perf: 空闲预热全部资料/热门资料,点击前已缓存

usePostStream 导出 prefetchPostStream(已缓存/mock 则跳过)。PublicLayout 在
requestIdleCallback 空闲时后台预取「全部资料」「热门资料」首页数据并写入缓存,
用户点击进入时直接读缓存秒显,不再进页面才开始加载。预取仅 JSON,不拉图片。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/messageStream/hooks/usePostStream.ts

@@ -112,6 +112,18 @@ function streamKey(params: PostStreamParams): string {
   return buildRealUrl(params);
 }
 
+/**
+ * Warm the cache for a stream view before the user navigates to it, so opening
+ * the page shows content immediately instead of starting to load on arrival.
+ * No-op for the mock backend or when the first page is already cached.
+ */
+export function prefetchPostStream(params: PostStreamParams): void {
+  if (USE_MOCK) return;
+  const url = buildRealUrl(params);
+  if (readJSONCache<PostListResponse>(url)) return;
+  getJSON<PostListResponse>(url).catch(() => {});
+}
+
 export function usePostStream(params: PostStreamParams): PostStreamResult {
   const [items, setItems] = useState<Post[]>([]);
   const [hasMore, setHasMore] = useState(true);