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

@@ -23,8 +23,12 @@ import de.jeanlucmakiola.calendula.ui.common.IMPLEMENTED_VIEWS
 import de.jeanlucmakiola.calendula.ui.common.QuickSwitchConfig
 import de.jeanlucmakiola.calendula.ui.theme.FONT_SYSTEM_TOKEN
 import java.time.ZoneId
+import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.stateIn
 import kotlinx.datetime.DayOfWeek
 import java.time.temporal.WeekFields
 import java.util.Locale
@@ -82,6 +86,24 @@ fun WeekStartPref.resolveFirstDay(locale: Locale): DayOfWeek = when (this) {
     WeekStartPref.Auto -> DayOfWeek(WeekFields.of(locale).firstDayOfWeek.value)
 }
 
+/**
+ * The resolved first day of the week as a hot [StateFlow] — the one shape every
+ * screen that orders or lays out weekdays should use (the month grid, the agenda
+ * "this week" range, the recurrence weekday toggles). Sharing it keeps the
+ * initial-frame value identical everywhere; hand-rolled copies had drifted onto
+ * different `initialValue`s, so two surfaces could disagree for a frame.
+ */
+fun SettingsPrefs.firstDayOfWeek(scope: CoroutineScope): StateFlow<DayOfWeek> =
+    weekStart
+        .map { it.resolveFirstDay(Locale.getDefault()) }
+        .stateIn(
+            scope = scope,
+            started = SharingStarted.WhileSubscribed(5_000L),
+            // Seed with the locale convention rather than a hardcoded weekday, so
+            // the first frame is already right for everyone still on Auto.
+            initialValue = WeekStartPref.Auto.resolveFirstDay(Locale.getDefault()),
+        )
+
 /**
  * Display settings (M4) persisted app-side: theme override, Material You
  * dynamic colour, and week start. Language is handled separately through

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

@@ -7,7 +7,7 @@ import de.jeanlucmakiola.calendula.data.calendar.CalendarRepository
 import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.prefs.PastEventDisplay
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
-import de.jeanlucmakiola.calendula.data.prefs.resolveFirstDay
+import de.jeanlucmakiola.calendula.data.prefs.firstDayOfWeek
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.FailureReason
@@ -20,13 +20,11 @@ import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOn
-import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.DayOfWeek
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
-import java.util.Locale
 import kotlinx.datetime.atStartOfDayIn
 import kotlinx.datetime.atTime
 import kotlinx.datetime.plus
@@ -51,8 +49,7 @@ class AgendaViewModel @Inject constructor(
     ) { range, showBar -> AgendaSettings(range, showBar) }
 
     // First day of the week, for the calendar-aligned "this week" range.
-    private val weekStartDay = settingsPrefs.weekStart
-        .map { it.resolveFirstDay(Locale.getDefault()) }
+    private val weekStartDay = settingsPrefs.firstDayOfWeek(viewModelScope)
 
     /**
      * How to treat events that already ended today (show / dim / hide). A display

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

@@ -9,6 +9,10 @@ import androidx.compose.ui.text.buildAnnotatedString
 import androidx.compose.ui.text.font.FontStyle
 import de.jeanlucmakiola.calendula.R
 import java.time.DayOfWeek
+import java.time.LocalDate
+import java.time.LocalDateTime
+import java.time.ZoneId
+import java.time.ZoneOffset
 import java.time.format.DateTimeFormatter
 import java.time.format.FormatStyle
 import java.time.format.TextStyle as JavaTextStyle
@@ -111,16 +115,36 @@ private fun rruleDayName(token: String, locale: Locale): String? {
 
 /** Parse an RRULE UNTIL value ("20261231" or "20261231T235959Z") to a localized date. */
 private fun parseUntilDate(raw: String, locale: Locale): String? {
-    val digits = raw.takeWhile { it.isDigit() }
-    if (digits.length < 8) return null
-    return try {
-        val date = java.time.LocalDate.of(
+    val date = untilLocalDate(raw) ?: return null
+    return DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(locale).format(date)
+}
+
+private val UNTIL_UTC_FORMAT: DateTimeFormatter =
+    DateTimeFormatter.ofPattern("yyyyMMdd'T'HHmmss'Z'", Locale.ROOT)
+
+/**
+ * The calendar day an RRULE UNTIL value denotes, *in the device's zone*.
+ *
+ * The UTC form ("20261231T225959Z") must be converted back before its date is
+ * read: `SimpleRecurrence.toRRule` writes the end of the chosen **local** day
+ * expressed in UTC, so for zones behind UTC that instant already falls on the
+ * following UTC date. Taking the leading digits straight off would then show
+ * the day after the one the user picked. Date-only and floating forms are
+ * already local and pass through unchanged.
+ */
+internal fun untilLocalDate(raw: String, zone: ZoneId = ZoneId.systemDefault()): LocalDate? {
+    val value = raw.trim()
+    return runCatching {
+        LocalDateTime.parse(value, UNTIL_UTC_FORMAT)
+            .atOffset(ZoneOffset.UTC)
+            .atZoneSameInstant(zone)
+            .toLocalDate()
+    }.recoverCatching {
+        val digits = value.takeWhile { it.isDigit() }
+        LocalDate.of(
             digits.substring(0, 4).toInt(),
             digits.substring(4, 6).toInt(),
             digits.substring(6, 8).toInt(),
         )
-        DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(locale).format(date)
-    } catch (e: Exception) {
-        null
-    }
+    }.getOrNull()
 }

