feat: duplicate, share as .ics and copy the meeting link of an event; link imported UIDs instead of skipping them (#113)

docs/parity/05-calendar.md

@@ -37,7 +37,7 @@ RN has a solid read path (month/week/agenda, shared-calendar namespacing, per-vi
   - What RN does: `handleSave` emits `undefined` for cleared fields (`recurrenceRules: undefined`, `participants: undefined`, `alerts: remindersToAlerts([]) === undefined`, `locations: undefined`) which JSON serialisation drops, so the server keeps the old value (ref `src/components/calendar/EventModal.tsx:262-281`, `src/lib/calendar-alerts.ts:72-73`). Setting "Does not repeat" on a recurring event, removing all attendees, deleting the last reminder or clearing the location silently does nothing.
   - Fix hint: in edit mode compare against `event` and send `null` for fields that existed and are now empty; RN's `cleanRecurrenceRules` already turns `[]`/`null` into `recurrenceRule: null` (`src/api/calendar.ts:115-118`), so `recurrenceRules: []` works today for recurrence.
 
-- [ ] **`this_and_future` / huge-span RRULE (#735) — RN not affected** — `P3` — `bugfix-parity`
+- [x] **`this_and_future` / huge-span RRULE (#735) — RN not affected** — `P3` — `bugfix-parity` — verified, nothing to fix (caps already in place; "this and following" truncates with `until` and drops `count`)
   - What WEB does: memory note on #735 (Stalwart u32 overflow for spans > 136 years). WEB's editor caps `until` to a picked date and `count` to 999.
   - What RN does: same caps (`src/lib/recurrence.ts:227-229`, `RecurrenceEditor.tsx:139-144, 244-249`), no alarms with absolute triggers far in the future. Not affected; noted so it isn't re-investigated.
 
@@ -265,7 +265,7 @@ RN has a solid read path (month/week/agenda, shared-calendar namespacing, per-vi
 
 ### Tasks
 
-- [ ] **Task sheet supports only title + due date; no edit, description, priority, due time, progress states, alerts, filters, "show on calendar"** — `P2` — `partial`
+- [x] **Task sheet supports only title + due date; no edit, description, priority, due time, progress states, alerts, filters, "show on calendar"** — `P2` — `partial` — fixed in 09c24fa (edit, description, priority, due date + time, calendar move, all/pending/completed/overdue filters, overdue-first sort, `needs-action` <-> `completed` with `progressUpdated`, due tasks overlaid on the grid; task alerts still come only from the server data)
   - What WEB does: task modal with description, due date + optional time, priority (none/high/medium/low -> 1-9), progress, calendar, alert; list filters all/pending/completed/overdue, overdue-first sort, `showTasksOnCalendar` overlays due tasks on the grid; completion toggles `needs-action` <-> `completed` with `progressUpdated` (ref `components/calendar/task-modal.tsx:55-140`, `task-list-view.tsx:80-110`, `stores/task-store.ts:366, 442-452`).
   - What RN does: `TasksSheet` creates `{ title, progress, due }` only, no tap-to-edit, delete + toggle only (`src/components/calendar/TasksSheet.tsx:117-135, 210-235`); un-completing sets `in-process` (`src/stores/calendar-store.ts:418-426`); `showTasksOnCalendar` (`settings-store.ts:174`) is unused; tasks are never drawn in month/week/agenda.
   - Fix hint: add a task edit sheet mirroring `task-modal.tsx`, filter chips, and render due tasks as all-day chips when `showTasksOnCalendar`.

