The special-dates mirrors were the last unexplained exclusion: writable, visible, syncing, and still not offered as an event target, because their events belong to the contact sync and anything authored there is removed on the next pass. Their rows now say "Filled from your contacts", and the pickers' footer names that third reason alongside switched-off and read-only. Their delete stays where it is rather than disappearing, but is held while special dates are on: reconcileCalendars recreates a missing mirror for an enabled type on the very next sync, so the delete would look like it worked and then quietly undo itself. The button dims, an info card in the editor says why and points at Settings → Special dates, and turning the feature off gives the delete back — at which point a leftover mirror really is the user's to remove. The lock is derived from the enabled types' stored calendar ids, which is what the sync itself reconciles against: a mirror whose type is switched off is already an orphan the next sync would delete anyway, so it stays deletable by hand. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>