Visibility and Management of Empty Recurring Series after Deleting All Occurrences

Is your feature request related to a problem? Please describe.

Yes. When a user deletes all individual instances of a recurring event in the Nextcloud Calendar, the underlying recurring rule (RRULE) still exists, but the event becomes invisible in the calendar UI. The user cannot:

• See that a recurring series still exists
• Manage or delete the recurring rule
• Restore any of the previously deleted occurrences

This leads to confusion and calendar clutter. It also prevents users from reactivating deleted instances or properly cleaning up the calendar.

Labels (for maintainers)

enhancement, ux, calendar

Describe the solution you'd like

• Keep the recurring series visible in the UI, even if all of its occurrences have been deleted.
• Provide an interface to manage the exceptions (deleted or modified instances) of a recurring event.
• Allow users to:
  • Permanently delete the whole series, even if it's currently empty
  • Restore individual deleted occurrences
  • View and manage a list of exceptions in the event editor

Possible UX options:

• Show a faint or grayed-out placeholder in the calendar for an "empty" recurring event
• Add a "Manage Exceptions" section to the recurring event detail window
• Allow undo of deletions within a timeframe or session

Describe alternatives you've considered

• Using a CalDAV client (e.g. Thunderbird) to manually manage or delete the invisible series.
• Exporting the calendar .ics file and editing it manually to remove or restore the series.
• Creating a new series from scratch to replace the one that became invisible.

These are technical workarounds and not user-friendly for most users.

Additional context

This issue also affects other platforms (e.g. kalender.digital) that rely on CalDAV but lack exception management.

Use Case Example:
A user has a recurring weekly event every Tuesday until the end of the year. They delete each occurrence because they cannot attend. In December, they want to join again, but the series is no longer visible, and the event cannot be restored or even managed. The only workaround is external tooling.

This change would greatly improve clarity and give users more control over recurring events.

Start with the calendar UI and event editor behavior for recurring events whose RRULE remains after all occurrences are deleted. Trace how deleted or modified instances are represented through CalDAV and the calendar data, then define completion around viewing, restoring, managing exceptions, and permanently deleting an empty series.