fix: 软刷新齐套前保留旧画面，避免一点击就卸光

Logo/下拉静默预热后一次覆盖；commit 不再先 reset/loading；顺带会话预取与可配置 Feed 排序标签。

frontend/src/utils/feedSortTabs.ts

@@ -0,0 +1,41 @@
+import type { FeedSortId, FeedSortTab } from '../api/types';
+import { DEFAULT_FEED_SORT_TABS } from '../api/types';
+
+const FEED_SORT_IDS: FeedSortId[] = ['reply', 'latest', 'hot'];
+
+const DEFAULT_LABELS: Record<FeedSortId, string> = {
+  reply: '新评论',
+  latest: '新帖子',
+  hot: '推荐帖',
+};
+
+/** 校验并补全 Feed 排序标签；至少保留一项启用 */
+export function normalizeFeedSortTabs(tabs?: FeedSortTab[] | null): FeedSortTab[] {
+  const seen = new Set<FeedSortId>();
+  const out: FeedSortTab[] = [];
+  for (const t of tabs ?? []) {
+    if (!FEED_SORT_IDS.includes(t.id) || seen.has(t.id)) continue;
+    seen.add(t.id);
+    const label = (t.label || '').trim() || DEFAULT_LABELS[t.id];
+    out.push({ id: t.id, label, enabled: !!t.enabled });
+  }
+  for (const id of FEED_SORT_IDS) {
+    if (seen.has(id)) continue;
+    const fallback = DEFAULT_FEED_SORT_TABS.find(t => t.id === id)!;
+    out.push({ ...fallback });
+  }
+  if (!out.some(t => t.enabled) && out.length > 0) {
+    out[0] = { ...out[0], enabled: true };
+  }
+  return out;
+}
+
+/** 启用中的排序标签（按配置顺序） */
+export function enabledFeedSortTabs(tabs?: FeedSortTab[] | null): FeedSortTab[] {
+  return normalizeFeedSortTabs(tabs).filter(t => t.enabled);
+}
+
+/** 默认排序 = 第一个启用项 */
+export function getDefaultFeedSort(tabs?: FeedSortTab[] | null): FeedSortId {
+  return enabledFeedSortTabs(tabs)[0]?.id ?? 'reply';
+}