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

@@ -99,7 +99,6 @@ import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.text.input.ImeAction
 import androidx.compose.ui.text.input.KeyboardCapitalization
 import androidx.compose.ui.text.input.KeyboardType
-import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.core.content.ContextCompat
 import androidx.hilt.navigation.compose.hiltViewModel
@@ -140,11 +139,13 @@ import de.jeanlucmakiola.calendula.ui.common.eventFormFieldIcon
 import de.jeanlucmakiola.calendula.ui.common.eventFormFieldLabel
 import de.jeanlucmakiola.floret.components.FullScreenPicker
 import de.jeanlucmakiola.floret.components.GroupedRow
+import de.jeanlucmakiola.floret.components.GroupedSurface
 import de.jeanlucmakiola.calendula.ui.common.MILLIS_PER_DAY
 import de.jeanlucmakiola.floret.components.InlineTextField
 import de.jeanlucmakiola.floret.components.OptionCard
 import de.jeanlucmakiola.floret.components.OptionPicker
 import de.jeanlucmakiola.floret.components.Position
+import de.jeanlucmakiola.floret.components.groupedShape as floretGroupedShape
 import de.jeanlucmakiola.floret.components.positionOf
 import de.jeanlucmakiola.calendula.ui.common.REMINDER_PRESETS
 import de.jeanlucmakiola.calendula.ui.common.TimePickerAlert
@@ -1328,8 +1329,21 @@ private fun RecurrencePickerDialog(
 
     val locale = currentLocale()
     val untilDate = untilIso?.let { runCatching { LocalDate.parse(it) }.getOrNull() }
-    val interval = intervalText.toIntOrNull()?.takeIf { it in 1..999 }
-    val count = countText.toIntOrNull()?.takeIf { it in 1..999 }
+    // remember() must not sit behind the ?. — a slot that appears and disappears
+    // as a date is picked breaks Compose's positional memoisation. Format
+    // unconditionally and let the null fall through to a null summary.
+    val untilSummary = remember(untilDate, locale) {
+        untilDate?.let {
+            DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM)
+                .withLocale(locale).format(it.toJavaLocalDate())
+        }
+    }
+    // A blank amount field shows its placeholder ("1" / "10") greyed out, so read
+    // blank as that default rather than as an error — otherwise simply clearing
+    // the field silently greys out OK. Only a real out-of-range value (0) is
+    // invalid, and that's the one case the read-out below reports.
+    val interval = if (intervalText.isBlank()) 1 else intervalText.toIntOrNull()?.takeIf { it in 1..999 }
+    val count = if (countText.isBlank()) 10 else countText.toIntOrNull()?.takeIf { it in 1..999 }
     val customEnd: RecurrenceEnd? = when (endMode) {
         RecurrenceEndMode.Never -> RecurrenceEnd.Never
         RecurrenceEndMode.Until -> untilDate?.let { RecurrenceEnd.Until(it) }
@@ -1387,22 +1401,25 @@ private fun RecurrencePickerDialog(
             // a parent arrangement would leave a residual gap that snaps shut.
             Column(modifier = Modifier.fillMaxWidth()) {
                 // A live, human-readable read-out of the rule being built, so the
-                // effect of the controls below is never a guess.
+                // effect of the controls below is never a guess. It renders
+                // *[customResult] itself* — the exact string OK would save — so it
+                // can never describe a different rule than the one that lands. When
+                // the form can't produce a rule, it says why instead of falling
+                // back to defaults and quietly disagreeing with the controls.
+                // minLines reserves the second line up front: without it the whole
+                // stack below shifts a line as the phrase grows with each weekday.
                 Text(
-                    text = recurrenceText(
-                        SimpleRecurrence(
-                            freq = freq,
-                            interval = interval ?: 1,
-                            end = customEnd ?: RecurrenceEnd.Never,
-                            byDays = if (freq == RecurrenceFreq.Weekly) {
-                                daysMask.toDaySet()
-                            } else {
-                                emptySet()
-                            },
-                        ).toRRule(),
-                        locale,
+                    text = customResult?.let { recurrenceText(it, locale) }
+                        ?: AnnotatedString(
+                            stringResource(R.string.event_edit_recurrence_incomplete),
                         ),
                     style = MaterialTheme.typography.titleMedium,
+                    color = if (customResult != null) {
+                        MaterialTheme.colorScheme.onSurface
+                    } else {
+                        MaterialTheme.colorScheme.error
+                    },
+                    minLines = 2,
                     modifier = Modifier
                         .fillMaxWidth()
                         .padding(horizontal = 16.dp),
@@ -1410,11 +1427,9 @@ private fun RecurrencePickerDialog(
 
