Resolves multiple issues with single occurrence modification to implement
correct CalDAV/RFC 5545 exception patterns:
## Key Fixes:
1. **Eliminate Double Updates**:
- Removed redundant client.update_event() call from update_single_occurrence
- Main handler now performs single CalDAV update, preventing conflicts
2. **Preserve Event Metadata**:
- Changed from creating new event to cloning existing event
- Maintains organizer, attendees, categories, and all original properties
- Only modifies necessary fields (times, title, recurrence rules)
3. **Fix UID Conflicts**:
- Generate unique UID for exception event (exception-{uuid})
- Prevents CalDAV from treating exception as update to original series
- Original series keeps its UID, exception gets separate identity
4. **Correct Date/Time Handling**:
- Use occurrence_date for both this_only and this_and_future scopes
- Exception event now gets dragged date/time instead of original series date
- Properly reflects user's drag operation in the exception event
## Implementation Details:
- Exception event clones original with unique UID and RECURRENCE-ID
- Original series gets EXDATE to exclude the modified occurrence
- Main handler performs single atomic CalDAV update
- Smart field preservation (keeps original values when request is empty)
## Result:
Single occurrence modifications now work correctly with proper RFC 5545
EXDATE + exception event pattern, maintaining all event metadata while
reflecting user modifications at the correct date/time.
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>
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