fix: keep all-day events all-day on Stalwart 0.16

src/api/__tests__/calendar.test.ts

@@ -251,7 +251,8 @@ describe('calendar operations', () => {
         id: 's1', baseEventId: 'base', recurrenceId: '2026-03-02', start: '2026-03-02T00:00:00',
         timeZone: 'Europe/Berlin', title: 'Daily',
       } as any;
-      const single = { id: 's9', baseEventId: 'other', start: '2026-03-02T09:00:00', title: 'Once' } as any;
+      // Stalwart 1.0 returns a one-off event under its own id.
+      const single = { id: 's9', baseEventId: null, start: '2026-03-02T09:00:00', title: 'Once' } as any;
 
       const [hydrated, untouched] = await hydrateExpandedOccurrences([occurrence, single]);
 
@@ -267,10 +268,40 @@ describe('calendar operations', () => {
     });
 
     it('skips the round trip when nothing recurs', async () => {
-      const single = { id: 's9', baseEventId: 'other', start: '2026-03-02T09:00:00' } as any;
-      expect(await hydrateExpandedOccurrences([single])).toEqual([single]);
+      const single = { id: 's9', baseEventId: null, start: '2026-03-02T09:00:00' } as any;
+      const own = { id: 'd', baseEventId: 'd', start: '2026-03-02T09:00:00' } as any;
+      expect(await hydrateExpandedOccurrences([single, own])).toEqual([single, own]);
       expect(mockRequest).not.toHaveBeenCalled();
     });
+
+    // Stalwart 0.16 hands a one-off event out under a synthetic id, with no
+    // recurrenceId and no showWithoutTime, in the query's time zone: the
+    // all-day "Company holiday" read as 00:00 to 00:00.
+    it('gives a one-off all-day event under a synthetic id its all-day flag back', async () => {
+      mockRequest.mockResolvedValue({
+        methodResponses: [['CalendarEvent/get', {
+          list: [
+            { id: 'c', showWithoutTime: true, duration: 'P1D' },
+            { id: 'd', timeZone: 'Europe/Berlin', duration: 'PT1H' },
+          ],
+        }, '0']],
+      });
+      const holiday = {
+        id: 'h1pceeaaaaac', baseEventId: 'c', '@type': 'Event', title: 'Company holiday',
+        start: '2026-11-01T00:00:00', duration: 'P1D', timeZone: 'Europe/Berlin',
+        utcStart: '2026-10-31T23:00:00Z', utcEnd: '2026-11-01T23:00:00Z',
+      } as any;
+      const review = {
+        id: 'h1pceeaaaaad', baseEventId: 'd', start: '2026-11-01T14:00:00', duration: 'PT1H', timeZone: 'Europe/Berlin',
+      } as any;
+
+      const [allDay, timed] = await hydrateExpandedOccurrences([holiday, review]);
+
+      expect(mockRequest.mock.calls[0][0][0][1]).toMatchObject({ ids: ['c', 'd'] });
+      expect(allDay).toMatchObject({ id: 'h1pceeaaaaac', showWithoutTime: true, timeZone: null, start: '2026-11-01T00:00:00' });
+      expect(allDay.recurrenceRules).toBeUndefined();
+      expect(timed).toBe(review);
+    });
   });
 
   describe('getEvents for expanded occurrences', () => {

src/api/__tests__/live-stalwart-calendar.test.ts

@@ -937,6 +937,28 @@ live('live Stalwart calendar', () => {
     }, 60_000);
   });
 
+  describe('an all-day event', () => {
+    // 0.16 expands a one-off event to a synthetic id without showWithoutTime;
+    // the detail sheet then said 00:00 - 00:00 and the editor's switch was off.
+    it('stays all-day on the calendar and in the editor', async () => {
+      await connectSingleton();
+      const created = await createEvent({
+        '@type': 'Event',
+        title: `${RUN} all day`,
+        start: '2027-11-10T00:00:00',
+        duration: 'P1D',
+        showWithoutTime: true,
+      } as Partial<CalendarEvent>, calendarId, false);
+      const uid = created.uid ?? (await getEvents([created.id]))[0].uid!;
+      const [event] = await loadOccurrences(uid, '2027-11-08T00:00:00Z', '2027-11-15T00:00:00Z');
+      expect(event, 'the event is on the calendar').toBeTruthy();
+      expect(event.showWithoutTime).toBe(true);
+      expect(event.timeZone ?? null).toBeNull();
+      expect(editorTimesFromEvent(event).allDay).toBe(true);
+      expect(getEventStartDate(event).getDate()).toBe(10);
+    }, 60_000);
+  });
+
   describe('a subscribed feed', () => {
     const FEED_URL = 'https://feeds.invalid/live.ics';
     let feed = '';

src/api/calendar.ts

@@ -865,7 +865,10 @@ async function queryExpandedRange(
  * rule / overrides (and all-day ones without showWithoutTime). Fetch those
  * from the base events in one batched get and merge them in, so an
  * occurrence carries the same series context the device-side expansion
- * copies from its master.
+ * copies from its master. Stalwart 0.16 also hands a one-off event out
+ * under a synthetic id, without a recurrenceId and without
+ * showWithoutTime: an all-day one would read as 00:00 to 00:00, so its base
+ * is fetched as well.
  */
 export async function hydrateExpandedOccurrences(
   events: CalendarEvent[],
@@ -873,7 +876,7 @@ export async function hydrateExpandedOccurrences(
 ): Promise<CalendarEvent[]> {
   const baseIds = Array.from(new Set(
     events
-      .filter((event) => isServerRecurrenceInstance(event) && event.recurrenceId)
+      .filter((event) => isServerRecurrenceInstance(event))
       .map((event) => event.baseEventId as string),
   ));
   if (baseIds.length === 0) return events;

src/lib/recurrence-instances.ts

@@ -349,9 +349,16 @@ export function hydrateRecurrenceInstances(
   bases: ReadonlyMap<string, Partial<CalendarEvent>>,
 ): CalendarEvent[] {
   return collapseDuplicateInstances(instances, bases).map((instance) => {
-    if (!isServerRecurrenceInstance(instance) || !instance.recurrenceId) return instance;
+    if (!isServerRecurrenceInstance(instance)) return instance;
     const base = instance.baseEventId ? bases.get(instance.baseEventId) : undefined;
     if (!base) return instance;
+    // Stalwart 0.16 expands a one-off event to a synthetic id too, without
+    // a recurrenceId and without showWithoutTime, in the query's time zone.
+    if (!instance.recurrenceId) {
+      return base.showWithoutTime
+        ? { ...instance, showWithoutTime: true, timeZone: base.timeZone ?? null }
+        : instance;
+    }
 
     const hydrated: CalendarEvent = {
       ...instance,