locales/en/common.json

@@ -2763,7 +2763,9 @@
       "new_all_day_event": "New all-day event",
       "new_task": "New task",
       "go_to_today": "Go to today",
-      "tap_to_create": "Tap + to create one"
+      "tap_to_create": "Tap + to create one",
+      "export_ics_short": ".ics",
+      "copy_link_short": "Link"
     },
     "detail": {
       "add_note": "Add a note...",

src/components/calendar/EventDetailSheet.tsx

@@ -21,8 +21,10 @@ import {
   Copy,
   HelpCircle,
   MapPin,
+  Link2,
   Pencil,
   Repeat,
+  Share2,
   Trash2,
   Users,
   Video,
@@ -64,6 +66,9 @@ interface EventDetailSheetProps {
   onEdit?: (event: CalendarEvent) => void;
   onDelete?: (event: CalendarEvent) => void;
   onDuplicate?: (event: CalendarEvent) => void;
+  onExport?: (event: CalendarEvent) => void;
+  // Copy the meeting link; only offered when the event has one.
+  onCopyLink?: (event: CalendarEvent, link: string) => void;
   onRsvp?: (event: CalendarEvent, participantId: string, status: RsvpStatus) => void | Promise<void>;
 }
 
@@ -130,6 +135,8 @@ export function EventDetailSheet({
   onEdit,
   onDelete,
   onDuplicate,
+  onExport,
+  onCopyLink,
   onRsvp,
 }: EventDetailSheetProps) {
   const c = useColors();
@@ -367,7 +374,7 @@ export function EventDetailSheet({
             )}
           </ScrollView>
 
-          {(canEdit || onDuplicate) && (
+          {(canEdit || onDuplicate || onExport || (onCopyLink && videoUri)) && (
             <View style={styles.actions}>
               {onEdit && canEdit && (
                 <ActionButton
@@ -383,6 +390,20 @@ export function EventDetailSheet({
                   onPress={() => onDuplicate(event)}
                 />
               )}
+              {onExport && (
+                <ActionButton
+                  icon={<Share2 size={18} color={c.text} />}
+                  label={t('calendar.events.export_ics_short', '.ics')}
+                  onPress={() => onExport(event)}
+                />
+              )}
+              {onCopyLink && videoUri && (
+                <ActionButton
+                  icon={<Link2 size={18} color={c.text} />}
+                  label={t('calendar.events.copy_link_short', 'Link')}
+                  onPress={() => onCopyLink(event, videoUri)}
+                />
+              )}
               {onDelete && canEdit && (
                 <ActionButton
                   icon={<Trash2 size={18} color={c.error} />}

src/lib/__tests__/calendar-ics-export.test.ts

@@ -0,0 +1,65 @@
+import { describe, it, expect } from 'vitest';
+import type { CalendarEvent } from '../../api/types';
+import { eventToICS, getMeetingLink, icsFilename } from '../calendar-ics-export';
+
+const event: CalendarEvent = {
+  id: 'ev1',
+  uid: 'uid-1',
