Keep timeline events in the right repeated hour on DST fall-back day (#387)

On the day the clocks go back, 02:00–03:00 happens twice. Event times now
remember which of the two they mean, so moving, resizing, editing and saving
keep them in the right one.

- The week and day timeline place blocks by clock time, so events after a DST
  change no longer sit an hour off.
- An event ending in the repeated hour is drawn up to the end of that hour,
  and its label shows its real end time.
- Drags, drops and resizes keep the event's real length across a clock
  change; a resize only changes the edge being dragged.
- A drop onto a repeated time lands on the first one, unless the event is
  already in the second one.
- The editor, event details and the "local time" line add the zone
  abbreviation to a repeated time so the two can be told apart.
- Saving checks and writes the real start and end times, so a span ending in
  the repeated hour is valid and switching between the two is saved.

Closes #387

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

@@ -1,5 +1,7 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.calendula.domain.resolveIn
+import kotlinx.datetime.toKotlinTimeZone
 import android.provider.CalendarContract
 import de.jeanlucmakiola.calendula.domain.AccessLevel
 import de.jeanlucmakiola.calendula.domain.Availability
@@ -48,8 +50,8 @@ internal fun EventForm.toWriteTimes(zone: ZoneId): EventWriteTimes = if (isAllDa
 } else {
     val writeZone = writeZone(zone)
     EventWriteTimes(
-        dtStartMillis = start.toJavaLocalDateTime().atZone(writeZone).toInstant().toEpochMilli(),
-        dtEndMillis = end.toJavaLocalDateTime().atZone(writeZone).toInstant().toEpochMilli(),
+        dtStartMillis = start.resolveIn(writeZone.toKotlinTimeZone(), startOffset).toEpochMilliseconds(),
+        dtEndMillis = end.resolveIn(writeZone.toKotlinTimeZone(), endOffset).toEpochMilliseconds(),
         timezone = writeZone.id,
     )
 }
@@ -181,12 +183,14 @@ internal fun buildEventUpdateValues(
 
     // A zone change counts as a time change even when the wall-clock is
     // untouched: the same 09:00 in another zone is a different instant, so
-    // DTSTART has to move with it.
+    // DTSTART has to move with it. So does a switch between the two passes of
+    // the fall-back hour, which only the resolved instants tell apart (#387).
     val timesChanged = updated.start != original.start ||
         updated.end != original.end ||
         updated.isAllDay != original.isAllDay ||
         updated.rrule != original.rrule ||
-        updated.timezone != original.timezone
+        updated.timezone != original.timezone ||
+        updated.toWriteTimes(zone) != original.toWriteTimes(zone)
     if (!timesChanged) return@buildMap
 
     val newTimes = updated.toWriteTimes(zone)

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

@@ -4,7 +4,8 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.toInstant
+import kotlinx.datetime.UtcOffset
+import kotlinx.datetime.offsetAt
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Instant
 
@@ -36,6 +37,13 @@ data class EventForm(
      * (see [EventFormField.Timezone] and the data layer's UTC-midnight rule).
      */
     val timezone: String? = null,
+    /**
+     * The UTC offsets [start]/[end] were read at, when they came from real
+     * instants. Only a wall-clock time the fall-back hour repeats needs them:
+     * both of its instants share one [LocalDateTime] (#387).
+     */
+    val startOffset: UtcOffset? = null,
+    val endOffset: UtcOffset? = null,
     val location: String = "",
     val description: String = "",
     /** Reminder lead times in minutes before the start, deduplicated. */
@@ -145,16 +153,15 @@ fun EventDetail.toEditForm(beginMillis: Long, endMillis: Long, zone: TimeZone):
             ?.takeIf { runCatching { TimeZone.of(it) }.isSuccess }
     }
     val formZone = pinnedZone?.let { TimeZone.of(it) } ?: zone
+    val begin = Instant.fromEpochMilliseconds(beginMillis)
+    val finish = Instant.fromEpochMilliseconds(endMillis)
     val (start, end) = if (instance.isAllDay) {
-        val startDate = Instant.fromEpochMilliseconds(beginMillis)
-            .toLocalDateTime(TimeZone.UTC).date
-        val endExclusive = Instant.fromEpochMilliseconds(endMillis)
-            .toLocalDateTime(TimeZone.UTC).date
+        val startDate = begin.toLocalDateTime(TimeZone.UTC).date
+        val endExclusive = finish.toLocalDateTime(TimeZone.UTC).date
         val endDate = maxOf(startDate, LocalDate.fromEpochDays(endExclusive.toEpochDays() - 1))
         LocalDateTime(startDate, LocalTime(9, 0)) to LocalDateTime(endDate, LocalTime(10, 0))
     } else {
-        Instant.fromEpochMilliseconds(beginMillis).toLocalDateTime(formZone) to
-            Instant.fromEpochMilliseconds(endMillis).toLocalDateTime(formZone)
+        begin.toLocalDateTime(formZone) to finish.toLocalDateTime(formZone)
     }
     return EventForm(
         calendarId = instance.calendarId,
@@ -163,6 +170,8 @@ fun EventDetail.toEditForm(beginMillis: Long, endMillis: Long, zone: TimeZone):
         start = start,
         end = end,
         timezone = pinnedZone,
+        startOffset = if (instance.isAllDay) null else formZone.offsetAt(begin),
+        endOffset = if (instance.isAllDay) null else formZone.offsetAt(finish),
         location = instance.location.orEmpty(),
         description = description.orEmpty(),
         reminders = reminders.map { it.minutes }.distinct().sorted(),
@@ -221,20 +230,18 @@ fun EventDetail.toEditSnapshot(beginMillis: Long, endMillis: Long, zone: TimeZon
     )
 
 /**
- * The form's times as they land in [target] — what a pinned event's wall-clock
- * actually means where the user is standing. Null when there's nothing to
- * disambiguate: an unpinned event (already in [target]), one pinned to [target]
- * itself, an all-day event (no zone), or an unparseable pinned zone.
+ * Whether this form's times mean something else in [target] — a timed event
+ * pinned to another zone. False when there's nothing to disambiguate: an
+ * unpinned event (already in [target]), one pinned to [target] itself, an
+ * all-day event (no zone), or an unparseable pinned zone.
  *
- * The form edits a pinned event in its own zone, so this is what lets the UI
- * show the other side of the pair rather than making the user do the arithmetic.
+ * The form edits a pinned event in its own zone, so this is what tells the UI
+ * to show the other side of the pair rather than making the user do the arithmetic.
  */
-fun EventForm.timesIn(target: TimeZone): Pair<LocalDateTime, LocalDateTime>? {
-    if (isAllDay) return null
-    val pinned = timezone?.let { runCatching { TimeZone.of(it) }.getOrNull() } ?: return null
-    if (pinned.id == target.id) return null
-    return start.toInstant(pinned).toLocalDateTime(target) to
-        end.toInstant(pinned).toLocalDateTime(target)
+fun EventForm.isPinnedAwayFrom(target: TimeZone): Boolean {
+    if (isAllDay) return false
+    val pinned = timezone?.let { runCatching { TimeZone.of(it) }.getOrNull() } ?: return false
+    return pinned.id != target.id
 }
 
 /**
@@ -254,9 +261,19 @@ fun EventForm.populatedFields(): Set<EventFormField> = buildSet {
     if (attendees.isNotEmpty()) add(EventFormField.Attendees)
 }
 
-fun EventForm.problems(): Set<EventFormProblem> = buildSet {
+/**
+ * What stops this form from saving. A timed span is checked as instants in the
+ * form's zone (else [deviceZone]): one ending in the fall-back hour's repeat can
+ * end on an earlier wall clock than it starts (#387).
+ */
+fun EventForm.problems(deviceZone: TimeZone): Set<EventFormProblem> = buildSet {
     if (calendarId == null) add(EventFormProblem.NoCalendar)
-    val endsTooEarly = if (isAllDay) end.date < start.date else end < start
+    val endsTooEarly = if (isAllDay) {
+        end.date < start.date
+    } else {
+        val zone = resolvedZone(deviceZone)
+        endInstant(zone) < startInstant(zone)
+    }
     if (endsTooEarly) add(EventFormProblem.EndBeforeStart)
     // An UNTIL before the first day would make the provider generate zero
     // occurrences — the event would silently vanish from every view.

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

@@ -3,10 +3,14 @@ package de.jeanlucmakiola.calendula.domain
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.TimeZone
+import kotlinx.datetime.UtcOffset
+import kotlinx.datetime.offsetAt
 import kotlinx.datetime.plus
 import kotlinx.datetime.toInstant
+import kotlinx.datetime.toJavaZoneId
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Instant
+import kotlin.time.toJavaInstant
 
 /**
  * The zone this form's wall-clock times mean, matching what the data layer
@@ -15,6 +19,43 @@ import kotlin.time.Instant
 fun EventForm.resolvedZone(deviceZone: TimeZone): TimeZone =
     timezone?.let { runCatching { TimeZone.of(it) }.getOrNull() } ?: deviceZone
 
+/**
+ * This wall-clock time in [zone], at [preferred] when the fall-back hour repeats
+ * it and that is one of its two offsets — otherwise the earlier one (#387).
+ */
+fun LocalDateTime.resolveIn(zone: TimeZone, preferred: UtcOffset?): Instant {
+    val kept = preferred?.let { toInstant(it) }
+    return kept?.takeIf { it.toLocalDateTime(zone) == this } ?: toInstant(zone)
+}
+
+/** Whether this instant's wall clock in [zone] is one the fall-back hour repeats. */
+fun Instant.inRepeatedHour(zone: TimeZone): Boolean {
+    val zid = zone.toJavaZoneId()
+    return zid.rules.getValidOffsets(java.time.LocalDateTime.ofInstant(toJavaInstant(), zid)).size > 1
+}
+
+/** The form's start as an instant in [zone], keeping its [EventForm.startOffset]. */
+fun EventForm.startInstant(zone: TimeZone): Instant = start.resolveIn(zone, startOffset)
+
+/** The form's end as an instant in [zone], keeping its [EventForm.endOffset]. */
+fun EventForm.endInstant(zone: TimeZone): Instant = end.resolveIn(zone, endOffset)
+
+/** The form's timed span set to these instants, read in [zone] with their offsets. */
+fun EventForm.withTimes(start: Instant, end: Instant, zone: TimeZone): EventForm = copy(
+    start = start.toLocalDateTime(zone),
+    end = end.toLocalDateTime(zone),
+    startOffset = zone.offsetAt(start),
+    endOffset = zone.offsetAt(end),
+)
+
+/**
+ * The form with its end picked by hand. A picked wall-clock time can't say which
+ * pass of a repeated hour it means, so it drops [EventForm.endOffset] and takes
+ * the earlier — unless it is the end the form already has.
+ */
+fun EventForm.withEnd(end: LocalDateTime): EventForm =
+    if (end == this.end) this else copy(end = end, endOffset = null)
+
 /**
  * The form moved so it starts at [newStart], keeping its **instant** duration —
  * a recurring event's length travels to the provider as `DURATION`, so keeping
@@ -26,11 +67,8 @@ fun EventForm.resolvedZone(deviceZone: TimeZone): TimeZone =
 fun EventForm.shiftedTo(newStart: Instant, deviceZone: TimeZone): EventForm {
     if (isAllDay) return this
     val zone = resolvedZone(deviceZone)
-    val span = end.toInstant(zone) - start.toInstant(zone)
-    return copy(
-        start = newStart.toLocalDateTime(zone),
-        end = (newStart + span).toLocalDateTime(zone),
-    )
+    val span = endInstant(zone) - startInstant(zone)
+    return withTimes(newStart, newStart + span, zone)
 }
 
