fix: 用 Zustand 缓存 Feed 列表，返回时恢复滚动且不重复请求

点击 Logo 仍强制刷新；后退忽略 history 上的 refreshFeed，并支持过期静默刷新与下拉刷新。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/store/homeStore.ts

@@ -0,0 +1,106 @@
+import { create } from 'zustand';
+import type { PostItem } from '../api/types';
+import type { FeedSort } from '../components/FeedSortBar';
+
+/** 列表缓存过期时间：超过后返回首页时静默刷新，仍先展示旧数据 */
+export const FEED_STALE_MS = 5 * 60 * 1000;
+
+/** 单条 Feed 筛选对应的缓存快照 */
+export type FeedCacheEntry = {
+  posts: PostItem[];
+  postTotal: number;
+  page: number;
+  scrollTop: number;
+  /** 上次成功拉取 API 的时间戳（ms） */
+  lastFetchTime: number;
+};
+
+type FeedKeyParts = {
+  boardId: number;
+  keyword: string;
+  sort: FeedSort;
+  tag?: string;
+  author?: string;
+  titleOnly?: boolean;
+};
+
+/** 与筛选条件一一对应的缓存键 */
+export function feedCacheKey(parts: FeedKeyParts): string {
+  const {
+    boardId,
+    keyword,
+    sort,
+    tag = '',
+    author = '',
+    titleOnly = false,
+  } = parts;
+  return `${boardId}:${keyword}:${tag}:${author}:${titleOnly ? 1 : 0}:${sort}`;
+}
+
+type HomeStoreState = {
+  /** 按筛选键存放多份列表，首页 / 板块 / 搜索互不覆盖 */
+  feeds: Record<string, FeedCacheEntry>;
+  getFeed: (key: string) => FeedCacheEntry | null;
+  setFeed: (key: string, data: Omit<FeedCacheEntry, 'lastFetchTime'> & { lastFetchTime?: number }) => void;
+  /** 滚动时只更新 scrollTop，不改动列表数据 */
+  patchScroll: (key: string, scrollTop: number) => void;
+  isStale: (key: string, now?: number) => boolean;
+  clearFeed: (key: string) => void;
+  clearAll: () => void;
+};
+
+export const useHomeStore = create<HomeStoreState>((set, get) => ({
+  feeds: {},
+
+  getFeed: (key) => get().feeds[key] ?? null,
+
+  setFeed: (key, data) => {
+    set((state) => ({
+      feeds: {
+        ...state.feeds,
+        [key]: {
+          posts: data.posts,
+          postTotal: data.postTotal,
+          page: data.page,
+          scrollTop: data.scrollTop,
+          lastFetchTime: data.lastFetchTime ?? Date.now(),
+        },
+      },
+    }));
+  },
+
+  patchScroll: (key, scrollTop) => {
+    const prev = get().feeds[key];
+    if (!prev) return;
+    // 数值未变则跳过，减少无意义的 store 更新
+    if (prev.scrollTop === scrollTop) return;
+    set((state) => ({
+      feeds: {
+        ...state.feeds,
+        [key]: { ...prev, scrollTop },
+      },
+    }));
+  },
+
+  isStale: (key, now = Date.now()) => {
+    const entry = get().feeds[key];
+    if (!entry) return true;
+    return now - entry.lastFetchTime > FEED_STALE_MS;
+  },
+
+  clearFeed: (key) => {
+    set((state) => {
+      if (!(key in state.feeds)) return state;
+      const next = { ...state.feeds };
+      delete next[key];
+      return { feeds: next };
+    });
+  },
+
+  clearAll: () => set({ feeds: {} }),
+}));
+
+/** 非 React 路径（如 feedCache 封装）直接读写 */
+export function getHomeStoreState() {
+  return useHomeStore.getState();
+}