Merge remote-tracking branch 'origin/release/v2.17.0' into fix/widget-fixed-size-steps

# Conflicts:
#	CHANGELOG.md

CHANGELOG.md

@@ -50,9 +50,47 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   either widget is measured any more: they draw at the size you pick under
   Settings → Widgets. The month widget can no longer be resized narrower than its
   grid needs, either ([#103], [#51]).
+- A month-grid widget stays a month grid. Since 2.16.0 a placed month widget
+  could redraw itself as the agenda widget a little after any change to your
+  events, because the release build merged the two widgets into a single class
+  and Android could no longer tell which of them a widget on your home screen
+  was ([#89]).
+- The back gesture on **Settings → Views** returns to Settings instead of
+  leaving Settings altogether and dropping you on the calendar. Special dates
+  did the same ([#81]).
+- The dots standing in for the events that didn't fit a day in the month view
+  now dim with everything else when **Dim completed events** is on. A past day
+  with four or more events kept its last events at full strength while the rest
+  faded ([#79]).
+- Two accounts that happen to share a name — a Google account and a DAVx5
+  account for the same address, say — are no longer merged into one group.
+  They were listed together in Settings → Calendars and in the drawer's filter,
+  which also meant the group's source icon and its "manage in app" button could
+  send you to the wrong app, "toggle all" spanned both accounts at once, and
+  collapsing one collapsed the other. Where a name really is shared, each group
+  now names the app it comes from ([#77]).
 - Search results now show an all-day event's real date. West of UTC — anywhere in
   the Americas, say — a search hit was dated one day early, disagreeing with the
   day the month, week and agenda views file the same event under ([#82]).
+- Reminders no longer depend on Android telling Calendula when they are due.
+  Calendula now works out each reminder's time itself and sets its own alarm for
+  it. On some phones — Samsung's among them — the system's calendar storage never
+  sends the signal a calendar app is meant to wake up on, and no amount of
+  battery or notification settings helps: the reminder is simply never announced.
+  None of that is visible from inside an app that waits to be told, which is why
+  it took a second pass to find ([#75]).
+
+  Reminders also survive things that used to lose them quietly. After a restart
+  or an app update Calendula re-arms its alarms, and a reminder whose moment
+  passed while the phone was off still arrives, as long as the event has not
+  ended yet.
+
+- All-day reminders now arrive at the time you chose in **Settings →
+  Notifications**, on every occurrence. A yearly birthday could drift an hour
+  either way depending on daylight saving, and all-day reminders on calendars
+  from an account fired in the middle of the night instead of in the morning
+  ([#75]).
+
 - Reminders now arrive for every calendar you have switched on. A calendar that
   was hidden at system level — switched off in another calendar app, or never
   switched on after being added — still showed its events and listed their
@@ -1182,5 +1220,9 @@ automatically, with zero telemetry and no internet permission.
 [#75]: https://codeberg.org/jlmakiola/calendula/issues/75
 [#76]: https://codeberg.org/jlmakiola/calendula/issues/76
 [#78]: https://codeberg.org/jlmakiola/calendula/issues/78
+[#77]: https://codeberg.org/jlmakiola/calendula/issues/77
+[#79]: https://codeberg.org/jlmakiola/calendula/issues/79
+[#81]: https://codeberg.org/jlmakiola/calendula/issues/81
 [#82]: https://codeberg.org/jlmakiola/calendula/issues/82
+[#89]: https://codeberg.org/jlmakiola/calendula/issues/89
 [#103]: https://codeberg.org/jlmakiola/calendula/issues/103

app/proguard-rules.pro

@@ -38,3 +38,15 @@
 # SessionWorker never ran, and widgets were stuck on their loading layout
 # (a blank spinner) in release builds. Keep every InputMerger's name + ctor.
 -keep class * extends androidx.work.InputMerger { <init>(...); }
+
+# Glance identifies a widget by its GlanceAppWidget subclass's *canonical name*:
+# GlanceAppWidgetManager persists a providerName -> receivers map under that
+# string, and `updateAll` looks the widget's app-widget ids up through it. Under
+# R8 full mode (AGP 9 default) MonthWidget and AgendaWidget — same supertype,
+# same overrides, no distinguishing members — were horizontally merged into one
+# class, so both receivers registered under the *same* provider name and
+# `AgendaWidget().updateAll()` resolved the month widget's id too, redrawing a
+# placed month widget as the agenda one on the next data change (#89). Keeping
+# the real names also survives app updates, which would otherwise renumber the
+# obfuscated name and orphan the stored mapping.
+-keep class * extends androidx.glance.appwidget.GlanceAppWidget

app/src/main/AndroidManifest.xml

@@ -33,6 +33,14 @@
         android:maxSdkVersion="32" />
     <uses-permission android:name="android.permission.USE_EXACT_ALARM" />
 
+    <!--
+      A reboot clears every pending alarm, including the one holding the next
+      reminder. Now that the app schedules that alarm itself (#75) rather than
+      leaning on the provider's, it has to hear about the reboot to re-arm it —
+      otherwise reminders simply stop after a restart.
+    -->
+    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
+
     <!-- Package visibility (Android 11+): without this, getLaunchIntentForPackage
          returns null and the calendar manager's per-account "manage" button can't
          open the source sync app (DAVx5, ICSx5, Google Calendar, …). The LAUNCHER
@@ -270,17 +278,22 @@
             </intent-filter>
         </service>
 
-        <!-- The provider broadcasts EVENT_REMINDER at reminder time but posts
-             no notification itself — a calendar app must (v1.4, Etar model).
-             Exported: the broadcast arrives from the provider's process. -->
+        <!-- Reminder delivery is the app's own (#75): it plans the alarms from
+             Instances + Reminders instead of waiting for the provider's
+             EVENT_REMINDER broadcast, which OEM-modified providers demonstrably
+             retarget or never send. This receiver takes our scan alarm plus
+             every outside event that invalidates it — boot and package-replace
+             wipe pending alarms, and a clock or timezone change moves every
+             reminder relative to the one that is armed.
+             Exported: the system broadcasts arrive from outside the app. -->
         <receiver
-            android:name=".data.reminders.EventReminderReceiver"
+            android:name=".data.reminders.ReminderScheduleReceiver"
             android:exported="true">
             <intent-filter>
-                <action android:name="android.intent.action.EVENT_REMINDER" />
-                <data
-                    android:host="com.android.calendar"
-                    android:scheme="content" />
+                <action android:name="android.intent.action.BOOT_COMPLETED" />
+                <action android:name="android.intent.action.MY_PACKAGE_REPLACED" />
+                <action android:name="android.intent.action.TIME_SET" />
+                <action android:name="android.intent.action.TIMEZONE_CHANGED" />
             </intent-filter>
         </receiver>
 

app/src/main/java/de/jeanlucmakiola/calendula/CalendulaApp.kt

@@ -8,6 +8,8 @@ import de.jeanlucmakiola.calendula.data.calendar.CalendarVisibilityReconciler
 import de.jeanlucmakiola.calendula.data.backup.BackupWorker
 import de.jeanlucmakiola.calendula.data.contacts.SpecialDatesScheduler
 import de.jeanlucmakiola.calendula.data.contacts.SpecialDatesSyncWorker
+import de.jeanlucmakiola.calendula.data.reminders.ReminderMaintenanceScheduler
+import de.jeanlucmakiola.calendula.data.reminders.ReminderMaintenanceWorker
 import de.jeanlucmakiola.floret.crash.CrashConfig
 import de.jeanlucmakiola.floret.crash.CrashReporter
 import kotlinx.coroutines.CoroutineScope
@@ -41,6 +43,25 @@ class CalendulaApp : Application() {
         reconcileAutoBackup()
         reconcileSpecialDates()
         reconcileCalendarVisibility()
+        startReminderDelivery()
+    }
+
+    /**
+     * Bring reminder delivery up with the process (#75). The app plans and arms
+     * its own reminder alarms now, so launch is one of the moments that has to
+     * re-check them: a scan re-arms whatever the system dropped, posts anything
+     * a missed alarm still owes, and starts watching the provider so an edit
+     * re-plans without waiting for the next pass. The daily worker is the
+     * backstop for a device that drops the alarm with no reboot to announce it.
+     */
+    private fun startReminderDelivery() {
+        val deps = EntryPointAccessors.fromApplication(
+            this, ReminderMaintenanceWorker.Deps::class.java,
+        )
+        val scanner = deps.reminderScanner()
+        scanner.startWatchingProvider()
+        scanner.scanInBackground()
+        ReminderMaintenanceScheduler.apply(this)
     }
 
     /**

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

@@ -1,11 +1,10 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
-import java.time.Instant
+import de.jeanlucmakiola.calendula.domain.reminders.allDayLeadDays
 import java.time.LocalDate
 import java.time.LocalTime
 import java.time.ZoneId
 import java.time.ZoneOffset
-import java.time.temporal.ChronoUnit
 
 /**
  * Translates an all-day reminder between the **semantic** lead time the UI
@@ -73,19 +72,14 @@ internal fun nextYearlyOccurrence(month: Int, day: Int, today: LocalDate): Local
 
 /**
  * Recover the semantic whole-day lead time from a raw all-day reminder
- * [rawMinutes]. Keys off the **local date** of the encoded fire instant, so it
- * returns the right day count regardless of which [timeOfDayMinutes] wrote the
- * row — including pre-feature rows (raw multiples of 1440, fired at UTC midnight)
- * and rows written under a different timezone. A negative [rawMinutes] (fire
- * after DTSTART) folds to day 0.
+ * [rawMinutes] — the inverse of [toProviderAllDayMinutes], for the form and the
+ * detail screen. Delegates to [allDayLeadDays] so what is displayed is the day
+ * the reminder actually fires on; see there for how an encoded row is told from
+ * a plain one written by another calendar app.
  */
 internal fun fromProviderAllDayMinutes(
     rawMinutes: Int,
     startDate: LocalDate,
     zone: ZoneId,
-): Int {
-    val utcMidnight = startDate.atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
-    val fireLocalDate = Instant.ofEpochMilli(utcMidnight - rawMinutes * MILLIS_PER_MINUTE)
-        .atZone(zone).toLocalDate()
-    return ChronoUnit.DAYS.between(fireLocalDate, startDate).toInt() * MINUTES_PER_DAY
-}
+    timeOfDayMinutes: Int,
+): Int = allDayLeadDays(rawMinutes, startDate, zone, timeOfDayMinutes).toInt() * MINUTES_PER_DAY

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

@@ -54,7 +54,12 @@ import javax.inject.Singleton
 interface CalendarDataSource {
     fun calendars(): List<CalendarSource>
     fun instances(beginMillis: Long, endMillis: Long): List<EventInstance>
-    fun eventDetail(eventId: Long): EventDetail?
+    /**
+     * [allDayReminderTimeMinutes]: the hour all-day reminders fire at, needed to
+     * decode their stored offsets back to whole-day lead times (see
+     * [fromProviderAllDayMinutes]).
+     */
+    fun eventDetail(eventId: Long, allDayReminderTimeMinutes: Int): EventDetail?
 
     /**
      * Master/one-off events whose title, description or location contains
@@ -670,7 +675,7 @@ class AndroidCalendarDataSource @Inject constructor(
         }
     }
 
-    override fun eventDetail(eventId: Long): EventDetail? {
+    override fun eventDetail(eventId: Long, allDayReminderTimeMinutes: Int): EventDetail? {
         val attendees = queryAttendees(eventId)
         val reminders = queryReminders(eventId)
         return resolver.query(
@@ -679,7 +684,9 @@ class AndroidCalendarDataSource @Inject constructor(
             null, null, null,
         )?.use { c ->
             if (!c.moveToFirst()) null
-            else CursorColumnReader(c).toEventDetailCore(attendees, reminders)
+            else CursorColumnReader(c).toEventDetailCore(
+                attendees, reminders, allDayReminderTimeMinutes,
+            )
         }
     }
 

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

@@ -179,7 +179,8 @@ class CalendarRepositoryImpl @Inject constructor(
     }
 
     override suspend fun eventDetail(eventId: Long): EventDetail = withContext(io) {
-        dataSource.eventDetail(eventId) ?: throw NoSuchEventException(eventId)
+        dataSource.eventDetail(eventId, allDayReminderTimeMinutes())
+            ?: throw NoSuchEventException(eventId)
     }
 
     override suspend fun searchEvents(query: String): List<EventInstance> = withContext(io) {

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

@@ -24,6 +24,7 @@ private const val TAG = "EventDetailMapper"
 internal fun ColumnReader.toEventDetailCore(
     attendees: List<Attendee>,
     reminders: List<Reminder>,
+    allDayReminderTimeMinutes: Int,
 ): EventDetail? {
     // DTSTART is epoch millis in UTC, so a series anchored before 1970 (common
     // for yearly birthdays/anniversaries synced over CalDAV) is legitimately
@@ -89,7 +90,13 @@ internal fun ColumnReader.toEventDetailCore(
     val displayReminders = if (isAllDay) {
         val startDate = Instant.ofEpochMilli(begin).atZone(ZoneOffset.UTC).toLocalDate()
         val zone = ZoneId.systemDefault()
-        reminders.map { it.copy(minutes = fromProviderAllDayMinutes(it.minutes, startDate, zone)) }
+        reminders.map {
+            it.copy(
+                minutes = fromProviderAllDayMinutes(
+                    it.minutes, startDate, zone, allDayReminderTimeMinutes,
+                ),
+            )
+        }
     } else {
         reminders
     }

app/src/main/java/de/jeanlucmakiola/calendula/data/di/DataModule.kt

@@ -18,8 +18,8 @@ import de.jeanlucmakiola.calendula.data.contacts.AndroidContactSpecialDatesDataS
 import de.jeanlucmakiola.calendula.data.contacts.AndroidSpecialDatesCalendarSpec
 import de.jeanlucmakiola.calendula.data.contacts.ContactSpecialDatesDataSource
 import de.jeanlucmakiola.calendula.data.contacts.SpecialDatesCalendarSpec
-import de.jeanlucmakiola.calendula.data.reminders.AndroidReminderAlertStore
-import de.jeanlucmakiola.calendula.data.reminders.ReminderAlertStore
+import de.jeanlucmakiola.calendula.data.reminders.ProviderReminderInstanceSource
+import de.jeanlucmakiola.calendula.data.reminders.ReminderInstanceSource
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.Dispatchers
 import javax.inject.Singleton
@@ -46,9 +46,9 @@ abstract class DataBindModule {
 
     @Binds
     @Singleton
-    abstract fun bindReminderAlertStore(
-        impl: AndroidReminderAlertStore,
-    ): ReminderAlertStore
+    abstract fun bindReminderInstanceSource(
+        impl: ProviderReminderInstanceSource,
+    ): ReminderInstanceSource
 
     @Binds
     @Singleton

app/src/main/java/de/jeanlucmakiola/calendula/data/prefs/ReminderStatePrefs.kt

@@ -0,0 +1,42 @@
+package de.jeanlucmakiola.calendula.data.prefs
+
+import androidx.datastore.core.DataStore
+import androidx.datastore.preferences.core.Preferences
+import androidx.datastore.preferences.core.edit
+import androidx.datastore.preferences.core.longPreferencesKey
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.map
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * How far reminder delivery has got. One number, and it replaces everything the
+ * provider's `CalendarAlerts.STATE` used to do for us (#75).
+ *
+ * A scan posts the reminders whose moment falls after this watermark and up to
+ * now, then moves it to now. That single rule gives both halves of what the
+ * retired path got from the provider: a scan that runs twice cannot post the
+ * same reminder again, and a scan that runs *late* — after a reboot, an app
+ * update or a doze window swallowed the alarm — still posts everything the
+ * missed alarm would have.
+ *
+ * Unset means "never scanned". It is deliberately not treated as zero: the first
+ * scan after an install or an upgrade would otherwise consider every reminder
+ * since the epoch overdue and bury the user in notifications.
+ */
+@Singleton
+class ReminderStatePrefs @Inject constructor(
+    private val store: DataStore<Preferences>,
+) {
+
+    /** The watermark, or `null` before the first scan has ever run. */
+    suspend fun lastScanMillis(): Long? = store.data.map { it[LAST_SCAN_KEY] }.first()
+
+    suspend fun setLastScanMillis(millis: Long) {
+        store.edit { prefs -> prefs[LAST_SCAN_KEY] = millis }
+    }
+
+    private companion object {
+        val LAST_SCAN_KEY = longPreferencesKey("reminder_last_scan_millis")
+    }
+}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/AlertHandling.kt

@@ -1,30 +0,0 @@
-package de.jeanlucmakiola.calendula.data.reminders
-
-/**
- * Still relevant while the event has not ended: a reminder for an event that is
- * already over is pointless to re-surface. Falls back to the begin time when the
- * end is unknown (0L).
- */
-internal fun ReminderAlert.isRelevantAt(nowMillis: Long): Boolean =
-    (endMillis.takeIf { it > 0L } ?: beginMillis) >= nowMillis
-
-/**
- * The alerts [EventReminderReceiver] may mark handled (`STATE_FIRED`): the ones
- * it posted, plus the ones it silenced whose event is already over.
- *
- * A silenced alert for an event still ahead is deliberately left
- * `STATE_SCHEDULED`. Silencing is not handling — the calendar is switched off in
- * Calendula while the provider still holds `VISIBLE = 1` (a read-only install,
- * or an upgrade whose flush hasn't landed), so switching it back on before the
- * event must still be able to surface the reminder. [ReminderAlertStore.dueAlerts]
- * only ever returns scheduled rows, so marking them here would lose them for
- * good; leaving them makes the provider's own table the stash
- * ([ReminderRecovery]).
- */
-internal fun handledAlertIds(
-    due: List<ReminderAlert>,
-    postedIds: Set<Long>,
-    nowMillis: Long,
-): List<Long> = due
-    .filter { it.alertId in postedIds || !it.isRelevantAt(nowMillis) }
-    .map { it.alertId }

