Merge pull request 'fix: address code-review findings on the 2.16.0 branch' (!87) from fix/code-review-2.16.0 into release/v2.16.0

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

@@ -6,9 +6,11 @@ import de.jeanlucmakiola.calendula.domain.Availability
 import de.jeanlucmakiola.calendula.domain.EventForm
 import kotlinx.datetime.toJavaLocalDate
 import kotlinx.datetime.toJavaLocalDateTime
+import java.time.Duration
 import java.time.Instant
 import java.time.ZoneId
 import java.time.ZoneOffset
+import java.time.LocalDateTime as JavaLocalDateTime
 
 /** Provider-ready DTSTART / DTEND / EVENT_TIMEZONE for an event write. */
 internal data class EventWriteTimes(
@@ -35,7 +37,7 @@ internal fun EventForm.toWriteTimes(zone: ZoneId): EventWriteTimes = if (isAllDa
         timezone = "UTC",
     )
 } else {
-    val writeZone = timezone?.let { runCatching { ZoneId.of(it) }.getOrNull() } ?: zone
+    val writeZone = writeZone(zone)
     EventWriteTimes(
         dtStartMillis = start.toJavaLocalDateTime().atZone(writeZone).toInstant().toEpochMilli(),
         dtEndMillis = end.toJavaLocalDateTime().atZone(writeZone).toInstant().toEpochMilli(),
@@ -43,6 +45,30 @@ internal fun EventForm.toWriteTimes(zone: ZoneId): EventWriteTimes = if (isAllDa
     )
 }
 
+/**
+ * The zone this form's DTSTART is expressed in: UTC for an all-day event (the
+ * provider's date anchor), otherwise the form's own pinned zone, falling back to
+ * [deviceZone] when it doesn't pin one or pins something the tz database can't
+ * parse.
+ */
+private fun EventForm.writeZone(deviceZone: ZoneId): ZoneId = if (isAllDay) {
+    ZoneOffset.UTC
+} else {
+    timezone?.let { runCatching { ZoneId.of(it) }.getOrNull() } ?: deviceZone
+}
+
+/**
+ * The form's start as a bare wall-clock value — what the user sees on the form,
+ * stripped of any zone. All-day events use their date's midnight rather than
+ * [EventForm.start]'s placeholder time-of-day, which exists only so switching the
+ * event back to timed has something to show.
+ */
+private fun EventForm.anchorLocal(): JavaLocalDateTime = if (isAllDay) {
+    start.date.toJavaLocalDate().atStartOfDay()
+} else {
+    start.toJavaLocalDateTime()
+}
+
 /**
  * RFC 2445 duration for a recurring event's row (the provider requires
  * DURATION instead of DTEND when an RRULE is set): whole days for all-day
@@ -109,10 +135,12 @@ internal fun buildEventInsertValues(
  * Time fields travel together (the provider validates them as a unit):
  * - unchanged times, all-day flag and rrule → no time columns at all;
  * - non-recurring result → DTSTART/DTEND, DURATION and RRULE cleared;
- * - recurring result → the *series* DTSTART moves by the same delta the user
- *   applied to the displayed occurrence ([seriesDtStartMillis] is the row's
- *   current DTSTART), DURATION replaces DTEND, RRULE is written. This keeps
- *   past occurrences intact when someone edits a later occurrence's time.
+ * - recurring result → the *series* DTSTART moves by the same **wall-clock**
+ *   shift the user applied to the displayed occurrence and is re-resolved in the
+ *   event's zone ([seriesDtStartMillis] is the row's current DTSTART), DURATION
+ *   replaces DTEND, RRULE is written. This keeps past occurrences intact when
+ *   someone edits a later occurrence's time, and keeps the anchor's time-of-day
+ *   stable across a DST boundary or a zone change between the two.
  */
 internal fun buildEventUpdateValues(
     original: EventForm,
@@ -158,8 +186,23 @@ internal fun buildEventUpdateValues(
         put(CalendarContract.Events.RRULE, null)
         put(CalendarContract.Events.DURATION, null)
     } else {
-        val startDelta = newTimes.dtStartMillis - original.toWriteTimes(zone).dtStartMillis
-        put(CalendarContract.Events.DTSTART, seriesDtStartMillis + startDelta)
+        // Move the series anchor by the *wall-clock* shift the user applied to the
+        // displayed occurrence, then re-resolve it in the event's (possibly new)
+        // zone — never by a millisecond delta. An instant delta silently bakes in
+        // the offset that happened to apply on the edited occurrence's date, which
+        // is a different offset from the series anchor's whenever a DST boundary
+        // sits between them, or whenever the zone itself changed. Working in wall
+        // clock keeps "09:00" meaning 09:00 at both ends.
+        val seriesLocal = Instant.ofEpochMilli(seriesDtStartMillis)
+            .atZone(original.writeZone(zone)).toLocalDateTime()
+        val wallClockShift = Duration.between(original.anchorLocal(), updated.anchorLocal())
+        val shifted = seriesLocal.plus(wallClockShift)
+        // An all-day series anchor must sit on a UTC midnight. A pure day move
+        // already lands there (both ends are midnights), but *switching* a
+        // recurring event to all-day shifts by a time-of-day too, so snap.
+        val newSeriesLocal = if (updated.isAllDay) shifted.toLocalDate().atStartOfDay() else shifted
+        val newSeriesStart = newSeriesLocal.atZone(updated.writeZone(zone))
+        put(CalendarContract.Events.DTSTART, newSeriesStart.toInstant().toEpochMilli())
         put(CalendarContract.Events.DTEND, null)
         put(CalendarContract.Events.RRULE, updated.rrule)
         put(CalendarContract.Events.DURATION, newTimes.toRfc2445Duration(updated.isAllDay))

