diff --git a/src/api.test.ts b/src/api.test.ts
index fbac350..9df985a 100644
--- a/src/api.test.ts
+++ b/src/api.test.ts
@@ -51,6 +51,47 @@ describe("api helpers", () => {
     await expect(getJSON("/api/fail")).rejects.toThrow("boom");
   });
 
+  it("cleans expired JSON cache entries", async () => {
+    vi.useFakeTimers();
+    try {
+      vi.setSystemTime(new Date("2026-05-31T00:00:00Z"));
+      const { getJSON, readJSONCache } = await loadApi();
+      const fetchMock = vi.fn().mockResolvedValue(jsonResponse({ items: [1] }));
+      vi.stubGlobal("fetch", fetchMock);
+
+      await getJSON("/api/posts");
+      expect(readJSONCache("/api/posts")).toEqual({ items: [1] });
+
+      vi.setSystemTime(new Date("2026-05-31T00:05:01Z"));
+      expect(readJSONCache("/api/posts")).toBeNull();
+      expect(window.localStorage.length).toBe(0);
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
+  it("prunes old JSON cache entries beyond the entry limit", async () => {
+    vi.useFakeTimers();
+    try {
+      const { getJSON, readJSONCache } = await loadApi();
+      const fetchMock = vi.fn((url: string) =>
+        Promise.resolve(jsonResponse({ url })),
+      );
+      vi.stubGlobal("fetch", fetchMock);
+
+      for (let index = 0; index < 81; index += 1) {
+        vi.setSystemTime(new Date(2026, 4, 31, 0, 0, index));
+        await getJSON(`/api/cache-${index}`);
+      }
+
+      expect(readJSONCache("/api/cache-0")).toBeNull();
+      expect(readJSONCache("/api/cache-80")).toEqual({ url: "/api/cache-80" });
+      expect(window.localStorage.length).toBe(80);
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
   it("posts JSON with optional bearer token", async () => {
     const { postJSON } = await loadApi();
     const fetchMock = vi.fn().mockResolvedValue(jsonResponse({ id: 1 }));
diff --git a/src/api.ts b/src/api.ts
index 28dee0a..50a900c 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -19,44 +19,139 @@ type JsonCacheEntry<T> = {
 
 const jsonMemoryCache = new Map<string, JsonCacheEntry<unknown>>();
 const jsonStoragePrefix = "ark-json-cache:v1:";
+const jsonCacheTtlMs = 5 * 60 * 1000;
+const jsonCacheMaxEntries = 80;
 
 function jsonCacheKey(path: string): string {
   return `${apiBase}${path}`;
 }
 
-export function readJSONCache<T>(path: string): T | null {
-  const key = jsonCacheKey(path);
-  const memoryEntry = jsonMemoryCache.get(key) as JsonCacheEntry<T> | undefined;
-  if (memoryEntry) return memoryEntry.value;
+function jsonStorageKey(key: string): string {
+  return `${jsonStoragePrefix}${key}`;
+}
 
+function isFreshJSONCacheEntry(entry: JsonCacheEntry<unknown>): boolean {
+  return Date.now() - entry.cachedAt <= jsonCacheTtlMs;
+}
+
+function removeStoredJSONCache(key: string): void {
+  jsonMemoryCache.delete(key);
+  if (typeof window === "undefined") return;
+  try {
+    window.localStorage.removeItem(jsonStorageKey(key));
+  } catch {
+    // Ignore privacy-mode storage failures.
+  }
+}
+
+function readStoredJSONCacheEntry<T>(key: string): JsonCacheEntry<T> | null {
   if (typeof window === "undefined") return null;
 
   try {
-    const raw = window.localStorage.getItem(`${jsonStoragePrefix}${key}`);
+    const raw = window.localStorage.getItem(jsonStorageKey(key));
     if (!raw) return null;
     const entry = JSON.parse(raw) as JsonCacheEntry<T>;
-    jsonMemoryCache.set(key, entry as JsonCacheEntry<unknown>);
-    return entry.value;
+    if (typeof entry.cachedAt !== "number") {
+      removeStoredJSONCache(key);
+      return null;
+    }
+    return entry;
   } catch {
+    removeStoredJSONCache(key);
     return null;
   }
 }
 
