fix(cli): bucket daily history by local date

The daily cache keyed days by UTC while period ranges used local midnight, so
any user outside UTC lost or double-counted a whole day in history.daily and
the menubar trend, forecast, and stats disagreed with the period totals.
Use the local date everywhere and bump the cache version to rebuild.

src/cli.ts

@@ -4,7 +4,7 @@ import { exportCsv, exportJson, type PeriodExport } from './export.js'
 import { loadPricing } from './models.js'
 import { parseAllSessions, filterProjectsByName } from './parser.js'
 import { convertCost } from './currency.js'
-import { renderStatusBar } from './format.js'
+import { localDateString, renderStatusBar } from './format.js'
 import { type PeriodData, type ProviderCost } from './menubar-json.js'
 import { buildMenubarPayload } from './menubar-json.js'
 import { addNewDays, getDaysInRange, loadDailyCache, saveDailyCache, withDailyCacheLock } from './daily-cache.js'
@@ -25,7 +25,12 @@ const MS_PER_DAY = 24 * 60 * 60 * 1000
 const BACKFILL_DAYS = 365
 
 function toDateString(date: Date): string {
-  return date.toISOString().slice(0, 10)
+  return localDateString(date)
+}
+
+function localMidnightAfter(dateStr: string): Date {
+  const [y, m, d] = dateStr.split('-').map(Number)
+  return new Date(y!, m! - 1, d! + 1)
 }
 
 function getDateRange(period: string): { range: DateRange; label: string } {
@@ -35,12 +40,12 @@ function getDateRange(period: string): { range: DateRange; label: string } {
   switch (period) {
     case 'today': {
       const start = new Date(now.getFullYear(), now.getMonth(), now.getDate())
-      return { range: { start, end }, label: `Today (${start.toISOString().slice(0, 10)})` }
+      return { range: { start, end }, label: `Today (${toDateString(start)})` }
     }
     case 'yesterday': {
       const start = new Date(now.getFullYear(), now.getMonth(), now.getDate() - 1)
       const yesterdayEnd = new Date(now.getFullYear(), now.getMonth(), now.getDate() - 1, 23, 59, 59, 999)
-      return { range: { start, end: yesterdayEnd }, label: `Yesterday (${start.toISOString().slice(0, 10)})` }
+      return { range: { start, end: yesterdayEnd }, label: `Yesterday (${toDateString(start)})` }
     }
     case 'week': {
       const start = new Date(now.getFullYear(), now.getMonth(), now.getDate() - 7)
@@ -342,7 +347,7 @@ program
       const cache = await withDailyCacheLock(async () => {
         let c = await loadDailyCache()
         const gapStart = c.lastComputedDate
-          ? new Date(new Date(`${c.lastComputedDate}T00:00:00.000Z`).getTime() + MS_PER_DAY)
+          ? localMidnightAfter(c.lastComputedDate)
           : new Date(todayStart.getTime() - BACKFILL_DAYS * MS_PER_DAY)
 
         if (gapStart.getTime() <= yesterdayEnd.getTime()) {

src/daily-cache.ts

@@ -4,7 +4,7 @@ import { mkdir, open, readFile, rename, unlink } from 'fs/promises'
 import { homedir } from 'os'
 import { join } from 'path'
 
-export const DAILY_CACHE_VERSION = 2
+export const DAILY_CACHE_VERSION = 3
 const DAILY_CACHE_FILENAME = 'daily-cache.json'
 
 export type DailyEntry = {

src/day-aggregator.ts

@@ -1,4 +1,5 @@
 import type { DailyEntry } from './daily-cache.js'
+import { localDateString } from './format.js'
 import type { PeriodData } from './menubar-json.js'
 import { CATEGORY_LABELS, type ProjectSummary, type TaskCategory } from './types.js'
 
@@ -21,7 +22,7 @@ function emptyEntry(date: string): DailyEntry {
 }
 
 function dateKey(iso: string): string {
-  return iso.slice(0, 10)
+  return localDateString(new Date(iso))
 }
 
 export function aggregateProjectsIntoDays(projects: ProjectSummary[]): DailyEntry[] {

src/format.ts

@@ -17,7 +17,7 @@ export function formatTokens(n: number): string {
 /// out to Intl.DateTimeFormat for every turn in a loop and avoids the UTC drift that bites
 /// `Date.toISOString().slice(0,10)` whenever the user runs this between local midnight and
 /// UTC midnight.
-function localDateString(d: Date): string {
+export function localDateString(d: Date): string {
   const y = d.getFullYear()
   const m = String(d.getMonth() + 1).padStart(2, '0')
   const day = String(d.getDate()).padStart(2, '0')

tests/day-aggregator.test.ts

@@ -135,8 +135,8 @@ describe('aggregateProjectsIntoDays', () => {
         sessions: [{
           sessionId: 's1',
           project: 'p',
-          firstTimestamp: '2026-04-09T23:59:00Z',
-          lastTimestamp: '2026-04-10T00:10:00Z',
+          firstTimestamp: new Date(2026, 3, 9, 23, 59).toISOString(),
+          lastTimestamp: new Date(2026, 3, 10, 0, 10).toISOString(),
           totalCostUSD: 1,
           totalInputTokens: 0, totalOutputTokens: 0, totalCacheReadTokens: 0, totalCacheWriteTokens: 0,
           apiCalls: 0,