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

@@ -31,8 +31,33 @@ data class TimeZoneOption(
 
     /** The leading segment ("Europe/Berlin" -> "Europe"); empty for bare ids like "UTC". */
     val region: String get() = id.substringBeforeLast('/', missingDelimiterValue = "")
+
+    /**
+     * The four fields [filterTimeZones] matches on, normalized once here rather
+     * than per query. Normalizing is not cheap — NFD decomposition plus a combining-
+     * mark strip — and a search re-examines every option on every keystroke, so
+     * doing it at construction turns ~2400 normalizations per character into a few
+     * hundred plain `startsWith`/`contains` calls.
+     *
+     * Declared in the class body, so it stays out of `equals`/`hashCode`/`copy`:
+     * it is derived state, and two options with the same id are the same option.
+     */
+    internal val searchKeys: TimeZoneSearchKeys = TimeZoneSearchKeys(
+        city = city.normalizeForSearch(),
+        id = id.normalizeForSearch(),
+        displayName = displayName.normalizeForSearch(),
+        shortName = shortName.normalizeForSearch(),
+    )
 }
 
+/** Pre-normalized match targets for one [TimeZoneOption]. */
+internal data class TimeZoneSearchKeys(
+    val city: String,
+    val id: String,
+    val displayName: String,
+    val shortName: String,
+)
+
 private fun optionFor(
     zone: ZoneId,
     locale: Locale,
@@ -87,9 +112,13 @@ private fun resolveAbbreviation(
 private fun String.looksLikeOffset(): Boolean = this == "UTC" || startsWith("GMT")
 
