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

@@ -0,0 +1,206 @@
+package de.jeanlucmakiola.calendula.ui.agenda
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Coffee
+import androidx.compose.material3.Card
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.alpha
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.dp
+import de.jeanlucmakiola.calendula.R
+import de.jeanlucmakiola.calendula.domain.EventInstance
+import de.jeanlucmakiola.calendula.ui.common.EventDimAlpha
+import de.jeanlucmakiola.calendula.ui.common.LocalSoftenColors
+import de.jeanlucmakiola.calendula.ui.common.LocalUse24HourFormat
+import de.jeanlucmakiola.calendula.ui.common.eventFill
+import de.jeanlucmakiola.calendula.ui.common.formatTimeOfDay
+import de.jeanlucmakiola.floret.components.GroupedRow
+import de.jeanlucmakiola.floret.components.Position
+import de.jeanlucmakiola.floret.locale.currentLocale
+import de.jeanlucmakiola.floret.locale.localizedDateFormatter
+import kotlinx.datetime.DateTimeUnit
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.plus
+import kotlinx.datetime.toLocalDateTime
+import kotlin.time.Instant
+import java.util.Locale
+
+// The agenda's row vocabulary, split out of AgendaScreen so the month view's
+// split style can list a day with exactly the same visual language instead of
+// growing a parallel set of event rows.
+
+@Composable
+internal fun AgendaDayHeader(
+    date: LocalDate,
+    today: LocalDate,
+    onOpenDay: (LocalDate) -> Unit,
+) {
+    Surface(
+        color = MaterialTheme.colorScheme.surface,
+        modifier = Modifier
+            .fillMaxWidth()
+            .clickable { onOpenDay(date) },
+    ) {
+        Text(
+            text = agendaDayLabel(date, today),
+            style = MaterialTheme.typography.titleSmall,
+            color = if (date == today) {
+                MaterialTheme.colorScheme.primary
+            } else {
+                MaterialTheme.colorScheme.onSurfaceVariant
+            },
+            modifier = Modifier.padding(start = 28.dp, end = 28.dp, top = 16.dp, bottom = 8.dp),
+        )
+    }
+}
+
+/**
+ * A card standing in for a day with no events — the same coffee-cup motif as the
+ * agenda's full-screen empty state, boxed into a card so the day keeps a visible slot
+ * rather than a bare header. Used for an anchored, event-less today (#35) and for
+ * an empty selected day in the month view's split style.
+ */
+@Composable
+internal fun AgendaEmptyDayRow(text: String, onClick: () -> Unit) {
+    Card(
+        // Match a single event row's resting corner radius (floret groupedShape).
+        shape = RoundedCornerShape(22.dp),
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(horizontal = 16.dp, vertical = 4.dp)
+            .clickable(onClick = onClick),
+    ) {
+        Column(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(vertical = 18.dp, horizontal = 16.dp),
+            horizontalAlignment = Alignment.CenterHorizontally,
+        ) {
+            Icon(
+                imageVector = Icons.Filled.Coffee,
+                contentDescription = null,
+                tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                modifier = Modifier.size(36.dp),
+            )
+            Spacer(Modifier.height(8.dp))
+            Text(
+                text = text,
+                style = MaterialTheme.typography.bodyLarge,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                textAlign = TextAlign.Center,
+            )
+        }
+    }
+}
+
+@Composable
+internal fun AgendaEventRow(
+    event: EventInstance,
+    day: LocalDate,
+    zone: TimeZone,
+    position: Position,
+    dimmed: Boolean,
+    modifier: Modifier = Modifier,
+    onClick: () -> Unit,
+) {
+    val dark = isSystemInDarkTheme()
+    val soften = LocalSoftenColors.current
+    val title = event.title.ifBlank { stringResource(R.string.event_untitled) }
+    GroupedRow(
+        modifier = if (dimmed) modifier.alpha(EventDimAlpha) else modifier,
+        title = title,
+        summary = agendaTimeSummary(event, day, zone),
+        position = position,
+        minHeight = 64.dp,
+        leading = {
+            Box(
+                modifier = Modifier
+                    .size(width = 6.dp, height = 36.dp)
+                    .clip(RoundedCornerShape(3.dp))
+                    .background(eventFill(event.color, dark, soften)),
+            )
+        },
+        onClick = onClick,
+    )
+}
+
+/** "Today · Wed, 17. Jun 2026" — relative word for today/tomorrow, else the date. */
+@Composable
+internal fun agendaDayLabel(date: LocalDate, today: LocalDate): String {
+    val relative = when (date) {
+        today -> stringResource(R.string.agenda_header_today)
+        today.plus(1, DateTimeUnit.DAY) -> stringResource(R.string.agenda_header_tomorrow)
+        else -> null
+    }
+    val formatted = formatAgendaDate(date)
+    return if (relative != null) "$relative · $formatted" else formatted
+}
+
+/**
+ * Time line under the title: "09:00 – 10:00 · Location", "All day", etc.
+ *
+ * A multi-day event shows only the part relevant to [day], spelled out so each
+ * day reads on its own: its first day names the start ("Starts 14:00"), its last
+ * day the end ("Ends 10:00"), and any whole day in between reads as "All day".
+ * An all-day multi-day event is simply "All day" on every day it covers.
+ */
+@Composable
+internal fun agendaTimeSummary(event: EventInstance, day: LocalDate, zone: TimeZone): String {
+    val is24Hour = LocalUse24HourFormat.current
+    val locale = currentLocale()
+
+    val time = when (val label = agendaTimeLabel(event, day, zone)) {
+        AgendaTimeLabel.AllDay -> stringResource(R.string.event_detail_all_day)
+        is AgendaTimeLabel.Starts -> stringResource(
+            R.string.agenda_span_starts,
+            formatTime(label.start, zone, is24Hour, locale),
+        )
+        is AgendaTimeLabel.Ends -> stringResource(
+            R.string.agenda_span_ends,
+            formatTime(label.end, zone, is24Hour, locale),
+        )
+        is AgendaTimeLabel.Range -> "${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,
+    zone: TimeZone,
+    is24Hour: Boolean,
+    locale: Locale,
+): String {
+    val t = instant.toLocalDateTime(zone).time
+    return formatTimeOfDay(t.hour, t.minute, is24Hour, locale)
+}
+
+private fun formatAgendaDate(date: LocalDate): String {
+    val locale = Locale.getDefault()
+    val java = java.time.LocalDate.of(date.year, date.month.ordinal + 1, date.day)
+    // Weekday + date in the locale's own field order (e.g. "Wed, Jun 17, 2026"
+    // vs "Mi., 17. Juni 2026") rather than a hardcoded day-month-year layout.
+    return localizedDateFormatter(locale, "EEEdMMMy").format(java)
+}