+  title: 'Team sync; weekly',
+  description: 'Line 1\nLine 2',
+  calendarIds: { 'cal-1': true },
+  start: '2026-03-02T09:00:00',
+  timeZone: 'Europe/Berlin',
+  utcEnd: '2026-03-02T08:30:00Z',
+  duration: 'PT30M',
+  status: 'confirmed',
+  organizerCalendarAddress: 'mailto:alice@example.com',
+  participants: {
+    a: { calendarAddress: 'mailto:alice@example.com', name: 'Alice' },
+    b: { calendarAddress: 'mailto:bob@example.com', name: 'Bob', roles: { attendee: true }, expectReply: true },
+  },
+  recurrenceRules: [{ frequency: 'weekly', interval: 2, byDay: [{ day: 'mo' }] }],
+  alerts: { r1: { trigger: { '@type': 'OffsetTrigger', offset: '-PT15M' }, action: 'display' } },
+  virtualLocations: { v: { uri: 'https://meet.example.com/abc' } },
+};
+
+describe('eventToICS', () => {
+  it('serialises a timed event with zone, organizer, attendees, rule and alarm', () => {
+    const ics = eventToICS(event);
+    expect(ics).toContain('BEGIN:VCALENDAR\r\n');
+    expect(ics).toContain('UID:uid-1');
+    expect(ics).toContain('DTSTART;TZID=Europe/Berlin:20260302T090000');
+    expect(ics).toContain('DTEND:20260302T083000Z');
+    expect(ics).toContain('SUMMARY:Team sync\\; weekly');
+    expect(ics).toContain('DESCRIPTION:Line 1\\nLine 2');
+    expect(ics).toContain('ORGANIZER;CN=Alice:mailto:alice@example.com');
+    expect(ics).toContain('ATTENDEE;CN=Bob;PARTSTAT=NEEDS-ACTION;RSVP=TRUE:mailto:bob@example.com');
+    expect(ics).not.toContain('ATTENDEE;CN=Alice');
+    expect(ics).toContain('RRULE:FREQ=WEEKLY;INTERVAL=2;BYDAY=MO');
+    expect(ics).toContain('BEGIN:VALARM\r\nACTION:DISPLAY\r\nTRIGGER:-PT15M');
+    expect(ics).toContain('URL:https://meet.example.com/abc');
+    expect(ics.endsWith('END:VCALENDAR\r\n')).toBe(true);
+  });
+
+  it('writes all-day events as DATE values with a duration', () => {
+    const ics = eventToICS({ ...event, showWithoutTime: true, start: '2026-03-02T00:00:00', duration: 'P2D', utcEnd: undefined });
+    expect(ics).toContain('DTSTART;VALUE=DATE:20260302');
+    expect(ics).toContain('DURATION:P2D');
+    expect(ics).not.toContain('DTEND');
+  });
+
+  it('folds long lines at 74 octets', () => {
+    const ics = eventToICS({ ...event, description: 'x'.repeat(200) });
+    const long = ics.split('\r\n').filter((l) => l.length > 75);
+    expect(long).toHaveLength(0);
+  });
+});
+
+describe('helpers', () => {
+  it('builds a safe filename and finds the meeting link', () => {
+    expect(icsFilename(event)).toBe('Team-sync-weekly.ics');
+    expect(icsFilename({ ...event, title: '' })).toBe('event.ics');
+    expect(getMeetingLink(event)).toBe('https://meet.example.com/abc');
+    expect(getMeetingLink({ virtualLocations: undefined })).toBeNull();
+  });
+});

