perf: preload and cache countdowns

frontend/src/lib/mvp-utils.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { calendarModeLabel, clampFabPosition, countdownDayText, countdownKindLabel, dateKey, defaultView, habitButtonValue, habitWeek, isFabDrag, isHabitComplete, isHabitScheduledToday, isTaskView, nextHabitSwipeValue, nextTotalAfterLocalTaskAdd, numericHabitInputValue, previousHabitSwipeValue, quickTaskFields, readHabitGridCache, shouldToggleRowSwipe, writeHabitGridCache } from './mvp-utils'
+import { calendarModeLabel, clampFabPosition, countdownDayText, countdownKindLabel, dateKey, defaultView, habitButtonValue, habitWeek, isFabDrag, isHabitComplete, isHabitScheduledToday, isTaskView, nextHabitSwipeValue, nextTotalAfterLocalTaskAdd, numericHabitInputValue, previousHabitSwipeValue, quickTaskFields, readCountdownCache, readHabitGridCache, shouldToggleRowSwipe, writeCountdownCache, writeHabitGridCache } from './mvp-utils'
 
 describe('MVP view utilities', () => {
   it('formats a local date as YYYY-MM-DD', () => {
@@ -77,6 +77,13 @@ describe('MVP view utilities', () => {
     expect(readHabitGridCache('2026-09-14')).toBeNull()
   })
 
+  it('reuses countdown data while the page refreshes in the background', () => {
+    const active = [{ id: 'countdown-1', title: '旅行' }]
+    const archived = [{ id: 'countdown-2', title: '旧日期' }]
+    writeCountdownCache(active, archived)
+    expect(readCountdownCache()).toEqual({ items: active, archived })
+  })
+
   it('renders countdown labels from date-only day values', () => {
     expect(countdownDayText(8)).toBe('还有 8 天')
     expect(countdownDayText(0)).toBe('就是今天')

frontend/src/lib/mvp-utils.ts

@@ -115,6 +115,7 @@ export function isFabDrag(deltaX: number, deltaY: number, threshold = 8) {
 }
 
 let habitGridCache: { week: string; habits: unknown[] } | null = null
+let countdownCache: { items: unknown[]; archived: unknown[] } | null = null
 
 export function readHabitGridCache<T>(week: string): T[] | null {
   return habitGridCache?.week === week ? habitGridCache.habits as T[] : null
@@ -124,6 +125,14 @@ export function writeHabitGridCache<T>(week: string, habits: T[]) {
   habitGridCache = { week, habits }
 }
 
+export function readCountdownCache<T>() {
+  return countdownCache as { items: T[]; archived: T[] } | null
+}
+
+export function writeCountdownCache<T>(items: T[], archived: T[]) {
+  countdownCache = { items, archived }
+}
+
 export function formatApiErrorDetail(detail: unknown): string {
   if (typeof detail === 'string') return detail
   if (Array.isArray(detail)) {