fix(contacts): seal managed calendars off from user edits

Managed special-dates calendars were only recognised by an id cached in
preferences, and were offered as ordinary write targets — so a user could
create an event in 'Birthdays' (which the next sync then deleted), and after
a backup restore wiped the prefs the editor lock silently disappeared.

CalendarSource now carries isManaged, read from the durable CAL_SYNC2 marker
the data layer already stamps, so identity survives a restore. With it:
- the new-event calendar picker excludes managed calendars (no user events
  land in a calendar the sync owns);
- the editor lock keys off the marker, not a stored id;
- a managed event's save is forced to the whole series instead of parking in
  the scope dialog (a 'this/following' split creates rows the sync reverts);
- the detail sheet hides Delete for managed events (the sync would just
  resurrect them — a contact date is removed at its source).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarMapper.kt

@@ -24,5 +24,12 @@ internal fun ColumnReader.toCalendarSource(): CalendarSource {
         } else {
             null
         },
+        // A special-dates mirror calendar, recognised by its durable CAL_SYNC2
+        // marker (only meaningful on the local calendars the app owns). This is
+        // the source of truth for the editor lock — independent of any stored
+        // preference that a backup restore could have wiped.
+        isManaged = isLocal &&
+            getString(CalendarProjection.IDX_MANAGED_MARKER)
+                ?.startsWith(CalendarProjection.MANAGED_MARKER_PREFIX) == true,
     )
 }

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/Projections.kt

@@ -15,9 +15,17 @@ internal object CalendarProjection {
         // own we stash one in CAL_SYNC1 (synced rows put their sync token here,
         // so the mapper only reads it for local calendars).
         DESCRIPTION_COLUMN,
+        // The special-dates marker (CAL_SYNC2) — the durable identity the app
+        // uses to recognise its own managed calendars, independent of any
+        // stored preference id (which a backup restore / data wipe can lose).
+        MANAGED_MARKER_COLUMN,
     )
 
     const val DESCRIPTION_COLUMN: String = CalendarContract.Calendars.CAL_SYNC1
+    const val MANAGED_MARKER_COLUMN: String = CalendarContract.Calendars.CAL_SYNC2
+
+    /** Namespace prefix of every managed-calendar [MANAGED_MARKER_COLUMN] value. */
+    const val MANAGED_MARKER_PREFIX = "calendula.specialdates"
 
     const val IDX_ID = 0
     const val IDX_DISPLAY_NAME = 1
@@ -27,6 +35,7 @@ internal object CalendarProjection {
     const val IDX_VISIBLE = 5
     const val IDX_ACCESS_LEVEL = 6
     const val IDX_DESCRIPTION = 7
+    const val IDX_MANAGED_MARKER = 8
 }
 
 internal object InstanceProjection {

app/src/main/java/de/jeanlucmakiola/calendula/domain/Models.kt

@@ -26,6 +26,14 @@ data class CalendarSource(
      * owns for its own calendars). Always null for synced calendars.
      */
     val description: String? = null,
+    /**
+     * A special-dates mirror calendar the app manages (birthdays/anniversaries
+     * from contacts). Its events' title/date/recurrence are owned by the sync,
+     * so it's hidden from the new-event calendar picker and its events lock those
+     * fields in the editor. Recognised by a durable provider marker, so it holds
+     * even after a backup restore clears the app's stored ids.
+     */
+    val isManaged: Boolean = false,
 )
 
 data class EventInstance(

app/src/main/java/de/jeanlucmakiola/calendula/ui/detail/EventDetailScreen.kt

@@ -250,6 +250,9 @@ fun EventDetailScreen(
                                 contentDescription = stringResource(R.string.event_detail_edit),
                             )
                         }
+                        // Managed special-dates events have no delete — the sync
+                        // would resurrect them; the date is removed at the contact.
+                        if (!s.isManaged) {
                             IconButton(
                                 onClick = onDeleteClick,
                                 enabled = deleteState != DeleteUiState.Deleting,
@@ -260,6 +263,7 @@ fun EventDetailScreen(
                                 )
                             }
                         }
+                    }
                 },
                 colors = TopAppBarDefaults.topAppBarColors(
                     containerColor = MaterialTheme.colorScheme.surface,