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/EventReminderReceiver.kt

@@ -1,67 +0,0 @@
-package de.jeanlucmakiola.calendula.data.reminders
-
-import android.Manifest
-import android.content.BroadcastReceiver
-import android.content.Context
-import android.content.Intent
-import android.content.pm.PackageManager
-import android.provider.CalendarContract
-import androidx.core.content.ContextCompat
-import dagger.hilt.android.AndroidEntryPoint
-import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
-import kotlinx.coroutines.CoroutineScope
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.SupervisorJob
-import kotlinx.coroutines.flow.first
-import kotlinx.coroutines.launch
-import javax.inject.Inject
-
-/**
- * Becomes the app that turns the calendar provider's reminder alarms into
- * visible notifications (the Etar model — the provider broadcasts
- * `EVENT_REMINDER` at reminder time but posts nothing itself).
- *
- * The broadcast's data URI only carries the alarm time, so it is ignored:
- * we query every still-scheduled, due `CalendarAlerts` row ourselves, post
- * them, and mark them fired. Posting happens before marking — a crash in
- * between re-posts silently (same tag) rather than losing the reminder.
- *
- * There is no per-calendar filtering here: a calendar switched off in
- * Settings → Calendars has `Calendars.VISIBLE = 0`, and the provider creates no
- * alert rows for it in the first place (#75). The one case that flag can't
- * cover — a read-only install, which keeps its switches app-side — is gated in
- * [ReminderNotifier.post], where the snoozed re-show passes too. What that gate
- * silences is *not* marked fired while the event is still ahead, so switching
- * the calendar back on can still surface it (see [handledAlertIds]).
- */
-@AndroidEntryPoint
-class EventReminderReceiver : BroadcastReceiver() {
-
-    @Inject lateinit var alertStore: ReminderAlertStore
-    @Inject lateinit var notifier: ReminderNotifier
-    @Inject lateinit var settingsPrefs: SettingsPrefs
-
-    override fun onReceive(context: Context, intent: Intent) {
-        if (intent.action != CalendarContract.ACTION_EVENT_REMINDER) return
-        val readGranted = ContextCompat.checkSelfPermission(
-            context, Manifest.permission.READ_CALENDAR,
-        ) == PackageManager.PERMISSION_GRANTED
-        if (!readGranted || !notifier.canPost()) return
-
-        val pendingResult = goAsync()
-        CoroutineScope(SupervisorJob() + Dispatchers.IO).launch {
-            try {
-                if (settingsPrefs.remindersEnabled.first()) {
-                    val now = System.currentTimeMillis()
-                    val due = alertStore.dueAlerts(now)
-                    val postedIds = due
-                        .filter { notifier.post(it) }
-                        .mapTo(mutableSetOf()) { it.alertId }
-                    alertStore.markFired(handledAlertIds(due, postedIds, now), now)
-                }
-            } finally {
-                pendingResult.finish()
-            }
-        }
-    }
-}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderActionReceiver.kt

@@ -3,6 +3,7 @@ package de.jeanlucmakiola.calendula.data.reminders
 import android.content.BroadcastReceiver
 import android.content.Context
 import android.content.Intent
+import androidx.core.net.toUri
 import dagger.hilt.android.AndroidEntryPoint
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import kotlinx.coroutines.CoroutineScope
@@ -18,14 +19,14 @@ import javax.inject.Inject
  * intents (notification action buttons and our own [ReminderSnoozeScheduler]
  * alarm), so the receiver is not exported.
  *
- * - **Dismiss** just cancels the notification — the `CalendarAlerts` row is
- *   already fired, so nothing re-posts it.
+ * - **Dismiss** just cancels the notification — the scan's watermark has moved
+ *   past this reminder, so nothing re-posts it.
  * - **Snooze** cancels the notification and schedules an exact alarm to re-show
  *   it after the user's snooze delay.
  * - **Show** (the alarm) re-posts the same notification, so the user can snooze
  *   or dismiss it again — unless the calendar was switched off during the
- *   snooze, which [ReminderNotifier.post] catches (this alarm is ours, so no
- *   provider alert row stands between it and the notification).
+ *   snooze, which [ReminderNotifier.post] catches — this alarm is its own
+ *   trigger, outside the ordinary scan.
  */
 @AndroidEntryPoint
 class ReminderActionReceiver : BroadcastReceiver() {
@@ -75,7 +76,14 @@ class ReminderActionReceiver : BroadcastReceiver() {
         const val ACTION_DISMISS = "de.jeanlucmakiola.calendula.reminders.DISMISS"
         const val ACTION_SHOW = "de.jeanlucmakiola.calendula.reminders.SHOW"
 
-        private const val EXTRA_ALERT_ID = "alert_id"
+        /**
+         * Not handled here — the notification body opens the detail screen
+         * directly. It only claims a slot in [requestCode] so that intent stays
+         * distinct from the three this receiver does handle.
+         */
+        const val ACTION_OPEN = "de.jeanlucmakiola.calendula.reminders.OPEN"
+
+        private const val EXTRA_ALERT_KEY = "alert_key"
         private const val EXTRA_EVENT_ID = "event_id"
         private const val EXTRA_CALENDAR_ID = "calendar_id"
         private const val EXTRA_BEGIN = "begin"
@@ -84,11 +92,20 @@ class ReminderActionReceiver : BroadcastReceiver() {
         private const val EXTRA_LOCATION = "location"
         private const val EXTRA_ALL_DAY = "all_day"
 
-        /** An explicit intent to this receiver carrying [alert] as extras. */
+        /**
+         * An explicit intent to this receiver carrying [alert] as extras.
+         *
+         * The data URI names the reminder and carries no information the extras
+         * don't. It is what actually keeps two reminders' `PendingIntent`s
+         * apart: `filterEquals` compares action, component, data, type and
+         * categories — never extras — so without it a request-code collision
+         * would have them share one alarm and one payload.
+         */
         fun intent(context: Context, action: String, alert: ReminderAlert): Intent =
             Intent(context, ReminderActionReceiver::class.java).apply {
                 this.action = action
-                putExtra(EXTRA_ALERT_ID, alert.alertId)
+                data = "calendula://reminder/${alert.key}".toUri()
+                putExtra(EXTRA_ALERT_KEY, alert.key)
                 putExtra(EXTRA_EVENT_ID, alert.eventId)
                 putExtra(EXTRA_CALENDAR_ID, alert.calendarId)
                 putExtra(EXTRA_BEGIN, alert.beginMillis)
@@ -99,23 +116,29 @@ class ReminderActionReceiver : BroadcastReceiver() {
             }
 
         /**
-         * A stable request code per (alert, action) so the three PendingIntents
-         * of one notification stay distinct and don't clobber each other.
+         * A stable request code per (alert, action) so one notification's
+         * PendingIntents stay distinct and don't clobber each other.
+         *
+         * The key is a hash now rather than a small row id, so the shift is what
+         * keeps the action slot intact; the top three bits it drops can make two
+         * *different* reminders share a code, which the per-reminder data URI in
+         * [intent] separates.
          */
         fun requestCode(alert: ReminderAlert, action: String): Int {
             val actionOffset = when (action) {
                 ACTION_SNOOZE -> 1
                 ACTION_DISMISS -> 2
                 ACTION_SHOW -> 3
+                ACTION_OPEN -> 4
                 else -> 0
             }
-            return alert.alertId.toInt() * 8 + actionOffset
+            return (alert.key.toInt() shl 3) + actionOffset
         }
 
         private fun alertFrom(intent: Intent): ReminderAlert? {
-            if (!intent.hasExtra(EXTRA_ALERT_ID)) return null
+            if (!intent.hasExtra(EXTRA_ALERT_KEY)) return null
             return ReminderAlert(
-                alertId = intent.getLongExtra(EXTRA_ALERT_ID, 0L),
+                key = intent.getLongExtra(EXTRA_ALERT_KEY, 0L),
                 eventId = intent.getLongExtra(EXTRA_EVENT_ID, 0L),
                 calendarId = intent.getLongExtra(EXTRA_CALENDAR_ID, 0L),
                 beginMillis = intent.getLongExtra(EXTRA_BEGIN, 0L),

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderAlarms.kt

@@ -0,0 +1,71 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import android.app.AlarmManager
+import android.app.PendingIntent
+import android.content.Context
+import android.content.Intent
+import android.os.Build
+import androidx.core.content.getSystemService
+import dagger.hilt.android.qualifiers.ApplicationContext
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * True on API < 31 (no restriction), and on 31+ when the exact-alarm capability
+ * is held — auto-granted via `USE_EXACT_ALARM` on API 33+ (Calendula is a
+ * calendar app), user-revocable on 31–32.
+ */
+internal fun AlarmManager.canScheduleExactCompat(): Boolean =
+    Build.VERSION.SDK_INT < Build.VERSION_CODES.S || canScheduleExactAlarms()
+
+/**
+ * Holds the app's own wake-up for the next reminder — the half of delivery that
+ * used to be the provider's (#75).
+ *
+ * Exactly **one** alarm exists at a time, for the earliest reminder still ahead.
+ * Every firing re-scans and re-arms, so a reminder added, moved or deleted in
+ * between is picked up on the next pass instead of needing an alarm per reminder
+ * to be kept in sync with the provider's tables.
+ *
+ * A reminder that lands late is a broken reminder, hence an *exact* alarm; the
+ * inexact allow-while-idle fallback only applies where the OS withholds the
+ * capability (API 31–32 with the user's permission revoked).
+ */
+@Singleton
+class ReminderAlarmScheduler @Inject constructor(
+    @ApplicationContext private val context: Context,
+) {
+
+    fun scheduleScan(triggerAtMillis: Long) {
+        val alarmManager = context.getSystemService<AlarmManager>() ?: return
+        val pendingIntent = scanPendingIntent(PendingIntent.FLAG_UPDATE_CURRENT)
+        if (alarmManager.canScheduleExactCompat()) {
+            alarmManager.setExactAndAllowWhileIdle(
+                AlarmManager.RTC_WAKEUP, triggerAtMillis, pendingIntent,
+            )
+        } else {
+            alarmManager.setAndAllowWhileIdle(
+                AlarmManager.RTC_WAKEUP, triggerAtMillis, pendingIntent,
+            )
+        }
+    }
+
+    /** Drop the pending wake-up — reminders are off, or there is nothing to wait for. */
+    fun cancelScan() {
+        val alarmManager = context.getSystemService<AlarmManager>() ?: return
+        alarmManager.cancel(scanPendingIntent(PendingIntent.FLAG_UPDATE_CURRENT))
+    }
+
+    private fun scanPendingIntent(flags: Int): PendingIntent = PendingIntent.getBroadcast(
+        context,
+        SCAN_REQUEST_CODE,
+        Intent(context, ReminderScheduleReceiver::class.java)
+            .setAction(ReminderScheduleReceiver.ACTION_SCAN),
+        flags or PendingIntent.FLAG_IMMUTABLE,
+    )
+
+    private companion object {
+        // Fixed: there is only ever one scan alarm, and re-arming must replace it.
+        const val SCAN_REQUEST_CODE = 0x5CA1
+    }
+}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderAlert.kt

@@ -0,0 +1,37 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import de.jeanlucmakiola.calendula.domain.reminders.PlannedReminder
+
+/**
+ * One reminder as the notification layer needs it: what to show, and the stable
+ * [key] that identifies it across a reboot, a re-scan and a reinstall.
+ *
+ * [key] used to be the `CalendarAlerts` row id. It is now derived from the
+ * reminder itself (see [PlannedReminder.key]) because there is no row any more —
+ * in-house delivery reads `Instances` and `Reminders` and owns the alarm (#75).
+ * Everything downstream only ever needed it to be stable and unique, which it
+ * still is: it keys the notification tag, so a reminder posted twice replaces
+ * itself instead of stacking, and it keys the snooze/dismiss `PendingIntent`s.
+ */
+data class ReminderAlert(
+    val key: Long,
+    val eventId: Long,
+    val calendarId: Long,
+    val beginMillis: Long,
+    val endMillis: Long,
+    /** Raw event title; may be blank — the notifier substitutes "(no title)". */
+    val title: String,
+    val location: String?,
+    val isAllDay: Boolean,
+)
+
+fun PlannedReminder.toAlert(): ReminderAlert = ReminderAlert(
+    key = key,
+    eventId = instance.eventId,
+    calendarId = instance.calendarId,
+    beginMillis = instance.beginMillis,
+    endMillis = instance.endMillis,
+    title = instance.title,
+    location = instance.location,
+    isAllDay = instance.isAllDay,
+)

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderAlertStore.kt

@@ -1,115 +0,0 @@
-package de.jeanlucmakiola.calendula.data.reminders
-
-import android.content.ContentValues
-import android.content.Context
-import android.provider.CalendarContract
-import android.util.Log
-import dagger.hilt.android.qualifiers.ApplicationContext
-import javax.inject.Inject
-import javax.inject.Singleton
-
-/**
- * One due row of the provider's `CalendarAlerts` table (a join with Events).
- * Stays in the data layer: alerts feed the notification path only and never
- * reach a screen, so there is no domain model for them.
- */
-data class ReminderAlert(
-    val alertId: Long,
-    val eventId: Long,
-    val calendarId: Long,
-    val beginMillis: Long,
-    val endMillis: Long,
-    /** Raw event title; may be blank — the notifier substitutes "(no title)". */
-    val title: String,
-    val location: String?,
-    val isAllDay: Boolean,
-)
-
-/**
- * Seam over the `CalendarAlerts` table so the receiver logic can be exercised
- * without a ContentResolver. The provider creates these rows itself — only
- * for `METHOD_ALERT` reminders (verified in AOSP `CalendarAlarmManager`), so
- * email reminders never show up here.
- */
-interface ReminderAlertStore {
-
-    /** Alerts that are due (`ALARM_TIME` has passed) and still unhandled. */
-    fun dueAlerts(nowMillis: Long): List<ReminderAlert>
-
-    /**
-     * Mark the given alerts handled (`STATE_FIRED`) so a later broadcast does
-     * not surface them again. Best effort: this write needs `WRITE_CALENDAR`,
-     * which the user may have declined — then re-broadcasts silently replace
-     * the already-posted notifications instead (same tag, alert-once).
-     */
-    fun markFired(alertIds: List<Long>, nowMillis: Long)
-}
-
-@Singleton
-class AndroidReminderAlertStore @Inject constructor(
-    @ApplicationContext private val context: Context,
-) : ReminderAlertStore {
-
-    override fun dueAlerts(nowMillis: Long): List<ReminderAlert> = context.contentResolver.query(
-        CalendarContract.CalendarAlerts.CONTENT_URI,
-        PROJECTION,
-        CalendarContract.CalendarAlerts.STATE + " = ? AND " +
-            CalendarContract.CalendarAlerts.ALARM_TIME + " <= ?",
-        arrayOf(
-            CalendarContract.CalendarAlerts.STATE_SCHEDULED.toString(),
-            nowMillis.toString(),
-        ),
-        CalendarContract.CalendarAlerts.BEGIN + " ASC",
-    )?.use { c ->
-        buildList {
-            while (c.moveToNext()) {
-                add(
-                    ReminderAlert(
-                        alertId = c.getLong(0),
-                        eventId = c.getLong(1),
-                        calendarId = c.getLong(2),
-                        beginMillis = c.getLong(3),
-                        endMillis = c.getLong(4),
-                        title = c.getString(5).orEmpty(),
-                        location = c.getString(6)?.takeIf { it.isNotBlank() },
-                        isAllDay = c.getInt(7) == 1,
-                    ),
-                )
-            }
-        }
-    } ?: emptyList()
-
-    override fun markFired(alertIds: List<Long>, nowMillis: Long) {
-        if (alertIds.isEmpty()) return
-        val values = ContentValues().apply {
-            put(CalendarContract.CalendarAlerts.STATE, CalendarContract.CalendarAlerts.STATE_FIRED)
-            put(CalendarContract.CalendarAlerts.RECEIVED_TIME, nowMillis)
-            put(CalendarContract.CalendarAlerts.NOTIFY_TIME, nowMillis)
-        }
-        try {
-            context.contentResolver.update(
-                CalendarContract.CalendarAlerts.CONTENT_URI,
-                values,
-                CalendarContract.CalendarAlerts._ID +
-                    " IN (" + alertIds.joinToString(",") + ")",
-                null,
-            )
-        } catch (e: SecurityException) {
-            Log.w(TAG, "Cannot mark alerts fired without WRITE_CALENDAR", e)
-        }
-    }
-
-    private companion object {
-        const val TAG = "ReminderAlertStore"
-        val PROJECTION = arrayOf(
-            CalendarContract.CalendarAlerts._ID,
-            CalendarContract.CalendarAlerts.EVENT_ID,
-            CalendarContract.CalendarAlerts.CALENDAR_ID,
-            CalendarContract.CalendarAlerts.BEGIN,
-            CalendarContract.CalendarAlerts.END,
-            CalendarContract.CalendarAlerts.TITLE,
-            CalendarContract.CalendarAlerts.EVENT_LOCATION,
-            CalendarContract.CalendarAlerts.ALL_DAY,
-        )
-    }
-}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderInstanceSource.kt

