feat: add calendar event normalization and sanitization functions with tests

lib/__tests__/calendar-event-normalization.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it } from 'vitest';
+import type { CalendarEvent } from '@/lib/jmap/types';
+import {
+  isAllDayEventLike,
+  normalizeCalendarEventLike,
+  sanitizeOutgoingCalendarEventData,
+} from '../calendar-event-normalization';
+
+function makeEvent(overrides: Partial<CalendarEvent> = {}): Partial<CalendarEvent> {
+  return {
+    start: '2026-03-16T00:00:00',
+    duration: 'PT24H',
+    showWithoutTime: false,
+    timeZone: null,
+    ...overrides,
+  };
+}
+
+describe('calendar event normalization', () => {
+  it('infers all-day events from midnight-to-midnight spans without the flag', () => {
+    expect(isAllDayEventLike(makeEvent())).toBe(true);
+  });
+
+  it('does not infer all-day for midnight events with non-day durations', () => {
+    expect(isAllDayEventLike(makeEvent({ duration: 'PT12H' }))).toBe(false);
+  });
+
+  it('normalizes inferred all-day durations to day units', () => {
+    expect(normalizeCalendarEventLike(makeEvent({ duration: 'PT48H' }))).toMatchObject({
+      showWithoutTime: true,
+      duration: 'P2D',
+    });
+  });
+
+  it('sanitizes outgoing all-day starts to date-only values', () => {
+    expect(sanitizeOutgoingCalendarEventData(makeEvent({
+      showWithoutTime: true,
+      start: '2026-03-16T00:00:00',
+      duration: 'PT24H',
+      timeZone: 'UTC',
+    }))).toMatchObject({
+      start: '2026-03-16',
+      duration: 'P1D',
+      timeZone: null,
+      showWithoutTime: true,
+    });
+  });
+});