+function cleanupExpiredJSONCache(): void {
+  for (const [key, entry] of jsonMemoryCache) {
+    if (!isFreshJSONCacheEntry(entry)) jsonMemoryCache.delete(key);
+  }
+
+  if (typeof window === "undefined") return;
+
+  try {
+    const keys: string[] = [];
+    for (let index = 0; index < window.localStorage.length; index += 1) {
+      const key = window.localStorage.key(index);
+      if (key?.startsWith(jsonStoragePrefix)) keys.push(key);
+    }
+
+    keys.forEach((storageKey) => {
+      const key = storageKey.slice(jsonStoragePrefix.length);
+      const entry = readStoredJSONCacheEntry(key);
+      if (!entry || !isFreshJSONCacheEntry(entry)) removeStoredJSONCache(key);
+    });
+  } catch {
+    // Ignore storage access failures; memory cleanup above still happened.
+  }
+}
+
+function pruneJSONCache(): void {
+  if (jsonMemoryCache.size > jsonCacheMaxEntries) {
+    [...jsonMemoryCache.entries()]
+      .sort(([, a], [, b]) => a.cachedAt - b.cachedAt)
+      .slice(0, jsonMemoryCache.size - jsonCacheMaxEntries)
+      .forEach(([key]) => jsonMemoryCache.delete(key));
+  }
+
+  if (typeof window === "undefined") return;
+
+  try {
+    const entries: Array<{ key: string; cachedAt: number }> = [];
+    for (let index = 0; index < window.localStorage.length; index += 1) {
+      const storageKey = window.localStorage.key(index);
+      if (!storageKey?.startsWith(jsonStoragePrefix)) continue;
+      const key = storageKey.slice(jsonStoragePrefix.length);
+      const entry = readStoredJSONCacheEntry(key);
+      if (entry) entries.push({ key, cachedAt: entry.cachedAt });
+    }
+
+    entries
+      .sort((a, b) => a.cachedAt - b.cachedAt)
+      .slice(0, Math.max(0, entries.length - jsonCacheMaxEntries))
+      .forEach(({ key }) => removeStoredJSONCache(key));
+  } catch {
+    // Ignore storage access failures.
+  }
+}
+
+export function readJSONCache<T>(path: string): T | null {
+  cleanupExpiredJSONCache();
+
+  const key = jsonCacheKey(path);
+  const memoryEntry = jsonMemoryCache.get(key) as JsonCacheEntry<T> | undefined;
+  if (memoryEntry) {
+    if (isFreshJSONCacheEntry(memoryEntry)) return memoryEntry.value;
+    removeStoredJSONCache(key);
+    return null;
+  }
+
+  const entry = readStoredJSONCacheEntry<T>(key);
+  if (!entry) return null;
+  if (!isFreshJSONCacheEntry(entry)) {
+    removeStoredJSONCache(key);
+    return null;
+  }
+
+  jsonMemoryCache.set(key, entry as JsonCacheEntry<unknown>);
+  return entry.value;
+}
+
 function writeJSONCache<T>(path: string, value: T): void {
   const key = jsonCacheKey(path);
   const entry: JsonCacheEntry<T> = { cachedAt: Date.now(), value };
   jsonMemoryCache.set(key, entry as JsonCacheEntry<unknown>);
 
