Fix review findings: error handling, constant dedup, migration persist

- Wrap hydrateCache() in try/catch so disk errors don't crash commands
  that previously never touched the cache
- Export MS_PER_DAY, BACKFILL_DAYS, toDateString from daily-cache.ts
  and remove duplicates from cli.ts
- Remove double hydrateCache() call in report JSON path
- Persist migrated cache to disk so old-version files aren't
  re-migrated on every run
- Export emptyCache() for use as fallback on hydration failure

src/cli.ts

@@ -7,7 +7,7 @@ import { convertCost } from './currency.js'
 import { renderStatusBar } from './format.js'
 import { type PeriodData, type ProviderCost } from './menubar-json.js'
 import { buildMenubarPayload } from './menubar-json.js'
-import { getDaysInRange, ensureCacheHydrated } from './daily-cache.js'
+import { getDaysInRange, ensureCacheHydrated, emptyCache, MS_PER_DAY, BACKFILL_DAYS, toDateString } from './daily-cache.js'
 import { aggregateProjectsIntoDays, buildPeriodDataFromDays, dateKey } from './day-aggregator.js'
 import { CATEGORY_LABELS, type DateRange, type ProjectSummary, type TaskCategory } from './types.js'
 import { renderDashboard } from './dashboard.js'
@@ -24,18 +24,15 @@ const require = createRequire(import.meta.url)
 const { version } = require('../package.json')
 import { loadCurrency, getCurrency, isValidCurrencyCode } from './currency.js'
 
-const MS_PER_DAY = 24 * 60 * 60 * 1000
-const BACKFILL_DAYS = 365
-
-function toDateString(date: Date): string {
-  return `${date.getFullYear()}-${String(date.getMonth() + 1).padStart(2, '0')}-${String(date.getDate()).padStart(2, '0')}`
-}
-
-function hydrateCache() {
-  return ensureCacheHydrated(
-    (range) => parseAllSessions(range, 'all'),
-    aggregateProjectsIntoDays,
-  )
+async function hydrateCache() {
+  try {
+    return await ensureCacheHydrated(
+      (range) => parseAllSessions(range, 'all'),
+      aggregateProjectsIntoDays,
+    )
+  } catch {
+    return emptyCache()
+  }
 }
 
 function getDateRange(period: string): { range: DateRange; label: string } {
@@ -129,7 +126,6 @@ function toJsonPlanSummary(planUsage: PlanUsage): JsonPlanSummary {
 
 async function runJsonReport(period: Period, provider: string, project: string[], exclude: string[]): Promise<void> {
   await loadPricing()
-  await hydrateCache()
   const { range, label } = getDateRange(period)
   const projects = filterProjectsByName(await parseAllSessions(range, provider), project, exclude)
   const report: ReturnType<typeof buildJsonReport> & { plan?: JsonPlanSummary } = buildJsonReport(projects, label, period)

src/daily-cache.ts

@@ -46,7 +46,7 @@ function getCachePath(): string {
   return join(getCacheDir(), DAILY_CACHE_FILENAME)
 }
 
-function emptyCache(): DailyCache {
+export function emptyCache(): DailyCache {
   return { version: DAILY_CACHE_VERSION, lastComputedDate: null, days: [] }
 }
 
@@ -88,11 +88,15 @@ export async function loadDailyCache(): Promise<DailyCache> {
     const raw = await readFile(path, 'utf-8')
     const parsed: unknown = JSON.parse(raw)
     if (isMigratableCache(parsed)) {
-      return {
+      const migrated: DailyCache = {
         version: DAILY_CACHE_VERSION,
         lastComputedDate: parsed.lastComputedDate,
         days: migrateDays(parsed.days),
       }
+      if (parsed.version < DAILY_CACHE_VERSION) {
+        await saveDailyCache(migrated).catch(() => {})
+      }
+      return migrated
     }
     const oldVersion = (parsed as { version?: number })?.version
     if (typeof oldVersion === 'number') await backupOldCache(path, oldVersion)
@@ -147,10 +151,10 @@ export function withDailyCacheLock<T>(fn: () => Promise<T>): Promise<T> {
   return next
 }
 
-const MS_PER_DAY = 24 * 60 * 60 * 1000
-const BACKFILL_DAYS = 365
+export const MS_PER_DAY = 24 * 60 * 60 * 1000
+export const BACKFILL_DAYS = 365
 
-function toDateString(date: Date): string {
+export function toDateString(date: Date): string {
   return `${date.getFullYear()}-${String(date.getMonth() + 1).padStart(2, '0')}-${String(date.getDate()).padStart(2, '0')}`
 }