sync: reminders survive the alarm ceiling, and a save is not undone by one

setExactAndAllowWhileIdle throws at 500 concurrent alarms per uid, which
the per-occurrence model reaches at roughly seventeen daily recurring
tasks over a thirty-day window. When it threw mid-loop store.replace
never ran, so every alarm armed on that pass went unrecorded —
uncancellable, and firing for tasks that no longer exist — and the
exception escaped into BootReceiver's goAsync(). The set is bounded
soonest-first well below the ceiling, since the far edge of the window
is what the next sync arms anyway, and a single refusal now costs that
one alarm rather than the pass.

And the reminder sync shared the write's runCatching in the edit screen,
so a scheduling failure reported a task that *was* written as unsaved.
The user taps Save again on a screen whose editingTaskId is still null
and gets a second task — the reminder would have been re-synced on the
next data change regardless. The created id is also remembered now, so a
second Save updates rather than duplicates whatever sent them back.

app/src/main/java/de/jeanlucmakiola/agendula/data/reminders/ReminderScheduler.kt

@@ -93,12 +93,24 @@ class ReminderScheduler @Inject constructor(
             // setExactAndAllowWhileIdle delivers a past trigger immediately. Anything
             // already armed stays armed (the diff below), so it can't re-fire.
             .filter { it.triggerAt in (now - MISSED_GRACE_MS)..horizon }
+            // ⚠️ Bounded, soonest first. Android 12+ throws at 500 concurrent
+            // exact alarms per app, and the per-occurrence model reaches that
+            // with about seventeen daily recurring tasks over this window. What
+            // falls off the end is the far edge of a thirty-day horizon, which
+            // the next sync arms as it comes closer; what an exception would
+            // cost is every alarm this pass touched.
+            .sortedBy { it.triggerAt }
+            .take(MAX_ALARMS)
             .toSet()
 
         val previous = store.all()
         (previous - desired).forEach { cancel(it) }
-        (desired - previous).forEach { schedule(it) }
-        store.replace(desired)
+        // ⚠️ Only what was actually armed. A throw mid-loop used to skip the
+        // write below entirely, so every alarm set on that pass went unrecorded
+        // — uncancellable, and firing for tasks that no longer exist — and the
+        // exception escaped into BootReceiver's goAsync().
+        val armed = (desired - previous).filter { schedule(it) }
+        store.replace(desired.intersect(previous) + armed)
     }
 
     private fun alarmManager(): AlarmManager = context.getSystemService(AlarmManager::class.java)
@@ -114,15 +126,26 @@ class ReminderScheduler @Inject constructor(
         )
     }
 
-    private fun schedule(reminder: ScheduledReminder) {
+    /** @return whether the alarm is now armed, and so worth recording. */
+    private fun schedule(reminder: ScheduledReminder): Boolean {
         val triggerAt = reminder.triggerAt
-        val pi = pendingIntent(reminder, create = true) ?: return
+        val pi = pendingIntent(reminder, create = true) ?: return false
         val am = alarmManager()
         val canExact = Build.VERSION.SDK_INT < Build.VERSION_CODES.S || am.canScheduleExactAlarms()
-        if (canExact) {
-            am.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, triggerAt, pi)
-        } else {
-            am.set(AlarmManager.RTC_WAKEUP, triggerAt, pi)
+        return try {
+            if (canExact) {
+                am.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, triggerAt, pi)
+            } else {
+                am.set(AlarmManager.RTC_WAKEUP, triggerAt, pi)
+            }
+            true
+        } catch (_: IllegalStateException) {
+            // The concurrent-alarm ceiling, which [MAX_ALARMS] keeps us under —
+            // but the count is per uid and nothing here owns all of it.
+            false
+        } catch (_: SecurityException) {
+            // Exact-alarm permission revoked between the check and the call.
+            false
         }
     }
 
@@ -142,5 +165,15 @@ class ReminderScheduler @Inject constructor(
         const val WINDOW_MS = 30L * 24 * 60 * 60 * 1000 // 30 days
         /** How long after its trigger a missed reminder is still worth firing. */
         const val MISSED_GRACE_MS = 6L * 60 * 60 * 1000 // 6 hours
+
+        /**
+         * Alarms this app will hold at once.
+         *
+         * Android 12+ throws at 500 per uid. Well under it, because the count is
+         * per *uid* and this is not the only thing in the process that can arm
+         * one — and because the alarms nearest in time are the ones that matter,
+         * while the far edge of the window is re-armed by the next sync.
+         */
+        const val MAX_ALARMS = 400
     }
 }

app/src/main/java/de/jeanlucmakiola/agendula/ui/edit/TaskEditViewModel.kt

@@ -227,11 +227,20 @@ class TaskEditViewModel @Inject constructor(
             runCatching {
                 val id = editingTaskId
                 if (id == null) {
-                    repository.createTask(form)
+                    // ⚠️ Remembered. A second Save on this screen would otherwise
+                    // take the create path again and write a second task —
+                    // whatever sent the user back to it.
+                    editingTaskId = repository.createTask(form)
                 } else {
                     repository.updateTask(id, form, expectedLastModified = if (force) null else baselineLastModified)
                 }
-                reminderScheduler.sync()
+                // ⚠️ Outside the write's own result. The task is saved by this
+                // point, and reporting a scheduling failure as a *save* failure
+                // sends the user back to tap Save again — on a screen whose
+                // editingTaskId is still null, which creates a second task. The
+                // reminder is re-synced on the next data change and on launch;
+                // the duplicate is forever.
+                runCatching { reminderScheduler.sync() }
             }.onSuccess {
                 _state.value = _state.value.copy(saved = true, saveFailed = false, saveConflict = false)
             }.onFailure { error ->