feat: refine task and countdown interactions

frontend/src/CountdownPanel.test.ts

@@ -195,7 +195,28 @@ describe('countdown modal accessibility', () => {
     newPin.resolve(json({})); await flush()
   })
 
-  it('keeps the normal current-detail pin flow working', async () => {
+  it('pins and unpins from detail without duplicate requests', async () => {
+    const mutation = deferred<Response>()
+    const pinned = { ...countdown, pinned: true }
+    const fetchMock = vi.fn((url: string, options?: RequestInit) => {
+      if (url.endsWith('/countdowns/c1/pin') && options?.method === 'DELETE') return mutation.promise
+      if (url.endsWith('/countdowns')) return Promise.resolve(json([pinned]))
+      if (url.includes('archived=true')) return Promise.resolve(json([]))
+      throw new Error(`unexpected ${url}`)
+    })
+    const { host, notices } = await mountWithFetch(fetchMock)
+    clickCountdown(host, '发布日'); await nextTick()
+    const button = detailButton('取消置顶')
+    button.click(); button.click()
+    await nextTick()
+    expect(fetchMock.mock.calls.filter(([url]) => String(url).endsWith('/countdowns/c1/pin'))).toHaveLength(1)
+    expect(button.disabled).toBe(true)
+    mutation.resolve(json({ ...pinned, pinned: false })); await flush()
+    expect(notices).toEqual(['已取消置顶'])
+    expect(document.querySelector('.countdown-detail-sheet')).toBeNull()
+  })
+
+  it('keeps normal current-detail pin flow working', async () => {
     const pin = deferred<Response>()
     const fetchMock = vi.fn((url: string) => {
       if (url.endsWith('/countdowns/c1/pin')) return pin.promise