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

@@ -1,9 +1,6 @@
 package de.jeanlucmakiola.calendula.ui.agenda
 
 import androidx.compose.foundation.ExperimentalFoundationApi
-import androidx.compose.foundation.background
-import androidx.compose.foundation.clickable
-import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -17,13 +14,11 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.itemsIndexed
-import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.Coffee
 import androidx.compose.material.icons.filled.Menu
 import androidx.compose.material.icons.filled.Search
 import androidx.compose.material3.ButtonDefaults
-import androidx.compose.material3.Card
 import androidx.compose.material3.DrawerValue
 import androidx.compose.material3.FilledTonalButton
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -32,7 +27,6 @@ import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.ModalNavigationDrawer
 import androidx.compose.material3.Scaffold
-import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.material3.TopAppBar
 import androidx.compose.material3.TopAppBarDefaults
@@ -46,8 +40,6 @@ import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.draw.alpha
-import androidx.compose.ui.draw.clip
 import androidx.compose.ui.input.nestedscroll.nestedScroll
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.style.TextAlign
@@ -59,8 +51,6 @@ import de.jeanlucmakiola.calendula.data.prefs.PastEventDisplay
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.hasEnded
 import de.jeanlucmakiola.calendula.ui.common.AgendaRangePicker
-import de.jeanlucmakiola.calendula.ui.common.LocalSoftenColors
-import de.jeanlucmakiola.calendula.ui.common.eventFill
 import de.jeanlucmakiola.calendula.ui.common.agendaRangeLabel
 import de.jeanlucmakiola.floret.identity.animateItemMotion
 import de.jeanlucmakiola.calendula.ui.common.CalendarDrawer
@@ -69,25 +59,15 @@ import de.jeanlucmakiola.calendula.ui.common.TodayAction
 import de.jeanlucmakiola.calendula.ui.common.CalendarFailure
 import de.jeanlucmakiola.calendula.ui.common.CalendarView
 import de.jeanlucmakiola.calendula.ui.common.IMPLEMENTED_VIEWS
-import de.jeanlucmakiola.floret.locale.localizedDateFormatter
-import de.jeanlucmakiola.calendula.ui.common.EventDimAlpha
-import de.jeanlucmakiola.floret.components.GroupedRow
-import de.jeanlucmakiola.floret.components.Position
 import de.jeanlucmakiola.calendula.ui.common.ViewSwitcherPill
 import de.jeanlucmakiola.calendula.ui.common.next
 import de.jeanlucmakiola.floret.components.positionOf
 import de.jeanlucmakiola.calendula.ui.common.rememberCurrentMinute
 import de.jeanlucmakiola.floret.locale.currentLocale
-import de.jeanlucmakiola.calendula.ui.common.LocalUse24HourFormat
-import de.jeanlucmakiola.calendula.ui.common.formatTimeOfDay
 import kotlinx.coroutines.launch
-import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.plus
-import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Instant
-import java.util.Locale
 
