fix(core): fix list hash stability for equivalent messages

Author: Weilong-Qin

agentscope-core/src/main/java/io/agentscope/core/session/ListHashUtil.java

@@ -16,6 +16,7 @@
 package io.agentscope.core.session;
 
 import io.agentscope.core.state.State;
+import io.agentscope.core.util.JsonUtils;
 import java.util.List;
 
 /**
@@ -88,7 +89,7 @@ public static String computeHash(List<? extends State> values) {
 
         for (int idx : sampleIndices) {
             State item = values.get(idx);
-            int itemHash = item != null ? item.hashCode() : 0;
+            int itemHash = item != null ? JsonUtils.getJsonCodec().toJson(item).hashCode() : 0;
             sb.append(idx).append(":").append(itemHash).append(",");
         }
 

agentscope-extensions/agentscope-extensions-session-mysql/src/test/java/io/agentscope/core/session/mysql/MysqlSessionTest.java

@@ -25,6 +25,10 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+import io.agentscope.core.message.Msg;
+import io.agentscope.core.message.MsgRole;
+import io.agentscope.core.message.TextBlock;
+import io.agentscope.core.session.ListHashUtil;
 import io.agentscope.core.state.SessionKey;
 import io.agentscope.core.state.SimpleSessionKey;
 import io.agentscope.core.state.State;
@@ -282,6 +286,45 @@ void testSaveAndGetListState() throws SQLException {
         assertEquals("value2", loaded.get(1).value());
     }
 
+    @Test
+    @DisplayName("Should compute same hash for equivalent message lists")
+    void testComputeHashEquivalentMessageLists() {
+        List<Msg> first =
+                List.of(
+                        Msg.builder()
+                                .id("m-user-1")
+                                .timestamp("2026-05-08 14:00:00.000")
+                                .role(MsgRole.USER)
+                                .content(TextBlock.builder().text("hello").build())
+                                .build(),
+                        Msg.builder()
+                                .id("m-assistant-1")
+                                .timestamp("2026-05-08 14:00:01.000")
+                                .role(MsgRole.ASSISTANT)
+                                .content(TextBlock.builder().text("hello").build())
+                                .build());
+
+        List<Msg> second =
+                List.of(
+                        Msg.builder()
+                                .id("m-user-1")
+                                .timestamp("2026-05-08 14:00:00.000")
+                                .role(MsgRole.USER)
+                                .content(TextBlock.builder().text("hello").build())
+                                .build(),
+                        Msg.builder()
+                                .id("m-assistant-1")
+                                .timestamp("2026-05-08 14:00:01.000")
+                                .role(MsgRole.ASSISTANT)
+                                .content(TextBlock.builder().text("hello").build())
+                                .build());
+
+        String h1 = ListHashUtil.computeHash(first);
+        String h2 = ListHashUtil.computeHash(second);
+
+        assertEquals(h1, h2);
+    }
+
     @Test
     @DisplayName("Should commit incremental list save when connection auto-commit is disabled")
     void testSaveListIncrementalAppendCommitsWhenAutoCommitDisabled() throws SQLException {