src/lib/calendar-ics-export.ts

@@ -0,0 +1,210 @@
+import type { CalendarEvent } from '../api/types';
+
+// Port of the webmail's lib/calendar-ics-export.ts: serialise one event as
+// an RFC 5545 VCALENDAR so it can be shared as a .ics file.
+
+const MAX_LINE_OCTETS = 74;
+
+function foldLine(line: string): string {
+  if (line.length <= MAX_LINE_OCTETS) return line;
+  const chunks: string[] = [line.slice(0, MAX_LINE_OCTETS)];
+  let pos = MAX_LINE_OCTETS;
+  while (pos < line.length) {
+    chunks.push(' ' + line.slice(pos, pos + MAX_LINE_OCTETS - 1));
+    pos += MAX_LINE_OCTETS - 1;
+  }
+  return chunks.join('\r\n');
+}
+
+// RFC 5545 §3.3.11 - escape backslash, semicolon, comma, and newline in TEXT values.
+export function escapeText(value: string): string {
+  return value
+    .replace(/\\/g, '\\\\')
+    .replace(/;/g, '\\;')
+    .replace(/,/g, '\\,')
+    .replace(/\r\n|\r|\n/g, '\\n');
+}
+
+function stripDateSeparators(value: string): string {
+  return value.replace(/[-:]/g, '').replace(/\.\d{3}/, '');
+}
+
+function dateOnly(value: string): string {
+  return value.replace(/-/g, '').substring(0, 8);
+}
+
+function formatNow(): string {
+  return stripDateSeparators(new Date().toISOString().replace(/\.\d{3}/, ''));
+}
+
+function pushDateProp(
+  lines: string[],
+  prop: 'DTSTART' | 'DTEND',
+  value: string,
+  showWithoutTime: boolean,
+  tz?: string | null,
+): void {
+  if (showWithoutTime) {
+    lines.push(`${prop};VALUE=DATE:${dateOnly(value)}`);
+    return;
+  }
+  if (value.endsWith('Z')) {
+    lines.push(`${prop}:${stripDateSeparators(value)}`);
+    return;
+  }
+  const basic = stripDateSeparators(value);
+  if (tz) {
+    lines.push(`${prop};TZID=${tz}:${basic}`);
+  } else {
+    lines.push(`${prop}:${basic}`);
+  }
+}
+
+function pushFrequencyRule(lines: string[], event: CalendarEvent): void {
+  const rule = event.recurrenceRules?.[0];
+  if (!rule) return;
+  const parts: string[] = [`FREQ=${rule.frequency.toUpperCase()}`];
+  if (rule.interval && rule.interval > 1) parts.push(`INTERVAL=${rule.interval}`);
+  if (rule.count != null) parts.push(`COUNT=${rule.count}`);
+  if (rule.until) parts.push(`UNTIL=${stripDateSeparators(rule.until)}`);
+  if (rule.byDay?.length) {
+    const days = rule.byDay
+      .map((d) => `${d.nthOfPeriod ?? ''}${d.day.toUpperCase()}`)
+      .join(',');
+    parts.push(`BYDAY=${days}`);
+  }
+  if (rule.byMonthDay?.length) parts.push(`BYMONTHDAY=${rule.byMonthDay.join(',')}`);
+  if (rule.byMonth?.length) parts.push(`BYMONTH=${rule.byMonth.join(',')}`);
+  lines.push(`RRULE:${parts.join(';')}`);
+}
+
+function pushAlerts(lines: string[], event: CalendarEvent): void {
+  if (!event.alerts) return;
+  for (const alert of Object.values(event.alerts)) {
+    const trigger = alert.trigger;
+    if (!trigger) continue;
+    lines.push('BEGIN:VALARM');
+    lines.push(`ACTION:${(alert.action || 'display').toUpperCase()}`);
+    if (trigger['@type'] === 'OffsetTrigger' && trigger.offset) {
+      const related = trigger.relativeTo === 'end' ? ';RELATED=END' : '';
+      lines.push(`TRIGGER${related}:${trigger.offset}`);
+    } else if (trigger['@type'] === 'AbsoluteTrigger' && trigger.when) {
+      lines.push(`TRIGGER;VALUE=DATE-TIME:${stripDateSeparators(trigger.when)}`);
+    }
+    lines.push(`DESCRIPTION:${escapeText(event.title || 'Reminder')}`);
+    lines.push('END:VALARM');
+  }
+}
+
+function participantEmail(p: { email?: string; calendarAddress?: string; sendTo?: Record<string, string> }): string | undefined {
+  return (
+    p.email
+    || p.calendarAddress?.replace(/^mailto:/i, '')
+    || p.sendTo?.imip?.replace(/^mailto:/i, '')
+  );
+}
+
+export function eventToICS(event: CalendarEvent): string {
+  const now = formatNow();
+  const lines: string[] = [
+    'BEGIN:VCALENDAR',