-  if (typeof window === "undefined") return;
-
-  try {
-    window.localStorage.setItem(
-      `${jsonStoragePrefix}${key}`,
-      JSON.stringify(entry),
-    );
-  } catch {
-    // Ignore storage quota / privacy-mode failures; memory cache still works.
+  if (typeof window !== "undefined") {
+    try {
+      window.localStorage.setItem(jsonStorageKey(key), JSON.stringify(entry));
+    } catch {
+      // Ignore storage quota / privacy-mode failures; memory cache still works.
+    }
   }
+
+  cleanupExpiredJSONCache();
+  pruneJSONCache();
 }
 
 export async function getJSON<T>(path: string): Promise<T> {
diff --git a/src/components/messageStream/hooks/usePostStream.test.tsx b/src/components/messageStream/hooks/usePostStream.test.tsx
new file mode 100644
index 0000000..16f6305
--- /dev/null
+++ b/src/components/messageStream/hooks/usePostStream.test.tsx
@@ -0,0 +1,67 @@
+import { renderHook, waitFor } from "@testing-library/react";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import type { Post } from "../../../types/post";
+import { usePostStream } from "./usePostStream";
+
+function jsonResponse(body: unknown) {
+  return new Response(JSON.stringify(body), {
+    status: 200,
+    headers: { "Content-Type": "application/json" },
+  });
+}
+
+function post(id: string): Post {
+  return {
+    id,
+    categoryId: 1,
+    categorySlug: "general",
+    language: "zh-CN",
+    attachments: [],
+    isRecommended: false,
+    publishedAt: "2026-05-31T00:00:00.000Z",
+  };
+}
+
+const params = {
+  scope: { kind: "all" as const },
+  type: "all",
+  q: "",
+  lang: "zh-CN" as const,
+};
+
+describe("usePostStream", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it("expires the in-memory stream cache", async () => {
+    const now = vi.spyOn(Date, "now").mockReturnValue(1000);
+    const fetchMock = vi
+      .fn()
+      .mockResolvedValueOnce(jsonResponse({ items: [post("fresh")] }))
+      .mockResolvedValueOnce(jsonResponse({ items: [post("refetched")] }));
+    vi.stubGlobal("fetch", fetchMock);
+
+    const first = renderHook(() => usePostStream(params));
+    await waitFor(() =>
+      expect(first.result.current.items[0]?.id).toBe("fresh"),
+    );
+    first.unmount();
+
+    now.mockReturnValue(1000 + 60 * 1000);
+    const cached = renderHook(() => usePostStream(params));
+    expect(cached.result.current.items[0]?.id).toBe("fresh");
+    expect(cached.result.current.isLoading).toBe(false);
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    cached.unmount();
+
+    now.mockReturnValue(1000 + 5 * 60 * 1000 + 1);
+    const expired = renderHook(() => usePostStream(params));
+    await waitFor(() =>
+      expect(expired.result.current.items[0]?.id).toBe("refetched"),
+    );
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    expired.unmount();
+  });
+});
diff --git a/src/components/messageStream/hooks/usePostStream.ts b/src/components/messageStream/hooks/usePostStream.ts
index 491e963..e78f4c3 100644
--- a/src/components/messageStream/hooks/usePostStream.ts
+++ b/src/components/messageStream/hooks/usePostStream.ts
@@ -98,6 +98,7 @@ type CachedStream = {
   items: Post[];
   cursor: string | undefined;
   hasMore: boolean;
+  cachedAt: number;
 };
 
 /**
@@ -107,16 +108,56 @@ type CachedStream = {
  * In-memory only: a full page reload starts fresh.
  */
 const streamCache = new Map<string, CachedStream>();
+const streamCacheTtlMs = 5 * 60 * 1000;
+const streamCacheMaxEntries = 8;
 
 function streamKey(params: PostStreamParams): string {
   return buildRealUrl(params);
 }
 
