[Bug]: Google Calendar zero-duration recurring exception can render on two days in list view

[martin-forge]

Bug Description

I’ve found another Google Calendar rendering bug, but this one looks distinct from the sync/export issues.

A Google Calendar event can show up on two different days in TaskNotes list/agenda-style calendar views, even though it only exists once in Google Calendar.

What seems to trigger it is:

• a recurring Google Calendar event
• one instance being moved off its original series date
• the moved instance being a timed event with start == end (zero-duration / point-in-time event)
• the moved time being late in the day

I hit this with a moved recurring Google event at 23:12, and TaskNotes rendered the same event once on the correct day and again on the following day.

This does not appear to be duplicate data coming from Google. I checked the Google Calendar event itself and there was only one instance in the relevant window.

Steps to Reproduce

1. Use the Google Calendar integration.
2. Have a recurring Google Calendar event.
3. Move one occurrence off its original series date to a different day.
4. Make that moved occurrence a timed event where the start and end are the same (for example 23:12 to 23:12).
5. Open a TaskNotes calendar view in listWeek / agenda-style mode.
6. Refresh calendars.

Expected Behavior

The event should appear once, on the actual day/time returned by Google Calendar.

Actual Behavior

The same Google Calendar event is rendered under two day headers: the correct day and the following day.

Why I think this is in TaskNotes, not Google

I checked the event through the Google Calendar connector and there was only one matching event in the time window.

The Google event had a real start and end, but they were equal:

• start: 2026-04-22T23:12:00+01:00
• end: 2026-04-22T23:12:00+01:00

From the installed bundle / source, it looks like:

• GoogleCalendarService.convertToICSEvent() preserves that as a timed event with identical start / end
• createICSEvent() passes it through to FullCalendar unchanged
• the duplicate happens at render time in the calendar/list view, not during fetch

So this looks like a rendering/normalisation bug around zero-duration timed Google recurring exceptions, not a duplicate-fetch bug.

Related but Distinct

This seems adjacent to the recurring exception work in #1696 / #1802, but it is not the same problem.

• [Bug]: Google Calendar export ignores independently rescheduled next occurrence for recurring tasks #1696 is about exporting moved recurring occurrences correctly
• this one is about displaying inbound Google Calendar events correctly in TaskNotes calendar/list views

Suggestion

I think the safest fix is probably to normalise zero-duration timed external events before handing them to FullCalendar, rather than letting them through as start == end.