+    'PRODID:-//Bulwark Mobile//EN',
+    'VERSION:2.0',
+    'CALSCALE:GREGORIAN',
+    'METHOD:PUBLISH',
+    'BEGIN:VEVENT',
+    `UID:${event.uid}`,
+    `DTSTAMP:${now}`,
+  ];
+
+  if (event.created) lines.push(`CREATED:${stripDateSeparators(event.created)}`);
+  if (event.updated) lines.push(`LAST-MODIFIED:${stripDateSeparators(event.updated)}`);
+  if (event.sequence != null) lines.push(`SEQUENCE:${event.sequence}`);
+
+  const allDay = !!event.showWithoutTime;
+  if (event.start) {
+    pushDateProp(lines, 'DTSTART', event.start, allDay, event.timeZone);
+  }
+  if (event.utcEnd && !allDay) {
+    pushDateProp(lines, 'DTEND', event.utcEnd, allDay, event.timeZone);
+  } else if (event.duration) {
+    lines.push(`DURATION:${event.duration}`);
+  }
+
+  if (event.title) lines.push(`SUMMARY:${escapeText(event.title)}`);
+  if (event.description) lines.push(`DESCRIPTION:${escapeText(event.description)}`);
+  if (event.status) lines.push(`STATUS:${event.status.toUpperCase()}`);
+  if (event.freeBusyStatus) {
+    lines.push(`TRANSP:${event.freeBusyStatus === 'free' ? 'TRANSPARENT' : 'OPAQUE'}`);
+  }
+
+  if (event.locations) {
+    const first = Object.values(event.locations)[0];
+    if (first?.name) lines.push(`LOCATION:${escapeText(first.name)}`);
+  }
+  if (event.virtualLocations) {
+    for (const loc of Object.values(event.virtualLocations)) {
+      if (loc.uri) lines.push(`URL:${loc.uri}`);
+    }
+  }
+
+  if (event.participants) {
+    const organizerEmail = event.organizerCalendarAddress?.replace(/^mailto:/i, '').toLowerCase();
+    const organizer = Object.values(event.participants).find(
+      (p) => p.roles?.owner || (organizerEmail && participantEmail(p)?.toLowerCase() === organizerEmail),
+    );
+    const orgEmail = organizer ? participantEmail(organizer) : organizerEmail;
+    if (orgEmail) {
+      const cn = organizer?.name ? `;CN=${escapeText(organizer.name)}` : '';
+      lines.push(`ORGANIZER${cn}:mailto:${orgEmail}`);
+    }
+    for (const p of Object.values(event.participants)) {
+      if (p === organizer) continue;
+      const email = participantEmail(p);
+      if (!email) continue;
+      const cn = p.name ? `;CN=${escapeText(p.name)}` : '';
+      const partstat = p.participationStatus
+        ? `;PARTSTAT=${p.participationStatus.toUpperCase()}`
+        : ';PARTSTAT=NEEDS-ACTION';
+      const rsvp = p.expectReply ? ';RSVP=TRUE' : '';
+      lines.push(`ATTENDEE${cn}${partstat}${rsvp}:mailto:${email}`);
+    }
+  }
+
+  pushFrequencyRule(lines, event);
+  pushAlerts(lines, event);
+
+  lines.push('END:VEVENT');
+  lines.push('END:VCALENDAR');
+
+  return lines.map(foldLine).join('\r\n') + '\r\n';
+}
+
+export function icsFilename(event: CalendarEvent): string {
+  const base = (event.title || 'event').replace(/[^a-z0-9\-_ ]/gi, '').trim().replace(/\s+/g, '-');
+  return `${base.slice(0, 60) || 'event'}.ics`;
+}
+
+/** The first meeting link of an event, if any. */
+export function getMeetingLink(event: Pick<CalendarEvent, 'virtualLocations'>): string | null {
+  if (!event.virtualLocations) return null;
+  for (const loc of Object.values(event.virtualLocations)) {
+    if (loc.uri) return loc.uri;
+  }
+  return null;
+}
+
+/** Write the .ics to the cache directory and open the OS share sheet. */
+export async function shareEventICS(event: CalendarEvent): Promise<void> {
+  const [{ File, Paths }, Sharing] = await Promise.all([
+    import('expo-file-system'),
+    import('expo-sharing'),
+  ]);
+  const file = new File(Paths.cache, icsFilename(event));
+  if (file.exists) file.delete();
+  file.write(eventToICS(event));
+  if (!(await Sharing.isAvailableAsync())) {
+    throw new Error('Sharing is not available on this device');
+  }
+  await Sharing.shareAsync(file.uri, { mimeType: 'text/calendar', UTI: 'com.apple.ical.ics' });
+}