 /**
@@ -48,16 +86,13 @@ fun EventForm.shiftedByDays(days: Int, deviceZone: TimeZone): EventForm {
         )
     }
     val zone = resolvedZone(deviceZone)
-    val span = end.toInstant(zone) - start.toInstant(zone)
-    return copy(start = newStart, end = (newStart.toInstant(zone) + span).toLocalDateTime(zone))
+    val span = endInstant(zone) - startInstant(zone)
+    val startAt = newStart.resolveIn(zone, startOffset)
+    return withTimes(startAt, startAt + span, zone)
 }
 
 /** The form with new start and end, each in the form's own zone — a resize. All-day is untouched. */
 fun EventForm.resizedTo(newStart: Instant, newEnd: Instant, deviceZone: TimeZone): EventForm {
     if (isAllDay) return this
-    val zone = resolvedZone(deviceZone)
-    return copy(
-        start = newStart.toLocalDateTime(zone),
-        end = newEnd.toLocalDateTime(zone),
-    )
+    return withTimes(newStart, newEnd, resolvedZone(deviceZone))
 }

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

@@ -4,7 +4,7 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.toInstant
+import kotlinx.datetime.offsetAt
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Duration.Companion.hours
 import kotlin.time.Instant
@@ -35,7 +35,15 @@ fun buildInsertEventForm(
     zone: TimeZone,
     now: Instant,
 ): EventForm {
-    val (start, end) = if (isAllDay) {
+    val timed = if (isAllDay) {
+        null
+    } else {
+        val startAt = beginMillis?.let(Instant::fromEpochMilliseconds) ?: nextFullHour(now)
+        val endAt = endMillis?.let(Instant::fromEpochMilliseconds)?.takeIf { it >= startAt }
+            ?: (startAt + 1.hours)
+        startAt to endAt
+    }
+    val (start, end) = if (timed == null) {
         // All-day provider times are UTC midnights with an exclusive end; show
         // the last covered day and keep placeholder wall-clock times in case the
         // user switches the event to timed (mirrors EventDetail.toEditForm).
@@ -48,14 +56,7 @@ fun buildInsertEventForm(
             ?: startDate
         LocalDateTime(startDate, LocalTime(9, 0)) to LocalDateTime(endDate, LocalTime(10, 0))
     } else {
-        val startTime = beginMillis
-            ?.let { Instant.fromEpochMilliseconds(it).toLocalDateTime(zone) }
-            ?: nextFullHour(now, zone)
-        val endTime = endMillis
-            ?.let { Instant.fromEpochMilliseconds(it).toLocalDateTime(zone) }
-            ?.takeIf { it >= startTime }
-            ?: (startTime.toInstant(zone) + 1.hours).toLocalDateTime(zone)
-        startTime to endTime
+        timed.first.toLocalDateTime(zone) to timed.second.toLocalDateTime(zone)
     }
     return EventForm(
         calendarId = null,
@@ -63,6 +64,8 @@ fun buildInsertEventForm(
         isAllDay = isAllDay,
         start = start,
         end = end,
+        startOffset = timed?.let { zone.offsetAt(it.first) },
+        endOffset = timed?.let { zone.offsetAt(it.second) },
         location = location.orEmpty(),
         description = description.orEmpty(),
         // Bare RRULE value (Events.RRULE convention); tolerate a leading "RRULE:"
@@ -71,8 +74,7 @@ fun buildInsertEventForm(
     )
 }
 
-private fun nextFullHour(now: Instant, zone: TimeZone): LocalDateTime {
+private fun nextFullHour(now: Instant): Instant {
     val hourMillis = 3_600_000L
-    val rounded = (now.toEpochMilliseconds() / hourMillis + 1) * hourMillis
-    return Instant.fromEpochMilliseconds(rounded).toLocalDateTime(zone)
+    return Instant.fromEpochMilliseconds((now.toEpochMilliseconds() / hourMillis + 1) * hourMillis)
 }

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

@@ -157,12 +157,18 @@ fun timeZoneOptionOf(
  * the offset isn't stated twice in ICU's spelling and ours.
  */
 fun zoneDescriptor(option: TimeZoneOption): String {
+    val name = zoneAbbreviation(option)
+    val statesOffset = option.shortName == "UTC" || option.shortName.startsWith("GMT")
+    return if (statesOffset) name else "$name · ${formatGmtOffset(option.offsetMinutes)}"
+}
+
+/**
+ * [option]'s short name on its own — "CEST", "UTC" — with an offset-shaped one
+ * normalised to our GMT form, as [zoneDescriptor] spells it.
+ */
+fun zoneAbbreviation(option: TimeZoneOption): String {
     val abbrev = option.shortName
-    return when {
-        abbrev == "UTC" -> "UTC"
-        abbrev.startsWith("GMT") -> formatGmtOffset(option.offsetMinutes)
-        else -> "$abbrev · ${formatGmtOffset(option.offsetMinutes)}"
-    }
+    return if (abbrev.startsWith("GMT")) formatGmtOffset(option.offsetMinutes) else abbrev
 }
 
 /**

app/src/main/java/de/jeanlucmakiola/calendula/domain/ics/ParsedIcsForm.kt

@@ -5,6 +5,7 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
+import kotlinx.datetime.offsetAt
 import kotlinx.datetime.toLocalDateTime
 
 /**
@@ -34,6 +35,8 @@ fun ParsedIcsEvent.toEventForm(zone: TimeZone): EventForm {
         isAllDay = isAllDay,
         start = start,
         end = end,
+        startOffset = if (isAllDay) null else zone.offsetAt(this.start),
+        endOffset = if (isAllDay) null else zone.offsetAt(this.end),
         location = location.orEmpty(),
         description = description.orEmpty(),
         reminders = semanticReminderMinutes(),

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

@@ -16,6 +16,8 @@ import de.jeanlucmakiola.calendula.domain.parseSimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.problems
 import de.jeanlucmakiola.calendula.domain.realignRecurrence
 import de.jeanlucmakiola.calendula.domain.resizedTo
+import de.jeanlucmakiola.calendula.domain.endInstant
+import de.jeanlucmakiola.calendula.domain.startInstant
 import de.jeanlucmakiola.calendula.domain.resolvedZone
 import de.jeanlucmakiola.calendula.domain.shiftedByDays
 import de.jeanlucmakiola.calendula.domain.shiftedTo
@@ -329,7 +331,7 @@ class RescheduleViewModel @Inject constructor(
 
         // The UNTIL check is deferred to the write, which knows how far the move
         // reaches and so which date has to clear it.
-        if ((shifted.problems() - EventFormProblem.RecurrenceEndsBeforeStart).isNotEmpty()) {
+        if ((shifted.problems(zone) - EventFormProblem.RecurrenceEndsBeforeStart).isNotEmpty()) {
             _outcome.value = MoveOutcome.Failed
             return null
         }
@@ -495,8 +497,7 @@ class RescheduleViewModel @Inject constructor(
     private fun resizedEndMillis(prepared: PreparedMove): Long? {
         if (prepared.request.target !is MoveTarget.Span) return null
         val form = prepared.updated
-        return form.end.toInstant(form.resolvedZone(TimeZone.currentSystemDefault()))
-            .toEpochMilliseconds()
+        return form.endInstant(form.resolvedZone(TimeZone.currentSystemDefault())).toEpochMilliseconds()
     }
 
     /**
@@ -508,8 +509,7 @@ class RescheduleViewModel @Inject constructor(
         return if (form.isAllDay) {
             form.start.date.atStartOfDayIn(TimeZone.UTC).toEpochMilliseconds()
         } else {
-            form.start.toInstant(form.resolvedZone(TimeZone.currentSystemDefault()))
-                .toEpochMilliseconds()
+            form.startInstant(form.resolvedZone(TimeZone.currentSystemDefault())).toEpochMilliseconds()
         }
     }
 

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

@@ -1,7 +1,13 @@
 package de.jeanlucmakiola.calendula.ui.common
 
 import androidx.compose.runtime.staticCompositionLocalOf
+import de.jeanlucmakiola.calendula.domain.inRepeatedHour
+import de.jeanlucmakiola.calendula.domain.timeZoneOptionOf
+import de.jeanlucmakiola.calendula.domain.zoneAbbreviation
+import kotlinx.datetime.TimeZone
 import java.time.LocalTime
+import kotlin.time.Instant
+import kotlin.time.toJavaInstant
 import java.time.format.DateTimeFormatter
 import java.util.Locale
 
@@ -68,3 +74,15 @@ fun formatHourLabel(hour: Int, is24Hour: Boolean, locale: Locale): String =
     }
 
 private const val MINUTES_PER_DAY = 1_440
+
+/**
+ * [formatted] — [instant]'s time in [zone] — with the zone's abbreviation after
+ * it ("2:30 AM CEST") when the fall-back hour repeats that time, the one case
+ * where the time alone doesn't say which instant it is (#387).
+ */
+fun withRepeatedHourZone(formatted: String, instant: Instant, zone: TimeZone, locale: Locale): String {
+    if (!instant.inRepeatedHour(zone)) return formatted
+    val option = timeZoneOptionOf(zone.id, locale, instant.toJavaInstant(), ::icuTimeZoneRegion)
+        ?: return formatted
+    return "$formatted ${zoneAbbreviation(option)}"
+}