 /**
- * Every zone the JVM knows, resolved at [at]. This is ~600 entries, so build it
- * once and filter the result rather than rebuilding per keystroke. [regionOf]
- * (see [resolveAbbreviation]) supplies the zone's region for the abbreviation.
+ * Every zone the JVM knows, resolved at [at]. [regionOf] (see
+ * [resolveAbbreviation]) supplies the zone's region for the abbreviation.
+ *
+ * This is ~600 entries, each costing a localized display name plus up to two ICU
+ * short-name lookups, so it is **not** cheap enough for the main thread — build
+ * it off-thread once and filter the result with [filterTimeZones] rather than
+ * rebuilding per keystroke.
  *
  * Bare three-letter ids ("EST", "CST6CDT") and the legacy SystemV tree are
  * dropped: they're aliases the tz database keeps for compatibility, they'd
@@ -154,18 +183,15 @@ fun filterTimeZones(options: List<TimeZoneOption>, query: String): List<TimeZone
     if (needle.isEmpty()) return options
     return options
         .mapNotNull { option ->
-            val city = option.city.normalizeForSearch()
-            val id = option.id.normalizeForSearch()
-            val name = option.displayName.normalizeForSearch()
-            val abbrev = option.shortName.normalizeForSearch()
+            val keys = option.searchKeys
             val rank = when {
-                city.startsWith(needle) -> 0
-                abbrev == needle -> 1
-                name.startsWith(needle) -> 2
-                abbrev.startsWith(needle) -> 3
-                city.contains(needle) -> 4
-                id.contains(needle) -> 5
-                name.contains(needle) -> 6
+                keys.city.startsWith(needle) -> 0
+                keys.shortName == needle -> 1
+                keys.displayName.startsWith(needle) -> 2
+                keys.shortName.startsWith(needle) -> 3
+                keys.city.contains(needle) -> 4
+                keys.id.contains(needle) -> 5
+                keys.displayName.contains(needle) -> 6
                 else -> return@mapNotNull null
             }
             rank to option
@@ -174,6 +200,9 @@ fun filterTimeZones(options: List<TimeZoneOption>, query: String): List<TimeZone
         .map { it.second }
 }
 
+/** Unicode combining marks — what NFD decomposition leaves an accent as. */
+private val COMBINING_MARKS = Regex("\\p{Mn}+")
+
 /**
  * Lowercased, accent-stripped, underscores and slashes flattened to spaces, so
  * a query types the way a place is spoken rather than the way the tz database
@@ -181,7 +210,7 @@ fun filterTimeZones(options: List<TimeZoneOption>, query: String): List<TimeZone
  */
 private fun String.normalizeForSearch(): String =
     Normalizer.normalize(this, Normalizer.Form.NFD)
-        .replace(Regex("\\p{Mn}+"), "")
+        .replace(COMBINING_MARKS, "")
         .replace('_', ' ')
         .replace('/', ' ')
         .lowercase(Locale.ROOT)

app/src/main/java/de/jeanlucmakiola/calendula/ui/agenda/AgendaScreen.kt

@@ -89,7 +89,9 @@ import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Instant
 import java.util.Locale
 
-private val zone = TimeZone.currentSystemDefault()
+// No file-level zone constant here on purpose: it would be fixed for the process
+// lifetime and drift from the zone AgendaViewModel groups in after a device
+// time-zone change. The zone travels on AgendaUiState.Success instead.
 
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
@@ -332,6 +334,7 @@ private fun AgendaContent(
                 AgendaList(
                     days = days,
                     today = state.today,
+                    zone = state.zone,
                     dimPast = pastDisplay == PastEventDisplay.DIM,
                     now = now,
                     onEventClick = onEventClick,
@@ -348,6 +351,7 @@ private fun AgendaContent(
 private fun AgendaList(
     days: List<AgendaDay>,
     today: LocalDate,
+    zone: TimeZone,
     dimPast: Boolean,
     now: Instant,
     onEventClick: (EventInstance) -> Unit,
@@ -379,6 +383,7 @@ private fun AgendaList(
                     AgendaEventRow(
                         event = event,
                         day = day.date,
+                        zone = zone,
                         position = positionOf(index, day.events.size),
                         dimmed = dimPast && event.hasEnded(now),
                         modifier = animateItemMotion(),
@@ -458,6 +463,7 @@ private fun AgendaEmptyDayRow(onClick: () -> Unit) {
 private fun AgendaEventRow(
     event: EventInstance,
     day: LocalDate,
+    zone: TimeZone,
     position: Position,
     dimmed: Boolean,
     modifier: Modifier = Modifier,
@@ -469,7 +475,7 @@ private fun AgendaEventRow(
     GroupedRow(
         modifier = if (dimmed) modifier.alpha(EventDimAlpha) else modifier,
         title = title,
-        summary = agendaTimeSummary(event, day),
+        summary = agendaTimeSummary(event, day, zone),
         position = position,
         minHeight = 64.dp,
         leading = {
@@ -575,25 +581,34 @@ private fun agendaDayLabel(date: LocalDate, today: LocalDate): String {
  * An all-day multi-day event is simply "All day" on every day it covers.
  */
 @Composable
-private fun agendaTimeSummary(event: EventInstance, day: LocalDate): String {
+private fun agendaTimeSummary(event: EventInstance, day: LocalDate, zone: TimeZone): String {
     val is24Hour = LocalUse24HourFormat.current
     val locale = currentLocale()
 
