fix: smooth mobile footer tab switching

src/components/messageStream/hooks/usePostStream.ts

@@ -112,6 +112,17 @@ function streamKey(params: PostStreamParams): string {
   return buildRealUrl(params);
 }
 
+function cacheFirstPage(
+  params: PostStreamParams,
+  page: PostListResponse,
+): void {
+  streamCache.set(streamKey(params), {
+    items: itemsOrEmpty(page.items),
+    cursor: page.nextCursor,
+    hasMore: !!page.nextCursor,
+  });
+}
+
 /**
  * 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.
@@ -119,20 +130,31 @@ function streamKey(params: PostStreamParams): string {
  */
 export function prefetchPostStream(params: PostStreamParams): void {
   if (USE_MOCK) return;
+  const key = streamKey(params);
+  if (streamCache.has(key)) return;
+
   const url = buildRealUrl(params);
-  if (readJSONCache<PostListResponse>(url)) return;
-  getJSON<PostListResponse>(url).catch(() => {});
+  const cachedPage = readJSONCache<PostListResponse>(url);
+  if (cachedPage) {
+    cacheFirstPage(params, cachedPage);
+    return;
+  }
+
+  getJSON<PostListResponse>(url)
+    .then((page) => cacheFirstPage(params, page))
+    .catch(() => {});
 }
 
 export function usePostStream(params: PostStreamParams): PostStreamResult {
-  const [items, setItems] = useState<Post[]>([]);
-  const [hasMore, setHasMore] = useState(true);
-  const [isLoading, setIsLoading] = useState(false);
+  const initialCached = streamCache.get(streamKey(params));
+  const [items, setItems] = useState<Post[]>(() => initialCached?.items ?? []);
+  const [hasMore, setHasMore] = useState(() => initialCached?.hasMore ?? true);
+  const [isLoading, setIsLoading] = useState(() => !initialCached);
   const [error, setError] = useState<string | null>(null);
 
   const reqIdRef = useRef(0);
-  const cursorRef = useRef<string | undefined>(undefined);
-  const hasMoreRef = useRef(true);
+  const cursorRef = useRef<string | undefined>(initialCached?.cursor);
+  const hasMoreRef = useRef(initialCached?.hasMore ?? true);
   const loadingRef = useRef(false);
 
   const fetchPage = useCallback(