src/screens/CalendarScreen.tsx

@@ -61,6 +61,7 @@ import {
   applySharedCalendarColors,
   buildEventDayIndex,
   eventsOnDayFromIndex,
+  getEventStartDate,
   getPrimaryCalendarId,
   pickUnusedCalendarColor,
   sharedCalendarColorKey,
@@ -81,6 +82,8 @@ import { useLocaleStore } from '../stores/locale-store';
 import { useUserCalendarAddresses } from '../lib/calendar-user-addresses';
 import { useCalendarSubscriptionsStore } from '../stores/calendar-subscriptions-store';
 import { startCalendarNotificationSync } from '../lib/calendar-notifications';
+import { shareEventICS } from '../lib/calendar-ics-export';
+import * as Clipboard from 'expo-clipboard';
 import type { Calendar, CalendarEvent, RecurrenceRule } from '../api/types';
 
 type ViewMode = 'month' | 'week' | 'agenda';
@@ -594,6 +597,54 @@ export default function CalendarScreen() {
     [t],
   );
 
+  // Clone the event one day later and open it in the editor (webmail's
+  // handleDuplicateFromDetail).
+  const handleDuplicateFromDetail = React.useCallback(
+    async (event: CalendarEvent) => {
+      setDetailEvent(null);
+      const newStart = addDays(getEventStartDate(event), 1);
+      const data: Partial<CalendarEvent> = {
+        title: event.title,
+        description: event.description,
+        start: event.showWithoutTime
+          ? format(newStart, "yyyy-MM-dd'T'00:00:00")
+          : format(newStart, "yyyy-MM-dd'T'HH:mm:ss"),
+        duration: event.duration,
+        timeZone: event.timeZone,
+        showWithoutTime: event.showWithoutTime,
+        status: 'confirmed',
+        freeBusyStatus: event.freeBusyStatus,
+      };
+      if (event.locations) data.locations = JSON.parse(JSON.stringify(event.locations));
+      if (event.virtualLocations) data.virtualLocations = JSON.parse(JSON.stringify(event.virtualLocations));
+      if (event.recurrenceRules?.length) data.recurrenceRules = JSON.parse(JSON.stringify(event.recurrenceRules));
+      if (event.alerts) data.alerts = JSON.parse(JSON.stringify(event.alerts));
+      const calendarId = getPrimaryCalendarId(event) || '';
+      try {
+        const created = await createEvent(data, calendarId);
+        const stored = useCalendarStore.getState().events.find((e) => e.id === created.id) ?? created;
+        openEditDirect(stored);
+      } catch (err) {
+        reportError(err);
+      }
+    },
+    [createEvent, openEditDirect, reportError],
+  );
+
+  const handleExportFromDetail = React.useCallback(
+    (event: CalendarEvent) => {
+      shareEventICS(event).catch(reportError);
+    },
+    [reportError],
+  );
+
+  const handleCopyLink = React.useCallback(
+    (_event: CalendarEvent, link: string) => {
+      Clipboard.setStringAsync(link).catch(reportError);
+    },
+    [reportError],
+  );
+
   const handleCalendarEditSave = React.useCallback(
     async (values: CalendarEditValues) => {
       if (!calendarEditTarget) return;
@@ -809,6 +860,9 @@ export default function CalendarScreen() {
         onClose={() => setDetailEvent(null)}
         onEdit={handleEditFromDetail}
         onDelete={handleDeleteFromDetail}
+        onDuplicate={(ev) => { if (!isReadOnlyEvent(ev)) void handleDuplicateFromDetail(ev); }}
+        onExport={handleExportFromDetail}
+        onCopyLink={handleCopyLink}
         onRsvp={async (ev, participantId, status) => {
           await rsvpEvent(ev.id, participantId, status, buildReplyTo(ev));
           setDetailEvent((cur) =>

src/stores/__tests__/calendar-store.test.ts

@@ -11,6 +11,7 @@ vi.mock('../../api/calendar', () => ({
   createEvent: vi.fn(),
   updateEvent: vi.fn(),
   deleteEvents: vi.fn(),
+  batchCreateEvents: vi.fn(),
   setDefaultCalendar: vi.fn(),
 }));
 
@@ -538,6 +539,46 @@ describe('calendar-store', () => {
     });
   });
 