     val time = when (val label = agendaTimeLabel(event, day, zone)) {
         AgendaTimeLabel.AllDay -> stringResource(R.string.event_detail_all_day)
-        is AgendaTimeLabel.Starts ->
-            stringResource(R.string.agenda_span_starts, formatTime(label.start, is24Hour, locale))
-        is AgendaTimeLabel.Ends ->
-            stringResource(R.string.agenda_span_ends, formatTime(label.end, is24Hour, locale))
-        is AgendaTimeLabel.Range ->
-            "${formatTime(label.start, is24Hour, locale)} – ${formatTime(label.end, is24Hour, locale)}"
+        is AgendaTimeLabel.Starts -> stringResource(
+            R.string.agenda_span_starts,
+            formatTime(label.start, zone, is24Hour, locale),
+        )
+        is AgendaTimeLabel.Ends -> stringResource(
+            R.string.agenda_span_ends,
+            formatTime(label.end, zone, is24Hour, locale),
+        )
+        is AgendaTimeLabel.Range -> "${formatTime(label.start, zone, is24Hour, locale)} – " +
+            formatTime(label.end, zone, is24Hour, locale)
     }
 
     val location = event.location?.takeIf { it.isNotBlank() }
     return if (location != null) "$time · $location" else time
 }
 
-private fun formatTime(instant: Instant, is24Hour: Boolean, locale: Locale): String {
+private fun formatTime(
+    instant: Instant,
+    zone: TimeZone,
+    is24Hour: Boolean,
+    locale: Locale,
+): String {
     val t = instant.toLocalDateTime(zone).time
     return formatTimeOfDay(t.hour, t.minute, is24Hour, locale)
 }

app/src/main/java/de/jeanlucmakiola/calendula/ui/agenda/AgendaUiState.kt

@@ -160,5 +160,12 @@ sealed interface AgendaUiState {
         val rangeEnd: LocalDate,
         /** Whether to show the top range bar — header + switcher (toggle, on by default). */
         val showRangeBar: Boolean,
+        /**
+         * The zone [days] were grouped in. Carried in the state rather than
+         * re-read by the screen so labelling and grouping cannot disagree: an
+         * event's "Starts …/Ends …/All day" line is only correct relative to the
+         * same zone that decided which day it was filed under.
+         */
+        val zone: TimeZone,
     ) : AgendaUiState
 }

app/src/main/java/de/jeanlucmakiola/calendula/ui/agenda/AgendaViewModel.kt

@@ -172,6 +172,7 @@ class AgendaViewModel @Inject constructor(
             rangeIsOverride = params.rangeIsOverride,
             rangeEnd = rangeEnd,
             showRangeBar = params.showRangeBar,
+            zone = zone,
         )
     }
 }

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

@@ -16,13 +16,19 @@ import java.util.Locale
  * sits directly above a grid that already says which year it is, and the year's
  * *absence* is itself the signal that you're in the current one — it appears the
  * moment you page out of it, which is when it starts carrying information.
+ *
+ * [forceYear] overrides that for titles whose [date] does not tell the whole
+ * story — a week view's title names only the month its *first* day falls in, so
+ * a week straddling New Year must still show the year even though [date] is in
+ * [currentYear].
  */
 fun formatCalendarTitle(
     date: java.time.LocalDate,
     locale: Locale,
     currentYear: Int,
     skeleton: String,
+    forceYear: Boolean = false,
 ): String {
-    val fields = if (date.year == currentYear) skeleton else skeleton + "y"
+    val fields = if (date.year == currentYear && !forceYear) skeleton else skeleton + "y"
     return localizedDateFormatter(locale, fields).format(date)
 }

