveManualNodes(String requestedCustomerId, long orderId,
                                                                         String idempotencyKey,
                                                                         LastlegOrderCommandDtos.ManualNodesRequest request,