fix: show zero-length events ending at their start instead of midnight #837

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

@@ -84,4 +84,36 @@ describe('calendar event normalization', () => {
       expect(result.excludedRecurrenceRules).toEqual([{ '@type': 'RecurrenceRule', frequency: 'daily' }]);
     });
   });
-});
+
+  describe('zero-duration timed events (#837)', () => {
+    // Stalwart drops a DTEND equal to DTSTART and returns no duration, but a
+    // utcEnd at 23:59:59 of the start day.
+    const fromServer = {
+      start: '2026-09-30T10:00:00',
+      timeZone: 'Etc/UTC',
+      showWithoutTime: false,
+      utcStart: '2026-09-30T10:00:00Z',
+      utcEnd: '2026-09-30T23:59:59Z',
+    } as Partial<CalendarEvent>;
+
+    it('ends a server event without a duration at its start', () => {
+      expect(normalizeCalendarEventLike(fromServer)).toMatchObject({
+        duration: 'PT0S',
+        utcEnd: '2026-09-30T10:00:00Z',
+      });
+    });
+
+    it('keeps the end of a server event that has a duration', () => {
+      const event = { ...fromServer, duration: 'PT8H', utcEnd: '2026-09-30T18:00:00Z' };
+      expect(normalizeCalendarEventLike(event)).toMatchObject({
+        duration: 'PT8H',
+        utcEnd: '2026-09-30T18:00:00Z',
+      });
+    });
+
+    it('leaves update patches without a duration alone', () => {
+      const patch = { start: '2026-09-30T11:00:00' } as Partial<CalendarEvent>;
+      expect(sanitizeOutgoingCalendarEventData(patch)).not.toHaveProperty('duration');
+    });
+  });
+});

lib/__tests__/calendar-invitation.test.ts

@@ -344,6 +344,7 @@ describe('formatEventSummary', () => {
       utcStart: '2026-02-17T15:00:00Z',
       utcEnd: '2026-02-17T16:00:00Z',
       start: '2026-02-17T10:00:00',
+      duration: 'PT1H',
     });
     expect(summary.start).toBe('2026-02-17T15:00:00Z');
     expect(summary.end).toBe('2026-02-17T16:00:00Z');

lib/calendar-event-normalization.ts

@@ -113,12 +113,25 @@ function normalizeStalwartPropertyNames<T extends Partial<CalendarEvent>>(event:
   return result;
 }
 
+/**
+ * A timed event without a duration lasts zero seconds (RFC 8984 default
+ * PT0S). Stalwart drops a DTEND equal to DTSTART and then ends such an
+ * event at 23:59:59 of its start day, so its utcEnd is wrong. Only server
+ * objects carry utcStart, which keeps partial update patches untouched. (#837)
+ */
+function withZeroDurationEnd<T extends Partial<CalendarEvent>>(event: T): T {
+  if (event.showWithoutTime || event.duration || !event.start || !event.utcStart) {
+    return event;
+  }
+  return { ...event, duration: 'PT0S', utcEnd: event.utcStart } as T;
+}
+
 export function normalizeCalendarEventLike<T extends Partial<CalendarEvent>>(event: T): T {
   // First normalize Stalwart's singular property names to RFC 8984 plural forms
   const normalized = normalizeStalwartPropertyNames(event);
 
   if (!isAllDayEventLike(normalized)) {
-    return normalized;
+    return withZeroDurationEnd(normalized);
   }
 
   return {

stores/__tests__/calendar-store-event-hooks.test.ts

@@ -275,3 +275,19 @@ describe('importEvents hooks', () => {
     expect(after).not.toHaveBeenCalled();
   });
 });
+
+describe('importEvents zero-duration events (#837)', () => {
+  it('sends an explicit zero duration for a timed event without one', async () => {
+    const client = fakeClient();
+    // CalendarEvent/parse of DTSTART == DTEND returns no duration.
+    const parsed = [
+      { uid: 'ci', title: 'C/I', start: '2026-09-30T10:00:00', timeZone: 'Etc/UTC' },
+      { uid: 'sb', title: 'Standby', start: '2026-09-30T10:00:00', timeZone: 'Etc/UTC', duration: 'PT8H' },
+    ] as Partial<CalendarEvent>[];
+
+    await useCalendarStore.getState().importEvents(client, parsed, 'c1');
+
+    const batch = vi.mocked(client.batchCreateCalendarEvents).mock.calls[0][0];
+    expect(batch.map((e) => e.duration)).toEqual(['PT0S', 'PT8H']);
+  });
+});

stores/calendar-store.ts

@@ -1909,7 +1909,10 @@ async function importEventsUnhooked(
       description: src.description,
       descriptionContentType: src.descriptionContentType,
       start: src.start,
-      duration: src.showWithoutTime ? normalizeAllDayDuration(src.duration) : src.duration,
+      // CalendarEvent/parse drops a DTEND equal to DTSTART; without an
+      // explicit zero duration Stalwart stores the event ending at
+      // 23:59:59 of its start day. (#837)
+      duration: src.showWithoutTime ? normalizeAllDayDuration(src.duration) : (src.duration || 'PT0S'),
       timeZone: src.showWithoutTime ? null : src.timeZone,
       showWithoutTime: src.showWithoutTime,
       status: src.status,