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

@@ -21,6 +21,7 @@ import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.produceState
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
@@ -35,6 +36,7 @@ import androidx.compose.ui.unit.dp
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.TimeZoneOption
 import de.jeanlucmakiola.calendula.domain.filterTimeZones
+import de.jeanlucmakiola.calendula.domain.timeZoneOptionOf
 import de.jeanlucmakiola.calendula.domain.timeZoneOptions
 import de.jeanlucmakiola.calendula.domain.zoneDescriptor
 import de.jeanlucmakiola.floret.components.FullScreenPicker
@@ -43,6 +45,8 @@ import de.jeanlucmakiola.floret.components.InlineTextField
 import de.jeanlucmakiola.floret.components.Position
 import de.jeanlucmakiola.floret.components.positionOf
 import de.jeanlucmakiola.floret.locale.currentLocale
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
 
 /**
  * Full-screen zone picker: a query field over every zone the JVM knows, with the
@@ -64,14 +68,28 @@ fun TimeZonePickerDialog(
     onDismiss: () -> Unit,
 ) {
     var query by rememberSaveable { mutableStateOf("") }
-    // ~600 zones, each resolving a localized name and a DST-aware offset: build
-    // once per open, then filter the result per keystroke.
     val locale = currentLocale()
-    val allZones = remember(locale) { timeZoneOptions(locale, regionOf = ::icuTimeZoneRegion) }
+    // ~600 zones, each resolving a localized name and up to two ICU short names:
+    // far too much to run inside composition, so build it on a worker and let the
+    // list fill in a frame later. Filtering the built catalogue is cheap (its
+    // search keys are pre-normalized), so that stays here.
+    val allZones by produceState(initialValue = emptyList<TimeZoneOption>(), locale) {
+        value = withContext(Dispatchers.Default) {
+            timeZoneOptions(locale, regionOf = ::icuTimeZoneRegion)
+        }
+    }
     val matches = remember(allZones, query) { filterTimeZones(allZones, query) }
     val recentZones = remember(allZones, recents) {
         recents.mapNotNull { id -> allZones.firstOrNull { it.id == id } }
     }
+    // Resolved on its own rather than looked up in the catalogue: it's one zone,
+    // so it costs nothing, and the device row can then render complete on the
+    // first frame instead of showing a bare id until the catalogue lands.
+    val deviceSummary = remember(deviceZoneId, locale) {
+        timeZoneOptionOf(deviceZoneId, locale, regionOf = ::icuTimeZoneRegion)
+            ?.let { zoneDescriptor(it) }
+            ?: deviceZoneId
+    }
     val searching = query.isNotBlank()
 
     fun choose(zoneId: String?) {
@@ -97,7 +115,7 @@ fun TimeZonePickerDialog(
                 item(key = "device") {
                     GroupedRow(
                         title = stringResource(R.string.event_edit_timezone_device),
-                        summary = zoneSummary(deviceZoneId, allZones),
+                        summary = deviceSummary,
                         position = Position.Alone,
                         selected = selected == null,
                         leading = { Icon(Icons.Default.Public, contentDescription = null) },
@@ -130,7 +148,10 @@ fun TimeZonePickerDialog(
                 }
             }
 
-            if (searching && matches.isEmpty()) {
+            // allZones.isNotEmpty() gates this: until the catalogue lands there is
+            // simply nothing to match yet, and claiming "no time zone matches"
+            // for that frame would be wrong.
+            if (searching && matches.isEmpty() && allZones.isNotEmpty()) {
                 item(key = "empty") {
                     Text(
                         text = stringResource(R.string.event_edit_timezone_none, query),
@@ -252,9 +273,3 @@ private fun ZoneRow(
         onClick = onClick,
     )
 }
-
-/** "CET · GMT+01:00" for [zoneId], or the bare id if the catalogue lacks it. */
-private fun zoneSummary(zoneId: String, allZones: List<TimeZoneOption>): String =
-    allZones.firstOrNull { it.id == zoneId }
-        ?.let { zoneDescriptor(it) }
-        ?: zoneId