@@ -0,0 +1,128 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import android.content.Context
+import android.content.ContentUris
+import android.provider.CalendarContract
+import dagger.hilt.android.qualifiers.ApplicationContext
+import de.jeanlucmakiola.calendula.domain.reminders.ReminderEventInstance
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * The read side of in-house reminder delivery: occurrences and the reminder
+ * offsets hanging off them, straight out of the provider's own tables.
+ *
+ * Deliberately *not* `CalendarAlerts`. That table is the provider's own working
+ * copy of this same information, and the whole point of #75's second round is
+ * that we can no longer assume it gets written. `Instances` and `Reminders` are
+ * plain data the app already reads everywhere else.
+ *
+ * An interface so [ReminderScanner] can be exercised on the JVM without a
+ * ContentResolver, in the shape the rest of `data/calendar` uses.
+ */
+interface ReminderInstanceSource {
+
+    /** Occurrences overlapping `[fromMillis, toMillis]`, of switched-on calendars. */
+    fun occurrences(fromMillis: Long, toMillis: Long): List<ReminderEventInstance>
+
+    /** `METHOD_ALERT` reminder offsets per event id, for the given events. */
+    fun reminderMinutes(eventIds: Collection<Long>): Map<Long, List<Int>>
+
+    /**
+     * The largest `METHOD_ALERT` offset anywhere in the table, so the query
+     * window can be stretched to cover it and a long-lead reminder is planned
+     * before it comes due rather than firing late.
+     */
+    fun longestReminderMinutes(): Int
+}
+
+@Singleton
+class ProviderReminderInstanceSource @Inject constructor(
+    @ApplicationContext private val context: Context,
+) : ReminderInstanceSource {
+
+    override fun occurrences(fromMillis: Long, toMillis: Long): List<ReminderEventInstance> {
+        val uri = CalendarContract.Instances.CONTENT_URI.buildUpon().apply {
+            ContentUris.appendId(this, fromMillis)
+            ContentUris.appendId(this, toMillis)
+        }.build()
+        // `visible` is the calendar's system flag, which the app's one visibility
+        // model writes (#75) — a switched-off calendar must not plan reminders.
+        // The status clause mirrors CalendarDataSource.instances: a cancelled
+        // single occurrence of a series is a real row, and NULL means "normal",
+        // so a bare `!= CANCELED` would drop every ordinary event.
+        val selection = "${CalendarContract.Calendars.VISIBLE} = 1 AND " +
+            "(${CalendarContract.Instances.STATUS} IS NULL OR " +
+            "${CalendarContract.Instances.STATUS} != ${CalendarContract.Events.STATUS_CANCELED})"
+        return context.contentResolver.query(
+            uri, OCCURRENCE_PROJECTION, selection, null, null,
+        )?.use { c ->
+            buildList {
+                while (c.moveToNext()) {
+                    add(
+                        ReminderEventInstance(
+                            eventId = c.getLong(0),
+                            calendarId = c.getLong(1),
+                            beginMillis = c.getLong(2),
+                            endMillis = if (c.isNull(3)) 0L else c.getLong(3),
+                            title = c.getString(4).orEmpty(),
+                            location = c.getString(5)?.takeIf { it.isNotBlank() },
+                            isAllDay = c.getInt(6) == 1,
+                        ),
+                    )
+                }
+            }
+        } ?: emptyList()
+    }
+
+    override fun reminderMinutes(eventIds: Collection<Long>): Map<Long, List<Int>> {
+        if (eventIds.isEmpty()) return emptyMap()
+        val out = mutableMapOf<Long, MutableList<Int>>()
+        // Batched because the ids go into the selection literally; an unbounded
+        // `IN (...)` on a busy calendar would grow the SQL past what SQLite takes.
+        eventIds.distinct().chunked(EVENT_ID_BATCH).forEach { batch ->
+            context.contentResolver.query(
+                CalendarContract.Reminders.CONTENT_URI,
+                REMINDER_PROJECTION,
+                "${CalendarContract.Reminders.METHOD} = " +
+                    "${CalendarContract.Reminders.METHOD_ALERT} AND " +
+                    "${CalendarContract.Reminders.EVENT_ID} IN (${batch.joinToString(",")})",
+                null,
+                null,
+            )?.use { c ->
+                while (c.moveToNext()) {
+                    out.getOrPut(c.getLong(0)) { mutableListOf() } += c.getInt(1)
+                }
+            }
+        }
+        return out
+    }
+
+    override fun longestReminderMinutes(): Int = context.contentResolver.query(
+        CalendarContract.Reminders.CONTENT_URI,
+        arrayOf(CalendarContract.Reminders.MINUTES),
+        "${CalendarContract.Reminders.METHOD} = ${CalendarContract.Reminders.METHOD_ALERT}",
+        null,
+        // One row is enough: the provider passes the sort order to SQLite.
+        "${CalendarContract.Reminders.MINUTES} DESC",
+    )?.use { c -> if (c.moveToFirst()) c.getInt(0) else 0 } ?: 0
+
+    private companion object {
+        const val EVENT_ID_BATCH = 50
+
+        val OCCURRENCE_PROJECTION = arrayOf(
+            CalendarContract.Instances.EVENT_ID,
+            CalendarContract.Instances.CALENDAR_ID,
+            CalendarContract.Instances.BEGIN,
+            CalendarContract.Instances.END,
+            CalendarContract.Instances.TITLE,
+            CalendarContract.Instances.EVENT_LOCATION,
+            CalendarContract.Instances.ALL_DAY,
+        )
+
+        val REMINDER_PROJECTION = arrayOf(
+            CalendarContract.Reminders.EVENT_ID,
+            CalendarContract.Reminders.MINUTES,
+        )
+    }
+}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderMaintenanceWorker.kt

@@ -0,0 +1,67 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import android.content.Context
+import android.util.Log
+import androidx.work.CoroutineWorker
+import androidx.work.ExistingPeriodicWorkPolicy
+import androidx.work.PeriodicWorkRequestBuilder
+import androidx.work.WorkManager
+import androidx.work.WorkerParameters
+import dagger.hilt.EntryPoint
+import dagger.hilt.InstallIn
+import dagger.hilt.android.EntryPointAccessors
+import dagger.hilt.components.SingletonComponent
+import java.util.concurrent.TimeUnit
+
+/**
+ * The backstop under the alarm: a daily scan that runs whether or not the alarm
+ * survived.
+ *
+ * The scan alarm re-arms itself at most a day out, so in the steady state this
+ * finds nothing to do. It exists for the case the whole feature is about — a
+ * device that quietly drops the alarm without a reboot to announce it. The
+ * scheduling half of reminder delivery must not have a single point of failure,
+ * which is exactly what the provider's broadcast turned out to be.
+ */
+object ReminderMaintenanceScheduler {
+
+    private const val WORK_NAME = "reminder-scan-maintenance"
+
+    /** Enqueue the daily backstop; idempotent, so every launch may call it. */
+    fun apply(context: Context) {
+        val request = PeriodicWorkRequestBuilder<ReminderMaintenanceWorker>(1, TimeUnit.DAYS)
+            // The launch scan covers now; let the first periodic run wait.
+            .setInitialDelay(1, TimeUnit.DAYS)
+            .build()
+        WorkManager.getInstance(context)
+            .enqueueUniquePeriodicWork(WORK_NAME, ExistingPeriodicWorkPolicy.UPDATE, request)
+    }
+}
+
+class ReminderMaintenanceWorker(
+    appContext: Context,
+    params: WorkerParameters,
+) : CoroutineWorker(appContext, params) {
+
+    @EntryPoint
+    @InstallIn(SingletonComponent::class)
+    interface Deps {
+        fun reminderScanner(): ReminderScanner
+    }
+
+    override suspend fun doWork(): Result = try {
+        EntryPointAccessors.fromApplication(applicationContext, Deps::class.java)
+            .reminderScanner()
+            .scan()
+        Result.success()
+    } catch (e: Exception) {
+        // The scan swallows its own failures; anything reaching here is the
+        // entry point itself, which a retry will not mend. Never fail the chain.
+        Log.w(TAG, "Reminder maintenance scan failed", e)
+        Result.success()
+    }
+
+    private companion object {
+        const val TAG = "ReminderMaintenance"
+    }
+}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderNotifier.kt

@@ -29,11 +29,13 @@ import javax.inject.Inject
 import javax.inject.Singleton
 
 /**
- * Posts one notification per due reminder alert on a dedicated channel.
- * Tapping opens the event's detail screen; the tag is the alert id, so a
- * re-broadcast of an alert we couldn't mark fired replaces its notification
- * silently ([NotificationCompat.Builder.setOnlyAlertOnce]) instead of
- * duplicating it.
+ * Posts one notification per due reminder on a dedicated channel. Tapping opens
+ * the event's detail screen.
+ *
+ * The tag is the reminder's stable key, so a scan that posts the same reminder
+ * again — a catch-up pass overlapping the alarm that already fired — replaces
+ * its notification silently ([NotificationCompat.Builder.setOnlyAlertOnce])
+ * instead of stacking a second one.
  */
 @Singleton
 class ReminderNotifier @Inject constructor(
@@ -52,13 +54,12 @@ class ReminderNotifier @Inject constructor(
     }
 
     /**
-     * The single choke point for "this calendar is switched off". The provider
-     * side needs no help — with `VISIBLE = 0` it creates no alert rows at all —
-     * but two paths reach [post] without one: a snooze we re-show from our own
-     * exact alarm, scheduled before the calendar was switched off, and a
-     * read-only install whose switch lives app-side ([CalendarPrefs]) because it
-     * may not write the flag. Both are covered here rather than in either
-     * receiver.
+     * The single choke point for "this calendar is switched off". The scan
+     * already filters on `Calendars.VISIBLE`, but two paths reach [post] around
+     * it: a snooze re-shown from its own alarm, armed before the calendar was
+     * switched off, and a read-only install whose switch lives app-side
+     * ([CalendarPrefs]) because it may not write the flag. Both are covered here
+     * rather than in either receiver.
      */
     private suspend fun isSilenced(calendarId: Long): Boolean =
         calendarId in calendarPrefs.pendingDisabledCalendarIds.first() ||
@@ -66,8 +67,8 @@ class ReminderNotifier @Inject constructor(
 
     /**
      * Post [alert], unless its calendar is switched off. Returns whether the
-     * notification was put up: a silenced alert must stay unhandled so that
-     * switching the calendar back on can still surface it (see [handledAlertIds]).
+     * notification was put up, which the snooze re-show path uses to tell a
+     * silenced reminder from a delivered one.
      */
     suspend fun post(alert: ReminderAlert): Boolean {
         if (isSilenced(alert.calendarId)) return false
@@ -117,7 +118,7 @@ class ReminderNotifier @Inject constructor(
             .build()
         try {
             NotificationManagerCompat.from(context)
-                .notify(alert.alertId.toString(), NOTIFICATION_ID, notification)
+                .notify(alert.key.toString(), NOTIFICATION_ID, notification)
         } catch (e: SecurityException) {
             // POST_NOTIFICATIONS was revoked between canPost() and here.
             Log.w(TAG, "Could not post reminder for event ${alert.eventId}", e)
@@ -128,7 +129,7 @@ class ReminderNotifier @Inject constructor(
 
     /** Remove a posted reminder (snooze re-shows it later; dismiss is final). */
     fun cancel(alert: ReminderAlert) {
-        NotificationManagerCompat.from(context).cancel(alert.alertId.toString(), NOTIFICATION_ID)
+        NotificationManagerCompat.from(context).cancel(alert.key.toString(), NOTIFICATION_ID)
     }
 
     private fun actionIntent(alert: ReminderAlert, action: String): PendingIntent =
@@ -141,7 +142,11 @@ class ReminderNotifier @Inject constructor(
 
     private fun detailIntent(alert: ReminderAlert): PendingIntent = PendingIntent.getActivity(
         context,
-        /* requestCode = */ alert.alertId.toInt(),
+        // Shares the per-(alert, action) request-code scheme with the buttons, so
+        // the key's wider value range can't collide one notification's intents.
+        /* requestCode = */ ReminderActionReceiver.requestCode(
+            alert, ReminderActionReceiver.ACTION_OPEN,
+        ),
         MainActivity.eventDetailIntent(context, alert.eventId, alert.beginMillis, alert.endMillis),
         PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE,
     )

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderRecovery.kt

@@ -1,46 +0,0 @@
-package de.jeanlucmakiola.calendula.data.reminders
-
-import de.jeanlucmakiola.calendula.data.di.IoDispatcher
-import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
-import kotlinx.coroutines.CoroutineDispatcher
-import kotlinx.coroutines.flow.first
-import kotlinx.coroutines.withContext
-import javax.inject.Inject
-import javax.inject.Singleton
-
-/**
- * Re-posts the reminders a switched-off calendar silenced, when it is switched
- * back on while they still matter.
- *
- * Only the app-side switch needs this — a read-only install, or an upgrade the
- * reconciler hasn't flushed yet. With `Calendars.VISIBLE = 0` the provider
- * deletes the calendar's alert rows itself and re-creates them on the way back;
- * app-side the rows stay, still `STATE_SCHEDULED`, because
- * [EventReminderReceiver] deliberately leaves the ones it silenced unhandled
- * (see [handledAlertIds]). So the provider's own table is the stash, and nothing
- * is mirrored locally.
- *
- * Best effort at switch-on time: it mirrors the receiver's gates (reminders on,
- * notifications postable) and there is no later re-scan, so an alert left
- * unposted because those are closed is simply released.
- */
-@Singleton
-class ReminderRecovery @Inject constructor(
-    private val alertStore: ReminderAlertStore,
-    private val notifier: ReminderNotifier,
-    private val settingsPrefs: SettingsPrefs,
-    @IoDispatcher private val io: CoroutineDispatcher,
-) {
-
-    suspend fun rePostFor(calendarIds: Collection<Long>) = withContext(io) {
-        if (calendarIds.isEmpty()) return@withContext
-        if (!settingsPrefs.remindersEnabled.first() || !notifier.canPost()) return@withContext
-        val now = System.currentTimeMillis()
-        val ids = calendarIds.toSet()
-        val recovered = alertStore.dueAlerts(now)
-            .filter { it.calendarId in ids && it.isRelevantAt(now) }
-        if (recovered.isEmpty()) return@withContext
-        val postedIds = recovered.filter { notifier.post(it) }.map { it.alertId }
-        alertStore.markFired(postedIds, now)
-    }
-}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderScanner.kt