app/src/main/java/de/jeanlucmakiola/calendula/ui/detail/EventDetailUiState.kt

@@ -15,6 +15,12 @@ sealed interface EventDetailUiState {
         val calendarName: String?,
         /** Whether the owning calendar allows modifying events (shows edit/delete). */
         val canModify: Boolean = false,
+        /**
+         * The event belongs to a managed special-dates calendar: its editable
+         * fields (reminders, notes) can still be edited, but delete is hidden —
+         * the sync would just resurrect it. Contact dates are removed at the source.
+         */
+        val isManaged: Boolean = false,
     ) : EventDetailUiState
 }
 

app/src/main/java/de/jeanlucmakiola/calendula/ui/detail/EventDetailViewModel.kt

@@ -154,6 +154,7 @@ class EventDetailViewModel @Inject constructor(
             detail = corrected,
             calendarName = calendar?.displayName,
             canModify = calendar?.canModifyContents == true,
+            isManaged = calendar?.isManaged == true,
         )
     } catch (e: CancellationException) {
         throw e

app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt

@@ -122,18 +122,24 @@ class EventEditViewModel @Inject constructor(
         val autofocusTitle: Boolean,
     )
 
+    /** Every calendar the provider exposes; the source for both lists below. */
+    private val allCalendars: Flow<List<CalendarSource>> =
+        repository.calendars().catch { emit(emptyList()) }
+
     /**
      * Writable calendars — the only valid event targets. Disabled calendars are
      * excluded, so you can't create into a calendar you've removed from the app;
      * a last-used preselect landing on a now-disabled calendar falls back to the
      * first remaining writable one (handled by [resolvedCalendarId] and [state]).
+     * Managed special-dates calendars are excluded too: their events are owned by
+     * the contact sync, which would delete any user event created there.
      */
     private val writableCalendars: Flow<List<CalendarSource>> = combine(
-        repository.calendars(),
+        allCalendars,
         prefs.disabledCalendarIds,
     ) { calendars, disabled ->
-        calendars.filter { it.canModifyContents && it.id !in disabled }
+        calendars.filter { it.canModifyContents && it.id !in disabled && !it.isManaged }
-    }.catch { emit(emptyList()) }
+    }
 
     /** The target calendar id, resolved exactly as the form shows it. */
     private val resolvedCalendarId: Flow<Long?> = combine(
@@ -165,24 +171,33 @@ class EventEditViewModel @Inject constructor(
             ::ExternalInputs,
         ).flowOn(io),
         colorPalette,
-        settingsPrefs.managedCalendarIds,
+        allCalendars,
-    ) { local, external, palette, managedIds ->
+    ) { local, external, palette, allCalendars ->
         val form = local.form ?: return@combine null
         val resolvedId = form.calendarId
             ?: external.lastUsed?.takeIf { id -> external.writable.any { it.id == id } }
             ?: external.writable.firstOrNull()?.id
         val resolved = form.copy(calendarId = resolvedId)
+        val resolvedCalendar = allCalendars.firstOrNull { it.id == resolvedId }
+        // Editing an event in a managed calendar locks its synced fields. Keyed
+        // off the calendar's durable marker, not a stored id, so it holds after a
+        // backup restore too.
+        val isManaged = local.editTarget != null && resolvedCalendar?.isManaged == true
+        // The picker offers writable calendars only; when editing a managed event
+        // its own (excluded) calendar is added back so the row still names it.
+        val pickerCalendars =
+            if (isManaged && resolvedCalendar != null) external.writable + resolvedCalendar
+            else external.writable
         val visibleFields = external.defaultFields + local.revealed
         EventEditUiState(
             form = resolved,
-            calendars = external.writable,
+            calendars = pickerCalendars,
             problems = if (local.showProblems) resolved.problems() else emptySet(),
             saveState = local.saveState,
             visibleFields = visibleFields,
             hiddenFields = (EventFormField.entries.toSet() - visibleFields).sorted(),
             isEditing = local.editTarget != null,
-            // Editing an event in a managed calendar locks its synced fields.
+            isManaged = isManaged,
-            isManaged = local.editTarget != null && resolvedId != null && resolvedId in managedIds,
             autofocusTitle = external.autofocusTitle,
             // A modified-occurrence exception can't carry its own rule, so
             // the scope dialog drops "only this event" after a rule change.
@@ -420,7 +435,10 @@ class EventEditViewModel @Inject constructor(
             _saveState.value = SaveUiState.Saved
             return
         }
-        if (target != null && target.original.rrule != null) {
+        // Managed events are a yearly series whose editable fields (reminders,
+        // notes, location) live on the series row — never offer the scope dialog,
+        // which would split the series into an exception the sync then reverts.
+        if (target != null && target.original.rrule != null && !current.isManaged) {
             _saveState.value = SaveUiState.AwaitingScope
             return
         }