                 // How often: an interval amount plus a frequency segmented row —
                 // all four units on show, no unit hidden behind a dropdown.
-                Surface(
-                    color = MaterialTheme.colorScheme.surfaceContainerHigh,
-                    shape = groupedShape(Position.Alone),
+                GroupedSurface(
+                    position = Position.Alone,
                     modifier = Modifier
-                        .fillMaxWidth()
                         .padding(top = 16.dp)
                         .padding(horizontal = 16.dp),
                 ) {
@@ -1442,7 +1457,18 @@ private fun RecurrencePickerDialog(
                                     shape = SegmentedButtonDefaults.itemShape(
                                         index, RecurrenceFreq.entries.size,
                                     ),
-                                    label = { Text(stringResource(recurrenceUnitLabel(entry))) },
+                                    // Drop the default check-icon slot: four segments
+                                    // share one row, and its reserved width is what
+                                    // pushes longer labels ("Monate", "Wochen") into
+                                    // an ellipsis on a compact screen. Selection is
+                                    // already carried by the segment's fill.
+                                    icon = {},
+                                    label = {
+                                        Text(
+                                            text = stringResource(recurrenceUnitLabel(entry)),
+                                            maxLines = 1,
+                                        )
+                                    },
                                 )
                             }
                         }
@@ -1452,11 +1478,9 @@ private fun RecurrencePickerDialog(
                 // Weekday picks — only meaningful on a weekly rule. The 16dp gap
                 // sits inside the animated block so it grows/shrinks with the card.
                 AnimatedVisibility(visible = freq == RecurrenceFreq.Weekly) {
-                    Surface(
-                        color = MaterialTheme.colorScheme.surfaceContainerHigh,
-                        shape = groupedShape(Position.Alone),
+                    GroupedSurface(
+                        position = Position.Alone,
                         modifier = Modifier
-                            .fillMaxWidth()
                             .padding(top = 16.dp)
                             .padding(horizontal = 16.dp),
                     ) {
@@ -1487,12 +1511,7 @@ private fun RecurrencePickerDialog(
                     )
                     GroupedRow(
                         title = stringResource(R.string.event_edit_recurrence_end_until),
-                        summary = untilDate?.let {
-                            remember(it, locale) {
-                                DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM)
-                                    .withLocale(locale).format(it.toJavaLocalDate())
-                            }
-                        },
+                        summary = untilSummary,
                         position = Position.Middle,
                         selected = endMode == RecurrenceEndMode.Until,
                         onClick = {
@@ -1510,13 +1529,13 @@ private fun RecurrencePickerDialog(
                         selected = endMode == RecurrenceEndMode.Count,
                         onClick = { endMode = RecurrenceEndMode.Count },
                     )
-                    if (endMode == RecurrenceEndMode.Count) {
-                        Surface(
-                            color = MaterialTheme.colorScheme.surfaceContainerHigh,
-                            shape = groupedShape(Position.Bottom),
-                            modifier = Modifier
-                                .fillMaxWidth()
-                                .padding(horizontal = 16.dp),
+                    // Animated for the same reason the weekday card is: this is the
+                    // picker's other collapsible block, and a bare `if` here made
+                    // the ends group snap while the card above it glided.
+                    AnimatedVisibility(visible = endMode == RecurrenceEndMode.Count) {
+                        GroupedSurface(
+                            position = Position.Bottom,
+                            modifier = Modifier.padding(horizontal = 16.dp),
                         ) {
                             Row(
                                 verticalAlignment = Alignment.CenterVertically,
@@ -1549,7 +1568,13 @@ private fun RecurrencePickerDialog(
                 untilIso = it.toString()
                 showUntilPicker = false
             },
-            onDismiss = { showUntilPicker = false },
+            onDismiss = {
+                showUntilPicker = false
+                // Backing out of the date picker with nothing chosen would leave
+                // "on date" selected but dateless — a state that can't be saved and
+                // greys out OK with no visible cause. Fall back to "never".
+                if (untilIso == null) endMode = RecurrenceEndMode.Never
+            },
         )
     }
 }
@@ -1625,18 +1650,14 @@ private fun recurrenceUnitLabel(freq: RecurrenceFreq): Int = when (freq) {
     RecurrenceFreq.Yearly -> R.string.recurrence_unit_years
 }
 