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

@@ -109,6 +109,7 @@ import de.jeanlucmakiola.calendula.ui.common.recurrenceText
 import de.jeanlucmakiola.calendula.ui.common.reminderLeadTimeLabel
 import kotlinx.coroutines.launch
 import kotlinx.datetime.TimeZone
+import kotlin.time.toJavaInstant
 import java.time.ZoneId
 import java.time.format.DateTimeFormatter
 import java.time.format.FormatStyle
@@ -463,8 +464,8 @@ private fun EventDetailContent(state: EventDetailUiState.Success, modifier: Modi
         // Same hierarchy as the When card above — the label carries the card,
         // the time sits small beneath it. The local time is the one the reader
         // acts on, so the original must stay quieter than it, not compete.
-        val foreignZone = remember(detail.eventTimezone, instance.isAllDay, locale) {
-            foreignTimeZone(detail.eventTimezone, instance.isAllDay, locale)
+        val foreignZone = remember(detail.eventTimezone, instance.isAllDay, instance.start, locale) {
+            foreignTimeZone(detail.eventTimezone, instance.isAllDay, locale, instance.start)
         }
         foreignZone?.let { zoneOption ->
             Spacer(Modifier.height(gap))
@@ -789,11 +790,26 @@ private fun reminderLeadText(reminder: Reminder): String = reminderLeadTimeLabel
  * pinned to a zone different from the device's — the cases where showing it
  * removes ambiguity. Null otherwise (all-day, device-zone, blank, or an id the
  * tz database doesn't know).
+ *
+ * Resolved *at [at]*, the event's own start, not at "now": the abbreviation and
+ * offset both move with DST, and the card prints them next to the event's time.
+ * Resolving at now would label a July event "CET · 10:00 AM" when read in
+ * January — an abbreviation that contradicts the time beside it.
  */
-private fun foreignTimeZone(tz: String?, isAllDay: Boolean, locale: Locale): TimeZoneOption? {
+private fun foreignTimeZone(
+    tz: String?,
+    isAllDay: Boolean,
+    locale: Locale,
+    at: Instant,
+): TimeZoneOption? {
     if (isAllDay || tz.isNullOrBlank()) return null
     if (tz == ZoneId.systemDefault().id) return null
-    return timeZoneOptionOf(tz, locale, regionOf = ::icuTimeZoneRegion)
+    return timeZoneOptionOf(
+        tz,
+        locale,
+        at = at.toJavaInstant(),
+        regionOf = ::icuTimeZoneRegion,
+    )
 }
 
 /** Wrap http(s) URLs in [text] as tappable links tinted [linkColor]. */

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

@@ -47,7 +47,6 @@ import androidx.compose.material.icons.filled.Person
 import androidx.compose.material.icons.filled.PersonAdd
 import androidx.compose.material.icons.filled.Place
 import androidx.compose.material.icons.filled.Public
-import androidx.compose.material.icons.filled.Public
 import androidx.compose.material.icons.filled.Repeat
 import androidx.compose.material.icons.filled.Schedule
 import androidx.compose.material.icons.filled.Tune
@@ -164,8 +163,10 @@ import kotlinx.datetime.isoDayNumber
 import kotlinx.datetime.toJavaDayOfWeek
 import kotlinx.datetime.toJavaLocalDate
 import kotlinx.datetime.toKotlinDayOfWeek
+import kotlinx.datetime.toInstant
 import kotlinx.datetime.toJavaLocalTime
 import kotlinx.datetime.toLocalDateTime
+import kotlin.time.toJavaInstant
 import java.time.ZoneId
 import java.time.format.DateTimeFormatter
 import java.time.format.FormatStyle
@@ -683,7 +684,13 @@ private fun EventEditContent(
             // 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.
-            form.timesIn(TimeZone.currentSystemDefault())?.let { (localStart, localEnd) ->
+            // 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) ->
                 Spacer(Modifier.height(2.dp))
                 Text(
                     text = stringResource(
@@ -741,8 +748,20 @@ private fun EventEditContent(
                     verticalAlignment = Alignment.CenterVertically,
                     modifier = Modifier.fillMaxWidth(),
                 ) {
-                    val pinned = remember(form.timezone, locale) {
-                        form.timezone?.let { timeZoneOptionOf(it, locale, regionOf = ::icuTimeZoneRegion) }
+                    // Resolved at the event's own start, not at "now": the
+                    // abbreviation and offset shown ("CEST · GMT+02:00") must be
+                    // the ones that apply when the event actually happens.
+                    val pinned = remember(form.timezone, form.start, locale) {
+                        form.timezone
+                            ?.let { id -> runCatching { id to TimeZone.of(id) }.getOrNull() }
+                            ?.let { (id, zone) ->
+                                timeZoneOptionOf(
+                                    id,
+                                    locale,
+                                    at = form.start.toInstant(zone).toJavaInstant(),
+                                    regionOf = ::icuTimeZoneRegion,
+                                )
+                            }
                     }
                     Column(modifier = Modifier.weight(1f)) {
                         Text(

