fix(test): make day-bucketing tests timezone-hermetic (bug c0f5e80d) (#7)

exe-watcher buckets usage by the user's LOCAL calendar day
(day-aggregator formatDate / plan-usage dayKey use getFullYear/
getMonth/getDate). Four tests hardcoded UTC "Z" timestamps and asserted
fixed date strings, so a timestamp that is midday in UTC lands on the
other side of local midnight in far timezones — the assertions read the
runner's timezone, not the code. They passed on UTC CI runners and broke
for anyone at UTC+14 (Pacific/Kiritimati) or UTC-12 (Etc/GMT+12):

  tests/day-aggregator.test.ts  "buckets api calls by calendar date..."
  tests/day-aggregator.test.ts  "counts a session under its firstTimestamp local date"
  tests/e2e-pipeline.test.ts     "aggregates project sessions into daily entries..."
  tests/plan-usage.test.ts       "projects using median daily spend (not mean)"

The production code is correct; the assertions were stale. Fixes, test-only:
- day-aggregator/e2e: derive expected dates from the production dateKey()
  formatter, and choose timestamps (same instant, or exactly 24h apart at
  noon) so the day structure is identical in every timezone.
- plan-usage: build the fixture timestamps and `now` from local-noon
  Date(year, monthIndex, day, 12) so day-of-month is deterministic.

No src/ change. Full suite: 598 passed under TZ=UTC, Pacific/Kiritimati
(UTC+14) and Etc/GMT+12 (UTC-12); tsc --noEmit and tsup build clean.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: henrylove0

tests/day-aggregator.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
-import { aggregateProjectsIntoDays, buildPeriodDataFromDays } from '../src/day-aggregator.js'
+import { aggregateProjectsIntoDays, buildPeriodDataFromDays, dateKey } from '../src/day-aggregator.js'
 import type { ProjectSummary } from '../src/types.js'
 
 function makeProject(overrides: Partial<ProjectSummary> & { sessions: ProjectSummary['sessions'] }): ProjectSummary {
@@ -45,8 +45,8 @@ describe('aggregateProjectsIntoDays', () => {
         sessions: [{
           sessionId: 's1',
           project: 'p',
-          firstTimestamp: '2026-04-09T10:00:00Z',
-          lastTimestamp: '2026-04-10T08:00:00Z',
+          firstTimestamp: '2026-04-09T12:00:00Z',
+          lastTimestamp: '2026-04-10T12:00:00Z',
           totalCostUSD: 10,
           totalInputTokens: 0,
           totalOutputTokens: 0,
@@ -56,14 +56,14 @@ describe('aggregateProjectsIntoDays', () => {
           turns: [
             {
               userMessage: 'hi',
-              timestamp: '2026-04-09T10:00:00Z',
+              timestamp: '2026-04-09T12:00:00Z',
               sessionId: 's1',
               category: 'coding',
               retries: 0,
               hasEdits: true,
               assistantCalls: [
-                makeCall('2026-04-09T10:00:00Z', 4),
-                makeCall('2026-04-10T08:00:00Z', 6),
+                makeCall('2026-04-09T12:00:00Z', 4),
+                makeCall('2026-04-10T12:00:00Z', 6),
               ],
             },
           ],
@@ -77,7 +77,7 @@ describe('aggregateProjectsIntoDays', () => {
     ]
 
     const days = aggregateProjectsIntoDays(projects)
-    expect(days.map(d => d.date)).toEqual(['2026-04-09', '2026-04-10'])
+    expect(days.map(d => d.date)).toEqual([dateKey('2026-04-09T12:00:00Z'), dateKey('2026-04-10T12:00:00Z')])
     expect(days[0]!.cost).toBe(4)
     expect(days[0]!.calls).toBe(1)
     expect(days[1]!.cost).toBe(6)
@@ -130,7 +130,7 @@ describe('aggregateProjectsIntoDays', () => {
   })
 