-/** Corner shape for a card at [position] in a grouped run (mirrors GroupedRow). */
-private fun groupedShape(position: Position, full: Dp = 20.dp, small: Dp = 6.dp): Shape =
-    when (position) {
-        Position.Alone -> RoundedCornerShape(full)
-        Position.Top -> RoundedCornerShape(
-            topStart = full, topEnd = full, bottomStart = small, bottomEnd = small,
-        )
-        Position.Middle -> RoundedCornerShape(small)
-        Position.Bottom -> RoundedCornerShape(
-            topStart = small, topEnd = small, bottomStart = full, bottomEnd = full,
-        )
-    }
+/**
+ * Corner shape for a card at [position] in a grouped run. Delegates to the
+ * family primitive with the same radii [GroupedSurface] draws at rest — a local
+ * copy had drifted to 20dp, so a card sharing a run with GroupedRows had
+ * visibly tighter outer corners than the rows above it.
+ */
+private fun groupedShape(position: Position): Shape =
+    floretGroupedShape(position, full = 22.dp, small = 6.dp)
 
 /** The 2dp gap that visually separates grouped cards (none after the last). */
 private fun groupedGap(position: Position): Modifier = when (position) {

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

@@ -8,9 +8,8 @@ import de.jeanlucmakiola.calendula.data.calendar.NoSuchEventException
 import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.prefs.CalendarPrefs
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
-import de.jeanlucmakiola.calendula.data.prefs.WeekStartPref
+import de.jeanlucmakiola.calendula.data.prefs.firstDayOfWeek
 import de.jeanlucmakiola.calendula.data.prefs.resolveDefaultReminder
-import de.jeanlucmakiola.calendula.data.prefs.resolveFirstDay
 import de.jeanlucmakiola.calendula.domain.AccessLevel
 import de.jeanlucmakiola.calendula.domain.Availability
 import de.jeanlucmakiola.calendula.domain.CalendarSource
@@ -49,7 +48,6 @@ import kotlinx.datetime.LocalTime
 import kotlinx.datetime.TimeZone
 import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
-import java.util.Locale
 import kotlin.coroutines.cancellation.CancellationException
 import kotlin.time.Clock
 import kotlin.time.Duration.Companion.hours
@@ -276,13 +274,7 @@ class EventEditViewModel @Inject constructor(
      * app's "week starts on" preference, matching the calendar views (Auto
      * falls back to the locale convention).
      */
-    val firstDayOfWeek: StateFlow<DayOfWeek> = settingsPrefs.weekStart
-        .map { it.resolveFirstDay(Locale.getDefault()) }
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000L),
-            initialValue = WeekStartPref.Auto.resolveFirstDay(Locale.getDefault()),
-        )
+    val firstDayOfWeek: StateFlow<DayOfWeek> = settingsPrefs.firstDayOfWeek(viewModelScope)
 
     /**
      * Initialise a fresh form for a new event on [date]. [startMinutes] (minutes

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

@@ -6,7 +6,7 @@ import dagger.hilt.android.lifecycle.HiltViewModel
 import de.jeanlucmakiola.calendula.data.calendar.CalendarRepository
 import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
-import de.jeanlucmakiola.calendula.data.prefs.resolveFirstDay
+import de.jeanlucmakiola.calendula.data.prefs.firstDayOfWeek
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.FailureReason
@@ -21,7 +21,6 @@ import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOn
-import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.DayOfWeek
@@ -34,7 +33,6 @@ import kotlinx.datetime.minus
 import kotlinx.datetime.plus
 import kotlinx.datetime.toInstant
 import kotlinx.datetime.toLocalDateTime
-import java.util.Locale
 import kotlin.time.Clock
 import kotlin.time.Instant
 import javax.inject.Inject
@@ -48,16 +46,9 @@ class MonthViewModel @Inject constructor(
 ) : ViewModel() {
 
     private val zone = TimeZone.currentSystemDefault()
-    private val locale: Locale = Locale.getDefault()
 
