task-125: similarasin /result 纯计算移出事务（payload 哈希在 prepare 阶段预计算，落库直接引用）+ 9 条事务边界守门测试

backend-java/src/main/java/com/nanri/aiimage/modules/similarasin/service/SimilarAsinTaskService.java

@@ -1030,15 +1030,17 @@ public class SimilarAsinTaskService {
         if (existing != null) {
             return new PreparedSubmittedChunk(
                     taskId, scopeKey, scopeHash, chunkIndex, chunkTotal, done, request.getError(),
-                    null, null, false, taskMetadata);
+                    null, null, false, taskMetadata, null);
         }
         String payloadJson = writeJson(flattenSubmittedRows(request), "结果序列化失败");
         String storedPayload = transientPayloadStorageService.storeChunkPayloadVersioned(
                 MODULE_TYPE, taskId, scopeHash, chunkIndex, payloadJson);
         boolean localFallback = transientPayloadStorageService.wasLastStoreLocalFallback();
+        // 纯计算在事务外完成：payload 哈希预计算，persist 落库时直接引用
         return new PreparedSubmittedChunk(
                 taskId, scopeKey, scopeHash, chunkIndex, chunkTotal, done, request.getError(),
-                payloadJson, storedPayload, localFallback, taskMetadata);
+                payloadJson, storedPayload, localFallback, taskMetadata,
+                DigestUtil.sha256Hex(payloadJson));
     }
 
     private SubmittedTaskMetadata readSubmittedTaskMetadata(FileTaskEntity task) {
@@ -1146,7 +1148,7 @@ public class SimilarAsinTaskService {
             chunk.setChunkIndex(prepared.chunkIndex());
             chunk.setChunkTotal(prepared.chunkTotal());
             chunk.setPayloadJson(prepared.storedPayload());
-            chunk.setPayloadHash(DigestUtil.sha256Hex(prepared.payloadJson()));
+            chunk.setPayloadHash(prepared.payloadHash());
             chunk.setCreatedAt(LocalDateTime.now());
             chunk.setUpdatedAt(LocalDateTime.now());
             try {
@@ -5750,7 +5752,8 @@ public class SimilarAsinTaskService {
                                           String payloadJson,
                                           String storedPayload,
                                           boolean localFallback,
-                                          SubmittedTaskMetadata taskMetadata) {
+                                          SubmittedTaskMetadata taskMetadata,
+                                          String payloadHash) {
     }
 
     private record PersistSubmittedChunkResult(SubmitContext context,