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

@@ -45,8 +45,12 @@ import androidx.compose.ui.unit.IntSize
 import androidx.compose.ui.unit.dp
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.EventInstance
+import de.jeanlucmakiola.calendula.domain.inRepeatedHour
+import de.jeanlucmakiola.calendula.domain.resolveIn
 import de.jeanlucmakiola.calendula.ui.week.MINUTES_PER_DAY
 import de.jeanlucmakiola.calendula.ui.week.TimedBlock
+import de.jeanlucmakiola.calendula.ui.week.minutesPast
+import de.jeanlucmakiola.calendula.ui.week.wallClockEndMinutes
 import de.jeanlucmakiola.floret.identity.rememberReduceMotion
 import de.jeanlucmakiola.floret.locale.currentLocale
 import kotlinx.coroutines.delay
@@ -54,6 +58,7 @@ import kotlinx.coroutines.flow.StateFlow
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.atStartOfDayIn
+import kotlinx.datetime.offsetAt
 import kotlinx.datetime.plus
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
@@ -61,6 +66,7 @@ import kotlinx.datetime.TimeZone
 import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
 import kotlin.math.roundToInt
+import kotlin.time.Duration
 import kotlin.time.Instant
 
 /** Start granularity a dragged block snaps to, matching the big calendar apps. */
@@ -506,6 +512,8 @@ class TimelineDragController {
      * finger is on; this is what turns where it lands back into an event start.
      */
     private var clipOffsetMin = 0
+    private var dragZone: TimeZone? = null
+    private var dragDuration = Duration.ZERO
 
     /** What the picked-up block drew its title over — see [TimelineDrag.titleLines]. */
     private var titleLines = 0
@@ -539,6 +547,7 @@ class TimelineDragController {
     fun begin(
         block: TimedBlock,
         clipOffsetMin: Int,
+        zone: TimeZone,
         titleLines: Int,
         pointerInRoot: Offset,
         blockInRoot: Offset,
@@ -547,6 +556,8 @@ class TimelineDragController {
         if (!isSelected(block)) deselect()
         source = block
         this.clipOffsetMin = clipOffsetMin
+        dragZone = zone
+        dragDuration = (block.event.end - block.event.start).coerceAtLeast(Duration.ZERO)
         this.titleLines = titleLines
         settling = null
         isDragging = true
@@ -573,6 +584,8 @@ class TimelineDragController {
         resizeSlot = null
         source = null
         clipOffsetMin = 0
+        dragZone = null
+        dragDuration = Duration.ZERO
         titleLines = 0
         isDragging = false
         pointerMoved = false
@@ -664,17 +677,12 @@ class TimelineDragController {
         pointerInRoot: Offset,
     ) {
         val start = block.event.start.toLocalDateTime(zone)
-        val end = block.event.end.toLocalDateTime(zone)
         source = block
         resizeEdge = edge
         resizeDay = start.date
         resizeStartMin = start.time.toSecondOfDay() / 60
         // Wall clock at both ends, as the drop resolves them (DST-safe).
-        resizeEndMin = maxOf(
-            resizeStartMin,
-            (end.date.toEpochDays() - start.date.toEpochDays()).toInt() * MINUTES_PER_DAY +
-                end.time.toSecondOfDay() / 60,
-        )
+        resizeEndMin = wallClockEndMinutes(resizeStartMin, block.event.start, block.event.end, start.date, zone)
         clipOffsetMin = 0
         this.titleLines = titleLines
         settling = null
@@ -701,6 +709,7 @@ class TimelineDragController {
     fun finishResize(zone: TimeZone): TimelineResizeDrop? {
         val landed = drag
         val origin = originSlot
+        val edge = resizeEdge
         cancel()
         if (landed == null || landed.slot == origin) return null
         settlingSelected = selection?.event?.instanceId == landed.event.instanceId
@@ -708,10 +717,26 @@ class TimelineDragController {
         liftedInstanceId = landed.event.instanceId
         settledOrigin = landed.event.eventId to landed.event.start
         settledAbandonedMark = abandonedTicks?.value ?: 0
+        // Only the held edge moves. The other keeps its own instant rather than
+        // a round trip through the grid, where an end in the fall-back hour's
+        // repeat is drawn to that hour's end, not at its own time (#387).
         val drop = TimelineResizeDrop(
             event = landed.event,
-            start = wallClockInstant(landed.date, landed.eventStartMin, zone),
-            end = wallClockInstant(landed.date, landed.eventStartMin + landed.eventSpanMin, zone),
+            start = if (edge == ResizeEdge.Top) {
+                wallClockInstant(landed.date, landed.eventStartMin, zone, keepOffsetOf = landed.event.start)
+            } else {
+                landed.event.start
+            },
+            end = if (edge == ResizeEdge.Bottom) {
+                wallClockInstant(
+                    landed.date,
+                    landed.eventStartMin + landed.eventSpanMin,
+                    zone,
+                    keepOffsetOf = landed.event.end,
+                )
+            } else {
+                landed.event.end
+            },
         )
         settledEnd = drop.end
         return drop
@@ -835,13 +860,22 @@ class TimelineDragController {
         val origin = grid.positionInRoot()
         val rawMinutes = (pointer.y - grab.y - origin.y) / hourPx * 60f
         val snapped = (rawMinutes / DRAG_SNAP_MINUTES).roundToInt() * DRAG_SNAP_MINUTES
-        val eventSpan = (block.event.end - block.event.start).inWholeMinutes.toInt()
-            .coerceAtLeast(0)
-        val floor = dragFloorMin(clipOffsetMin, eventSpan)
-        val startMin = snapped.coerceIn(floor, MINUTES_PER_DAY - DRAG_SNAP_MINUTES)
-        val eventStartMin = startMin - clipOffsetMin
+        val zone = dragZone ?: return
         val column = ((pointer.x - origin.x) / columnPx).toInt().coerceIn(0, days.lastIndex)
         val dayIndex = if (geometry.isRtl) days.lastIndex - column else column
+        val target = days[dayIndex]
+        val keep = block.event.start
+        // Measured where it would land: the drop keeps the real duration, which in
+        // wall clock gains or loses the hour of a DST change it crosses (#387).
+        val floor = dragFloorMin(
+            clipOffsetMin,
+            wallClockSpanMinutes(target, snapped - clipOffsetMin, dragDuration, zone, keep),
+        )
+        val held = snapped.coerceIn(floor, MINUTES_PER_DAY - DRAG_SNAP_MINUTES) - clipOffsetMin
+        // A start in the spring-forward gap lands an hour on; show it there.
+        val eventStartMin = wallClockInstant(target, held, zone, keep).minutesPast(target, zone)
+        val startMin = (eventStartMin + clipOffsetMin).coerceAtMost(MINUTES_PER_DAY - DRAG_SNAP_MINUTES)
+        val eventSpan = wallClockSpanMinutes(target, eventStartMin, dragDuration, zone, keep)
         val visible = -dayIndex..days.lastIndex - dayIndex
         val onGrid = dragSlices(eventStartMin, eventSpan, within = visible)
         val slices = onGrid.ifEmpty {
@@ -929,10 +963,7 @@ fun rememberTimelineDragController(): TimelineDragController {
  * so the offset has to come back off at the drop (#253).
  */
 fun TimedBlock.clipOffsetMinutes(day: LocalDate, zone: TimeZone): Int {
-    val start = event.start.toLocalDateTime(zone)
-    val days = (day.toEpochDays() - start.date.toEpochDays()).toInt()
-    val minutes = days * MINUTES_PER_DAY + startMin - start.time.toSecondOfDay() / 60
-    return minutes.coerceAtLeast(0)
+    return (startMin - event.start.minutesPast(day, zone)).coerceAtLeast(0)
 }
 
 /**
@@ -954,13 +985,41 @@ fun TimedBlock.continuesAfter(day: LocalDate, zone: TimeZone): Boolean =
  * visibly settles there.
  */
 fun TimelineDrop.startInstant(zone: TimeZone): Instant =
-    wallClockInstant(date, startMin - clipOffsetMin, zone)
+    wallClockInstant(date, startMin - clipOffsetMin, zone, keepOffsetOf = event.start)
 
-/** [minutes] past [date]'s midnight, either way past it, as wall clock in [zone] (DST-safe). */
-fun wallClockInstant(date: LocalDate, minutes: Int, zone: TimeZone): Instant {
+/**
+ * The wall-clock minutes an event lasting [duration] covers when it starts
+ * [startMin] past [date]'s midnight in [zone] — its real length, give or take a
+ * DST change in between (#387).
+ */
+internal fun wallClockSpanMinutes(
+    date: LocalDate,
+    startMin: Int,
+    duration: Duration,
+    zone: TimeZone,
+    keepOffsetOf: Instant? = null,
+): Int {
+    val start = wallClockInstant(date, startMin, zone, keepOffsetOf)
+    return wallClockEndMinutes(startMin, start, start + duration, date, zone) - startMin
+}
+
+/**
+ * [minutes] past [date]'s midnight, either way past it, as wall clock in [zone]
+ * (DST-safe). A time the fall-back hour repeats lands on its earlier pass, unless
+ * [keepOffsetOf] is itself in that hour's later one: an event there stays on it
+ * (#387). An instant outside the hour says nothing about which pass the grid
+ * slot means, so a drop never depends on the season the event came from.
+ */
+fun wallClockInstant(
+    date: LocalDate,
+    minutes: Int,
+    zone: TimeZone,
+    keepOffsetOf: Instant? = null,
+): Instant {
     val day = date.plus(minutes.floorDiv(MINUTES_PER_DAY), DateTimeUnit.DAY)
     val minute = minutes.mod(MINUTES_PER_DAY)
-    return LocalDateTime(day, LocalTime(minute / 60, minute % 60)).toInstant(zone)
+    val kept = keepOffsetOf?.takeIf { it.inRepeatedHour(zone) }?.let(zone::offsetAt)
+    return LocalDateTime(day, LocalTime(minute / 60, minute % 60)).resolveIn(zone, kept)
 }
 