@@ -0,0 +1,170 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import android.Manifest
+import android.content.Context
+import android.content.pm.PackageManager
+import android.util.Log
+import androidx.core.content.ContextCompat
+import dagger.hilt.android.qualifiers.ApplicationContext
+import de.jeanlucmakiola.calendula.data.calendar.CalendarDataSource
+import de.jeanlucmakiola.calendula.data.di.IoDispatcher
+import de.jeanlucmakiola.calendula.data.prefs.ReminderStatePrefs
+import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
+import de.jeanlucmakiola.calendula.domain.reminders.planReminders
+import de.jeanlucmakiola.calendula.domain.reminders.reminderQueryHorizon
+import de.jeanlucmakiola.calendula.domain.reminders.reminderWatermark
+import de.jeanlucmakiola.calendula.domain.reminders.scheduleReminders
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.CoroutineStart
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.channels.BufferOverflow
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.debounce
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.launchIn
+import kotlinx.coroutines.flow.onEach
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.withContext
+import java.time.ZoneId
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * One pass of in-house reminder delivery: read what is planned, post what has
+ * come due, and arm the next wake-up.
+ *
+ * This is the whole loop. Every trigger — the alarm firing, boot, a clock or
+ * timezone change, an edit landing in the provider, the app starting, the daily
+ * safety net — runs the same [scan], so there is a single path to reason about
+ * and no ordering between triggers to get wrong. Re-running it is always safe:
+ * the watermark in [ReminderStatePrefs] decides what is owed, not the trigger.
+ */
+@Singleton
+class ReminderScanner @Inject constructor(
+    @ApplicationContext private val context: Context,
+    private val source: ReminderInstanceSource,
+    private val calendarDataSource: CalendarDataSource,
+    private val notifier: ReminderNotifier,
+    private val alarms: ReminderAlarmScheduler,
+    private val state: ReminderStatePrefs,
+    private val settingsPrefs: SettingsPrefs,
+    @IoDispatcher private val io: kotlinx.coroutines.CoroutineDispatcher,
+) {
+
+    // Triggers overlap freely (an alarm during a burst of edits); serialize so
+    // two passes can't both read the same watermark and post the same reminder.
+    private val scanLock = Mutex()
+
+    private val scope = CoroutineScope(SupervisorJob() + io)
+    private val providerChanges = MutableSharedFlow<Unit>(
+        replay = 0, extraBufferCapacity = 1, onBufferOverflow = BufferOverflow.DROP_OLDEST,
+    )
+    private var watching = false
+
+    suspend fun scan() = withContext(io) {
+        scanLock.withLock {
+            try {
+                runScan()
+            } catch (e: SecurityException) {
+                // The calendar permission was revoked mid-flight. Nothing to
+                // re-arm and nothing to recover from — the next grant re-scans.
+                Log.w(TAG, "Reminder scan lacks the calendar permission", e)
+            } catch (e: Exception) {
+                Log.w(TAG, "Reminder scan failed", e)
+            }
+        }
+    }
+
+    private suspend fun runScan() {
+        val now = System.currentTimeMillis()
+        if (!hasReadCalendar()) return
+
+        if (!settingsPrefs.remindersEnabled.first()) {
+            // Reminders off: drop the wake-up, but keep the watermark moving so
+            // switching them back on doesn't replay everything missed meanwhile.
+            alarms.cancelScan()
+            state.setLastScanMillis(now)
+            return
+        }
+
+        val lookahead = reminderQueryHorizon(LOOKAHEAD_MILLIS, source.longestReminderMinutes())
+        // Reach a little into the past as well: an event already under way can
+        // still owe a reminder (an all-day "at time of event" encodes to a
+        // negative offset, which fires after begin), and a catch-up pass needs
+        // to see the occurrences whose moment it missed.
+        val occurrences = source.occurrences(now - PAST_WINDOW_MILLIS, now + lookahead)
+        val planned = planReminders(
+            instances = occurrences,
+            minutesByEvent = source.reminderMinutes(occurrences.map { it.eventId }),
+            zone = ZoneId.systemDefault(),
+            allDayTimeMinutes = settingsPrefs.allDayReminderTimeMinutes.first(),
+        )
+
+        val schedule = scheduleReminders(
+            planned = planned,
+            lastFiredMillis = reminderWatermark(state.lastScanMillis(), now),
+            nowMillis = now,
+            horizonMillis = now + MAX_ALARM_INTERVAL_MILLIS,
+        )
+
+        if (notifier.canPost()) {
+            schedule.due.forEach { notifier.post(it.toAlert()) }
+        }
+        // Advance regardless of whether anything could be posted: a user who
+        // muted notifications is not owed a backlog when they unmute.
+        state.setLastScanMillis(now)
+        alarms.scheduleScan(schedule.nextAlarmMillis)
+    }
+
+    private fun hasReadCalendar(): Boolean = ContextCompat.checkSelfPermission(
+        context, Manifest.permission.READ_CALENDAR,
+    ) == PackageManager.PERMISSION_GRANTED
+
+    /**
+     * Re-scan when the provider changes, so an event saved or deleted in the app
+     * re-arms the alarm immediately rather than waiting for the next pass.
+     *
+     * Debounced: a single save writes the event, its reminders and its
+     * attendees, and each lands as its own notification. Only useful while the
+     * process is alive — every other trigger covers the rest, which is why
+     * nothing here needs to survive it.
+     */
+    fun startWatchingProvider() {
+        if (watching) return
+        watching = true
+        providerChanges
+            .debounce(PROVIDER_CHANGE_DEBOUNCE_MILLIS)
+            .onEach { scan() }
+            .launchIn(scope)
+        calendarDataSource.registerChangeListener { providerChanges.tryEmit(Unit) }
+    }
+
+    /** Fire-and-forget scan for callers that are not in a coroutine already. */
+    fun scanInBackground() {
+        scope.launch(start = CoroutineStart.DEFAULT) { scan() }
+    }
+
+    private companion object {
+        const val TAG = "ReminderScanner"
+
+        /**
+         * How far ahead occurrences are read. Stretched further by the longest
+         * reminder offset in the table, so this is only the floor.
+         */
+        const val LOOKAHEAD_MILLIS = 7L * 24 * 60 * 60 * 1000
+
+        /** How far back to look for occurrences that may still owe a reminder. */
+        const val PAST_WINDOW_MILLIS = 24L * 60 * 60 * 1000
+
+        /**
+         * Never wait longer than a day for the next pass, even with nothing
+         * pending: it rolls the lookahead window forward and re-arms an alarm
+         * the system may have dropped.
+         */
+        const val MAX_ALARM_INTERVAL_MILLIS = 24L * 60 * 60 * 1000
+
+        const val PROVIDER_CHANGE_DEBOUNCE_MILLIS = 2_000L
+    }
+}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderScheduleReceiver.kt

@@ -0,0 +1,63 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+import dagger.hilt.android.AndroidEntryPoint
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+
+/**
+ * Every reason to re-run a reminder scan that arrives from outside the process.
+ *
+ * All of them do the same thing, because [ReminderScanner.scan] is idempotent
+ * and works out what is owed from its watermark rather than from why it was
+ * called:
+ *
+ * - **our own alarm** ([ACTION_SCAN]) — the ordinary case, a reminder is due;
+ * - **boot** and **package replaced** — both wipe pending alarms, so the app has
+ *   to re-arm or reminders stop silently, which is the failure #75 is about;
+ * - **time and timezone changes** — they move every reminder relative to the
+ *   armed alarm, and an all-day reminder's fire hour is recomposed in the
+ *   current zone, so both need a fresh plan.
+ *
+ * Exported because the system broadcasts arrive from outside. [ACTION_SCAN] is
+ * ours and always sent as an explicit intent; another app triggering a scan
+ * early would only make it re-read the provider and re-arm, which is harmless.
+ */
+@AndroidEntryPoint
+class ReminderScheduleReceiver : BroadcastReceiver() {
+
+    @Inject lateinit var scanner: ReminderScanner
+
+    override fun onReceive(context: Context, intent: Intent) {
+        // Every action here does the same thing, but the filter still has to be
+        // checked: the receiver is exported, and the system broadcasts it takes
+        // are protected, so an intent arriving with any other action did not
+        // come from where it claims to.
+        if (intent.action !in HANDLED_ACTIONS) return
+        val pendingResult = goAsync()
+        CoroutineScope(SupervisorJob() + Dispatchers.IO).launch {
+            try {
+                scanner.scan()
+            } finally {
+                pendingResult.finish()
+            }
+        }
+    }
+
+    companion object {
+        const val ACTION_SCAN = "de.jeanlucmakiola.calendula.reminders.SCAN"
+
+        private val HANDLED_ACTIONS = setOf(
+            ACTION_SCAN,
+            Intent.ACTION_BOOT_COMPLETED,
+            Intent.ACTION_MY_PACKAGE_REPLACED,
+            Intent.ACTION_TIME_CHANGED,
+            Intent.ACTION_TIMEZONE_CHANGED,
+        )
+    }
+}

app/src/main/java/de/jeanlucmakiola/calendula/data/reminders/ReminderSnoozeScheduler.kt

@@ -12,9 +12,12 @@ import javax.inject.Singleton
 /**
  * Schedules a one-off exact alarm that re-shows a snoozed reminder.
  *
- * The app otherwise relies entirely on the calendar provider's `EVENT_REMINDER`
- * broadcast (the Etar model), but a snoozed reminder has no provider backing —
- * its `CalendarAlerts` row is already fired — so we must re-fire it ourselves.
+ * Separate from [ReminderAlarmScheduler]'s scan alarm, and deliberately so: a
+ * snooze is pinned to one reminder at a time the user chose, while the scan
+ * alarm is a single moving wake-up for whatever comes next. A re-show also has
+ * to outlive the scan's watermark moving past that reminder, so it carries the
+ * reminder in its own intent rather than re-deriving it.
+ *
  * A snooze that lands late is a broken snooze, hence an *exact* alarm; we fall
  * back to an inexact allow-while-idle alarm only if the OS withholds the
  * exact-alarm capability (API 31–32 where the user revoked it).

app/src/main/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlan.kt

@@ -0,0 +1,258 @@
+package de.jeanlucmakiola.calendula.domain.reminders
+
+import java.time.Instant
+import java.time.LocalDate
+import java.time.LocalTime
+import java.time.ZoneId
+import java.time.ZoneOffset
+import java.time.temporal.ChronoUnit
+
+/**
+ * Works out *when* each reminder has to fire and *which* ones are due, with no
+ * provider and no clock of its own — the whole decision layer of in-house
+ * reminder delivery (#75).
+ *
+ * Calendula used to leave both halves to the calendar provider: it scheduled the
+ * alarms, wrote the `CalendarAlerts` rows, and broadcast `EVENT_REMINDER` at the
+ * right moment. That chain is intact on stock Android but demonstrably not on
+ * every device — AOSP's own unbundled calendar carries three separate
+ * workarounds for OEMs that retarget the broadcast, or that only write the alert
+ * row at alert time. An app that can only *react* to that broadcast has no way
+ * to notice it never came.
+ *
+ * So the offsets in `CalendarContract.Reminders` are now read as data and turned
+ * into alarms we own. Everything here is pure: instances and reminder offsets in,
+ * fire instants out.
+ */
+
+/** An occurrence that reminders can hang off, flattened out of `Instances`. */
+data class ReminderEventInstance(
+    val eventId: Long,
+    val calendarId: Long,
+    val beginMillis: Long,
+    val endMillis: Long,
+    val title: String,
+    val location: String?,
+    val isAllDay: Boolean,
+)
+
+/**
+ * One occurrence paired with one of its reminder offsets, and the instant that
+ * pairing has to fire at.
+ */
+data class PlannedReminder(
+    val instance: ReminderEventInstance,
+    val minutes: Int,
+    val alarmMillis: Long,
+) {
+    /**
+     * Stable identity of this reminder, derived from what defines it rather
+     * than from a provider row id (there is none any more). It keys the
+     * notification tag and the snooze/dismiss `PendingIntent`s, so it has to
+     * survive a reboot, a re-scan and a reinstall — the same reminder must land
+     * on the same notification instead of stacking a second one.
+     */
+    val key: Long = key(instance.eventId, instance.beginMillis, minutes)
+
+    private companion object {
+        fun key(eventId: Long, beginMillis: Long, minutes: Int): Long {
+            var h = eventId * 1_000_003L
+            h = (h xor beginMillis) * 31L
+            return h + minutes
+        }
+    }
+}
+
+/** What one scan concluded: post these now, and wake up again at [nextAlarmMillis]. */
+data class ReminderSchedule(
+    val due: List<PlannedReminder>,
+    val nextAlarmMillis: Long,
+)
+
+private const val MILLIS_PER_MINUTE = 60_000L
+private const val MINUTES_PER_DAY = 1_440
+
+/**
+ * Pair every instance with each of its event's reminder offsets.
+ *
+ * A **timed** occurrence is trivial: `begin` is an absolute instant, so
+ * `begin − minutes` is exact by construction, in any timezone, across any DST
+ * boundary.
+ *
+ * An **all-day** occurrence is not, and taking the offset at face value is what
+ * makes reminders land at the wrong hour. Its `begin` is UTC midnight, and the
+ * stored offset is not a plain lead time — `AllDayReminderEncoding` folds the
+ * wanted wall-clock hour into it, sampled against *one* date's UTC offset. Fire
+ * at `begin − minutes` and every occurrence in a different DST phase than the one
+ * that was sampled drifts by the offset delta, an hour early in one direction and
+ * an hour late in the other. Rows written by other apps carry no wall-clock at
+ * all — a conventional `1440` fires at UTC midnight, which is 01:00 or 02:00
+ * local in Berlin and the wrong day west of UTC.
+ *
+ * So the offset is only read for *which day* it means, via [allDayLeadDays], and
+ * the hour comes from [allDayTimeMinutes] — the one global "show all-day
+ * reminders at" setting — recomposed against each occurrence's own date in
+ * [zone]. 09:00 Berlin is then 09:00 Berlin on every occurrence, whatever the
+ * offset was when the row was written.
+ *
+ * [minutesByEvent] may hold duplicate offsets (two identical reminder rows on one
+ * event); they collapse, because they would otherwise fight over one notification.
+ */
+fun planReminders(
+    instances: List<ReminderEventInstance>,
+    minutesByEvent: Map<Long, List<Int>>,
+    zone: ZoneId,
+    allDayTimeMinutes: Int,
+): List<PlannedReminder> = instances.flatMap { instance ->
+    minutesByEvent[instance.eventId].orEmpty().distinct().map { minutes ->
+        PlannedReminder(
+            instance = instance,
+            minutes = minutes,
+            alarmMillis = if (instance.isAllDay) {
+                allDayAlarmMillis(instance.beginMillis, minutes, zone, allDayTimeMinutes)
+            } else {
+                instance.beginMillis - minutes * MILLIS_PER_MINUTE
+            },
+        )
+    }
+}
+
+/** UTC midnight of an all-day occurrence, as the calendar date it stands for. */
+private fun allDayDate(beginMillis: Long): LocalDate =
+    Instant.ofEpochMilli(beginMillis).atZone(ZoneOffset.UTC).toLocalDate()
+
+/**
+ * How many whole days before its occurrence a raw all-day offset means.
+ *
+ * Normally the local date of the encoded fire instant answers it: our own rows
+ * fold the wanted hour into the offset, so that date *is* the day the reminder
+ * belongs to, whatever the offset was when it was written.
+ *
+ * A plain multiple of 1440 is the exception. Those come from calendar apps that
+ * store a bare lead time against UTC midnight, and east of UTC both readings
+ * agree anyway — but west of UTC the instant falls on the previous local date,
+ * so the day count has to be taken at face value or it comes out one too many.
+ *
+ * Except when the row is one of ours after all: our offset lands on a multiple
+ * whenever the all-day hour equals the zone's UTC offset (20:00 in New York,
+ * 19:00 an hour further west, and so on), and reading those at face value fired
+ * them a day late — a "1 day before" arriving on the morning of the event. So
+ * the hour decides, not the shape of the number: an instant landing on the hour
+ * the setting names is ours. Within an hour or so of it counts, because a fixed
+ * offset written in one DST phase drifts by the offset delta in the other.
+ *
+ * The two are genuinely indistinguishable in that band — the encodings collide
+ * exactly there — so the tie goes to the reading that honours the lead time the
+ * user chose in this app.
+ *
+ * [de.jeanlucmakiola.calendula.data.calendar.fromProviderAllDayMinutes] calls
+ * this for display, so the notification arrives on the day the event screen says
+ * it will.
+ */
+internal fun allDayLeadDays(
+    rawMinutes: Int,
+    startDate: LocalDate,
+    zone: ZoneId,
+    allDayTimeMinutes: Int,
+): Long {
+    val utcMidnight = startDate.atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
+    val encoded = Instant.ofEpochMilli(utcMidnight - rawMinutes * MILLIS_PER_MINUTE).atZone(zone)
+    val minutesFromNamedHour = encoded.toLocalTime().let {
+        val delta = (it.hour * 60 + it.minute - allDayTimeMinutes).mod(MINUTES_PER_DAY)
+        minOf(delta, MINUTES_PER_DAY - delta)
+    }
+    if (rawMinutes % MINUTES_PER_DAY == 0 && minutesFromNamedHour > NAMED_HOUR_TOLERANCE_MINUTES) {
+        return (rawMinutes / MINUTES_PER_DAY).toLong()
+    }
+    return ChronoUnit.DAYS.between(encoded.toLocalDate(), startDate)
+}
+
+/** DST drift a row written in the other phase carries, rounded up past Lord Howe's half hour. */
+private const val NAMED_HOUR_TOLERANCE_MINUTES = 90
+
+private fun allDayAlarmMillis(
+    beginMillis: Long,
+    rawMinutes: Int,
+    zone: ZoneId,
+    allDayTimeMinutes: Int,
+): Long = allDayDate(beginMillis)
+    .minusDays(allDayLeadDays(rawMinutes, allDayDate(beginMillis), zone, allDayTimeMinutes))
+    .atTime(LocalTime.of(allDayTimeMinutes / 60, allDayTimeMinutes % 60))
+    .atZone(zone)
+    .toInstant()
+    .toEpochMilli()
+
+/**
+ * Split [planned] into what is due now and when to wake up next.
+ *
+ * Due means the fire instant falls in `(lastFiredMillis, nowMillis]` — a
+ * half-open watermark, so a scan triggered twice cannot post the same reminder
+ * twice, while a scan that runs late still catches everything the missed alarm
+ * would have posted. That catch-up is the point: an alarm dropped by a reboot,
+ * an app update or a doze window is recovered by the next scan rather than lost.
+ *
+ * A reminder whose event has already ended is dropped rather than posted late —
+ * see [isStillRelevant].
+ *
+ * [nextAlarmMillis] is capped at [horizonMillis] even when nothing is pending, so
+ * the scan re-runs at least that often and the lookahead window rolls forward.
+ */
+fun scheduleReminders(
+    planned: List<PlannedReminder>,
+    lastFiredMillis: Long,
+    nowMillis: Long,
+    horizonMillis: Long,
+): ReminderSchedule {
+    val due = planned
+        .filter { it.alarmMillis in (lastFiredMillis + 1)..nowMillis }
+        .filter { it.instance.isStillRelevant(nowMillis) }
+        .distinctBy { it.key }
+        .sortedWith(compareBy({ it.instance.beginMillis }, { it.key }))
+    val nextPending = planned
+        .filter { it.alarmMillis > nowMillis }
+        .minOfOrNull { it.alarmMillis }
+    return ReminderSchedule(
+        due = due,
+        nextAlarmMillis = minOf(nextPending ?: horizonMillis, horizonMillis),
+    )
+}
+
+/**
+ * Still worth showing while the occurrence has not ended. Falls back to the
+ * begin time when the end is unknown (0L).
+ */
+fun ReminderEventInstance.isStillRelevant(nowMillis: Long): Boolean =
+    (endMillis.takeIf { it > 0L } ?: beginMillis) >= nowMillis
+
+/**
+ * The watermark a scan at [nowMillis] should measure against, given what the
+ * last one recorded.
+ *
+ * A first-ever scan ([lastScanMillis] `null`) claims the present, so an install
+ * or an upgrade onto in-house delivery does not treat every reminder since the
+ * epoch as overdue and bury the user in notifications. A watermark in the
+ * *future* — the clock was moved back, or the user travelled across the date
+ * line — is clamped for the mirror-image reason: left alone it would silence
+ * every reminder until real time caught up with it.
+ */
+fun reminderWatermark(lastScanMillis: Long?, nowMillis: Long): Long =
+    lastScanMillis?.coerceAtMost(nowMillis) ?: nowMillis
+
+/**
+ * How far ahead instances must be queried for [scheduleReminders] to see every
+ * reminder in time: the plain lookahead plus the longest offset any reminder row
+ * carries, so a "two weeks before" reminder is planned before it comes due
+ * instead of firing late (the limitation Etar's equivalent documents).
+ *
+ * The stretch is capped at [MAX_REMINDER_LEAD_MILLIS]. `maxReminderMinutes` is
+ * whatever the largest row in the whole provider says, across every calendar and
+ * whoever wrote it — an imported `TRIGGER:-P100W`, or a sync adapter writing
+ * nonsense, would otherwise make every scan (launch, every provider change, every
+ * alarm) expand every recurring series over years. A lead beyond the cap is not
+ * delivered; a year is far past anything the picker composes.
+ */
+fun reminderQueryHorizon(lookaheadMillis: Long, maxReminderMinutes: Int): Long =
+    lookaheadMillis + (maxReminderMinutes * MILLIS_PER_MINUTE).coerceIn(0L, MAX_REMINDER_LEAD_MILLIS)
+
+/** Longest reminder offset a scan stretches its query window for — one year. */
+const val MAX_REMINDER_LEAD_MILLIS = 365L * 24 * 60 * 60 * 1000