+  describe('importEvents', () => {
+    it('links UIDs that exist in another calendar instead of skipping them and whitelists properties (#113)', async () => {
+      useCalendarStore.setState({
+        calendars: [{ id: 'cal-1' }, { id: 'cal-2' }] as any,
+        loadedRange: { after: '2026-03-01T00:00:00Z', before: '2026-03-31T00:00:00Z' },
+      });
+      mockQueryEvents.mockResolvedValue(['e1', 'e2']);
+      mockGetEvents.mockResolvedValue([
+        { id: 'e1', uid: 'uid-elsewhere', calendarIds: { 'cal-1': true } },
+        { id: 'e2', uid: 'uid-here', calendarIds: { 'cal-2': true } },
+      ]);
+      mockUpdateEvent.mockResolvedValue(undefined);
+      const batch = calendarApi.batchCreateEvents as ReturnType<typeof vi.fn>;
+      batch.mockResolvedValue(1);
+
+      const count = await useCalendarStore.getState().importEvents(
+        [
+          { uid: 'uid-elsewhere', title: 'Linked', start: '2026-03-02T09:00:00' },
+          { uid: 'uid-here', title: 'Dup', start: '2026-03-02T09:00:00' },
+          {
+            uid: 'uid-new', title: 'New', start: '2026-03-03T00:00:00', showWithoutTime: true,
+            duration: 'PT23H59M59S', timeZone: 'Europe/Berlin', utcStart: '2026-03-03T00:00:00Z',
+            participants: { p: { email: 'x@y', sendTo: { imip: 'mailto:x@y' }, roles: { attendee: true } } },
+          } as any,
+        ],
+        'cal-2',
+      );
+
+      // The UID in cal-1 is linked into cal-2; the one already in cal-2 is skipped.
+      expect(mockUpdateEvent).toHaveBeenCalledWith('e1', { calendarIds: { 'cal-1': true, 'cal-2': true } }, undefined, undefined);
+      expect(count).toBe(2);
+      const created = batch.mock.calls[0][0][0];
+      expect(created.duration).toBe('P1D');
+      expect(created.timeZone).toBeUndefined();
+      expect(created.utcStart).toBeUndefined();
+      expect(created.participants.p.calendarAddress).toBe('mailto:x@y');
+      expect(created.participants.p.sendTo).toBeUndefined();
+    });
+  });
+
   describe('recurring series mutations', () => {
     it('updateEvent on an occurrence patches the master and refetches the range', async () => {
       useCalendarStore.setState({

src/stores/calendar-store.ts

@@ -1,7 +1,8 @@
 import { create } from 'zustand';
 import { persist, createJSONStorage } from 'zustand/middleware';
 import AsyncStorage from '@react-native-async-storage/async-storage';
-import type { Calendar, CalendarEvent, CalendarRights, StateChange } from '../api/types';
+import type { Calendar, CalendarEvent, CalendarRights, Participant, StateChange } from '../api/types';
+import { normalizeAllDayDuration } from '../lib/calendar-utils';
 import {
   type CalendarUpdates,
   updateCalendar as apiUpdateCalendar,
@@ -67,6 +68,73 @@ function mapServerEventToStoreEvent(
   };
 }
 