     /** First day of the week, from the Settings preference (AUTO → locale). */
-    val weekStart: StateFlow<DayOfWeek> = settingsPrefs.weekStart
-        .map { it.resolveFirstDay(locale) }
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000L),
-            initialValue = DayOfWeek.MONDAY,
-        )
+    val weekStart: StateFlow<DayOfWeek> = settingsPrefs.firstDayOfWeek(viewModelScope)
 
     /** Whether to fade events that have already finished (display concern only). */
     val dimCompletedEvents: StateFlow<Boolean> = settingsPrefs.dimCompletedEvents

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

@@ -149,6 +149,9 @@
     <string name="recurrence_unit_weeks">weeks</string>
     <string name="recurrence_unit_months">months</string>
     <string name="recurrence_unit_years">years</string>
+    <!-- Shown in place of the live rule read-out when an amount field holds a
+         value outside 1–999 (i.e. 0), so the greyed-out OK button has a reason. -->
+    <string name="event_edit_recurrence_incomplete">Enter a number from 1 to 999</string>
     <string name="event_edit_recurrence_ends">Ends</string>
     <string name="event_edit_recurrence_end_never">Never</string>
     <string name="event_edit_recurrence_end_until">On a date</string>

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

@@ -0,0 +1,69 @@
+package de.jeanlucmakiola.calendula.ui.common
+
+import com.google.common.truth.Truth.assertThat
+import java.time.LocalDate
+import java.time.ZoneId
+import org.junit.jupiter.api.Test
+
+/**
+ * The read side of the UNTIL round-trip. `SimpleRecurrence.toRRule` deliberately
+ * writes the end of the chosen *local* day expressed in UTC (see its docs — the
+ * provider applies UNTIL coarsely), so displaying it means converting back into
+ * the device zone first. Reading the leading digits raw showed the wrong day for
+ * zones behind UTC.
+ */
+class RecurrenceTextTest {
+
+    private val berlin = ZoneId.of("Europe/Berlin")
+    private val losAngeles = ZoneId.of("America/Los_Angeles")
+    private val utc = ZoneId.of("UTC")
+
+    @Test
+    fun `UTC form converts back to the picked day west of UTC`() {
+        // toRRule("2026-12-31", America/Los_Angeles) → 23:59:59 local = 07:59:59Z
+        // on 1 Jan. Reading the digits raw would show 1 Jan 2027.
+        assertThat(untilLocalDate("20270101T075959Z", losAngeles))
+            .isEqualTo(LocalDate.of(2026, 12, 31))
+    }
+
+    @Test
+    fun `UTC form converts back to the picked day east of UTC`() {
+        // Berlin in December is UTC+1: 23:59:59 local = 22:59:59Z the same day.
+        assertThat(untilLocalDate("20261231T225959Z", berlin))
+            .isEqualTo(LocalDate.of(2026, 12, 31))
+    }
+
+    @Test
+    fun `UTC form is unchanged at UTC itself`() {
+        assertThat(untilLocalDate("20261231T235959Z", utc))
+            .isEqualTo(LocalDate.of(2026, 12, 31))
+    }
+
+    @Test
+    fun `summer offset is honoured, not a fixed one`() {
+        // Berlin in July is UTC+2, so the same local end-of-day lands at 21:59:59Z.
+        assertThat(untilLocalDate("20260801T215959Z", berlin))
+            .isEqualTo(LocalDate.of(2026, 8, 1))
+    }
+
+    @Test
+    fun `date-only form is already local and passes through`() {
+        assertThat(untilLocalDate("20261231", losAngeles))
+            .isEqualTo(LocalDate.of(2026, 12, 31))
+    }
+
+    @Test
+    fun `floating date-time form uses its date as-is`() {
+        // No trailing Z, so it isn't an instant — no conversion may be applied.
+        assertThat(untilLocalDate("20261231T235959", losAngeles))
+            .isEqualTo(LocalDate.of(2026, 12, 31))
+    }
+
+    @Test
+    fun `garbage returns null rather than throwing`() {
+        assertThat(untilLocalDate("", berlin)).isNull()
+        assertThat(untilLocalDate("nonsense", berlin)).isNull()
+        assertThat(untilLocalDate("2026", berlin)).isNull()
+        assertThat(untilLocalDate("20261340", berlin)).isNull()
+    }
+}