app/src/main/java/de/jeanlucmakiola/calendula/ui/RootScreen.kt

@@ -51,6 +51,10 @@ fun RootScreen(
         )
     }
 
+    // Whether the app came up already holding it — a launch scan has covered
+    // that case, so only a grant made during this session owes a re-scan.
+    val grantedAtLaunch = remember { hasPermission }
+
     val lifecycle = LocalLifecycleOwner.current.lifecycle
     DisposableEffect(lifecycle) {
         val obs = LifecycleEventObserver { _, event ->
@@ -88,7 +92,10 @@ fun RootScreen(
             // Runs on entry however the permission was granted — including from
             // Android's app-settings screen, which only comes back through the
             // ON_RESUME check above. Cheap once there is nothing left to do.
-            LaunchedEffect(Unit) { visibilityNotice.reconcile() }
+            LaunchedEffect(Unit) {
+                visibilityNotice.reconcile()
+                if (!grantedAtLaunch) reminderOnboarding.rearmAfterGrant()
+            }
             if (onboardingDone == true && noticePending) {
                 CalendarVisibilityNoticeDialog(onDismiss = visibilityNotice::dismiss)
             }

app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsScreen.kt

@@ -99,7 +99,10 @@ import de.jeanlucmakiola.calendula.domain.isNotSynced
 import de.jeanlucmakiola.calendula.domain.orderedForManager
 import de.jeanlucmakiola.calendula.domain.stateLabels
 import de.jeanlucmakiola.calendula.data.calendar.CalendarColorPalette
+import de.jeanlucmakiola.calendula.ui.common.AccountKey
 import de.jeanlucmakiola.calendula.ui.common.CalendarColorChip
+import de.jeanlucmakiola.calendula.ui.common.accountGroupTitle
+import de.jeanlucmakiola.calendula.ui.common.groupByAccount
 import de.jeanlucmakiola.calendula.ui.common.LocalSoftenColors
 import de.jeanlucmakiola.calendula.ui.common.eventFill
 import de.jeanlucmakiola.calendula.ui.common.LeadingAvatar
@@ -228,7 +231,7 @@ private fun CalendarsList(
     val snackbarHostState = remember { SnackbarHostState() }
     // Accounts the user has folded shut; empty = all expanded (keeps every
     // calendar visible by default, the section is collapsible for tidiness).
-    var collapsedAccounts by remember { mutableStateOf(emptySet<String>()) }
+    var collapsedAccounts by remember { mutableStateOf(emptySet<AccountKey>()) }
     var localExpanded by remember { mutableStateOf(true) }
     val writeErrorText = stringResource(R.string.calendars_write_error)
 
@@ -417,10 +420,11 @@ private fun CalendarsList(
         SectionHeader(stringResource(R.string.calendars_synced_header))
         HintText(stringResource(R.string.calendars_synced_hint))
         synced
-            .groupBy { it.accountName.ifBlank { it.accountType } }
-            .forEach { (account, cals) ->
-                val expanded = account !in collapsedAccounts
-                val accountType = cals.first().accountType
+            .groupByAccount()
+            .forEach { group ->
+                val cals = group.calendars
+                val expanded = group.key !in collapsedAccounts
+                val accountType = group.accountType
                 // A non-syncing calendar has no switch, so it neither counts
                 // towards "the whole account is off" nor moves with toggle-all.
                 val switchable = cals.filter { it.hasVisibilitySwitch }
@@ -428,7 +432,7 @@ private fun CalendarsList(
                     switchable.none { it.isVisibleInSystem }
                 Spacer(Modifier.height(16.dp))
                 CalendarGroup(
-                    title = account,
+                    title = accountGroupTitle(group),
                     expanded = expanded,
                     bodyHasRows = true,
                     headerDisabled = accountDisabled,
@@ -440,9 +444,9 @@ private fun CalendarsList(
                     },
                     onToggleExpand = {
                         collapsedAccounts = if (expanded) {
-                            collapsedAccounts + account
+                            collapsedAccounts + group.key
                         } else {
-                            collapsedAccounts - account
+                            collapsedAccounts - group.key
                         }
                     },
                     showToggleAll = switchable.isNotEmpty(),

app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsViewModel.kt

@@ -13,7 +13,6 @@ import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.ics.IcsExporter
 import de.jeanlucmakiola.calendula.data.prefs.BackupStatus
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
-import de.jeanlucmakiola.calendula.data.reminders.ReminderRecovery
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.ics.IcsWriter
 import kotlinx.coroutines.CoroutineDispatcher
@@ -44,7 +43,6 @@ class CalendarsViewModel @Inject constructor(
     private val repository: CalendarRepository,
     private val icsExporter: IcsExporter,
     private val settingsPrefs: SettingsPrefs,
-    private val reminderRecovery: ReminderRecovery,
     @IoDispatcher private val io: CoroutineDispatcher,
 ) : ViewModel() {
 
@@ -155,24 +153,24 @@ class CalendarsViewModel @Inject constructor(
      * reminders. Nothing is patched by hand — the provider notifies and the
      * observer re-queries.
      *
-     * Switching one back on also re-posts the reminders it silenced while it was
-     * off and that are still relevant — those the app kept app-side because it
-     * may not write the flag ([ReminderRecovery]).
+     * A reminder that came due while the calendar was off stays gone when it is
+     * switched back on. Delivery plans from `Instances` and `Reminders` on every
+     * scan (#75), but the watermark has already moved past that moment, so no
+     * scan returns it again — and on a read-only install the switch never
+     * reaches the provider at all, so nothing even triggers one. Deliberate: the
+     * reminder was silenced on purpose, and the event itself is back in view.
      */
     fun setCalendarVisible(id: Long, visible: Boolean) = write {
         repository.setCalendarsVisible(listOf(id), visible)
-        if (visible) reminderRecovery.rePostFor(listOf(id))
     }
 
     /**
      * Switch every calendar of one account on or off — the "toggle all"
-     * affordance on an account header. Each row is written on its own (the
-     * provider only re-arms reminder alarms for a single-id update), in one
+     * affordance on an account header. Each row is written on its own, in one
      * coroutine so the writes can't race each other.
      */
     fun setAccountVisible(ids: Collection<Long>, visible: Boolean) = write {
         repository.setCalendarsVisible(ids, visible)
-        if (visible) reminderRecovery.rePostFor(ids)
     }
 
     // --- Automatic backup (issue #8) ------------------------------------

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/AccountGroups.kt

@@ -0,0 +1,86 @@
+package de.jeanlucmakiola.calendula.ui.common
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
+import de.jeanlucmakiola.calendula.R
+import de.jeanlucmakiola.calendula.domain.CalendarSource
+
+/**
+ * One account's calendars, as every surface that lists calendars by account
+ * shows them.
+ *
+ * An account is identified by name **and** type (#77). A Google account and a
+ * DAVx5 account can carry the same address and still be two separate accounts,
+ * from separate apps: merging them mixed their calendars into one group whose
+ * header — source logo, "manage in app", toggle-all, collapsed state — was
+ * derived from whichever calendar happened to sort first.
+ */
+data class CalendarAccountGroup(
+    /** Stable identity: what makes two calendars belong to the same account. */
+    val key: AccountKey,
+    /** The account's own name, as shown when it is unambiguous. */
+    val label: String,
+    /** True when another group shows the same [label] under a different type. */
+    val ambiguous: Boolean,
+    val calendars: List<CalendarSource>,
+) {
+    val accountType: String get() = key.type
+}
+
+/** The pair a group is keyed on. */
+data class AccountKey(val name: String, val type: String)
+
+/**
+ * Group [calendars] under their owning account, preserving the provider's order
+ * within each group and ordering groups by first appearance.
+ *
+ * The label falls back through name → type → the first calendar's own name, so
+ * a calendar with no account still lands somewhere sensible.
+ */
+fun List<CalendarSource>.groupByAccount(): List<CalendarAccountGroup> {
+    val grouped = groupBy { AccountKey(it.accountName, it.accountType) }
+    val labels = grouped.mapValues { (key, cals) ->
+        key.name.ifBlank { key.type }.ifBlank { cals.first().displayName }
+    }
+    val shared = labels.values.groupingBy { it }.eachCount()
+    return grouped.map { (key, cals) ->
+        val label = labels.getValue(key)
+        CalendarAccountGroup(
+            key = key,
+            label = label,
+            ambiguous = shared.getValue(label) > 1,
+            calendars = cals,
+        )
+    }
+}
+
+/**
+ * What to write above a group: its account name, qualified with the app the
+ * account comes from when another account shares the name (#77).
+ */
+@Composable
+fun accountGroupTitle(group: CalendarAccountGroup): String =
+    if (!group.ambiguous) {
+        group.label
+    } else {
+        stringResource(R.string.calendars_account_from_source, group.label, sourceAppName(group.accountType))
+    }
+
+/**
+ * The human name of the app backing [accountType] — the same app whose icon
+ * [SourceLogo] draws. Falls back to the raw account type, which is at least
+ * unique, when no installed app resolves for it.
+ */
+@Composable
+fun sourceAppName(accountType: String): String {
+    val context = LocalContext.current
+    return remember(accountType) {
+        val pm = context.packageManager
+        val packages = sourceAppPackages(context, accountType)
+        packages.firstNotNullOfOrNull { pkg ->
+            runCatching { pm.getApplicationLabel(pm.getApplicationInfo(pkg, 0)).toString() }.getOrNull()
+        } ?: accountType
+    }
+}

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/CalendarPickerGroups.kt

@@ -60,9 +60,7 @@ fun ColumnScope.CalendarPickerGroups(
 ) {
     val local = remember(calendars) { calendars.filter { it.isLocal } }
     val syncedGroups = remember(calendars) {
-        calendars.filterNot { it.isLocal }
-            .groupBy { it.accountName.ifBlank { it.accountType }.ifBlank { it.displayName } }
-            .toList()
+        calendars.filterNot { it.isLocal }.groupByAccount()
     }
 
     if (local.isNotEmpty()) {
@@ -74,12 +72,12 @@ fun ColumnScope.CalendarPickerGroups(
             onSelect = onSelect,
         )
     }
-    syncedGroups.forEachIndexed { index, (account, cals) ->
+    syncedGroups.forEachIndexed { index, group ->
         if (local.isNotEmpty() || index > 0) Spacer(Modifier.height(16.dp))
         CalendarPickerGroup(
-            title = account,
-            leading = { SourceLogo(cals.first().accountType) },
-            calendars = cals,
+            title = accountGroupTitle(group),
+            leading = { SourceLogo(group.accountType) },
+            calendars = group.calendars,
             selectedId = selectedId,
             onSelect = onSelect,
         )
@@ -181,20 +179,22 @@ fun LeadingAvatar(icon: ImageVector) {
 /** The launcher icon of the app backing [accountType], preferring the human-facing app. */
 private fun sourceAppLogo(context: Context, accountType: String): ImageBitmap? {
     val pm = context.packageManager
-    val candidates = buildList {
-        curatedSourcePackage(accountType)?.let { add(it) }
-        AccountManager.get(context).authenticatorTypes
-            .firstOrNull { it.type.equals(accountType, ignoreCase = true) }
-            ?.packageName
-            ?.let { add(it) }
-    }
-    for (pkg in candidates) {
+    for (pkg in sourceAppPackages(context, accountType)) {
         val bitmap = runCatching { pm.getApplicationIcon(pkg).toBitmap() }.getOrNull()
         if (bitmap != null) return bitmap.asImageBitmap()
     }
     return null
 }
 
+/** Apps that could stand for [accountType], best candidate first. */
+internal fun sourceAppPackages(context: Context, accountType: String): List<String> = buildList {
+    curatedSourcePackage(accountType)?.let { add(it) }
+    AccountManager.get(context).authenticatorTypes
+        .firstOrNull { it.type.equals(accountType, ignoreCase = true) }
+        ?.packageName
+        ?.let { add(it) }
+}
+
 /** Preferred app for account types whose authenticator isn't the app to open. */
 internal fun curatedSourcePackage(accountType: String): String? = when {
     accountType.equals("com.google", ignoreCase = true) -> "com.google.android.calendar"

app/src/main/java/de/jeanlucmakiola/calendula/ui/filter/CalendarFilterList.kt

@@ -21,6 +21,7 @@ import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.FailureReason
 import de.jeanlucmakiola.calendula.ui.common.CalendarColorChip
+import de.jeanlucmakiola.calendula.ui.common.sourceAppName
 import de.jeanlucmakiola.floret.components.GroupedRow
 import de.jeanlucmakiola.floret.components.positionOf
 
@@ -61,7 +62,15 @@ private fun FilterList(
     Column(modifier = modifier.fillMaxWidth()) {
         groups.forEach { group ->
             Text(
-                text = group.account,
+                text = if (group.ambiguous) {
+                    stringResource(
+                        R.string.calendars_account_from_source,
+                        group.account,
+                        sourceAppName(group.accountType),
+                    )
+                } else {
+                    group.account
+                },
                 style = MaterialTheme.typography.labelMedium,
                 color = MaterialTheme.colorScheme.onSurfaceVariant,
                 modifier = Modifier.padding(start = 28.dp, end = 28.dp, top = 12.dp, bottom = 4.dp),

app/src/main/java/de/jeanlucmakiola/calendula/ui/filter/FilterUiState.kt

@@ -13,9 +13,17 @@ sealed interface FilterUiState {
     data class Success(val groups: List<AccountGroup>) : FilterUiState
 }
 
-/** Calendars grouped under the account that owns them (Nextcloud / Local / …). */
+/**
+ * Calendars grouped under the account that owns them (Nextcloud / Local / …).
+ *
+ * [accountType] and [ambiguous] carry what the header needs to tell two
+ * same-named accounts from different apps apart (#77); the label itself is
+ * built in the UI layer, which is where the source app's name can be looked up.
+ */
 data class AccountGroup(
     val account: String,
+    val accountType: String,
+    val ambiguous: Boolean,
     val calendars: List<CalendarRow>,
 )
 

app/src/main/java/de/jeanlucmakiola/calendula/ui/filter/FilterViewModel.kt

@@ -8,6 +8,7 @@ import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.prefs.CalendarPrefs
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.FailureReason
+import de.jeanlucmakiola.calendula.ui.common.groupByAccount
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
@@ -38,7 +39,7 @@ class FilterViewModel @Inject constructor(
             if (enabled.isEmpty()) {
                 FilterUiState.Failure(FailureReason.NoCalendarsConfigured)
             } else {
-                FilterUiState.Success(groupByAccount(enabled, hidden))
+                FilterUiState.Success(groupCalendarsForFilter(enabled, hidden))
             }
         }
             .catch { emit(FilterUiState.Failure(FailureReason.ProviderUnavailable)) }
@@ -60,30 +61,27 @@ class FilterViewModel @Inject constructor(
 }
 