+// Whitelist the JSCalendar properties an imported (parsed) event may carry:
+// drop server-computed / identity fields (utcStart, utcEnd, isOrigin, created,
+// updated, id) that CalendarEvent/set rejects, rewrite participants onto
+// `calendarAddress` and normalise all-day duration / time zone. Mirrors the
+// webmail's import preparation (#113).
+export function prepareImportedEvent(event: Partial<CalendarEvent>): Partial<CalendarEvent> {
+  const src = event as Record<string, unknown> & Partial<CalendarEvent>;
+  let participants: Record<string, Participant> | undefined;
+  if (src.participants) {
+    participants = {};
+    for (const [key, p] of Object.entries(src.participants)) {
+      const cleaned: Record<string, unknown> = {
+        '@type': 'Participant',
+        name: p.name,
+        email: p.email,
+        calendarAddress: p.calendarAddress || p.sendTo?.imip,
+        description: p.description,
+        kind: p.kind,
+        roles: p.roles,
+        participationStatus: p.participationStatus,
+        participationComment: p.participationComment,
+        expectReply: p.expectReply,
+        scheduleAgent: p.scheduleAgent,
+      };
+      for (const k of Object.keys(cleaned)) {
+        if (cleaned[k] === undefined || cleaned[k] === null) delete cleaned[k];
+      }
+      participants[key] = cleaned as Participant;
+    }
+  }
+  const data: Record<string, unknown> = {
+    uid: src.uid,
+    title: src.title,
+    description: src.description,
+    start: src.start,
+    duration: src.showWithoutTime ? normalizeAllDayDuration(src.duration) : src.duration,
+    timeZone: src.showWithoutTime ? null : src.timeZone,
+    showWithoutTime: src.showWithoutTime,
+    status: src.status,
+    freeBusyStatus: src.freeBusyStatus,
+    color: src.color,
+    keywords: src.keywords,
+    // Stalwart derives the iCalendar ORGANIZER solely from
+    // organizerCalendarAddress; dropping it would strip the ORGANIZER from
+    // imported invites and break RSVP replies afterwards.
+    organizerCalendarAddress: src.organizerCalendarAddress || src.replyTo?.imip,
+    locations: src.locations,
+    virtualLocations: src.virtualLocations,
+    links: src.links,
+    recurrenceRules: src.recurrenceRules,
+    recurrenceOverrides: src.recurrenceOverrides,
+    excludedRecurrenceRules: src.excludedRecurrenceRules,
+    alerts: src.alerts,
+    useDefaultAlerts: src.useDefaultAlerts,
+    participants,
+    '@type': src['@type'],
+    due: src.due,
+    progress: src.progress,
+    priority: src.priority,
+    percentComplete: src.percentComplete,
+  };
+  for (const k of Object.keys(data)) {
+    if (data[k] === undefined || data[k] === null) delete data[k];
+  }
+  return data as Partial<CalendarEvent>;
+}
+
 export interface LoadedRange {
   after: string;
   before: string;
@@ -499,22 +567,49 @@ export const useCalendarStore = create<CalendarState>()(
     const cal = get().calendars.find((c) => c.id === calendarId);
     const accountId = cal?.accountId;
     const serverCalendarId = cal?.originalId || calendarId;
-    // Stalwart enforces UID uniqueness across calendars. Skip events whose UID
-    // already exists; create the rest. (We don't attempt cross-calendar linking
-    // on mobile — a duplicate is simply skipped.)
+    // Stalwart enforces UID uniqueness across calendars (#113):
+    // - UID already in the target calendar -> skip (true duplicate)
+    // - UID in another calendar -> link it to the target via calendarIds
+    // - new UID -> create
     let toCreate = events;
+    let linked = 0;
     try {
       const existingIds = await queryEvents([], '', '', accountId);
       const existing = existingIds.length > 0 ? await fetchEvents(existingIds, accountId) : [];
-      const seenUids = new Set(existing.map((e) => e.uid).filter(Boolean) as string[]);
-      toCreate = events.filter((e) => !e.uid || !seenUids.has(e.uid));
+      const byUid = new Map<string, CalendarEvent>();
+      for (const e of existing) if (e.uid) byUid.set(e.uid, e);
+      const fresh: Partial<CalendarEvent>[] = [];
+      for (const e of events) {
+        const found = e.uid ? byUid.get(e.uid) : undefined;
+        if (!found) {
+          fresh.push(e);
+          continue;
+        }
+        if (found.calendarIds?.[serverCalendarId]) continue;
+        try {
+          await apiUpdateEvent(
+            found.id,
+            { calendarIds: { ...(found.calendarIds || {}), [serverCalendarId]: true } },
+            undefined,
+            accountId,
+          );
+          linked++;
+        } catch {
+          // Leave it where it is; the import of the rest continues.
+        }
+      }
+      toCreate = fresh;
     } catch {
       // Couldn't dedupe — proceed and let the server reject genuine dupes.
     }
-    if (toCreate.length === 0) return 0;
-    const count = await apiBatchCreateEvents(toCreate, serverCalendarId, accountId);
-    await get().refresh();
-    return count;
+    const prepared = toCreate.map(prepareImportedEvent);
+    let count = 0;
+    // Batch in chunks of 50 to avoid oversized requests.
+    for (let i = 0; i < prepared.length; i += 50) {
+      count += await apiBatchCreateEvents(prepared.slice(i, i + 50), serverCalendarId, accountId);
+    }
+    if (count > 0 || linked > 0) await get().refresh();
+    return count + linked;
   },
 
   createCalendar: async (name, color, description) => {