Shared cancelled event does not propagate to attendees

Steps to reproduce

1. Create a calendar C by user U1
2. Share calendar C with users U2 and U3 in sharing options
3. (as user U2) Create event E in calendar C, inviting user U3
4. (as user U2) Delete/cancel event E in calendar C
5. (as user U3) Observe as the event E is NOT deleted/not marked as cancelled in personal calendar of user U3.

Expected behavior

Event E is deleted from both calendar C and personal calendar of U3 (or deleted from calendar C and marked as cancelled in personal calendar of U3)

Actual behavior

Event E is only deleted from calendar C

Calendar app version

5.3.2

CalDAV-clients used

Thunderbird/Nextcloud UI

Browser

Firefox

Web server

Apache

Database engine version

PostgreSQL

Nextcloud version

Nextcloud Hub 9 (30.0.10)

Updated from an older installed version or fresh install

Updated from an older version

Additional info

Interestingly, updates to event times ARE indeed pushed down to the personal calendar of user U3. It's only the deletes that are not pushed.

Start by reproducing the shared-calendar cancellation flow with U1, U2, and U3 using the Nextcloud UI or Thunderbird, then inspect the CalDAV sharing and event-deletion path. Compare deletion propagation with the event-time update behavior described in the issue. Done means cancelling an event created in a shared calendar removes it or marks it cancelled in the attendee's personal calendar.