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

@@ -213,10 +213,22 @@ class SettingsViewModel @Inject constructor(
      * imperatively via [LauncherNameManager] and held here in its own flow — the
      * main settings combine is already at its arity limit and this isn't a
      * DataStore flow anyway.
+     *
+     * Seeded with the manifest default and corrected off-thread rather than read
+     * in the initializer: `getComponentEnabledSetting` is a binder round-trip to
+     * system_server, and this ViewModel is constructed on the main thread while
+     * Settings is opening. The row it feeds is well below the fold, so the
+     * one-frame correction is never visible.
      */
-    private val _launcherName = MutableStateFlow(launcherNameManager.current())
+    private val _launcherName = MutableStateFlow(LauncherName.CALENDULA)
     val launcherName: StateFlow<LauncherName> = _launcherName.asStateFlow()
 
+    init {
+        viewModelScope.launch {
+            _launcherName.value = withContext(io) { launcherNameManager.current() }
+        }
+    }
+
     // Emitted when a picked font file couldn't be read as a font; the screen
     // surfaces it and the previous selection stays put.
     private val _fontImportFailed = MutableSharedFlow<Unit>(extraBufferCapacity = 1)
@@ -484,11 +496,20 @@ class SettingsViewModel @Inject constructor(
         viewModelScope.launch { prefs.setTodayButtonInToolbar(enabled) }
     }
 
-    /** Switch the launcher label between "Calendula" and "Calendar" (issue #44). */
+    /**
+     * Switch the launcher label between "Calendula" and "Calendar" (issue #44).
+     * The card highlights immediately, then settles on whatever the component
+     * state actually reports — the two `setComponentEnabledSetting` calls are
+     * binder round-trips, so they don't belong on the main thread either.
+     */
     fun setLauncherName(name: LauncherName) {
-        launcherNameManager.set(name)
-        // Re-read so the UI reflects the actual component state, not an assumption.
-        _launcherName.value = launcherNameManager.current()
+        _launcherName.value = name
+        viewModelScope.launch {
+            _launcherName.value = withContext(io) {
+                launcherNameManager.set(name)
+                launcherNameManager.current()
+            }
+        }
     }
 
     fun setPastEventDisplay(mode: PastEventDisplay) {

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

@@ -880,13 +880,21 @@ private fun minToHm(min: Int, is24Hour: Boolean, locale: java.util.Locale): Stri
  * month of [weekStart] means a week straddling a boundary keeps the outgoing
  * month until it is fully gone — a week is seven contiguous days, so the earlier
  * month has a day in it exactly while [weekStart] is still inside it. That also
- * makes the title depend on nothing but [weekStart], so it cannot drift with the
- * direction you paged in from.
+ * makes the *month* depend on nothing but [weekStart], so it cannot drift with
+ * the direction you paged in from.
+ *
+ * The *year* is decided from the whole week, not just its start: a week running
+ * Dec 28 – Jan 3 has four of its seven visible columns in the new year, so
+ * "December" with no year would be actively misleading while the reader is
+ * looking straight at January dates.
  */
-private fun formatWeekTitle(weekStart: LocalDate, locale: Locale, currentYear: Int): String =
-    formatCalendarTitle(
+private fun formatWeekTitle(weekStart: LocalDate, locale: Locale, currentYear: Int): String {
+    val weekEnd = weekStart.plus(6, kotlinx.datetime.DateTimeUnit.DAY)
+    return formatCalendarTitle(
         date = java.time.LocalDate.of(weekStart.year, weekStart.month.ordinal + 1, 1),
         locale = locale,
         currentYear = currentYear,
         skeleton = "LLLL",
+        forceYear = weekEnd.year != weekStart.year,
     )
+}