 /**

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

@@ -102,6 +102,7 @@ import de.jeanlucmakiola.calendula.ui.common.eventFill
 import de.jeanlucmakiola.floret.locale.currentLocale
 import de.jeanlucmakiola.calendula.ui.common.LocalUse24HourFormat
 import de.jeanlucmakiola.calendula.ui.common.timeOfDayFormatter
+import de.jeanlucmakiola.calendula.ui.common.withRepeatedHourZone
 import de.jeanlucmakiola.calendula.ui.common.recurrenceText
 import de.jeanlucmakiola.calendula.ui.common.reminderLeadTimeLabel
 import kotlinx.coroutines.launch
@@ -807,12 +808,13 @@ private fun formatWhen(
     }
 
     val endLdt = instance.end.toJavaLocalDateTime(zid)
+    val startTime = withRepeatedHourZone(timeShort.format(startLdt), instance.start, zone, locale)
+    val endTime = withRepeatedHourZone(timeShort.format(endLdt), instance.end, zone, locale)
     return if (startLdt.toLocalDate() == endLdt.toLocalDate()) {
-        dateFull.format(startLdt.toLocalDate()) to
-            "${timeShort.format(startLdt)} – ${timeShort.format(endLdt)}"
+        dateFull.format(startLdt.toLocalDate()) to "$startTime – $endTime"
     } else {
-        val start = "${dateMedium.format(startLdt.toLocalDate())} ${timeShort.format(startLdt)}"
-        val end = "${dateMedium.format(endLdt.toLocalDate())} ${timeShort.format(endLdt)}"
+        val start = "${dateMedium.format(startLdt.toLocalDate())} $startTime"
+        val end = "${dateMedium.format(endLdt.toLocalDate())} $endTime"
         "$start – $end" to null
     }
 }

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

@@ -116,10 +116,13 @@ import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventAttendee
 import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventForm
+import de.jeanlucmakiola.calendula.domain.startInstant
+import de.jeanlucmakiola.calendula.domain.endInstant
+import de.jeanlucmakiola.calendula.domain.resolvedZone
+import de.jeanlucmakiola.calendula.domain.isPinnedAwayFrom
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.zoneDescriptor
 import de.jeanlucmakiola.calendula.domain.timeZoneOptionOf
-import de.jeanlucmakiola.calendula.domain.timesIn
 import de.jeanlucmakiola.calendula.domain.EventFormProblem
 import de.jeanlucmakiola.calendula.domain.RecurrenceEnd
 import de.jeanlucmakiola.calendula.domain.RecurrenceFreq
@@ -162,6 +165,7 @@ import de.jeanlucmakiola.floret.reminders.ReminderUnit
 import de.jeanlucmakiola.floret.locale.currentLocale
 import de.jeanlucmakiola.calendula.ui.common.LocalUse24HourFormat
 import de.jeanlucmakiola.calendula.ui.common.timeOfDayFormatter
+import de.jeanlucmakiola.calendula.ui.common.withRepeatedHourZone
 import de.jeanlucmakiola.calendula.ui.common.reminderLeadTimeLabel
 import de.jeanlucmakiola.calendula.ui.common.reminderUnitLabel
 import de.jeanlucmakiola.calendula.ui.common.nextOccurrencesText
@@ -174,7 +178,6 @@ import kotlinx.datetime.TimeZone
 import kotlinx.datetime.isoDayNumber
 import kotlinx.datetime.toJavaDayOfWeek
 import kotlinx.datetime.toJavaLocalDate
-import kotlinx.datetime.toInstant
 import kotlinx.datetime.toJavaLocalTime
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.toJavaInstant
@@ -184,6 +187,7 @@ import java.time.format.FormatStyle
 import java.time.format.TextStyle as JavaTextStyle
 import java.util.Locale
 import kotlin.time.Clock
+import kotlin.time.Instant
 
 /**
  * Full-screen event form: create (v1.2, from the FAB's anchor date) and edit
@@ -662,9 +666,14 @@ private fun EventEditContent(
             },
         ) {
             Spacer(Modifier.height(4.dp))
+            val formZone = remember(form.timezone) { form.resolvedZone(TimeZone.currentSystemDefault()) }
+            val startAt = remember(form.start, form.startOffset, formZone) { form.startInstant(formZone) }
+            val endAt = remember(form.end, form.endOffset, formZone) { form.endInstant(formZone) }
             ScheduleRow(
                 label = stringResource(R.string.event_edit_starts),
                 dateTime = form.start,
+                instant = startAt,
+                zone = formZone,
                 isAllDay = form.isAllDay,
                 locale = locale,
                 onDateClick = { picker = PickerTarget.StartDate },
@@ -674,6 +683,8 @@ private fun EventEditContent(
             ScheduleRow(
                 label = stringResource(R.string.event_edit_ends),
                 dateTime = form.end,
+                instant = endAt,
+                zone = formZone,
                 isAllDay = form.isAllDay,
                 locale = locale,
                 onDateClick = { picker = PickerTarget.EndDate },
@@ -692,20 +703,14 @@ private fun EventEditContent(
             // The rows above edit a pinned event in *its own* zone, which is the
             // time it was set at — but that says nothing about when it lands for
             // whoever is reading it. Spell the local equivalent out rather than
-            // leaving the user to do the offset arithmetic. Absent (null) unless
-            // the event is pinned somewhere other than here.
-            // Keyed rather than recomputed: this sits in the same Column as the
-            // title field, so it would otherwise re-parse the zone on every
-            // keystroke.
-            val localTimes = remember(form.timezone, form.start, form.end, form.isAllDay) {
-                form.timesIn(TimeZone.currentSystemDefault())
-            }
-            localTimes?.let { (localStart, localEnd) ->
+            // leaving the user to do the offset arithmetic. Absent unless the
+            // event is pinned somewhere other than here.
+            if (form.isPinnedAwayFrom(TimeZone.currentSystemDefault())) {
                 Spacer(Modifier.height(2.dp))
                 Text(
                     text = stringResource(
                         R.string.event_edit_timezone_local_time,
-                        formatTimeRange(localStart, localEnd, locale),
+                        formatTimeRange(startAt, endAt, TimeZone.currentSystemDefault(), locale),
                     ),
                     style = MaterialTheme.typography.bodySmall,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
@@ -769,7 +774,7 @@ private fun EventEditContent(
                                 timeZoneOptionOf(
                                     id,
                                     locale,
-                                    at = form.start.toInstant(zone).toJavaInstant(),
+                                    at = form.startInstant(zone).toJavaInstant(),
                                     regionOf = ::icuTimeZoneRegion,
                                 )
                             }
@@ -2251,18 +2256,21 @@ private fun EditCard(
 }
 
 /**
- * "2:00 PM – 3:00 PM", honouring the user's 12/24-hour setting. Collapses to one
- * time when both land on the same minute (an instant event shouldn't read as a
- * range against itself). Dates are deliberately absent — the rows above carry
- * them.
+ * "2:00 PM – 3:00 PM" in [zone], honouring the user's 12/24-hour setting. Collapses
+ * to one time for an instant event, which shouldn't read as a range against
+ * itself. Dates are deliberately absent — the rows above carry them.
  */
 @Composable
-private fun formatTimeRange(start: LocalDateTime, end: LocalDateTime, locale: Locale): String {
+private fun formatTimeRange(start: Instant, end: Instant, zone: TimeZone, locale: Locale): String {
     val use24Hour = LocalUse24HourFormat.current
     val timeFormat = remember(locale, use24Hour) { timeOfDayFormatter(use24Hour, locale) }
-    val from = timeFormat.format(start.time.toJavaLocalTime())
-    val to = timeFormat.format(end.time.toJavaLocalTime())
-    return if (from == to) from else "$from – $to"
+    fun format(at: Instant) = withRepeatedHourZone(
+        timeFormat.format(at.toLocalDateTime(zone).time.toJavaLocalTime()),
+        at,
+        zone,
+        locale,
+    )
+    return if (start == end) format(start) else "${format(start)} – ${format(end)}"
 }
 
 /**
@@ -2344,6 +2352,8 @@ private fun firstLineHeight(
 private fun ScheduleRow(
     label: String,
     dateTime: LocalDateTime,
+    instant: Instant,
+    zone: TimeZone,
     isAllDay: Boolean,
     locale: Locale,
     onDateClick: () -> Unit,
@@ -2386,7 +2396,7 @@ private fun ScheduleRow(
         )
         if (!isAllDay) {
             Text(
-                text = timeFormat.format(dateTime.time.toJavaLocalTime()),
+                text = withRepeatedHourZone(timeFormat.format(dateTime.time.toJavaLocalTime()), instant, zone, locale),
                 style = MaterialTheme.typography.titleMedium,
                 color = valueColor,
                 modifier = Modifier

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

@@ -19,6 +19,12 @@ import de.jeanlucmakiola.calendula.domain.EditSnapshot
 import de.jeanlucmakiola.calendula.domain.EventAttendee
 import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventForm
+import de.jeanlucmakiola.calendula.domain.endInstant
+import de.jeanlucmakiola.calendula.domain.resolveIn
+import de.jeanlucmakiola.calendula.domain.resolvedZone
+import de.jeanlucmakiola.calendula.domain.startInstant
+import de.jeanlucmakiola.calendula.domain.withEnd
+import de.jeanlucmakiola.calendula.domain.withTimes
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.RecurringWriteScope
 import de.jeanlucmakiola.calendula.domain.isEventTarget
@@ -49,6 +55,7 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
+import kotlinx.datetime.offsetAt
 import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
 import kotlin.coroutines.cancellation.CancellationException
@@ -289,7 +296,11 @@ class EventEditViewModel @Inject constructor(
         EventEditUiState(
             form = resolved,
             calendars = pickerCalendars,
-            problems = if (local.showProblems) resolved.problems() else emptySet(),
+            problems = if (local.showProblems) {
+                resolved.problems(TimeZone.currentSystemDefault())
+            } else {
+                emptySet()
+            },
             saveState = local.saveState,
             visibleFields = visibleFields,
             hiddenFields = (offerableFields - visibleFields).sorted(),
@@ -331,20 +342,24 @@ class EventEditViewModel @Inject constructor(
         if (_form.value != null) return
         val zone = TimeZone.currentSystemDefault()
         val now = Clock.System.now()
-        val start = when {
+        val startAt = when {
             startMinutes != null ->
-                LocalDateTime(date, LocalTime(startMinutes / 60, startMinutes % 60))
+                LocalDateTime(date, LocalTime(startMinutes / 60, startMinutes % 60)).toInstant(zone)
             date == now.toLocalDateTime(zone).date -> {
                 // Today: the next full hour (may roll into tomorrow before midnight).
                 val hourMillis = 3_600_000L
-                val rounded = (now.toEpochMilliseconds() / hourMillis + 1) * hourMillis
-                Instant.fromEpochMilliseconds(rounded).toLocalDateTime(zone)
+                Instant.fromEpochMilliseconds((now.toEpochMilliseconds() / hourMillis + 1) * hourMillis)
             }
-            else -> LocalDateTime(date, LocalTime(9, 0))
+            else -> LocalDateTime(date, LocalTime(9, 0)).toInstant(zone)
         }
-        val end = (start.toInstant(zone) + SettingsPrefs.DEFAULT_EVENT_DURATION.minutes)
-            .toLocalDateTime(zone)
-        _form.value = EventForm(calendarId = null, start = start, end = end)
+        val endAt = startAt + SettingsPrefs.DEFAULT_EVENT_DURATION.minutes
+        _form.value = EventForm(
+            calendarId = null,
+            start = startAt.toLocalDateTime(zone),
+            end = endAt.toLocalDateTime(zone),
+            startOffset = zone.offsetAt(startAt),
+            endOffset = zone.offsetAt(endAt),
+        )
         applyDefaultReminder()
         applyDefaultDuration()
     }
@@ -454,11 +469,10 @@ class EventEditViewModel @Inject constructor(
             if (_editTarget.value != null || _durationTouched.value) return@launch
             if (_form.value?.isAllDay != false) return@launch
             val duration = resolveDefaultEventDuration(global, overrides, targetId)
-            val zone = TimeZone.currentSystemDefault()
             update { form ->
-                form.copy(
-                    end = (form.start.toInstant(zone) + duration.minutes).toLocalDateTime(zone),
-                )
+                val zone = form.resolvedZone(TimeZone.currentSystemDefault())
+                val start = form.startInstant(zone)
+                form.withTimes(start, start + duration.minutes, zone)
             }
         }
     }
@@ -663,12 +677,12 @@ class EventEditViewModel @Inject constructor(
     // default duration, so a later calendar switch keeps their span (#54).
     fun setEndDate(date: LocalDate) {
         _durationTouched.value = true
-        update { it.copy(end = LocalDateTime(date, it.end.time)) }
+        update { it.withEnd(LocalDateTime(date, it.end.time)) }
     }
 