 /**
- * Group calendars under their owning account, preserving the provider's order
- * within each group and ordering groups by first appearance. A calendar is
- * "visible" when its id is *not* in [hidden].
+ * Group calendars under their owning account — by name *and* type, so two
+ * accounts that merely share a name stay apart (#77) — preserving the
+ * provider's order within each group and ordering groups by first appearance.
+ * A calendar is "visible" when its id is *not* in [hidden].
  */
-internal fun groupByAccount(
+internal fun groupCalendarsForFilter(
     calendars: List<CalendarSource>,
     hidden: Set<Long>,
 ): List<AccountGroup> =
-    calendars
-        .groupBy { it.accountLabel() }
-        .map { (account, cals) ->
-            AccountGroup(
-                account = account,
-                calendars = cals.map { c ->
-                    CalendarRow(
-                        id = c.id,
-                        displayName = c.displayName,
-                        color = c.color,
-                        visible = c.id !in hidden,
-                    )
-                },
-            )
-        }
-
-/** Account header text: the account name, falling back to its type. */
-private fun CalendarSource.accountLabel(): String =
-    accountName.takeIf { it.isNotBlank() } ?: accountType.takeIf { it.isNotBlank() } ?: displayName
+    calendars.groupByAccount().map { group ->
+        AccountGroup(
+            account = group.label,
+            accountType = group.accountType,
+            ambiguous = group.ambiguous,
+            calendars = group.calendars.map { c ->
+                CalendarRow(
+                    id = c.id,
+                    displayName = c.displayName,
+                    color = c.color,
+                    visible = c.id !in hidden,
+                )
+            },
+        )
+    }

app/src/main/java/de/jeanlucmakiola/calendula/ui/month/MonthScreen.kt

@@ -137,6 +137,7 @@ import kotlinx.datetime.toJavaLocalDate
 import kotlinx.datetime.toLocalDateTime
 import kotlin.math.abs
 import kotlin.time.Clock
+import kotlin.time.Instant
 import java.time.format.TextStyle as JavaTextStyle
 import java.util.Locale
 
@@ -1277,7 +1278,7 @@ internal fun SplitMonthGrid(
                     SplitDayCell(
                         date = day,
                         events = seated,
-                        hidden = (week.countByDay[day] ?: 0) - seated.size,
+                        hidden = week.overflowEvents(col, day, MAX_EVENT_ROWS),
                         isToday = day == state.today,
                         // A page marks only the days its own month owns. Paging
                         // moves the selection before this month's replacement
@@ -1318,7 +1319,7 @@ private fun SplitDayCell(
     date: LocalDate,
     events: List<EventInstance>,
     /** Events on this day that didn't fit a lane, shown as a "+N" beside the dots. */
-    hidden: Int,
+    hidden: List<EventInstance>,
     isToday: Boolean,
     isSelected: Boolean,
     inMonth: Boolean,
@@ -1436,9 +1437,15 @@ private fun SplitDayCell(
  * bar with no dot to grow out of.
  */
 @Composable
-private fun SplitDots(date: LocalDate, events: List<EventInstance>, hidden: Int, dark: Boolean) {
+private fun SplitDots(
+    date: LocalDate,
+    events: List<EventInstance>,
+    hidden: List<EventInstance>,
+    dark: Boolean,
+) {
     if (events.isEmpty()) return
     val soften = LocalSoftenColors.current
+    val dimCutoff = LocalDimCutoff.current
     Row(
         horizontalArrangement = Arrangement.spacedBy(2.dp),
         verticalAlignment = Alignment.CenterVertically,
@@ -1461,18 +1468,21 @@ private fun SplitDots(date: LocalDate, events: List<EventInstance>, hidden: Int,
                 modifier = Modifier
                     .morphBounds(MonthMorphKey.Event(date, event.instanceId))
                     .size(SPLIT_DOT_SIZE)
+                    .alpha(if (dimCutoff != null && event.hasEnded(dimCutoff)) EventDimAlpha else 1f)
                     .background(eventFill(event.color, dark, soften), CircleShape),
             )
         }
-        if (hidden > 0) {
+        if (hidden.isNotEmpty()) {
             // Tagged, not lifted: this count and the expanded grid's dot row are
             // the same marker on the same day, so it travels with its cell like
             // everything else rather than riding above the grid on its own layer.
             Text(
-                text = "+$hidden",
+                text = "+${hidden.size}",
                 style = MaterialTheme.typography.labelSmall,
                 color = MaterialTheme.colorScheme.onSurfaceVariant,
-                modifier = Modifier.morphBounds(MonthMorphKey.Overflow(date)),
+                modifier = Modifier
+                    .morphBounds(MonthMorphKey.Overflow(date))
+                    .alpha(if (allEnded(hidden, dimCutoff)) EventDimAlpha else 1f),
             )
         }
     }
@@ -1870,15 +1880,15 @@ private fun MonthWeekRow(
                         }
                         val hidden = (week.countByDay[d] ?: 0) - occupied.size - pillsShown.size
                         if (hidden > 0) {
-                            val hiddenColors = buildList {
+                            val hiddenEvents = buildList {
                                 week.spans
                                     .filter { it.lane >= shownLanes && col in it.startCol..it.endCol }
-                                    .forEach { add(it.event.color) }
-                                timed.drop(pillsShown.size).forEach { add(it.color) }
-                            }.distinct().take(3)
+                                    .forEach { add(it.event) }
+                                addAll(timed.drop(pillsShown.size))
+                            }
                             OverflowDots(
-                                colors = hiddenColors,
-                                extra = hidden - hiddenColors.size,
+                                events = hiddenEvents,
+                                total = hidden,
                                 dark = dark,
                                 modifier = Modifier
                                     .offset(x = colW * col, y = EVENT_ROW_HEIGHT * MAX_EVENT_ROWS)
@@ -2058,37 +2068,52 @@ private fun MonthBar(
     }
 }
 
-/** Overflow row: a dot per hidden event (up to three) plus "+N" for the rest. */
+/**
+ * Overflow row: a dot per hidden colour (up to three) plus "+N" for the rest.
+ *
+ * A dot stands for every hidden event sharing its colour, so it dims only once
+ * all of them have ended; the "+N" dims once the whole overflow has (#79).
+ */
 @Composable
 private fun OverflowDots(
-    colors: List<Int>,
-    extra: Int,
+    events: List<EventInstance>,
+    total: Int,
     dark: Boolean,
     modifier: Modifier = Modifier,
 ) {
     val soften = LocalSoftenColors.current
+    val dimCutoff = LocalDimCutoff.current
+    val byColor = events.groupBy { it.color }
+    val dots = byColor.keys.take(3)
     Row(
         modifier = modifier.height(EVENT_ROW_HEIGHT),
         horizontalArrangement = Arrangement.spacedBy(2.dp),
         verticalAlignment = Alignment.CenterVertically,
     ) {
-        colors.forEach { argb ->
+        dots.forEach { argb ->
             Box(
                 modifier = Modifier
                     .size(6.dp)
+                    .alpha(if (allEnded(byColor.getValue(argb), dimCutoff)) EventDimAlpha else 1f)
                     .background(eventFill(argb, dark, soften), CircleShape),
             )
         }
+        val extra = total - dots.size
         if (extra > 0) {
             Text(
                 text = "+$extra",
                 style = MaterialTheme.typography.labelSmall,
                 color = MaterialTheme.colorScheme.onSurfaceVariant,
+                modifier = Modifier.alpha(if (allEnded(events, dimCutoff)) EventDimAlpha else 1f),
             )
         }
     }
 }
 
+/** True when dimming is on and every one of [events] is already over. */
+private fun allEnded(events: List<EventInstance>, dimCutoff: Instant?): Boolean =
+    dimCutoff != null && events.isNotEmpty() && events.all { it.hasEnded(dimCutoff) }
+
 @Composable
 private fun MonthGridLoading() {
     val shape = MaterialTheme.shapes.medium

app/src/main/java/de/jeanlucmakiola/calendula/ui/month/MonthUiState.kt

@@ -67,6 +67,24 @@ fun MonthWeek.laneEvents(col: Int, day: LocalDate, laneCap: Int): List<EventInst
     return byLane.filterNotNull()
 }
 
+/**
+ * The events on [day] that [laneEvents] had no lane left for — the exact
+ * complement of what it seats, in the same bars-then-pills order. Together the
+ * two partition the day, so their sizes add up to [countByDay].
+ *
+ * The "+N" marker needs the events themselves, not just how many there are:
+ * dimming a completed event is a per-event question (#79).
+ */
+fun MonthWeek.overflowEvents(col: Int, day: LocalDate, laneCap: Int): List<EventInstance> {
+    val seatedLanes = spans.count { it.lane < laneCap && col in it.startCol..it.endCol }
+    return buildList {
+        spans.forEach { span ->
+            if (span.lane >= laneCap && col in span.startCol..span.endCol) add(span.event)
+        }
+        addAll(timedByDay[day].orEmpty().drop(laneCap - seatedLanes))
+    }
+}
+
 /**
  * State for the continuous style (#38): a vertical stream of *self-contained*
  * months rather than one undifferentiated run of weeks. Each month is keyed by

app/src/main/java/de/jeanlucmakiola/calendula/ui/permission/ReminderOnboardingViewModel.kt

@@ -4,6 +4,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
+import de.jeanlucmakiola.calendula.data.reminders.ReminderScanner
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.map
@@ -19,6 +20,7 @@ import javax.inject.Inject
 @HiltViewModel
 class ReminderOnboardingViewModel @Inject constructor(
     private val prefs: SettingsPrefs,
+    private val scanner: ReminderScanner,
 ) : ViewModel() {
 
     val onboardingDone: StateFlow<Boolean?> = prefs.reminderOnboardingDone
@@ -34,6 +36,19 @@ class ReminderOnboardingViewModel @Inject constructor(
         viewModelScope.launch {
             prefs.setRemindersEnabled(remindersEnabled)
             prefs.setReminderOnboardingDone()
+            // Nothing else re-arms the scan: turning reminders off cancels the
+            // alarm, so a later "on" would sit without one until a provider
+            // change or the daily worker happened to run (#75).
+            scanner.scan()
         }
     }
+
+    /**
+     * Re-scan after the calendar permission is granted. The launch scan runs
+     * before the grant and bails out without arming anything, so without this
+     * the first alarm waits on the daily worker.
+     */
+    fun rearmAfterGrant() {
+        scanner.scanInBackground()
+    }
 }

app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsScreen.kt

@@ -889,6 +889,7 @@ private fun ViewsScreen(
     CollapsingScaffold(
         title = stringResource(R.string.settings_section_views),
         onBack = onBack,
+        predictiveBack = true,
     ) {
         val config = state.quickSwitchConfig
 
@@ -1430,6 +1431,7 @@ private fun SpecialDatesScreen(
     CollapsingScaffold(
         title = stringResource(R.string.settings_section_special_dates),
         onBack = onBack,
+        predictiveBack = true,
     ) {
         // Paused banner: the permission was revoked after enabling.
         if (state.enabled && state.stalledPermission) {

app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsViewModel.kt

@@ -27,6 +27,7 @@ import de.jeanlucmakiola.calendula.data.prefs.SpecialDatesStalledReason
 import de.jeanlucmakiola.calendula.data.prefs.ThemeMode
 import de.jeanlucmakiola.calendula.data.prefs.TimeFormatPref
 import de.jeanlucmakiola.calendula.data.prefs.WeekStartPref
+import de.jeanlucmakiola.calendula.data.reminders.ReminderScanner
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.FontRole
@@ -71,6 +72,7 @@ class SettingsViewModel @Inject constructor(
     private val specialDatesEngine: SpecialDatesSyncEngine,
     specialDatesSpec: SpecialDatesCalendarSpec,
     private val launcherNameManager: LauncherNameManager,
+    private val reminderScanner: ReminderScanner,
     @IoDispatcher private val io: CoroutineDispatcher,
     @ApplicationContext private val appContext: Context,
 ) : ViewModel() {
@@ -611,8 +613,16 @@ class SettingsViewModel @Inject constructor(
         viewModelScope.launch { prefs.setDrawerViewOrder(order) }
     }
 
+    /**
+     * A scan follows the write, in that order. Switching reminders off cancels
+     * the scan alarm, so switching them back on has to arm a new one — nothing
+     * else would until a provider change or the daily worker came along (#75).
+     */
     fun setRemindersEnabled(enabled: Boolean) {
-        viewModelScope.launch { prefs.setRemindersEnabled(enabled) }
+        viewModelScope.launch {
+            prefs.setRemindersEnabled(enabled)
+            reminderScanner.scan()
+        }
     }
 
     fun setAutofocusEventTitle(enabled: Boolean) {
@@ -627,8 +637,12 @@ class SettingsViewModel @Inject constructor(
         viewModelScope.launch { prefs.setDefaultAllDayReminderMinutes(minutes) }
     }
 
+    /** The armed alarm was planned for the old hour, so re-plan against the new one. */
     fun setAllDayReminderTimeMinutes(minutesOfDay: Int) {
-        viewModelScope.launch { prefs.setAllDayReminderTimeMinutes(minutesOfDay) }
+        viewModelScope.launch {
+            prefs.setAllDayReminderTimeMinutes(minutesOfDay)
+            reminderScanner.scan()
+        }
     }
 
     fun setSnoozeMinutes(minutes: Int) {

app/src/main/res/values/strings.xml

@@ -496,6 +496,8 @@
     <string name="calendars_synced_header">Synced calendars</string>
     <string name="calendars_synced_hint">These come from accounts on your device. Create and edit them in their own app.</string>
     <string name="calendars_manage_in_app">Manage in app</string>
+    <!-- Account header when two accounts share a name: %1$s is the account, %2$s the app it comes from. -->
+    <string name="calendars_account_from_source">%1$s (%2$s)</string>
     <string name="calendars_account_menu_a11y">More options for %1$s</string>
     <string name="calendars_enable_all">Enable all</string>
     <string name="calendars_disable_all">Disable all</string>

app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/AllDayReminderEncodingTest.kt

@@ -54,7 +54,8 @@ class AllDayReminderEncodingTest {
             for (time in listOf(0, nineAm, 20 * 60)) {
                 for (semantic in listOf(0, 1_440, 2_880, 10_080)) {
                     val raw = toProviderAllDayMinutes(semantic, date, berlin, time)
-                    assertThat(fromProviderAllDayMinutes(raw, date, berlin)).isEqualTo(semantic)
+                    assertThat(fromProviderAllDayMinutes(raw, date, berlin, time))
+                        .isEqualTo(semantic)
                 }
             }
         }
@@ -64,9 +65,31 @@ class AllDayReminderEncodingTest {
     fun `pre-feature rows (raw multiple of 1440) still decode to whole days`() {
         // Reminders written before this feature stored raw N*1440 (fired at UTC
         // midnight). They must still read back as "N days before".
-        assertThat(fromProviderAllDayMinutes(1_440, summer, berlin)).isEqualTo(1_440)
-        assertThat(fromProviderAllDayMinutes(1_440, winter, berlin)).isEqualTo(1_440)
-        assertThat(fromProviderAllDayMinutes(2_880, summer, berlin)).isEqualTo(2_880)
+        assertThat(fromProviderAllDayMinutes(1_440, summer, berlin, nineAm)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(1_440, winter, berlin, nineAm)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(2_880, summer, berlin, nineAm)).isEqualTo(2_880)
+    }
+
+    @Test
+    fun `an offset that encodes to a multiple still decodes to its own lead time`() {
+        // New York at 20:00 is the collision: "1 day before" encodes to a plain 0,
+        // which read at face value would say "at time of event". The screen has to
+        // show what the reminder does, which is fire the evening before.
+        val newYork = ZoneId.of("America/New_York")
+        val eightPm = 20 * 60
+        val raw = toProviderAllDayMinutes(1_440, summer, newYork, eightPm)
+
+        assertThat(raw).isEqualTo(0)
+        assertThat(fromProviderAllDayMinutes(raw, summer, newYork, eightPm)).isEqualTo(1_440)
+    }
+
+    @Test
+    fun `a foreign multiple west of UTC keeps its face-value lead time`() {
+        // No encoded hour in this row, and its instant lands on the evening two
+        // days out in New York — the local-date reading would say "2 days before".
+        val newYork = ZoneId.of("America/New_York")
+
+        assertThat(fromProviderAllDayMinutes(1_440, summer, newYork, nineAm)).isEqualTo(1_440)
     }
 
     @Test
@@ -74,8 +97,8 @@ class AllDayReminderEncodingTest {
         val atNine = toProviderAllDayMinutes(1_440, summer, berlin, nineAm)
         val atEight = toProviderAllDayMinutes(1_440, summer, berlin, 8 * 60)
         assertThat(atNine).isNotEqualTo(atEight)
-        assertThat(fromProviderAllDayMinutes(atNine, summer, berlin)).isEqualTo(1_440)
-        assertThat(fromProviderAllDayMinutes(atEight, summer, berlin)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(atNine, summer, berlin, nineAm)).isEqualTo(1_440)
+        assertThat(fromProviderAllDayMinutes(atEight, summer, berlin, nineAm)).isEqualTo(1_440)
     }
 