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

@@ -110,7 +110,6 @@
     <string name="event_edit_timezone_recent">Recent</string>
     <string name="event_edit_timezone_all">All time zones</string>
     <string name="event_edit_timezone_none">No time zone matches “%1$s”</string>
-    <string name="event_edit_timezone_clear">Use device zone</string>
     <!-- Shown under the time fields when the event is pinned to another zone:
          the same event expressed where the user actually is. %1$s is a time
          range, e.g. "2:00 PM – 3:00 PM". -->

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

@@ -123,8 +123,18 @@ class EventWriteMapperTest {
 
     private val seriesStart = 1_700_000_000_000L
 
-    private fun update(original: EventForm, updated: EventForm): Map<String, Any?> =
-        buildEventUpdateValues(original, updated, seriesStart, berlin)
+    private fun update(
+        original: EventForm,
+        updated: EventForm,
+        series: Long = seriesStart,
+    ): Map<String, Any?> = buildEventUpdateValues(original, updated, series, berlin)
+
+    /** The instant [local] names in [zoneId], as the provider would store it. */
+    private fun instantAt(local: String, zoneId: String): Long =
+        java.time.LocalDateTime.parse(local)
+            .atZone(java.time.ZoneId.of(zoneId))
+            .toInstant()
+            .toEpochMilli()
 
     @Test
     fun `pristine form produces no values`() {
@@ -219,6 +229,77 @@ class EventWriteMapperTest {
         assertThat(values[CalendarContract.Events.DURATION]).isEqualTo("P5400S")
     }
 
+    @Test
+    fun `pinning a recurring event to another zone keeps the series wall clock`() {
+        // The regression this guards: the series DTSTART used to move by a
+        // millisecond delta measured at the *edited occurrence*. Here the series
+        // anchor sits in January (Berlin CET, +1) and the edited occurrence in
+        // July (Berlin CEST, +2), so the July delta is an hour off for January —
+        // the whole series would have drifted to 10:00 Tokyo.
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = form(
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(9, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+
+        val values = update(original, original.copy(timezone = "Asia/Tokyo"), series)
+
+        assertThat(values[CalendarContract.Events.EVENT_TIMEZONE]).isEqualTo("Asia/Tokyo")
+        // The anchor still reads 09:00 — now 09:00 in Tokyo, not 10:00.
+        assertThat(values[CalendarContract.Events.DTSTART])
+            .isEqualTo(instantAt("2026-01-07T09:00", "Asia/Tokyo"))
+    }
+
+    @Test
+    fun `a time edit moves the series anchor in wall clock across a DST boundary`() {
+        // Anchor in winter, edited occurrence in summer: pushing the occurrence
+        // one hour later must leave the anchor at 10:00 winter time, not at an
+        // instant that re-reads as 11:00 once the offset differs.
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = form(
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(9, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+        val moved = original.copy(
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(11, 0)),
+        )
+
+        assertThat(update(original, moved, series)[CalendarContract.Events.DTSTART])
+            .isEqualTo(instantAt("2026-01-07T10:00", "Europe/Berlin"))
+    }
+
+    @Test
+    fun `moving a recurring occurrence to another day shifts the anchor by whole days`() {
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = form(
+            start = LocalDateTime(LocalDate(2026, 1, 7), LocalTime(9, 0)),
+            end = LocalDateTime(LocalDate(2026, 1, 7), LocalTime(10, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+        val moved = original.copy(
+            start = LocalDateTime(LocalDate(2026, 1, 9), LocalTime(14, 30)),
+            end = LocalDateTime(LocalDate(2026, 1, 9), LocalTime(15, 30)),
+        )
+
+        assertThat(update(original, moved, series)[CalendarContract.Events.DTSTART])
+            .isEqualTo(instantAt("2026-01-09T14:30", "Europe/Berlin"))
+    }
+
+    @Test
+    fun `switching a recurring event to all-day anchors the series on a UTC midnight`() {
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = form(
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(9, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+
+        val values = update(original, original.copy(isAllDay = true), series)
+
+        assertThat(values[CalendarContract.Events.EVENT_TIMEZONE]).isEqualTo("UTC")
+        val dtStart = values[CalendarContract.Events.DTSTART] as Long
+        assertThat(dtStart % (24L * 60 * 60 * 1000)).isEqualTo(0L)
+    }
+
     @Test
     fun `adding a recurrence keeps the times and writes rule plus duration`() {
         val original = form()