     fun setEndTime(time: LocalTime) {
         _durationTouched.value = true
-        update { it.copy(end = LocalDateTime(it.end.date, time)) }
+        update { it.withEnd(LocalDateTime(it.end.date, time)) }
     }
 
     /**
@@ -681,7 +695,7 @@ class EventEditViewModel @Inject constructor(
         val current = state.value ?: return
         if (current.saveState == SaveUiState.Saving) return
         val form = current.form
-        if (form.problems().isNotEmpty()) {
+        if (form.problems(TimeZone.currentSystemDefault()).isNotEmpty()) {
             _showProblems.value = true
             return
         }
@@ -810,11 +824,13 @@ class EventEditViewModel @Inject constructor(
     }
 
     private fun moveStart(transform: (LocalDateTime) -> LocalDateTime) = update { form ->
-        val zone = TimeZone.currentSystemDefault()
-        val newStart = transform(form.start)
-        val duration = form.end.toInstant(zone) - form.start.toInstant(zone)
-        val newEnd = (newStart.toInstant(zone) + duration).toLocalDateTime(zone)
-        form.copy(start = newStart, end = newEnd)
+        val zone = form.resolvedZone(TimeZone.currentSystemDefault())
+        val duration = form.endInstant(zone) - form.startInstant(zone)
+        // A picked time can't say which pass of a repeated hour it means; only
+        // an unchanged start keeps its own (see [withEnd]).
+        val picked = transform(form.start)
+        val newStart = picked.resolveIn(zone, form.startOffset.takeIf { picked == form.start })
+        form.withTimes(newStart, newStart + duration, zone)
     }
 
     private inline fun update(block: (EventForm) -> EventForm) {

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekScreen.kt

@@ -52,6 +52,7 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.staticCompositionLocalOf
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.key
@@ -299,6 +300,12 @@ internal val CalendarView.timelineKind: TimelineKind
         else -> TimelineKind.Week
     }
 
+/**
+ * The zone the shown timeline is laid out in, so its blocks, drags and drops all
+ * read the same wall clock (#387).
+ */
+internal val LocalTimelineZone = staticCompositionLocalOf { TimeZone.currentSystemDefault() }
+
 /** How long a switch waits for the view it goes to before resizing into it without its events. */
 private const val MORPH_DATA_WAIT_MS = 150L
 
@@ -435,7 +442,8 @@ private fun PagedTimelineScreen(
 
     // Off the ticking clock rather than the loaded page, so it turns over at
     // midnight; derived, so the per-minute tick doesn't recompose the screen.
-    val zone = remember { TimeZone.currentSystemDefault() }
+    // The timeline's own zone, so "today" agrees with the blocks and drops (#387).
+    val zone = viewModel.zone
     val today by remember(zone) { derivedStateOf { nowState.value.toLocalDateTime(zone).date } }
     val isOnCurrentWeek = state !is WeekUiState.Success || (today >= weekStart && today <= weekEnd)
 
@@ -476,7 +484,10 @@ private fun PagedTimelineScreen(
     )
 
     ScreenBody(modifier = modifier) { innerPadding ->
-        CompositionLocalProvider(LocalDimCutoff provides dimCutoff) {
+        CompositionLocalProvider(
+            LocalDimCutoff provides dimCutoff,
+            LocalTimelineZone provides viewModel.zone,
+        ) {
             WeekContent(
                 state = state,
                 today = today,
@@ -527,7 +538,7 @@ private fun WeekContent(
     // inside the outgoing page.
     val dragController = rememberTimelineDragController()
     val move = LocalEventMove.current
-    val zone = remember { TimeZone.currentSystemDefault() }
+    val zone = LocalTimelineZone.current
     val onDrop: (TimelineDrop) -> Unit = { drop ->
         // A selected event stays selected where it landed (#141).
         if (dragController.selection?.event?.instanceId == drop.event.instanceId) {
@@ -1369,7 +1380,7 @@ private fun DayColumnCard(
     val hourPx = with(density) { hourHeight.toPx() }
     val morphing = LocalViewMorph.current != null
     val showHourGrid = LocalShowHourGrid.current
-    val zone = remember { TimeZone.currentSystemDefault() }
+    val zone = LocalTimelineZone.current
     // Tells a settled drop when this column has caught up with it.
     LaunchedEffect(blocks, dragController.settling) {
         dragController.noteGrid(date, blocks)
@@ -1524,8 +1535,10 @@ private fun EventBlock(
     val title = block.event.title.ifBlank { stringResource(R.string.event_untitled) }
     val use24Hour = LocalUse24HourFormat.current
     val locale = currentLocale()
+    val zone = LocalTimelineZone.current
+    val labelEndMin = remember(block, date, zone) { block.labelEndMin(date, zone) }
     val timeLabel = "${minToHm(block.startMin, use24Hour, locale)}–" +
-        minToHm(block.endMin, use24Hour, locale)
+        minToHm(labelEndMin, use24Hour, locale)
     val density = LocalDensity.current
     val metrics = rememberBlockTextMetrics(height)
     // Only full-width (non-overlapping) blocks that are tall enough show the
@@ -1539,7 +1552,7 @@ private fun EventBlock(
     val textWidth = width - (BLOCK_OUTER_INSET + BLOCK_TEXT_PADDING) * 2
     val shownTime = rememberBlockTimeRange(
         minToHm(block.startMin, use24Hour, locale),
-        minToHm(block.endMin, use24Hour, locale),
+        minToHm(labelEndMin, use24Hour, locale),
         textWidth,
     )
     // A short block drops the title rather than serving a horizontally sliced
@@ -1570,7 +1583,6 @@ private fun EventBlock(
     val timeMaxLines = if (showTime) blockTimeLines(shownTime, textWidth, spare) else 1
     val dimCutoff = LocalDimCutoff.current
     val dimmed = dimCutoff != null && block.event.isPastOn(date, dimCutoff)
-    val zone = remember { TimeZone.currentSystemDefault() }
     val moveAction = eventMoveAction(block.event)
     val draggable = eventDragAllowed(block.event)
     val selectable = eventSelectAllowed()
@@ -1591,6 +1603,7 @@ private fun EventBlock(
                 dragController.begin(
                     block = block,
                     clipOffsetMin = clipOffset,
+                    zone = zone,
                     titleLines = if (showTitle) titleMaxLines else 0,
                     pointerInRoot = pointer,
                     // Measured off the block's placement rather than off where the

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekViewModel.kt

@@ -35,6 +35,7 @@ import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.DayOfWeek
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
+import kotlinx.datetime.toJavaZoneId
 import kotlinx.datetime.atStartOfDayIn
 import kotlinx.datetime.atTime
 import kotlinx.datetime.daysUntil
@@ -81,7 +82,8 @@ abstract class PagedTimelineViewModel(
     initialRule: (LocalDate) -> PageGrid,
 ) : ViewModel() {
 
-    private val zone = TimeZone.currentSystemDefault()
+    /** The zone every page is laid out in; drags and drops resolve in it too (#387). */
+    val zone: TimeZone = TimeZone.currentSystemDefault()
 
     /** Whether to fade events that have already finished (display concern only). */
     val dimCompletedEvents: StateFlow<Boolean> = settingsPrefs.dimCompletedEvents
@@ -331,6 +333,62 @@ internal fun spanRange(start: LocalDate, count: Int, zone: TimeZone): ClosedRang
     return from..to
 }
 
