PUT fails (`CALDAV:same-organizer-in-all-components`) because iCalendar contains different `ORGANIZER` values in components

[devvv4ever]

Server: OpenXchange

PUT upload fails if a user (not the owner of the account) has write privileges on the collection. Seems to happen when CALDAV:same-organizer-in-all-components precondition is set.

See RFC 6638, section 3.2.4.2

More information in the ticket (internal view only): https://bitfire-at.zammad.com/#ticket/zoom/18479

[rfc2822]

DAVx5 generated this iCalendar:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:DAVx5/4.5.9-gplay ical4j/3.2.19

BEGIN:VEVENT
DTSTAMP:20260303T185757Z
...
DTSTART;TZID=Europe/Zurich:20260109T170000
DTEND;TZID=Europe/Zurich:20260109T180000
RRULE:FREQ=WEEKLY;WKST=MO;UNTIL=20260221T235959Z;INTERVAL=2;BYDAY=FR
ORGANIZER:mailto:someuser@example.com
...
END:VEVENT
BEGIN:VEVENT
RECURRENCE-ID;TZID=Europe/Zurich:20260206T170000
# No ORGANIZER in this exception!
...
END:VEVENT

However ORGANIZER must be the same value for all components (= main event + exceptions). See

• https://datatracker.ietf.org/doc/html/rfc6638#section-3.2.4.2
• RFC 6638 3.1

That code was present in ical4android before the events mappers were rewritten:

synctools/lib/src/main/kotlin/at/bitfire/ical4android/AndroidEvent.kt

Lines 543 to 545 in 366184e

	} else /* exceptionEvent.status != Status.VEVENT_CANCELLED */ {
	// make sure that all components have the same ORGANIZER [RFC 6638 3.1]
	exceptionEvent.organizer = event.organizer

We should fix it and also add a test to avoid further regression.