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Microsoft Graph's delta API returns @removed={reason:'changed'} when an
event drifts outside the original delta-query window — the event still
exists upstream. The old code treated any truthy @removed the same as a
real delete and archived the local calendar.event. Combined with
_find_existing_event filtering by active=True, every subsequent sync
recreated a duplicate (then archived it on the next pass), accumulating
5x duplicates and emptying the user's calendar.
- _process_microsoft_event: only archive on isCancelled or
@removed.reason='deleted'; skip on @removed.reason='changed'
- _process_microsoft_event link path: reactivate when MS Graph confirms
a previously-archived event still exists
- _process_microsoft_event iCalUId path: same reactivation
- _find_existing_event: include archived records so wrongly-archived
duplicates are reused instead of piling up
- callers reactivate the matched archived record
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>