+/**
+ * This instant's wall-clock time as minutes past [day]'s midnight in [zone] —
+ * negative before that day, past 1440 after it. Elapsed time since midnight would
+ * put everything after a DST change an hour off on that day's grid (#387).
+ */
+internal fun Instant.minutesPast(day: LocalDate, zone: TimeZone): Int {
+    val local = toLocalDateTime(zone)
+    val days = (local.date.toEpochDays() - day.toEpochDays()).toInt()
+    return days * MINUTES_PER_DAY + local.time.toSecondOfDay() / 60
+}
+
+/** [instant]'s [minutesPast] clamped to [day]. */
+internal fun wallClockMinutes(instant: Instant, day: LocalDate, zone: TimeZone): Int =
+    instant.minutesPast(day, zone).coerceIn(0, MINUTES_PER_DAY)
+
+/**
+ * Where a run from [start] to [end] that begins at [startMin] ends on [day]'s
+ * wall clock. One ending in the fall-back hour's repeat can read as ending before
+ * it began: it starts in that hour's first pass, so it covers the hour's wall
+ * clock from its start to where the hour ends, and is drawn to there.
+ */
+internal fun wallClockEndMinutes(
+    startMin: Int,
+    start: Instant,
+    end: Instant,
+    day: LocalDate,
+    zone: TimeZone,
+): Int {
+    val wall = end.minutesPast(day, zone)
+    if (wall > startMin || end <= start) return maxOf(wall, startMin)
+    return repeatedHourEndMinutes(end, day, zone) ?: (startMin + (end - start).inWholeMinutes.toInt())
+}
+
+/**
+ * Where the repeated hour [end] falls in ends, as minutes past [day]'s midnight:
+ * the wall clock the zone fell back from (03:00 in Berlin). Null when the last
+ * change before [end] was no fall-back.
+ */
+private fun repeatedHourEndMinutes(end: Instant, day: LocalDate, zone: TimeZone): Int? {
+    // Just past [end], so an end on the transition itself still finds it.
+    val after = java.time.Instant.ofEpochMilli(end.toEpochMilliseconds() + 1)
+    val transition = zone.toJavaZoneId().rules.previousTransition(after)
+        ?.takeIf { it.isOverlap } ?: return null
+    val local = transition.dateTimeBefore
+    val days = (local.toLocalDate().toEpochDay() - day.toEpochDays()).toInt()
+    return days * MINUTES_PER_DAY + local.toLocalTime().toSecondOfDay() / 60
+}
+
+/**
+ * The end a block's time label names on [day]: its event's own wall-clock end,
+ * which for one ending in the fall-back hour's repeat is earlier than the
+ * [TimedBlock.endMin] it is drawn to (#387).
+ */
+internal fun TimedBlock.labelEndMin(day: LocalDate, zone: TimeZone): Int =
+    minOf(endMin, wallClockMinutes(event.end, day, zone))
+
 /** True if this event overlaps the calendar [day] in [zone] (any portion). */
 internal fun EventInstance.coversDay(day: LocalDate, zone: TimeZone): Boolean {
     if (isAllDay) {
@@ -384,14 +442,14 @@ internal fun layoutDay(
             if (ev.start == ev.end) {
                 // Instant event: keep only if the point falls inside this day.
                 if (ev.start < dayStart || ev.start >= dayEnd) return@mapNotNull null
-                val m = (ev.start - dayStart).inWholeMinutes.toInt().coerceIn(0, MINUTES_PER_DAY)
+                val m = wallClockMinutes(ev.start, day, zone)
                 Raw(ev, m, m)
             } else {
                 val s = maxOf(ev.start, dayStart)
                 val e = minOf(ev.end, dayEnd)
                 if (e <= s) return@mapNotNull null
-                val startMin = (s - dayStart).inWholeMinutes.toInt().coerceIn(0, MINUTES_PER_DAY)
-                val endMin = (e - dayStart).inWholeMinutes.toInt().coerceIn(startMin, MINUTES_PER_DAY)
+                val startMin = wallClockMinutes(s, day, zone)
+                val endMin = wallClockEndMinutes(startMin, s, e, day, zone).coerceAtMost(MINUTES_PER_DAY)
                 Raw(ev, startMin, endMin)
             }
         }

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

@@ -9,8 +9,10 @@ import de.jeanlucmakiola.calendula.domain.realignRecurrence
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
+import kotlinx.datetime.UtcOffset
 import org.junit.jupiter.api.Test
 import java.time.ZoneId
+import kotlin.time.Instant
 
 class EventWriteMapperTest {
 
@@ -1387,4 +1389,37 @@ class EventWriteMapperTest {
         assertThat(parent[CalendarContract.Events.DTSTART]).isEqualTo(1_780_560_000_000L)
         assertThat(parent[CalendarContract.Events.RRULE]).isEqualTo("FREQ=WEEKLY")
     }
+
+    @Test
+    fun `a time in the repeated fall-back hour is written at its own offset`() {
+        val repeated = LocalDateTime(LocalDate(2026, 10, 25), LocalTime(2, 0))
+        val times = form(start = repeated, end = repeated)
+            .copy(startOffset = UtcOffset(hours = 2), endOffset = UtcOffset(hours = 1))
+            .toWriteTimes(berlin)
+        assertThat(times.dtStartMillis).isEqualTo(Instant.parse("2026-10-25T00:00:00Z").toEpochMilliseconds())
+        assertThat(times.dtEndMillis).isEqualTo(Instant.parse("2026-10-25T01:00:00Z").toEpochMilliseconds())
+    }
+
+    @Test
+    fun `a move between the two repeated fall-back hours writes the new times`() {
+        // 02:30 CEST to 02:30 CET: the same wall clock, an hour later.
+        val repeated = LocalDateTime(LocalDate(2026, 10, 25), LocalTime(2, 30))
+        val original = form(start = repeated, end = repeated)
+            .copy(startOffset = UtcOffset(hours = 2), endOffset = UtcOffset(hours = 2))
+        val updated = original.copy(startOffset = UtcOffset(hours = 1), endOffset = UtcOffset(hours = 1))
+        val values = update(original, updated)
+        assertThat(values[CalendarContract.Events.DTSTART])
+            .isEqualTo(Instant.parse("2026-10-25T01:30:00Z").toEpochMilliseconds())
+        assertThat(values[CalendarContract.Events.DTEND])
+            .isEqualTo(Instant.parse("2026-10-25T01:30:00Z").toEpochMilliseconds())
+    }
+
+    @Test
+    fun `an untouched form in the repeated fall-back hour writes no times`() {
+        val repeated = LocalDateTime(LocalDate(2026, 10, 25), LocalTime(2, 30))
+        val original = form(start = repeated, end = repeated)
+            .copy(startOffset = UtcOffset(hours = 2), endOffset = UtcOffset(hours = 1))
+        assertThat(update(original, original.copy(title = "Renamed")))
+            .doesNotContainKey(CalendarContract.Events.DTSTART)
+    }
 }

app/src/test/java/de/jeanlucmakiola/calendula/domain/EventFormTest.kt

@@ -19,25 +19,25 @@ class EventFormTest {
 
     @Test
     fun `valid timed form has no problems`() {
-        assertThat(form().problems()).isEmpty()
+        assertThat(form().problems(berlin)).isEmpty()
     }
 
     @Test
     fun `missing calendar is a problem`() {
-        assertThat(form(calendarId = null).problems())
+        assertThat(form(calendarId = null).problems(berlin))
             .containsExactly(EventFormProblem.NoCalendar)
     }
 
     @Test
     fun `timed end before start is a problem`() {
         val bad = form(end = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(9, 0)))
-        assertThat(bad.problems()).containsExactly(EventFormProblem.EndBeforeStart)
+        assertThat(bad.problems(berlin)).containsExactly(EventFormProblem.EndBeforeStart)
     }
 
     @Test
     fun `zero-length timed event is allowed`() {
         val instant = form(end = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(10, 0)))
-        assertThat(instant.problems()).isEmpty()
+        assertThat(instant.problems(berlin)).isEmpty()
     }
 
     @Test
@@ -47,7 +47,7 @@ class EventFormTest {
             start = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(0, 0)),
             end = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(0, 0)),
         )
-        assertThat(allDay.problems()).isEmpty()
+        assertThat(allDay.problems(berlin)).isEmpty()
     }
 
     @Test
@@ -57,7 +57,7 @@ class EventFormTest {
             start = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(0, 0)),
             end = LocalDateTime(LocalDate(2026, 6, 10), LocalTime(0, 0)),
         )
-        assertThat(bad.problems()).containsExactly(EventFormProblem.EndBeforeStart)
+        assertThat(bad.problems(berlin)).containsExactly(EventFormProblem.EndBeforeStart)
     }
 
     @Test
@@ -66,7 +66,7 @@ class EventFormTest {
             calendarId = null,
             end = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(9, 0)),
         )
-        assertThat(bad.problems()).containsExactly(
+        assertThat(bad.problems(berlin)).containsExactly(
             EventFormProblem.NoCalendar,
             EventFormProblem.EndBeforeStart,
         )
@@ -76,28 +76,28 @@ class EventFormTest {
     fun `recurrence until before the first day is a problem`() {
         // Days before the start, so it parses to an earlier date in any zone.
         val bad = form().copy(rrule = "FREQ=DAILY;UNTIL=20260601T120000Z")
-        assertThat(bad.problems())
+        assertThat(bad.problems(berlin))
             .containsExactly(EventFormProblem.RecurrenceEndsBeforeStart)
     }
 
     @Test
     fun `recurrence until on or after the first day is fine`() {
         // Date-only UNTIL parses zone-independently.
-        assertThat(form().copy(rrule = "FREQ=DAILY;UNTIL=20260611").problems()).isEmpty()
-        assertThat(form().copy(rrule = "FREQ=WEEKLY").problems()).isEmpty()
+        assertThat(form().copy(rrule = "FREQ=DAILY;UNTIL=20260611").problems(berlin)).isEmpty()
+        assertThat(form().copy(rrule = "FREQ=WEEKLY").problems(berlin)).isEmpty()
     }
 
     @Test
     fun `complex rrules are not validated against the start`() {
         // The picker can't have produced this ("second Monday" ordinal BYDAY);
         // it is preserved verbatim and never flagged.
-        assertThat(form().copy(rrule = "FREQ=MONTHLY;BYDAY=2MO;UNTIL=20200101").problems()).isEmpty()
+        assertThat(form().copy(rrule = "FREQ=MONTHLY;BYDAY=2MO;UNTIL=20200101").problems(berlin)).isEmpty()
     }
 
     @Test
     fun `weekly byday rules are validated against the start`() {
         val bad = form().copy(rrule = "FREQ=WEEKLY;BYDAY=MO,FR;UNTIL=20200101")
-        assertThat(bad.problems())
+        assertThat(bad.problems(berlin))
             .containsExactly(EventFormProblem.RecurrenceEndsBeforeStart)
     }
 
