feat: 支持聊天多版本答案切换

- 为管理端、公共聊天和用户中心补充回答变体查询与切换能力

- 支持基于指定轮次重新生成并同步前后端多版本状态

- 保留 application.yml 与本地截图文件为未提交状态

easyflow-ui-usercenter/app/src/views/chatHistory/index.vue

@@ -4,7 +4,11 @@ import type { ChatTimeTimelineItem } from '@easyflow/types';
 import { computed, onMounted, ref, watch } from 'vue';
 import { useRoute, useRouter } from 'vue-router';
 
-import { ChatTimeHistoryMapper } from '@easyflow/utils';
+import {
+  ChatTimeHistoryMapper,
+  ChatTimeTimelineBuilder,
+  createChatVariantSwitchController,
+} from '@easyflow/utils';
 import { Delete, Edit, Search } from '@element-plus/icons-vue';
 import {
   ElButton,
@@ -47,12 +51,23 @@ const drawerVisible = ref(false);
 const drawerLoading = ref(false);
 const currentSession = ref<any>();
 const messageList = ref<ChatTimeTimelineItem[]>([]);
+const variantSwitchStateVersion = ref(0);
 const loadedMessageRecordCount = ref(0);
 const messagePage = ref({
   total: 0,
   pageNumber: 1,
   pageSize: 20,
 });
+const variantSwitchController = createChatVariantSwitchController<any, ChatTimeTimelineItem>({
+  mapRecords: (records) => ChatTimeHistoryMapper.fromHistoryRecords(records),
+  onError: () => ElMessage.error('答案版本切换失败'),
+  onStateChange: () => {
+    variantSwitchStateVersion.value += 1;
+  },
+  replaceRound(items, roundId, nextItems) {
+    ChatTimeTimelineBuilder.replaceRoundMessages(items, roundId, nextItems);
+  },
+});
 
 const filteredSessions = computed(() => {
   const keyword = queryParams.value.keyword.trim().toLowerCase();
@@ -167,6 +182,7 @@ async function loadMessages(reset = false) {
   } else {
     messageList.value = [...normalized, ...messageList.value];
   }
+  prefetchVisibleVariants();
   loadedMessageRecordCount.value = reset
     ? (res.data?.records || []).length
     : loadedMessageRecordCount.value + (res.data?.records || []).length;
@@ -178,6 +194,90 @@ function normalizeMessages(records: any[]) {
   return ChatTimeHistoryMapper.fromHistoryRecords([...records].reverse());
 }
 
+async function handleSelectVariant(
+  item: ChatTimeTimelineItem,
+  direction: 'next' | 'previous',
+) {
+  if (!currentSession.value?.id || !item.roundId) {
+    return;
+  }
+  const current = Number(item.variantIndex || item.selectedVariantIndex || 1);
+  const variantIndex = direction === 'previous' ? current - 1 : current + 1;
+  const sessionId = String(currentSession.value.id);
+  await variantSwitchController.switchVariant({
+    fetchVariants: () => fetchRoundVariants(sessionId, item.roundId!),
+    items: messageList.value,
+    persistVariant: async () => {
+      const [, res] = await tryit(api.post)(
+        `/userCenter/chatHistory/sessions/${sessionId}/rounds/${item.roundId}/selectVariant`,
+        {
+          variantIndex,
+        },
+      );
+      if (res?.errorCode !== 0 || !res?.data) {
+        throw new Error(String((res as any)?.message || '答案版本切换失败'));
+      }
+      return res.data;
+    },
+    roundId: item.roundId,
+    sessionId,
+    targetVariantIndex: variantIndex,
+  });
+}
+
+async function fetchRoundVariants(sessionId: string, roundId: string | number) {
+  const [, res] = await tryit(api.get)(
+    `/userCenter/chatHistory/sessions/${sessionId}/rounds/${roundId}/variants`,
+  );
+  if (res?.errorCode !== 0) {
+    throw new Error(String((res as any)?.message || '答案版本加载失败'));
+  }
+  return res?.data || [];
+}
+
+function prefetchVisibleVariants() {
+  if (!currentSession.value?.id) {
+    return;
+  }
+  const sessionId = String(currentSession.value.id);
+  const prefetchedRoundIds = new Set<string>();
+  for (const item of messageList.value) {
+    if (
+      item.role !== 'assistant' ||
+      !item.roundId ||
+      Number(item.variantCount || 0) <= 1 ||
+      prefetchedRoundIds.has(String(item.roundId))
+    ) {
+      continue;
+    }
+    prefetchedRoundIds.add(String(item.roundId));
+    variantSwitchController.prefetchVariants({
+      fetchVariants: () => fetchRoundVariants(sessionId, item.roundId!),
+      roundId: item.roundId,
+      sessionId,
+    });
+  }
+}
+
+function currentSwitchingRoundIds() {
+  void variantSwitchStateVersion.value;
+  if (!currentSession.value?.id) {
+    return [];
+  }
+  const sessionId = String(currentSession.value.id);
+  return Array.from(
+    new Set(
+      messageList.value
+        .filter(
+          (item) =>
+            item.roundId &&
+            variantSwitchController.isSwitching(sessionId, item.roundId),
+        )
+        .map((item) => String(item.roundId)),
+    ),
+  );
+}
+
 function closeDrawer() {
   drawerVisible.value = false;
   currentSession.value = undefined;
@@ -355,6 +455,10 @@ function formatTime(value?: string) {
         <ChatBubbleList
           :bot="{ icon: '', title: currentSession?.assistantName || '' }"
           :messages="messageList"
+          allow-variant-switch
+          :switching-round-ids="currentSwitchingRoundIds()"
+          @select-next-variant="handleSelectVariant($event, 'next')"
+          @select-previous-variant="handleSelectVariant($event, 'previous')"
         />
       </div>
     </div>