Fix talk reminders firing 2h late by using device timezone

shared/core/src/androidMain/kotlin/com/paligot/confily/core/AlarmScheduler.android.kt

@@ -8,11 +8,7 @@ import com.paligot.confily.resources.Resource
 import com.paligot.confily.resources.title_notif_reminder_talk
 import com.paligot.confily.schedules.ui.models.TalkItemUi
 import kotlinx.coroutines.coroutineScope
-import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.minus
-import kotlinx.datetime.toInstant
-import kotlinx.datetime.toLocalDateTime
 import org.jetbrains.compose.resources.getString
 import java.util.Locale
 
@@ -34,11 +30,11 @@ actual class AlarmScheduler(
         val pendingIntent =
             PendingIntent.getBroadcast(context, talkItem.id.hashCode(), intent, flags)
         if (isFavorite) {
-            val triggerAtMillis = talkItem.startTime
-                .toLocalDateTime()
-                .toInstant(TimeZone.UTC)
-                .minus(ReminderInMinutes, DateTimeUnit.MINUTE)
-                .toEpochMilliseconds()
+            val triggerAtMillis = reminderTriggerAtMillis(
+                startTime = talkItem.startTime,
+                timeZone = TimeZone.currentSystemDefault(),
+                reminderInMinutes = ReminderInMinutes
+            )
             alarmManager.setAndAllowWhileIdle(
                 AlarmManager.RTC_WAKEUP,
                 triggerAtMillis,

shared/core/src/commonMain/kotlin/com/paligot/confily/core/ReminderTime.kt

@@ -0,0 +1,25 @@
+package com.paligot.confily.core
+
+import kotlinx.datetime.DateTimeUnit
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.minus
+import kotlinx.datetime.toInstant
+import kotlinx.datetime.toLocalDateTime
+
+/**
+ * Computes the absolute trigger instant (epoch millis) of a session reminder alarm.
+ *
+ * [startTime] is the session's wall-clock start time at the event location (e.g. "2026-06-11T08:30")
+ * and carries no timezone. It is interpreted in [timeZone] before being turned into an absolute
+ * instant: pass the device timezone so the alarm fires at the time displayed in the app rather than
+ * being offset by the difference from UTC. The reminder is scheduled [reminderInMinutes] earlier.
+ */
+internal fun reminderTriggerAtMillis(
+    startTime: String,
+    timeZone: TimeZone,
+    reminderInMinutes: Int
+): Long = startTime
+    .toLocalDateTime()
+    .toInstant(timeZone)
+    .minus(reminderInMinutes, DateTimeUnit.MINUTE)
+    .toEpochMilliseconds()

shared/core/src/commonTest/kotlin/com/paligot/confily/core/ReminderTimeTest.kt

@@ -0,0 +1,31 @@
+package com.paligot.confily.core
+
+import kotlinx.datetime.Instant
+import kotlinx.datetime.TimeZone
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotEquals
+
+class ReminderTimeTest {
+    @Test
+    fun reminder_trigger_uses_event_local_wall_clock_not_utc() {
+        // "2026-06-11T08:30" is a wall-clock time at the event (Lille / Europe/Paris, CEST = UTC+2
+        // in June) and carries no timezone. A 10-minute reminder must fire at 08:20 local = 06:20 UTC.
+        val triggerAtMillis = reminderTriggerAtMillis(
+            startTime = "2026-06-11T08:30",
+            timeZone = TimeZone.of("Europe/Paris"),
+            reminderInMinutes = 10
+        )
+
+        assertEquals(
+            Instant.parse("2026-06-11T06:20:00Z").toEpochMilliseconds(),
+            triggerAtMillis
+        )
+        // Regression guard: the previous code interpreted the wall-clock time as UTC, which would
+        // have fired the alarm at 08:20 UTC (10:20 local) — two hours late.
+        assertNotEquals(
+            Instant.parse("2026-06-11T08:20:00Z").toEpochMilliseconds(),
+            triggerAtMillis
+        )
+    }
+}