perf: 资料流会话级缓存,切换页面不再重载

usePostStream 增加按筛选参数为 key 的内存缓存,保存已加载的全部内容与分页
游标。再次进入同一视图(如首页⇄全部资料来回切)时直接还原,不重置、不重新
请求、不显示骨架屏。整页刷新清空缓存以获取最新数据。

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

src/components/messageStream/hooks/usePostStream.ts

@@ -94,6 +94,24 @@ function buildRealUrl(params: PostStreamParams, cursor?: string): string {
   return `${q ? "/api/posts/search" : "/api/posts"}?${sp.toString()}`;
 }
 
+type CachedStream = {
+  items: Post[];
+  cursor: string | undefined;
+  hasMore: boolean;
+};
+
+/**
+ * Session cache of loaded stream state, keyed by the request params. Lets a
+ * view that's been seen before (e.g. switching Home ⇄ All) restore instantly —
+ * all loaded pages, no skeleton, no refetch — instead of reloading from page 1.
+ * In-memory only: a full page reload starts fresh.
+ */
+const streamCache = new Map<string, CachedStream>();
+
+function streamKey(params: PostStreamParams): string {
+  return buildRealUrl(params);
+}
+
 export function usePostStream(params: PostStreamParams): PostStreamResult {
   const [items, setItems] = useState<Post[]>([]);
   const [hasMore, setHasMore] = useState(true);
@@ -172,6 +190,17 @@ export function usePostStream(params: PostStreamParams): PostStreamResult {
   );
 
   useEffect(() => {
+    // Restore a previously-loaded view instantly (no reset, no refetch).
+    const cached = streamCache.get(streamKey(params));
+    if (cached) {
+      setItems(cached.items);
+      cursorRef.current = cached.cursor;
+      setHasMore(cached.hasMore);
+      hasMoreRef.current = cached.hasMore;
+      setIsLoading(false);
+      setError(null);
+      return;
+    }
     setItems([]);
     cursorRef.current = undefined;
     setHasMore(true);
@@ -188,6 +217,17 @@ export function usePostStream(params: PostStreamParams): PostStreamResult {
     params.lang,
   ]);
 
+  // Persist loaded state so returning to this view restores it from cache.
+  useEffect(() => {
+    if (items.length === 0) return;
+    streamCache.set(streamKey(params), {
+      items,
+      cursor: cursorRef.current,
+      hasMore,
+    });
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [items, hasMore]);
+
   const loadMore = useCallback(() => {
     fetchPage(false);
   }, [fetchPage]);