 // 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
@@ -370,7 +350,10 @@ private fun AgendaList(
             if (day.events.isEmpty()) {
                 // An anchored, event-less today (#35) — "nothing left today".
                 item(key = "placeholder-${day.date}") {
-                    AgendaEmptyDayRow(onClick = { onOpenDay(day.date) })
+                    AgendaEmptyDayRow(
+                        text = stringResource(R.string.agenda_no_more_today),
+                        onClick = { onOpenDay(day.date) },
+                    )
                 }
             } else {
                 itemsIndexed(
@@ -396,100 +379,6 @@ private fun AgendaList(
     }
 }
 
-@Composable
-private fun AgendaDayHeader(
-    date: LocalDate,
-    today: LocalDate,
-    onOpenDay: (LocalDate) -> Unit,
-) {
-    Surface(
-        color = MaterialTheme.colorScheme.surface,
-        modifier = Modifier
-            .fillMaxWidth()
-            .clickable { onOpenDay(date) },
-    ) {
-        Text(
-            text = agendaDayLabel(date, today),
-            style = MaterialTheme.typography.titleSmall,
-            color = if (date == today) {
-                MaterialTheme.colorScheme.primary
-            } else {
-                MaterialTheme.colorScheme.onSurfaceVariant
-            },
-            modifier = Modifier.padding(start = 28.dp, end = 28.dp, top = 16.dp, bottom = 8.dp),
-        )
-    }
-}
-
-/**
- * A card under an anchored, event-less today (#35) — the same coffee-cup motif
- * as the full-screen [AgendaEmpty] state, boxed into a card so today keeps a
- * visible slot when nothing is left rather than a bare header.
- */
-@Composable
-private fun AgendaEmptyDayRow(onClick: () -> Unit) {
-    Card(
-        // Match a single event row's resting corner radius (floret groupedShape).
-        shape = RoundedCornerShape(22.dp),
-        modifier = Modifier
-            .fillMaxWidth()
-            .padding(horizontal = 16.dp, vertical = 4.dp)
-            .clickable(onClick = onClick),
-    ) {
-        Column(
-            modifier = Modifier
-                .fillMaxWidth()
-                .padding(vertical = 18.dp, horizontal = 16.dp),
-            horizontalAlignment = Alignment.CenterHorizontally,
-        ) {
-            Icon(
-                imageVector = Icons.Filled.Coffee,
-                contentDescription = null,
-                tint = MaterialTheme.colorScheme.onSurfaceVariant,
-                modifier = Modifier.size(36.dp),
-            )
-            Spacer(Modifier.height(8.dp))
-            Text(
-                text = stringResource(R.string.agenda_no_more_today),
-                style = MaterialTheme.typography.bodyLarge,
-                color = MaterialTheme.colorScheme.onSurfaceVariant,
-                textAlign = TextAlign.Center,
-            )
-        }
-    }
-}
-
-@Composable
-private fun AgendaEventRow(
-    event: EventInstance,
-    day: LocalDate,
-    zone: TimeZone,
-    position: Position,
-    dimmed: Boolean,
-    modifier: Modifier = Modifier,
-    onClick: () -> Unit,
-) {
-    val dark = isSystemInDarkTheme()
-    val soften = LocalSoftenColors.current
-    val title = event.title.ifBlank { stringResource(R.string.event_untitled) }
-    GroupedRow(
-        modifier = if (dimmed) modifier.alpha(EventDimAlpha) else modifier,
-        title = title,
-        summary = agendaTimeSummary(event, day, zone),
-        position = position,
-        minHeight = 64.dp,
-        leading = {
-            Box(
-                modifier = Modifier
-                    .size(width = 6.dp, height = 36.dp)
-                    .clip(RoundedCornerShape(3.dp))
-                    .background(eventFill(event.color, dark, soften)),
-            )
-        },
-        onClick = onClick,
-    )
-}
-
 @Composable
 private fun AgendaEmpty(modifier: Modifier = Modifier) {
     Column(
@@ -559,64 +448,3 @@ private fun AgendaTopBar(
         scrollBehavior = scrollBehavior,
     )
 }
-
-/** "Today · Wed, 17. Jun 2026" — relative word for today/tomorrow, else the date. */
-@Composable
-private fun agendaDayLabel(date: LocalDate, today: LocalDate): String {
-    val relative = when (date) {
-        today -> stringResource(R.string.agenda_header_today)
-        today.plus(1, DateTimeUnit.DAY) -> stringResource(R.string.agenda_header_tomorrow)
-        else -> null
-    }
-    val formatted = formatAgendaDate(date)
-    return if (relative != null) "$relative · $formatted" else formatted
-}
-
-/**
- * Time line under the title: "09:00 – 10:00 · Location", "All day", etc.
- *
- * A multi-day event shows only the part relevant to [day], spelled out so each
- * day reads on its own: its first day names the start ("Starts 14:00"), its last
- * day the end ("Ends 10:00"), and any whole day in between reads as "All day".
- * An all-day multi-day event is simply "All day" on every day it covers.
- */
-@Composable
-private fun agendaTimeSummary(event: EventInstance, day: LocalDate, zone: TimeZone): String {
-    val is24Hour = LocalUse24HourFormat.current
-    val locale = currentLocale()
-
-    val time = when (val label = agendaTimeLabel(event, day, zone)) {
-        AgendaTimeLabel.AllDay -> stringResource(R.string.event_detail_all_day)
-        is AgendaTimeLabel.Starts -> stringResource(
-            R.string.agenda_span_starts,
-            formatTime(label.start, zone, is24Hour, locale),
-        )
-        is AgendaTimeLabel.Ends -> stringResource(
-            R.string.agenda_span_ends,
-            formatTime(label.end, zone, is24Hour, locale),
-        )
-        is AgendaTimeLabel.Range -> "${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,
-    zone: TimeZone,
-    is24Hour: Boolean,
-    locale: Locale,
-): String {
-    val t = instant.toLocalDateTime(zone).time
-    return formatTimeOfDay(t.hour, t.minute, is24Hour, locale)
-}
-
-private fun formatAgendaDate(date: LocalDate): String {
-    val locale = Locale.getDefault()
-    val java = java.time.LocalDate.of(date.year, date.month.ordinal + 1, date.day)
-    // Weekday + date in the locale's own field order (e.g. "Wed, Jun 17, 2026"
-    // vs "Mi., 17. Juni 2026") rather than a hardcoded day-month-year layout.
-    return localizedDateFormatter(locale, "EEEdMMMy").format(java)
-}