@@ -210,64 +210,23 @@ class EventFormTest {
     }
 
     @Test
-    fun `timesIn converts a pinned event into the target zone`() {
-        val form = EventForm(
-            calendarId = 1L,
-            start = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(8, 0)),
-            end = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(9, 0)),
-            timezone = "America/New_York",
-        )
-        val (start, end) = form.timesIn(berlin)!!
-        // 08:00 New York (EDT, UTC-4) is 14:00 Berlin (CEST, UTC+2).
-        assertThat(start).isEqualTo(LocalDateTime(LocalDate(2026, 7, 17), LocalTime(14, 0)))
-        assertThat(end).isEqualTo(LocalDateTime(LocalDate(2026, 7, 17), LocalTime(15, 0)))
-    }
-
-    @Test
-    fun `timesIn crosses the date line when the offset pushes past midnight`() {
-        val form = EventForm(
-            calendarId = 1L,
-            start = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(20, 0)),
-            end = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(21, 0)),
-            timezone = "America/New_York",
-        )
-        val (start, _) = form.timesIn(berlin)!!
-        // 20:00 New York is 02:00 the NEXT day in Berlin — the date has to move
-        // with it, not just the clock.
-        assertThat(start).isEqualTo(LocalDateTime(LocalDate(2026, 7, 18), LocalTime(2, 0)))
-    }
-
-    @Test
-    fun `timesIn tracks each zone's own DST rather than a fixed offset`() {
-        // In January both are on standard time: 08:00 EST is 14:00 CET — the
-        // same six hours as July, but only because both shifted. Late March,
-        // when the US has sprung forward and Europe hasn't, the gap is five.
-        val march = EventForm(
-            calendarId = 1L,
-            start = LocalDateTime(LocalDate(2026, 3, 20), LocalTime(8, 0)),
-            end = LocalDateTime(LocalDate(2026, 3, 20), LocalTime(9, 0)),
-            timezone = "America/New_York",
-        )
-        assertThat(march.timesIn(berlin)!!.first)
-            .isEqualTo(LocalDateTime(LocalDate(2026, 3, 20), LocalTime(13, 0)))
-    }
-
-    @Test
-    fun `timesIn returns null when there is nothing to disambiguate`() {
+    fun `isPinnedAwayFrom is false when there is nothing to disambiguate`() {
         val base = EventForm(
             calendarId = 1L,
             start = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(8, 0)),
             end = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(9, 0)),
         )
         // Unpinned: the form's times already are the local times.
-        assertThat(base.timesIn(berlin)).isNull()
+        assertThat(base.isPinnedAwayFrom(berlin)).isFalse()
         // Pinned to the target itself: same thing.
-        assertThat(base.copy(timezone = "Europe/Berlin").timesIn(berlin)).isNull()
+        assertThat(base.copy(timezone = "Europe/Berlin").isPinnedAwayFrom(berlin)).isFalse()
         // All-day: date-anchored, so there's no zone conversion to show.
-        assertThat(base.copy(isAllDay = true, timezone = "America/New_York").timesIn(berlin))
-            .isNull()
+        assertThat(base.copy(isAllDay = true, timezone = "America/New_York").isPinnedAwayFrom(berlin))
+            .isFalse()
         // Unparseable: can't convert, mustn't throw.
-        assertThat(base.copy(timezone = "Mars/Olympus_Mons").timesIn(berlin)).isNull()
+        assertThat(base.copy(timezone = "Mars/Olympus_Mons").isPinnedAwayFrom(berlin)).isFalse()
+        // Pinned elsewhere: worth spelling out.
+        assertThat(base.copy(timezone = "America/New_York").isPinnedAwayFrom(berlin)).isTrue()
     }
 
     @Test
@@ -425,4 +384,43 @@ class EventFormTest {
         assertThat(prefilled.color).isNull()
         assertThat(prefilled.populatedFields()).doesNotContain(EventFormField.Color)
     }
+
+    @Test
+    fun `toEditForm keeps which repeated fall-back hour each end is in`() {
+        val start = Instant.parse("2026-10-25T00:00:00Z")
+        val end = Instant.parse("2026-10-25T01:00:00Z")
+        val prefilled = detail().toEditForm(start.toEpochMilliseconds(), end.toEpochMilliseconds(), berlin)
+        assertThat(prefilled.start).isEqualTo(prefilled.end)
+        assertThat(prefilled.startInstant(berlin)).isEqualTo(start)
+        assertThat(prefilled.endInstant(berlin)).isEqualTo(end)
+    }
+
+    @Test
+    fun `a span ending in the repeated fall-back hour is valid`() {
+        // 02:45 CEST to 02:15 CET: half an hour, though the clock reads backwards.
+        val form = form().withTimes(
+            Instant.parse("2026-10-25T00:45:00Z"),
+            Instant.parse("2026-10-25T01:15:00Z"),
+            berlin,
+        )
+        assertThat(form.end).isLessThan(form.start)
+        assertThat(form.problems(berlin)).isEmpty()
+        // Read as the same pass at both ends, it really does end first.
+        assertThat(form.copy(startOffset = null, endOffset = null).problems(berlin))
+            .containsExactly(EventFormProblem.EndBeforeStart)
+    }
+
+    @Test
+    fun `an end picked by hand takes the earlier repeated hour`() {
+        val form = form().withTimes(
+            Instant.parse("2026-10-25T00:45:00Z"),
+            Instant.parse("2026-10-25T01:15:00Z"),
+            berlin,
+        )
+        // Picking the end it already has keeps its pass.
+        assertThat(form.withEnd(form.end)).isEqualTo(form)
+        val picked = form.withEnd(LocalDateTime(LocalDate(2026, 10, 25), LocalTime(2, 50)))
+        assertThat(picked.endOffset).isNull()
+        assertThat(picked.endInstant(berlin)).isEqualTo(Instant.parse("2026-10-25T00:50:00Z"))
+    }
 }

app/src/test/java/de/jeanlucmakiola/calendula/domain/EventShiftTest.kt

@@ -5,8 +5,10 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.LocalDateTime
 import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
+import kotlinx.datetime.UtcOffset
 import kotlinx.datetime.toInstant
 import org.junit.jupiter.api.Test
+import kotlin.time.Instant
 
 class EventShiftTest {
 
@@ -88,8 +90,10 @@ class EventShiftTest {
 
     @Test
     fun `a zero-distance drop leaves the form untouched`() {
-        val original = form()
-        assertThat(original.shiftedTo(original.start.toInstant(berlin), berlin)).isEqualTo(original)
+        // As read from the provider, offsets and all.
+        val start = form().start.toInstant(berlin)
+        val original = form().withTimes(start, form().end.toInstant(berlin), berlin)
+        assertThat(original.shiftedTo(start, berlin)).isEqualTo(original)
     }
 
     @Test
@@ -197,4 +201,35 @@ class EventShiftTest {
 
         assertThat(allDay.resizedTo(start, start, berlin)).isEqualTo(allDay)
     }
+
+    // 02:00 CEST to 02:00 CET on 2026-10-25: one real hour, one wall-clock value.
+    private val repeatStart = Instant.parse("2026-10-25T00:00:00Z")
+    private val repeatEnd = Instant.parse("2026-10-25T01:00:00Z")
+
+    @Test
+    fun `moving an event in the repeated fall-back hour keeps its length`() {
+        val original = form().withTimes(repeatStart, repeatEnd, berlin)
+        val moved = original.shiftedTo(Instant.parse("2026-10-25T00:30:00Z"), berlin)
+        assertThat(moved.startInstant(berlin)).isEqualTo(Instant.parse("2026-10-25T00:30:00Z"))
+        assertThat(moved.endInstant(berlin)).isEqualTo(Instant.parse("2026-10-25T01:30:00Z"))
+    }
+
+    @Test
+    fun `a move onto the second repeated hour stays there`() {
+        val target = Instant.parse("2026-10-25T01:30:00Z")
+        val moved = form().withTimes(repeatStart, repeatEnd, berlin).shiftedTo(target, berlin)
+        assertThat(moved.start).isEqualTo(LocalDateTime(LocalDate(2026, 10, 25), LocalTime(2, 30)))
+        assertThat(moved.startInstant(berlin)).isEqualTo(target)
+    }
+
+    @Test
+    fun `resolveIn takes the preferred offset only where the hour repeats`() {
+        val repeated = LocalDateTime(LocalDate(2026, 10, 25), LocalTime(2, 30))
+        val cet = UtcOffset(hours = 1)
+        assertThat(repeated.resolveIn(berlin, cet)).isEqualTo(Instant.parse("2026-10-25T01:30:00Z"))
+        assertThat(repeated.resolveIn(berlin, null)).isEqualTo(Instant.parse("2026-10-25T00:30:00Z"))
+        // Not one of 14:00's offsets on a summer day: ignored.
+        val summer = LocalDateTime(LocalDate(2026, 6, 11), LocalTime(14, 0))
+        assertThat(summer.resolveIn(berlin, cet)).isEqualTo(summer.toInstant(berlin))
+    }
 }

app/src/test/java/de/jeanlucmakiola/calendula/ui/common/RepeatedHourZoneTest.kt

@@ -0,0 +1,30 @@
+package de.jeanlucmakiola.calendula.ui.common
+
+import com.google.common.truth.Truth.assertThat
+import kotlinx.datetime.TimeZone
+import org.junit.jupiter.api.Test
+import java.util.Locale
+import kotlin.time.Instant
+
+/** The zone named after a time only where the fall-back hour repeats it (#387). */
+class RepeatedHourZoneTest {
+
+    private val brussels = TimeZone.of("Europe/Brussels")
+
+    @Test
+    fun `both 02 30s of the fall-back day are told apart`() {
+        val first = withRepeatedHourZone("2:30 AM", Instant.parse("2026-10-25T00:30:00Z"), brussels, Locale.UK)
+        val second = withRepeatedHourZone("2:30 AM", Instant.parse("2026-10-25T01:30:00Z"), brussels, Locale.UK)
+        assertThat(first).startsWith("2:30 AM ")
+        assertThat(second).startsWith("2:30 AM ")
+        assertThat(first).isNotEqualTo(second)
+    }
+
+    @Test
+    fun `an unambiguous time stays bare`() {
+        assertThat(withRepeatedHourZone("2:45 PM", Instant.parse("2026-10-25T13:45:00Z"), brussels, Locale.UK))
+            .isEqualTo("2:45 PM")
+        assertThat(withRepeatedHourZone("3:30 AM", Instant.parse("2026-10-25T02:30:00Z"), brussels, Locale.UK))
+            .isEqualTo("3:30 AM")
+    }
+}

app/src/test/java/de/jeanlucmakiola/calendula/ui/common/TimelineDropTest.kt

@@ -4,12 +4,15 @@ import com.google.common.truth.Truth.assertThat
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.ui.week.TimedBlock
 import de.jeanlucmakiola.calendula.ui.week.layoutDay
+import de.jeanlucmakiola.calendula.ui.week.minutesPast
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
 import kotlinx.datetime.atTime
 import kotlinx.datetime.plus
 import kotlinx.datetime.toInstant
+import kotlin.time.Duration.Companion.hours
+import kotlin.time.Instant
 import org.junit.jupiter.api.Test
 