+function isFreshStreamCache(entry: CachedStream): boolean {
+  return Date.now() - entry.cachedAt <= streamCacheTtlMs;
+}
+
+function pruneStreamCache(): void {
+  for (const [key, entry] of streamCache) {
+    if (!isFreshStreamCache(entry)) streamCache.delete(key);
+  }
+
+  while (streamCache.size > streamCacheMaxEntries) {
+    const oldestKey = streamCache.keys().next().value as string | undefined;
+    if (!oldestKey) break;
+    streamCache.delete(oldestKey);
+  }
+}
+
+function readStreamCache(key: string): CachedStream | undefined {
+  const entry = streamCache.get(key);
+  if (!entry) return undefined;
+  if (!isFreshStreamCache(entry)) {
+    streamCache.delete(key);
+    return undefined;
+  }
+
+  streamCache.delete(key);
+  streamCache.set(key, entry);
+  return entry;
+}
+
+function writeStreamCache(
+  key: string,
+  entry: Omit<CachedStream, "cachedAt">,
+): void {
+  streamCache.delete(key);
+  streamCache.set(key, { ...entry, cachedAt: Date.now() });
+  pruneStreamCache();
+}
+
 function cacheFirstPage(
   params: PostStreamParams,
   page: PostListResponse,
 ): void {
-  streamCache.set(streamKey(params), {
+  writeStreamCache(streamKey(params), {
     items: itemsOrEmpty(page.items),
     cursor: page.nextCursor,
     hasMore: !!page.nextCursor,
@@ -131,7 +172,7 @@ function cacheFirstPage(
 export function prefetchPostStream(params: PostStreamParams): void {
   if (USE_MOCK) return;
   const key = streamKey(params);
-  if (streamCache.has(key)) return;
+  if (readStreamCache(key)) return;
 
   const url = buildRealUrl(params);
   const cachedPage = readJSONCache<PostListResponse>(url);
@@ -146,7 +187,7 @@ export function prefetchPostStream(params: PostStreamParams): void {
 }
 
 export function usePostStream(params: PostStreamParams): PostStreamResult {
-  const initialCached = streamCache.get(streamKey(params));
+  const initialCached = readStreamCache(streamKey(params));
   const [items, setItems] = useState<Post[]>(() => initialCached?.items ?? []);
   const [hasMore, setHasMore] = useState(() => initialCached?.hasMore ?? true);
   const [isLoading, setIsLoading] = useState(() => !initialCached);
@@ -156,6 +197,7 @@ export function usePostStream(params: PostStreamParams): PostStreamResult {
   const cursorRef = useRef<string | undefined>(initialCached?.cursor);
   const hasMoreRef = useRef(initialCached?.hasMore ?? true);
   const loadingRef = useRef(false);
+  const restoredFromCacheRef = useRef(!!initialCached);
 
   const fetchPage = useCallback(
     async (resetting: boolean) => {
@@ -225,7 +267,7 @@ export function usePostStream(params: PostStreamParams): PostStreamResult {
 
   useEffect(() => {
     // Restore a previously-loaded view instantly (no reset, no refetch).
-    const cached = streamCache.get(streamKey(params));
+    const cached = readStreamCache(streamKey(params));
     if (cached) {
       setItems(cached.items);
       cursorRef.current = cached.cursor;
@@ -233,8 +275,10 @@ export function usePostStream(params: PostStreamParams): PostStreamResult {
       hasMoreRef.current = cached.hasMore;
       setIsLoading(false);
       setError(null);
+      restoredFromCacheRef.current = true;
       return;
     }
+    restoredFromCacheRef.current = false;
     setItems([]);
     cursorRef.current = undefined;
     setHasMore(true);
@@ -254,7 +298,11 @@ export function usePostStream(params: PostStreamParams): PostStreamResult {
   // Persist loaded state so returning to this view restores it from cache.
   useEffect(() => {
     if (items.length === 0) return;
-    streamCache.set(streamKey(params), {
+    if (restoredFromCacheRef.current) {
+      restoredFromCacheRef.current = false;
+      return;
+    }
+    writeStreamCache(streamKey(params), {
       items,
       cursor: cursorRef.current,
       hasMore,