     @Test

app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapperTest.kt

@@ -79,7 +79,8 @@ class EventDetailMapperTest {
     private fun MapColumnReader.toDetail(
         attendees: List<de.jeanlucmakiola.calendula.domain.Attendee> = emptyList(),
         reminders: List<Reminder> = emptyList(),
-    ) = toEventDetailCore(attendees, reminders)
+        allDayReminderTimeMinutes: Int = 9 * 60,
+    ) = toEventDetailCore(attendees, reminders, allDayReminderTimeMinutes)
 
     @Test
     fun `happy path detail maps all fields and embeds matching EventInstance`() {

app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/FakeCalendarDataSource.kt

@@ -72,7 +72,8 @@ internal class FakeCalendarDataSource : CalendarDataSource {
     override fun instances(beginMillis: Long, endMillis: Long): List<EventInstance> =
         instancesResult(beginMillis, endMillis)
     override fun searchEvents(query: String): List<EventInstance> = searchResult(query)
-    override fun eventDetail(eventId: Long): EventDetail? = eventDetailResult(eventId)
+    override fun eventDetail(eventId: Long, allDayReminderTimeMinutes: Int): EventDetail? =
+        eventDetailResult(eventId)
     override fun eventColorPalette(calendarId: Long): List<EventColorOption> =
         eventColorPaletteResult(calendarId)
     override fun exportableEvents(calendarIds: Set<Long>?): List<IcsEvent> {

app/src/test/java/de/jeanlucmakiola/calendula/data/reminders/AlertHandlingTest.kt

@@ -1,66 +0,0 @@
-package de.jeanlucmakiola.calendula.data.reminders
-
-import com.google.common.truth.Truth.assertThat
-import org.junit.jupiter.api.Test
-
-/**
- * What the reminder receiver may mark handled. The silenced-but-still-ahead case
- * is the one that matters: those rows are the only copy of the reminder (#75).
- */
-class AlertHandlingTest {
-
-    private val now = 1_700_000_000_000L
-
-    private fun alert(
-        id: Long,
-        calendarId: Long = 1L,
-        beginMillis: Long = now + 60_000L,
-        endMillis: Long = now + 3_600_000L,
-    ) = ReminderAlert(
-        alertId = id,
-        eventId = id * 10,
-        calendarId = calendarId,
-        beginMillis = beginMillis,
-        endMillis = endMillis,
-        title = "E $id",
-        location = null,
-        isAllDay = false,
-    )
-
-    @Test
-    fun `posted alerts are handled`() {
-        val due = listOf(alert(1L), alert(2L))
-
-        assertThat(handledAlertIds(due, postedIds = setOf(1L, 2L), nowMillis = now))
-            .containsExactly(1L, 2L)
-    }
-
-    @Test
-    fun `a silenced alert whose event is still ahead stays unhandled`() {
-        // Switching its calendar back on before the event has to bring it back,
-        // and dueAlerts only ever returns STATE_SCHEDULED rows.
-        val due = listOf(alert(1L), alert(2L))
-
-        assertThat(handledAlertIds(due, postedIds = setOf(1L), nowMillis = now))
-            .containsExactly(1L)
-    }
-
-    @Test
-    fun `a silenced alert whose event is over is handled`() {
-        // Nothing left to re-surface, so it must not linger as scheduled.
-        val over = alert(2L, beginMillis = now - 7_200_000L, endMillis = now - 3_600_000L)
-        val due = listOf(alert(1L), over)
-
-        assertThat(handledAlertIds(due, postedIds = setOf(1L), nowMillis = now))
-            .containsExactly(1L, 2L)
-    }
-
-    @Test
-    fun `an unknown end time falls back to the begin time`() {
-        val started = alert(1L, beginMillis = now - 1L, endMillis = 0L)
-        val notYet = alert(2L, beginMillis = now + 1L, endMillis = 0L)
-
-        assertThat(handledAlertIds(listOf(started, notYet), postedIds = emptySet(), nowMillis = now))
-            .containsExactly(1L)
-    }
-}

app/src/test/java/de/jeanlucmakiola/calendula/domain/reminders/ReminderPlanTest.kt

@@ -0,0 +1,526 @@
+package de.jeanlucmakiola.calendula.domain.reminders
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+import java.time.LocalDate
+import java.time.LocalTime
+import java.time.ZoneId
+import java.time.ZoneOffset
+import java.time.ZonedDateTime
+
+/**
+ * The decision layer of in-house reminder delivery (#75). The watermark rules are
+ * the load-bearing part: they are what makes a dropped alarm recoverable and a
+ * double scan harmless, now that no provider row records "already fired".
+ */
+class ReminderPlanTest {
+
+    private val now = 1_700_000_000_000L
+    private val minute = 60_000L
+    private val day = 24 * 60 * minute
+
+    private fun instance(
+        eventId: Long,
+        beginMillis: Long = now + 30 * minute,
+        endMillis: Long = now + 90 * minute,
+        calendarId: Long = 7L,
+        isAllDay: Boolean = false,
+    ) = ReminderEventInstance(
+        eventId = eventId,
+        calendarId = calendarId,
+        beginMillis = beginMillis,
+        endMillis = endMillis,
+        title = "Event $eventId",
+        location = null,
+        isAllDay = isAllDay,
+    )
+
+    /** [planReminders] with the fixtures' zone and all-day hour filled in. */
+    private fun plan(
+        instances: List<ReminderEventInstance>,
+        minutesByEvent: Map<Long, List<Int>>,
+        zone: ZoneId = berlin,
+        allDayTimeMinutes: Int = nineAm,
+    ) = planReminders(instances, minutesByEvent, zone, allDayTimeMinutes)
+
+    @Test
+    fun `a reminder fires its offset before the occurrence begins`() {
+        val begin = now + 30 * minute
+        val planned = plan(
+            instances = listOf(instance(1L, beginMillis = begin)),
+            minutesByEvent = mapOf(1L to listOf(10)),
+        )
+
+        assertThat(planned.map { it.alarmMillis }).containsExactly(begin - 10 * minute)
+    }
+
+    // --- all-day: the hour the user picked, on every occurrence -------------
+
+    private val berlin = ZoneId.of("Europe/Berlin")
+    private val nineAm = 540
+
+    /** UTC midnight of [date] — how the provider stores an all-day occurrence. */
+    private fun allDayBegin(date: String): Long =
+        LocalDate.parse(date).atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
+
+    private fun firedAt(alarmMillis: Long, zone: ZoneId = berlin): ZonedDateTime =
+        java.time.Instant.ofEpochMilli(alarmMillis).atZone(zone)
+
+    /**
+     * The offset AllDayReminderEncoding would store for "[days] before, at
+     * [timeOfDayMinutes]" when sampled against [eventDate] — i.e. exactly the row
+     * the app writes today.
+     */
+    private fun encodedAllDayMinutes(
+        eventDate: String,
+        days: Long,
+        timeOfDayMinutes: Int = nineAm,
+        zone: ZoneId = berlin,
+    ): Int {
+        val date = LocalDate.parse(eventDate)
+        val utcMidnight = date.atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
+        val fire = date.minusDays(days)
+            .atTime(LocalTime.of(timeOfDayMinutes / 60, timeOfDayMinutes % 60))
+            .atZone(zone).toInstant().toEpochMilli()
+        return ((utcMidnight - fire) / minute).toInt()
+    }
+
+    private fun allDayAlarm(eventDate: String, rawMinutes: Int, zone: ZoneId = berlin): Long =
+        plan(
+            instances = listOf(
+                instance(1L, beginMillis = allDayBegin(eventDate), isAllDay = true),
+            ),
+            minutesByEvent = mapOf(1L to listOf(rawMinutes)),
+            zone = zone,
+            allDayTimeMinutes = nineAm,
+        ).single().alarmMillis
+
+    @Test
+    fun `an all-day reminder fires at the hour the setting names`() {
+        // Winter: Berlin is UTC+1. "1 day before" on the 15th means the 14th, 09:00.
+        val alarm = allDayAlarm("2026-01-15", encodedAllDayMinutes("2026-01-15", days = 1))
+
+        assertThat(firedAt(alarm).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-01-14").atTime(9, 0))
+    }
+
+    @Test
+    fun `a summer occurrence of a row written in winter is not an hour early`() {
+        // The drift this replaces: the offset was sampled at UTC+1, the occurrence
+        // falls at UTC+2, and firing at `begin - minutes` would land at 08:00.
+        val winterRow = encodedAllDayMinutes("2026-01-15", days = 1)
+
+        val alarm = allDayAlarm("2026-07-15", winterRow)
+
+        assertThat(firedAt(alarm).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-07-14").atTime(9, 0))
+    }
+
+    @Test
+    fun `a winter occurrence of a row written in summer is not an hour late`() {
+        // The same drift in the other direction: sampled at UTC+2, fires at UTC+1.
+        val summerRow = encodedAllDayMinutes("2026-07-15", days = 1)
+
+        val alarm = allDayAlarm("2026-01-15", summerRow)
+
+        assertThat(firedAt(alarm).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-01-14").atTime(9, 0))
+    }
+
+    @Test
+    fun `every occurrence of a yearly all-day series fires at the same wall clock`() {
+        // A birthday's offset is sampled once; the series must not walk off it.
+        val row = encodedAllDayMinutes("2026-07-15", days = 1)
+        val fired = listOf("2026-07-15", "2027-01-15", "2027-07-15", "2028-01-15")
+            .map { firedAt(allDayAlarm(it, row)).toLocalTime() }
+
+        assertThat(fired.toSet()).containsExactly(LocalTime.of(9, 0))
+    }
+
+    @Test
+    fun `an all-day reminder on the day itself fires that morning`() {
+        // "At time of event" on an all-day event encodes to a negative offset.
+        val sameDay = encodedAllDayMinutes("2026-07-15", days = 0)
+        assertThat(sameDay).isLessThan(0)
+
+        val alarm = allDayAlarm("2026-07-15", sameDay)
+
+        assertThat(firedAt(alarm).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-07-15").atTime(9, 0))
+    }
+
+    @Test
+    fun `a plain 1440 row from another calendar app means one day before`() {
+        // Foreign rows carry no encoded hour. Read at face value they would fire
+        // at UTC midnight — 02:00 local in summer Berlin.
+        val alarm = allDayAlarm("2026-07-15", rawMinutes = 1_440)
+
+        assertThat(firedAt(alarm).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-07-14").atTime(9, 0))
+    }
+
+    @Test
+    fun `a plain 1440 row west of UTC still means one day before`() {
+        // UTC midnight of the 15th is the evening of the 14th in New York, so a
+        // local-date reading of the offset would put this two days out.
+        val newYork = ZoneId.of("America/New_York")
+
+        val alarm = allDayAlarm("2026-07-15", rawMinutes = 1_440, zone = newYork)
+
+        assertThat(firedAt(alarm, newYork).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-07-14").atTime(9, 0))
+    }
+
+    @Test
+    fun `an encoded row west of UTC fires at the named hour`() {
+        val newYork = ZoneId.of("America/New_York")
+        val row = encodedAllDayMinutes("2026-07-15", days = 1, zone = newYork)
+
+        val alarm = allDayAlarm("2026-07-15", row, zone = newYork)
+
+        assertThat(firedAt(alarm, newYork).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-07-14").atTime(9, 0))
+    }
+
+    @Test
+    fun `a zero-day row fires on the event's own date`() {
+        assertThat(
+            allDayLeadDays(
+                rawMinutes = 0,
+                startDate = LocalDate.parse("2026-07-15"),
+                zone = berlin,
+                allDayTimeMinutes = nineAm,
+            ),
+        ).isEqualTo(0L)
+    }
+
+    @Test
+    fun `our own row that encodes to a multiple is not read at face value`() {
+        // New York with the all-day hour at 20:00: "1 day before" encodes to a
+        // plain 0, because 20:00 EDT *is* UTC midnight. Read at face value it
+        // fired at 20:00 on the day of the event instead of the evening before.
+        val newYork = ZoneId.of("America/New_York")
+        val eightPm = 20 * 60
+        val row = encodedAllDayMinutes("2026-07-15", days = 1, timeOfDayMinutes = eightPm, zone = newYork)
+        assertThat(row % 1_440).isEqualTo(0)
+
+        val alarm = plan(
+            instances = listOf(
+                instance(1L, beginMillis = allDayBegin("2026-07-15"), isAllDay = true),
+            ),
+            minutesByEvent = mapOf(1L to listOf(row)),
+            zone = newYork,
+            allDayTimeMinutes = eightPm,
+        ).single().alarmMillis
+
+        assertThat(firedAt(alarm, newYork).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-07-14").atTime(20, 0))
+    }
+
+    @Test
+    fun `such a row keeps its lead time across the DST boundary that wrote it`() {
+        // Same row, sampled in EDT, on a winter occurrence: its instant lands an
+        // hour off the named hour, which still has to read as "one of ours".
+        val newYork = ZoneId.of("America/New_York")
+        val eightPm = 20 * 60
+        val summerRow = encodedAllDayMinutes("2026-07-15", days = 1, timeOfDayMinutes = eightPm, zone = newYork)
+
+        val alarm = plan(
+            instances = listOf(
+                instance(1L, beginMillis = allDayBegin("2027-01-15"), isAllDay = true),
+            ),
+            minutesByEvent = mapOf(1L to listOf(summerRow)),
+            zone = newYork,
+            allDayTimeMinutes = eightPm,
+        ).single().alarmMillis
+
+        assertThat(firedAt(alarm, newYork).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2027-01-14").atTime(20, 0))
+    }
+
+    @Test
+    fun `a timed reminder is exact across a DST boundary`() {
+        // Nothing to re-anchor: begin is an absolute instant either way.
+        val begin = LocalDate.parse("2026-03-29").atTime(14, 0)
+            .atZone(berlin).toInstant().toEpochMilli()
+        val planned = plan(
+            instances = listOf(instance(1L, beginMillis = begin, isAllDay = false)),
+            minutesByEvent = mapOf(1L to listOf(30)),
+            zone = berlin,
+            allDayTimeMinutes = nineAm,
+        )
+
+        assertThat(firedAt(planned.single().alarmMillis).toLocalDateTime())
+            .isEqualTo(LocalDate.parse("2026-03-29").atTime(13, 30))
+    }
+
+    @Test
+    fun `every occurrence of a series gets its own reminder`() {
+        val planned = plan(
+            instances = listOf(
+                instance(1L, beginMillis = now + day),
+                instance(1L, beginMillis = now + 2 * day),
+            ),
+            minutesByEvent = mapOf(1L to listOf(15)),
+        )
+
+        assertThat(planned.map { it.alarmMillis })
+            .containsExactly(now + day - 15 * minute, now + 2 * day - 15 * minute)
+        assertThat(planned.map { it.key }.toSet()).hasSize(2)
+    }
+
+    @Test
+    fun `duplicate reminder rows collapse to one`() {
+        val planned = plan(
+            instances = listOf(instance(1L)),
+            minutesByEvent = mapOf(1L to listOf(10, 10)),
+        )
+
+        assertThat(planned).hasSize(1)
+    }
+
+    @Test
+    fun `an event with no reminders plans nothing`() {
+        val planned = plan(
+            instances = listOf(instance(1L)),
+            minutesByEvent = emptyMap(),
+        )
+
+        assertThat(planned).isEmpty()
+    }
+
+    @Test
+    fun `the same reminder keeps its key across scans`() {
+        val plan = {
+            plan(listOf(instance(1L)), mapOf(1L to listOf(10))).single().key
+        }
+
+        assertThat(plan()).isEqualTo(plan())
+    }
+
+    @Test
+    fun `occurrences of one series get different keys`() {
+        val planned = plan(
+            instances = listOf(
+                instance(1L, beginMillis = now + day),
+                instance(1L, beginMillis = now + 2 * day),
+            ),
+            minutesByEvent = mapOf(1L to listOf(15)),
+        )
+
+        assertThat(planned[0].key).isNotEqualTo(planned[1].key)
+    }
+
+    @Test
+    fun `two reminders on one occurrence get different keys`() {
+        val planned = plan(
+            instances = listOf(instance(1L)),
+            minutesByEvent = mapOf(1L to listOf(10, 30)),
+        )
+
+        assertThat(planned[0].key).isNotEqualTo(planned[1].key)
+    }
+
+    @Test
+    fun `a reminder whose moment has passed since the last scan is due`() {
+        val planned = plan(
+            instances = listOf(instance(1L, beginMillis = now + 5 * minute)),
+            minutesByEvent = mapOf(1L to listOf(10)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now - 10 * minute, nowMillis = now,
+            horizonMillis = now + day,
+        )
+
+        assertThat(schedule.due).hasSize(1)
+    }
+
+    @Test
+    fun `a reminder already covered by the watermark does not fire twice`() {
+        // The scan runs again (a provider change, a reboot) after the alarm that
+        // already posted this one. Nothing records "fired" but the watermark.
+        val planned = plan(
+            instances = listOf(instance(1L, beginMillis = now + 5 * minute)),
+            minutesByEvent = mapOf(1L to listOf(10)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now - 4 * minute, nowMillis = now,
+            horizonMillis = now + day,
+        )
+
+        assertThat(schedule.due).isEmpty()
+    }
+
+    @Test
+    fun `a reminder exactly on the watermark does not fire again`() {
+        val begin = now + 5 * minute
+        val planned = plan(
+            instances = listOf(instance(1L, beginMillis = begin)),
+            minutesByEvent = mapOf(1L to listOf(10)),
+        )
+        val alarm = planned.single().alarmMillis
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = alarm, nowMillis = now, horizonMillis = now + day,
+        )
+
+        assertThat(schedule.due).isEmpty()
+    }
+
+    @Test
+    fun `a missed alarm is caught up by a much later scan`() {
+        // The device was off over the reminder; the scan on boot must still post it
+        // while the event is ahead. This is what the provider path could never do.
+        val planned = plan(
+            instances = listOf(instance(1L, beginMillis = now + 5 * minute)),
+            minutesByEvent = mapOf(1L to listOf(60)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now - 5 * day, nowMillis = now,
+            horizonMillis = now + day,
+        )
+
+        assertThat(schedule.due).hasSize(1)
+    }
+
+    @Test
+    fun `a reminder for an occurrence that already ended is dropped`() {
+        val planned = plan(
+            instances = listOf(
+                instance(1L, beginMillis = now - 3 * 60 * minute, endMillis = now - 2 * 60 * minute),
+            ),
+            minutesByEvent = mapOf(1L to listOf(10)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now - 5 * day, nowMillis = now,
+            horizonMillis = now + day,
+        )
+
+        assertThat(schedule.due).isEmpty()
+    }
+
+    @Test
+    fun `an occurrence with no end falls back to its begin for relevance`() {
+        val planned = plan(
+            instances = listOf(
+                instance(1L, beginMillis = now - minute, endMillis = 0L),
+            ),
+            minutesByEvent = mapOf(1L to listOf(10)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now - day, nowMillis = now, horizonMillis = now + day,
+        )
+
+        assertThat(schedule.due).isEmpty()
+    }
+
+    @Test
+    fun `due reminders come out in occurrence order`() {
+        val planned = plan(
+            instances = listOf(
+                instance(1L, beginMillis = now + 20 * minute),
+                instance(2L, beginMillis = now + 5 * minute),
+            ),
+            minutesByEvent = mapOf(1L to listOf(30), 2L to listOf(30)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now - day, nowMillis = now, horizonMillis = now + day,
+        )
+
+        assertThat(schedule.due.map { it.instance.eventId }).containsExactly(2L, 1L).inOrder()
+    }
+
+    @Test
+    fun `the next wake-up is the earliest reminder still ahead`() {
+        val planned = plan(
+            instances = listOf(
+                instance(1L, beginMillis = now + 20 * minute),
+                instance(2L, beginMillis = now + 90 * minute),
+            ),
+            minutesByEvent = mapOf(1L to listOf(5), 2L to listOf(5)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now, nowMillis = now, horizonMillis = now + day,
+        )
+
+        assertThat(schedule.nextAlarmMillis).isEqualTo(now + 15 * minute)
+    }
+
+    @Test
+    fun `with nothing pending the scan still re-runs at the horizon`() {
+        val schedule = scheduleReminders(
+            planned = emptyList(), lastFiredMillis = now, nowMillis = now,
+            horizonMillis = now + day,
+        )
+
+        assertThat(schedule.nextAlarmMillis).isEqualTo(now + day)
+    }
+
+    @Test
+    fun `a reminder beyond the horizon waits for the next scan`() {
+        // Capping keeps the rolling window honest: the far-off reminder is picked
+        // up by a later scan rather than pinned to an alarm we may never re-check.
+        val planned = plan(
+            instances = listOf(instance(1L, beginMillis = now + 30 * day)),
+            minutesByEvent = mapOf(1L to listOf(5)),
+        )
+
+        val schedule = scheduleReminders(
+            planned, lastFiredMillis = now, nowMillis = now, horizonMillis = now + day,
+        )
+
+        assertThat(schedule.nextAlarmMillis).isEqualTo(now + day)
+    }
+
+    @Test
+    fun `the query horizon stretches past the longest reminder offset`() {
+        // A "2 weeks before" reminder has to be planned while its event is still
+        // outside the plain lookahead, or it fires late.
+        assertThat(reminderQueryHorizon(lookaheadMillis = 7 * day, maxReminderMinutes = 20_160))
+            .isEqualTo(7 * day + 14 * day)
+    }
+
+    @Test
+    fun `the query horizon is capped against an outlier row`() {
+        // The longest offset comes from any row in the provider — an imported
+        // TRIGGER:-P100W would otherwise expand every series over two years, on
+        // every scan.
+        val hundredWeeks = 100 * 7 * 24 * 60
+
+        assertThat(reminderQueryHorizon(lookaheadMillis = 7 * day, maxReminderMinutes = hundredWeeks))
+            .isEqualTo(7 * day + MAX_REMINDER_LEAD_MILLIS)
+    }
+
+    @Test
+    fun `a first-ever scan starts from now, not from the epoch`() {
+        // Otherwise an install — or the upgrade onto in-house delivery — treats
+        // every reminder ever set as overdue and posts the lot.
+        assertThat(reminderWatermark(lastScanMillis = null, nowMillis = now)).isEqualTo(now)
+    }
+
+    @Test
+    fun `an ordinary watermark is used as recorded`() {
+        assertThat(reminderWatermark(lastScanMillis = now - day, nowMillis = now))
+            .isEqualTo(now - day)
+    }
+
+    @Test
+    fun `a watermark left in the future by a clock change is clamped`() {
+        // Left alone it would silence every reminder until real time caught up.
+        assertThat(reminderWatermark(lastScanMillis = now + 5 * day, nowMillis = now))
+            .isEqualTo(now)
+    }
+
+    @Test
+    fun `a negative longest offset does not shrink the query horizon`() {
+        assertThat(reminderQueryHorizon(lookaheadMillis = 7 * day, maxReminderMinutes = -420))
+            .isEqualTo(7 * day)
+    }
+}

