diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesScheduler.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesScheduler.kt
index a906f9b..ba5cff5 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesScheduler.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesScheduler.kt
@@ -30,6 +30,7 @@ object SpecialDatesScheduler {
 
     private const val WORK_NAME = "special-dates-sync"
     private const val WORK_NAME_NOW = "special-dates-sync-now"
+    private const val WORK_NAME_FOREGROUND = "special-dates-sync-foreground"
     private const val KEY_FOREGROUND = "foreground"
 
     /** Enqueue (or cancel) the daily periodic reconcile to match [enabled]. */
@@ -38,6 +39,7 @@ object SpecialDatesScheduler {
         if (!enabled) {
             workManager.cancelUniqueWork(WORK_NAME)
             workManager.cancelUniqueWork(WORK_NAME_NOW)
+            workManager.cancelUniqueWork(WORK_NAME_FOREGROUND)
             return
         }
         val request = PeriodicWorkRequestBuilder<SpecialDatesSyncWorker>(1, TimeUnit.DAYS)
@@ -48,15 +50,19 @@ object SpecialDatesScheduler {
     }
 
     /**
-     * Run one reconcile immediately. [foreground] runs are debounced (the app can
-     * resume often); enable/"Sync now" runs ([foreground] false) always sync.
+     * Run one reconcile immediately. [foreground] runs (the app resuming) are
+     * debounced inside the worker and use their own work name, so a frequent
+     * foreground resync can never REPLACE — and swallow — a pending enable /
+     * "Sync now" run, which always syncs. The engine serializes the two if they
+     * overlap.
      */
     fun runNow(context: Context, foreground: Boolean = false) {
         val request = OneTimeWorkRequestBuilder<SpecialDatesSyncWorker>()
             .setInputData(Data.Builder().putBoolean(KEY_FOREGROUND, foreground).build())
             .build()
+        val name = if (foreground) WORK_NAME_FOREGROUND else WORK_NAME_NOW
         WorkManager.getInstance(context)
-            .enqueueUniqueWork(WORK_NAME_NOW, ExistingWorkPolicy.REPLACE, request)
+            .enqueueUniqueWork(name, ExistingWorkPolicy.REPLACE, request)
     }
 
     internal const val INPUT_FOREGROUND = KEY_FOREGROUND
@@ -107,6 +113,13 @@ class SpecialDatesSyncWorker(
             }
             if (foreground) prefs.setSpecialDatesLastForegroundSync(now)
             Result.success()
+        } catch (e: SecurityException) {
+            // A revoked calendar/contacts permission won't fix itself on retry —
+            // park the feature in a stalled state (surfaced in settings) instead
+            // of retrying with backoff forever.
+            Log.w(TAG, "Special-dates sync lacks a required permission", e)
+            prefs.recordSpecialDatesRun(now, SpecialDatesStalledReason.PermissionRevoked)
+            Result.success()
         } catch (e: Exception) {
             Log.w(TAG, "Special-dates sync failed", e)
             Result.retry()
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesSyncEngine.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesSyncEngine.kt
index 082d3bc..74ba06a 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesSyncEngine.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/contacts/SpecialDatesSyncEngine.kt
@@ -13,10 +13,12 @@ import de.jeanlucmakiola.calendula.domain.SimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.contacts.ContactSpecialDate
 import de.jeanlucmakiola.calendula.domain.contacts.SpecialDateType
 import de.jeanlucmakiola.calendula.domain.contacts.anchorDate
-import de.jeanlucmakiola.calendula.domain.contacts.managedEventUid
+import de.jeanlucmakiola.calendula.domain.contacts.managedUid
 import de.jeanlucmakiola.calendula.domain.contacts.renderSpecialDateTitle
 import de.jeanlucmakiola.calendula.domain.toRRule
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import java.time.ZoneId
@@ -64,11 +66,19 @@ class SpecialDatesSyncEngine @Inject constructor(
     private val spec: SpecialDatesCalendarSpec,
 ) {
 
+    // Serializes calendar-lifecycle work: two overlapping syncs (the daily job
+    // racing a "Sync now"/foreground run) would each see no managed calendar and
+    // both create one; a teardown racing an in-flight sync would delete calendars
+    // the sync then recreates. Holding this for the whole of sync()/teardown()
+    // makes those check-then-act sequences atomic, and — because sync() re-reads
+    // the enabled flag inside the lock — a teardown always wins the race.
+    private val lifecycleMutex = Mutex()
+
     /**
      * Reconcile every enabled type against the device's contacts. Returns why it
      * stopped early (disabled / permission gone) or [SpecialDatesSyncResult.Success].
      */
-    suspend fun sync(): SpecialDatesSyncResult {
+    suspend fun sync(): SpecialDatesSyncResult = lifecycleMutex.withLock {
         if (!prefs.specialDatesEnabled.first()) return SpecialDatesSyncResult.Disabled
         if (!contacts.hasPermission()) return SpecialDatesSyncResult.PermissionMissing
 
@@ -91,7 +101,7 @@ class SpecialDatesSyncEngine @Inject constructor(
                 reminderCtx = reminderCtx,
             )
         }
-        return SpecialDatesSyncResult.Success
+        SpecialDatesSyncResult.Success
     }
 
     /**
@@ -117,7 +127,7 @@ class SpecialDatesSyncEngine @Inject constructor(
     }
 
     /** Delete every managed calendar and forget its id — used when the feature is turned off. */
-    suspend fun teardown() {
+    suspend fun teardown() = lifecycleMutex.withLock {
         calendars.findManagedCalendars().forEach { calendars.deleteCalendar(it.id) }
         SpecialDateType.entries.forEach { prefs.setSpecialDatesCalendarId(it, null) }
     }
@@ -211,7 +221,7 @@ class SpecialDatesSyncEngine @Inject constructor(
         val dtStartMillis = form.toWriteTimes(ZoneId.systemDefault()).dtStartMillis
         return BuiltManagedEvent(
             desired = ManagedEventDesired(
-                uid = managedEventUid(type, sd.lookupKey),
+                uid = sd.managedUid(),
                 title = title,
                 dtStartMillis = dtStartMillis,
                 rrule = YEARLY_RRULE,