 /**
@@ -153,4 +156,88 @@ class TimelineDropTest {
         val block = layoutDay(listOf(plain), sat, zone).single()
         assertThat(block.clipOffsetMinutes(sat, zone)).isEqualTo(0)
     }
+
+    private val brussels = TimeZone.of("Europe/Brussels")
+    private val fallBack = LocalDate(2026, 10, 25)
+
+    @Test
+    fun `a block on the fall-back day carries no clip offset`() {
+        // #387: 13:45Z is 14:45 CET, drawn and picked up at 14:45.
+        val event = overnight.copy(
+            start = Instant.parse("2026-10-25T13:45:00Z"),
+            end = Instant.parse("2026-10-25T15:45:00Z"),
+        )
+        val block = layoutDay(listOf(event), fallBack, brussels).single()
+        assertThat(block.clipOffsetMinutes(fallBack, brussels)).isEqualTo(0)
+        val drop = TimelineDrop(event, fallBack, block.startMin, clipOffsetMin = 0)
+        assertThat(drop.startInstant(brussels)).isEqualTo(event.start)
+    }
+
+    @Test
+    fun `a tail on the fall-back day is offset by wall-clock time`() {
+        val event = overnight.copy(
+            start = LocalDate(2026, 10, 24).atTime(22, 0).toInstant(brussels),
+            end = fallBack.atTime(6, 0).toInstant(brussels),
+        )
+        val tail = layoutDay(listOf(event), fallBack, brussels).single()
+        val offset = tail.clipOffsetMinutes(fallBack, brussels)
+        assertThat(offset).isEqualTo(2 * 60)
+        val drop = TimelineDrop(event, fallBack, tail.startMin, clipOffsetMin = offset)
+        assertThat(drop.startInstant(brussels)).isEqualTo(event.start)
+    }
+
+    @Test
+    fun `wall-clock span follows the clock change`() {
+        // 01:00 to 04:00 on the fall-back day is four real hours.
+        assertThat(wallClockSpanMinutes(fallBack, 60, 4.hours, brussels)).isEqualTo(3 * 60)
+        // 01:00 to 04:00 on the spring-forward day is two.
+        assertThat(wallClockSpanMinutes(LocalDate(2026, 3, 29), 60, 2.hours, brussels)).isEqualTo(3 * 60)
+        assertThat(wallClockSpanMinutes(sat, 20 * 60, 12.hours, zone)).isEqualTo(12 * 60)
+    }
+
+    @Test
+    fun `a drop in the repeated fall-back hour keeps the event's offset`() {
+        // 02:30 CET, the second 02:30 of the day, dragged 15 minutes later.
+        val event = overnight.copy(
+            start = Instant.parse("2026-10-25T01:30:00Z"),
+            end = Instant.parse("2026-10-25T02:30:00Z"),
+        )
+        val block = layoutDay(listOf(event), fallBack, brussels).single()
+        val drop = TimelineDrop(event, fallBack, block.startMin + 15, clipOffsetMin = 0)
+        assertThat(drop.startInstant(brussels)).isEqualTo(Instant.parse("2026-10-25T01:45:00Z"))
+    }
+
+    @Test
+    fun `an ambiguous time without an offset to keep takes the earlier one`() {
+        assertThat(wallClockInstant(fallBack, 2 * 60 + 45, brussels))
+            .isEqualTo(Instant.parse("2026-10-25T00:45:00Z"))
+    }
+
+    @Test
+    fun `a start in the spring-forward gap resolves an hour on`() {
+        val springForward = LocalDate(2026, 3, 29)
+        val landed = wallClockInstant(springForward, 2 * 60 + 30, brussels, keepOffsetOf = overnight.start)
+        assertThat(landed.minutesPast(springForward, brussels)).isEqualTo(3 * 60 + 30)
+        assertThat(wallClockSpanMinutes(springForward, 3 * 60 + 30, 1.hours, brussels)).isEqualTo(60)
+    }
+
+    @Test
+    fun `a span ending in the repeated fall-back hour reaches that hour's end`() {
+        // 02:00 CEST plus one hour is 02:00 CET; 02:30 CEST plus one is 02:30 CET.
+        assertThat(wallClockSpanMinutes(fallBack, 2 * 60, 1.hours, brussels)).isEqualTo(60)
+        assertThat(wallClockSpanMinutes(fallBack, 2 * 60 + 30, 1.hours, brussels)).isEqualTo(30)
+    }
+
+    @Test
+    fun `a drop onto the repeated fall-back hour doesn't depend on the event's season`() {
+        val slot = 2 * 60 + 30
+        val first = Instant.parse("2026-10-25T00:30:00Z")
+        val july = Instant.parse("2026-07-01T10:00:00Z")
+        val november = Instant.parse("2026-11-10T10:00:00Z")
+        assertThat(wallClockInstant(fallBack, slot, brussels, keepOffsetOf = july)).isEqualTo(first)
+        assertThat(wallClockInstant(fallBack, slot, brussels, keepOffsetOf = november)).isEqualTo(first)
+        // Later the same day, after the clocks went back: still no say.
+        val evening = Instant.parse("2026-10-25T18:00:00Z")
+        assertThat(wallClockInstant(fallBack, slot, brussels, keepOffsetOf = evening)).isEqualTo(first)
+    }
 }

app/src/test/java/de/jeanlucmakiola/calendula/ui/week/WeekLayoutTest.kt

@@ -190,5 +190,108 @@ class WeekLayoutTest {
         assertThat(spans.all { it.lane == 0 }).isTrue()
     }
 
+    // Europe/Brussels falls back on 2026-10-25 (25 h) and springs forward on 2026-03-29 (23 h).
+    private val brussels = TimeZone.of("Europe/Brussels")
+
+    private fun brusselsEvent(date: LocalDate, from: Pair<Int, Int>, to: Pair<Int, Int>) = event(
+        date.atTime(from.first, from.second).toInstant(brussels),
+        date.atTime(to.first, to.second).toInstant(brussels),
+    )
+
+    @Test
+    fun `timed block sits at its wall-clock time on the fall-back day`() {
+        val day = LocalDate(2026, 10, 25)
+        // The event from #387: 13:45Z is 14:45 CET.
+        val ev = event(Instant.parse("2026-10-25T13:45:00Z"), Instant.parse("2026-10-25T15:45:00Z"))
+        val b = layoutDay(listOf(ev), day, brussels).single()
+        assertThat(b.startMin).isEqualTo(14 * 60 + 45)
+        assertThat(b.endMin).isEqualTo(16 * 60 + 45)
+    }
+
+    @Test
+    fun `timed block sits at its wall-clock time on the spring-forward day`() {
+        val day = LocalDate(2026, 3, 29)
+        val b = layoutDay(listOf(brusselsEvent(day, 14 to 45, 16 to 45)), day, brussels).single()
+        assertThat(b.startMin).isEqualTo(14 * 60 + 45)
+        assertThat(b.endMin).isEqualTo(16 * 60 + 45)
+    }
+
+    @Test
+    fun `late block on the fall-back day is not cut short`() {
+        val day = LocalDate(2026, 10, 25)
+        val b = layoutDay(listOf(brusselsEvent(day, 22 to 30, 23 to 59)), day, brussels).single()
+        assertThat(b.startMin).isEqualTo(22 * 60 + 30)
+        assertThat(b.endMin).isEqualTo(23 * 60 + 59)
+    }
+
+    @Test
+    fun `block running past midnight on the fall-back day reaches the day's end`() {
+        val day = LocalDate(2026, 10, 25)
+        val ev = event(
+            day.atTime(23, 0).toInstant(brussels),
+            day.plusDays(1).atTime(1, 0).toInstant(brussels),
+        )
+        val b = layoutDay(listOf(ev), day, brussels).single()
+        assertThat(b.startMin).isEqualTo(23 * 60)
+        assertThat(b.endMin).isEqualTo(MINUTES_PER_DAY)
+    }
+
+    @Test
+    fun `instant event on the fall-back day sits at its wall-clock time`() {
+        val day = LocalDate(2026, 10, 25)
+        val at = day.atTime(9, 0).toInstant(brussels)
+        val b = layoutDay(listOf(event(at, at)), day, brussels).single()
+        assertThat(b.startMin).isEqualTo(9 * 60)
+        assertThat(b.endMin).isEqualTo(9 * 60)
+    }
+
+    @Test
+    fun `block ending in the repeated fall-back hour is drawn to that hour's end`() {
+        val day = LocalDate(2026, 10, 25)
+        // 02:00 CEST to 02:00 CET: one real hour, the same wall-clock time at both ends.
+        val ev = event(Instant.parse("2026-10-25T00:00:00Z"), Instant.parse("2026-10-25T01:00:00Z"))
+        val b = layoutDay(listOf(ev), day, brussels).single()
+        assertThat(b.startMin).isEqualTo(2 * 60)
+        assertThat(b.endMin).isEqualTo(3 * 60)
+    }
+
+    @Test
+    fun `block ending in the repeated fall-back hour leaves the next hour free`() {
+        val day = LocalDate(2026, 10, 25)
+        // 02:15 CEST to 02:15 CET, then 03:00 CET: an hour apart in real time.
+        val repeat = event(Instant.parse("2026-10-25T00:15:00Z"), Instant.parse("2026-10-25T01:15:00Z"))
+        val next = event(Instant.parse("2026-10-25T02:00:00Z"), Instant.parse("2026-10-25T03:00:00Z"))
+        val blocks = layoutDay(listOf(repeat, next), day, brussels)
+        assertThat(blocks.map { it.startMin to it.endMin })
+            .containsExactly(2 * 60 + 15 to 3 * 60, 3 * 60 to 4 * 60)
+        assertThat(blocks.all { it.lane == 0 && it.laneCount == 1 }).isTrue()
+    }
+
+    @Test
+    fun `minutesPast reads wall clock either side of the day`() {
+        val day = LocalDate(2026, 10, 25)
+        assertThat(Instant.parse("2026-10-24T21:00:00Z").minutesPast(day, brussels)).isEqualTo(-60)
+        assertThat(Instant.parse("2026-10-25T13:45:00Z").minutesPast(day, brussels)).isEqualTo(14 * 60 + 45)
+        assertThat(Instant.parse("2026-10-25T23:30:00Z").minutesPast(day, brussels))
+            .isEqualTo(MINUTES_PER_DAY + 30)
+    }
+
+    @Test
+    fun `a block ending in the repeated fall-back hour is labelled with its own end`() {
+        val day = LocalDate(2026, 10, 25)
+        // 02:30 CEST to 02:30 CET: drawn to the repeated hour's end, but it ends at 02:30.
+        val ev = event(Instant.parse("2026-10-25T00:30:00Z"), Instant.parse("2026-10-25T01:30:00Z"))
+        val b = layoutDay(listOf(ev), day, brussels).single()
+        assertThat(b.endMin).isEqualTo(3 * 60)
+        assertThat(b.labelEndMin(day, brussels)).isEqualTo(2 * 60 + 30)
+    }
+
+    @Test
+    fun `an ordinary block is labelled with its drawn end`() {
+        val day = LocalDate(2026, 10, 25)
+        val b = layoutDay(listOf(brusselsEvent(day, 14 to 45, 16 to 45)), day, brussels).single()
+        assertThat(b.labelEndMin(day, brussels)).isEqualTo(b.endMin)
+    }
+
     private fun LocalDate.plusDays(n: Int): LocalDate = plus(n, DateTimeUnit.DAY)
 }