app/src/test/java/de/jeanlucmakiola/calendula/ui/filter/FilterGroupingTest.kt

@@ -28,7 +28,7 @@ class FilterGroupingTest {
             cal(3, "Shared", "team@dav"),
         )
 
-        val groups = groupByAccount(calendars, hidden = emptySet())
+        val groups = groupCalendarsForFilter(calendars, hidden = emptySet())
 
         assertThat(groups.map { it.account }).containsExactly("alice@dav", "team@dav").inOrder()
         assertThat(groups[0].calendars.map { it.displayName })
@@ -43,7 +43,7 @@ class FilterGroupingTest {
             cal(2, "Work", "alice@dav"),
         )
 
-        val groups = groupByAccount(calendars, hidden = setOf(2L))
+        val groups = groupCalendarsForFilter(calendars, hidden = setOf(2L))
         val rows = groups.single().calendars.associateBy { it.id }
 
         assertThat(rows.getValue(1L).visible).isTrue()
@@ -52,10 +52,52 @@ class FilterGroupingTest {
 
     @Test
     fun `blank account name falls back to type`() {
-        val groups = groupByAccount(
+        val groups = groupCalendarsForFilter(
             listOf(cal(1, "Birthdays", account = "", type = "LOCAL")),
             hidden = emptySet(),
         )
         assertThat(groups.single().account).isEqualTo("LOCAL")
     }
+
+    /** #77: same address, two apps — two accounts, and they must read as two. */
+    @Test
+    fun `one name under two account types stays two groups`() {
+        val calendars = listOf(
+            cal(1, "Personal", "me@example.com", type = "com.google"),
+            cal(2, "Shared", "me@example.com", type = "bitfire.at.davdroid"),
+        )
+
+        val groups = groupCalendarsForFilter(calendars, hidden = emptySet())
+
+        assertThat(groups).hasSize(2)
+        assertThat(groups.map { it.accountType })
+            .containsExactly("com.google", "bitfire.at.davdroid").inOrder()
+        assertThat(groups.map { it.calendars.single().id }).containsExactly(1L, 2L).inOrder()
+        assertThat(groups.all { it.ambiguous }).isTrue()
+    }
+
+    @Test
+    fun `one name under one type is not ambiguous`() {
+        val groups = groupCalendarsForFilter(
+            listOf(cal(1, "Personal", "me@example.com")),
+            hidden = emptySet(),
+        )
+
+        assertThat(groups.single().ambiguous).isFalse()
+    }
+
+    /** Two different names from the same app are still two plain groups. */
+    @Test
+    fun `different names under one type are not ambiguous`() {
+        val groups = groupCalendarsForFilter(
+            listOf(
+                cal(1, "Personal", "alice@example.com"),
+                cal(2, "Shared", "bob@example.com"),
+            ),
+            hidden = emptySet(),
+        )
+
+        assertThat(groups).hasSize(2)
+        assertThat(groups.none { it.ambiguous }).isTrue()
+    }
 }

app/src/test/java/de/jeanlucmakiola/calendula/ui/month/LaneEventsTest.kt

@@ -122,6 +122,42 @@ class LaneEventsTest {
             .containsNoneIn(seated)
     }
 
+    @Test
+    fun `overflow is exactly what seating left behind`() {
+        val events = (0 until 5).map { timed(LocalDate(2026, 7, 6), hour = 8 + it, id = it + 1L) }
+        val week = rowOfJuly6(events)
+        val day = LocalDate(2026, 7, 6)
+
+        val seated = week.laneEvents(col = 0, day = day, laneCap = 3)
+        val overflow = week.overflowEvents(col = 0, day = day, laneCap = 3)
+
+        assertThat(overflow).containsExactlyElementsIn(events.drop(3)).inOrder()
+        assertThat(seated + overflow).containsExactlyElementsIn(events)
+        assertThat(seated.size + overflow.size).isEqualTo(week.countByDay[day])
+    }
+
+    @Test
+    fun `a bar beyond the cap overflows on every day it covers`() {
+        val bars = (0 until 4).map {
+            allDay(LocalDate(2026, 7, 6), LocalDate(2026, 7, 8), id = it + 1L)
+        }
+        val week = rowOfJuly6(bars)
+        val parked = week.spans.filter { it.lane >= 3 }.map { it.event }
+
+        (0..2).forEach { col ->
+            val day = LocalDate(2026, 7, 6 + col)
+            assertThat(week.overflowEvents(col, day, laneCap = 3))
+                .containsExactlyElementsIn(parked)
+        }
+    }
+
+    @Test
+    fun `a day that fits has no overflow`() {
+        val week = rowOfJuly6(listOf(timed(LocalDate(2026, 7, 6), hour = 9, id = 1L)))
+
+        assertThat(week.overflowEvents(col = 0, day = LocalDate(2026, 7, 6), laneCap = 3)).isEmpty()
+    }
+
     private companion object {
         const val BLUE = 0xFF3366CC.toInt()
         const val RED = 0xFFCC3333.toInt()

docs/ARCHITECTURE.md

@@ -33,7 +33,7 @@ flowchart TD
         Repo["CalendarRepository\n(interface + impl, Flow-based, io-dispatched)"]
         DS["CalendarDataSource\n(interface + AndroidCalendarDataSource)"]
         Prefs["SettingsPrefs / CalendarPrefs\n(DataStore)"]
-        Rem["reminders/\nReminderAlertStore + ReminderNotifier"]
+        Rem["reminders/\nReminderScanner + ReminderNotifier"]
     end
     Provider[("CalendarContract\n(system calendar provider)")]
 
@@ -137,29 +137,67 @@ can't fake a conflict.
 
 ## Reminder delivery
 
-The provider schedules reminder alarms (for `METHOD_ALERT` rows only) and
-broadcasts `EVENT_REMINDER` — but posts no notification; a calendar app
-must (the Etar model):
+Calendula plans and fires its own reminders. It reads the offsets in
+`Reminders` as data, works out when each occurrence's reminder is due, and holds
+**one** exact alarm for the earliest one still ahead:
 
 ```mermaid
 sequenceDiagram
-    participant P as CalendarProvider
-    participant R as EventReminderReceiver
-    participant S as ReminderAlertStore
+    participant T as Trigger (alarm / boot / time change / edit / launch / daily worker)
+    participant Sc as ReminderScanner
+    participant Src as ReminderInstanceSource
+    participant P as ReminderPlan (pure)
     participant N as ReminderNotifier
-    P->>R: EVENT_REMINDER broadcast (manifest receiver, exported)
-    R->>S: dueAlerts(now) — CalendarAlerts: SCHEDULED, alarmTime ≤ now
-    S-->>R: due alerts
-    R->>N: post(alert) — one notification per alert, tag = alert id
-    R->>S: markFired(ids) — best effort, needs WRITE_CALENDAR
+    participant A as ReminderAlarmScheduler
+    T->>Sc: scan()
+    Sc->>Src: occurrences(window) + reminderMinutes(ids)
+    Src-->>Sc: Instances ⋈ Reminders
+    Sc->>P: planReminders / scheduleReminders(watermark, now)
+    P-->>Sc: due + next alarm
+    Sc->>N: post(alert) — tag = reminder key
+    Sc->>A: scheduleScan(next)
 ```
 
-Posting happens before marking: a crash in between re-posts silently (same
-tag + `setOnlyAlertOnce`) rather than losing a reminder. Swiped
-notifications never return because `FIRED` rows are never re-queried.
+**Why not the provider's broadcast.** It used to schedule the alarms, write the
+`CalendarAlerts` rows and broadcast `EVENT_REMINDER`, and the app only reacted.
+That chain holds on stock Android and demonstrably not everywhere: AOSP's own
+unbundled calendar carries three separate workarounds for OEM providers that
+retarget the broadcast or only write the alert row at alert time. A reacting app
+cannot tell "nothing was due" from "the broadcast never came" (#75) — and the
+reporter's silent events were in a calendar Calendula created itself, so
+`VISIBLE` was never the cause there.
 
-**One visibility model.** The provider only schedules alarms for calendars with
-`Calendars.VISIBLE = 1`, so that flag *is* the app's on/off switch: Settings →
+**The watermark replaces `CalendarAlerts.STATE`.** A scan posts the reminders
+whose moment falls in `(lastScan, now]`, then moves the mark
+(`ReminderStatePrefs`). Half-open, so a scan that runs twice cannot post twice,
+while a scan that runs *late* still posts what the missed alarm owed — a reboot,
+an app update or a doze window costs nothing. A first-ever scan claims the
+present rather than the epoch, and a watermark left in the future by a clock
+change is clamped. Every trigger runs the same idempotent `scan()`, so there is
+no ordering between them to get wrong; `BOOT_COMPLETED` and `MY_PACKAGE_REPLACED`
+matter because both wipe pending alarms. Turning reminders off cancels the alarm
+and granting the calendar permission arms none, so those transitions scan too —
+without it, switching reminders back on would sit silent until the daily worker.
+The window a scan reads is the 7-day lookahead plus the longest reminder offset
+in the provider, capped at a year: that offset is whatever the largest row says,
+including one imported from a stray `TRIGGER:-P100W`.
+
+**All-day reminders fire at the hour the setting names.** The stored offset is
+not a plain lead time — `AllDayReminderEncoding` folds a wall-clock hour into it,
+sampled against one date's UTC offset — so taking it at face value drifts by the
+offset delta across a DST boundary, and rows from other apps carry no hour at
+all. The offset is therefore read only for *which day* it means; the hour comes
+from the global all-day reminder setting, recomposed against each occurrence's
+own date. Which day that is comes from the local date the encoded instant falls
+on — except for a plain multiple of 1440, read at face value because a foreign
+row means literal days from UTC midnight. The two collide where the all-day hour
+equals the zone's UTC offset (20:00 in New York), and there the instant landing
+on the named hour decides it is ours; the display path decodes through the same
+function, so the screen and the notification agree. Timed reminders need none of
+this: `begin` is an absolute instant.
+
+**One visibility model.** The scan only plans occurrences of calendars with
+`Calendars.VISIBLE = 1`, and that flag *is* the app's on/off switch: Settings →
 Calendars writes it (one calendar per update — `CalendarProvider2` skips its own
 `checkNextAlarm()` reschedule for any selection that isn't `_id=`), and every
 display predicate reads `CalendarSource.isVisibleInSystem`. The reconciliation
@@ -171,16 +209,14 @@ the app has not been allowed to write yet (read-only permission grant, or a
 pre-permission launch); `CalendarVisibilityReconciler` drains it entry by entry,
 and until it does, the repository and `ReminderNotifier.post` honour it. That
 gate also covers a snooze re-shown from our own alarm after its calendar was
-switched off. Silencing is not handling: an alert the gate drops keeps its
-`SCHEDULED` state while its event is still ahead (`handledAlertIds`), so
-switching the calendar back on re-posts it (`ReminderRecovery`) instead of
-losing it — the provider's own table is the stash. The drawer's filter sheet
-(`CalendarPrefs.hiddenCalendarIds`) is a separate in-app declutter that never
-touches reminders.
+switched off. The drawer's filter sheet (`CalendarPrefs.hiddenCalendarIds`) is a
+separate in-app declutter that never touches reminders.
 
-Deliberately absent until real devices prove it necessary: own alarm
-scheduling, `BOOT_COMPLETED`, snooze/dismiss actions, battery-exemption
-prompts.
+Deliberately absent: a fallback to the provider's `EVENT_REMINDER` broadcast.
+Keeping both would double-post wherever the provider works, and Etar's way out —
+a latch that disables its own scheduling once a real broadcast arrives — cannot
+be copied, because our failure mode includes a broadcast that arrives with no
+alert row behind it.
 
 ## Testing