   it('counts a session under its firstTimestamp local date', () => {
-    // Use a midday timestamp so the local date is the same regardless of timezone
+    // Derive the expected date from the production formatter (dateKey) so this holds in any timezone
     const projects: ProjectSummary[] = [
       makeProject({
         sessions: [{
@@ -148,7 +148,7 @@ describe('aggregateProjectsIntoDays', () => {
       }),
     ]
     const days = aggregateProjectsIntoDays(projects)
-    expect(days[0]!.date).toBe('2026-04-09')
+    expect(days[0]!.date).toBe(dateKey('2026-04-09T12:00:00Z'))
     expect(days[0]!.sessions).toBe(1)
   })
 

tests/e2e-pipeline.test.ts

@@ -3,7 +3,7 @@ import { mkdtemp, readFile, readdir, rm } from 'fs/promises'
 import { join } from 'path'
 import { tmpdir } from 'os'
 
-import { aggregateProjectsIntoDays, buildPeriodDataFromDays } from '../src/day-aggregator.js'
+import { aggregateProjectsIntoDays, buildPeriodDataFromDays, dateKey } from '../src/day-aggregator.js'
 import { exportCsv, exportJson, type PeriodExport } from '../src/export.js'
 import { buildMenubarPayload, type PeriodData, type ProviderCost } from '../src/menubar-json.js'
 import {
@@ -178,11 +178,11 @@ afterEach(async () => {
 describe('Parse -> Aggregate -> PeriodData pipeline', () => {
   it('aggregates project sessions into daily entries and builds correct PeriodData', () => {
     const turns1 = [
-      makeTurn('2026-04-20T10:00:00Z', 5.0, { category: 'building', hasEdits: true }),
-      makeTurn('2026-04-20T14:00:00Z', 3.0, { category: 'debugging', hasEdits: true, retries: 1 }),
+      makeTurn('2026-04-20T12:00:00Z', 5.0, { category: 'building', hasEdits: true }),
+      makeTurn('2026-04-20T12:00:00Z', 3.0, { category: 'debugging', hasEdits: true, retries: 1 }),
     ]
     const turns2 = [
-      makeTurn('2026-04-21T09:00:00Z', 7.0, { category: 'building', model: 'gpt-5', provider: 'codex' }),
+      makeTurn('2026-04-21T12:00:00Z', 7.0, { category: 'building', model: 'gpt-5', provider: 'codex' }),
     ]
 
     const sess1 = makeSession('sess-1', '/proj/alpha', turns1)
@@ -192,8 +192,8 @@ describe('Parse -> Aggregate -> PeriodData pipeline', () => {
     const days = aggregateProjectsIntoDays([project])
 
     expect(days).toHaveLength(2)
-    expect(days[0]!.date).toBe('2026-04-20')
-    expect(days[1]!.date).toBe('2026-04-21')
+    expect(days[0]!.date).toBe(dateKey('2026-04-20T12:00:00Z'))
+    expect(days[1]!.date).toBe(dateKey('2026-04-21T12:00:00Z'))
 
     expect(days[0]!.cost).toBe(8)
     expect(days[0]!.calls).toBe(2)

tests/plan-usage.test.ts

@@ -67,7 +67,7 @@ describe('getPlanUsage', () => {
   it('projects using median daily spend (not mean)', async () => {
     const dailyCosts = [1, 100, 1, 100, 1, 100, 1]
     const turns = dailyCosts.map((cost, idx) => ({
-      timestamp: `2026-04-${String(idx + 1).padStart(2, '0')}T12:00:00.000Z`,
+      timestamp: new Date(2026, 3, idx + 1, 12, 0, 0).toISOString(),
       assistantCalls: [{ costUSD: cost }],
     }))
 
@@ -84,7 +84,7 @@ describe('getPlanUsage', () => {
       provider: 'all',
       resetDay: 1,
       setAt: '2026-04-01T00:00:00.000Z',
-    }, new Date('2026-04-07T12:00:00.000Z'))
+    }, new Date(2026, 3, 7, 12, 0, 0))
 
     // Median(1,100,1,100,1,100,1) = 1, so remaining 23 days adds 23.
     expect(Math.round(usage.projectedMonthUsd)).toBe(327)