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

@@ -40,9 +40,17 @@ data class MonthWeek(
 sealed interface MonthUiState {
     data object Loading : MonthUiState
     data class Failure(val reason: FailureReason) : MonthUiState
+
+    /**
+     * [weeks] is what the grid draws; [instancesByDay] is the same events keyed by
+     * date and *uncapped*, so the split style's day pane can list everything on a
+     * date without a second provider query — the month grid range already covers
+     * it. All-day events sort first, then by start.
+     */
     data class Success(
         val month: YearMonth,
         val today: LocalDate,
         val weeks: List<MonthWeek>,
+        val instancesByDay: Map<LocalDate, List<EventInstance>> = emptyMap(),
     ) : MonthUiState
 }

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

@@ -117,10 +117,12 @@ class MonthViewModel @Inject constructor(
         if (calendars.isEmpty()) {
             return MonthUiState.Failure(FailureReason.NoCalendarsConfigured)
         }
+        val weeks = layoutMonthWeeks(ym, weekStart, instances, zone)
         return MonthUiState.Success(
             month = ym,
             today = todayDate,
-            weeks = layoutMonthWeeks(ym, weekStart, instances, zone),
+            weeks = weeks,
+            instancesByDay = instancesByDay(weeks.flatMap { it.days }, instances, zone),
         )
     }
 }
@@ -149,6 +151,22 @@ internal fun layoutMonthWeeks(
 
     return (0 until weekCount).map { row ->
         val days = (0 until 7).map { gridStart.plus(row * 7 + it, DateTimeUnit.DAY) }
+        layoutCalendarWeek(days, instances, zone)
+    }
+}
+
+/**
+ * Resolve one week row's events for rendering. Split out of [layoutMonthWeeks] so
+ * the continuous style — which streams weeks rather than months and so has no
+ * enclosing [YearMonth] to slice by — lays each row out identically.
+ *
+ * [days] must be the row's seven consecutive dates, in display order.
+ */
+internal fun layoutCalendarWeek(
+    days: List<LocalDate>,
+    instances: List<EventInstance>,
+    zone: TimeZone,
+): MonthWeek {
     val weekEvents = instances.filter { ev -> days.any { ev.coversDay(it, zone) } }
     val (bars, singles) = weekEvents.partition { ev ->
         ev.isAllDay || days.count { ev.coversDay(it, zone) } > 1
@@ -163,7 +181,7 @@ internal fun layoutMonthWeeks(
             continuesRight = s.event.coversDay(days.last().plus(1, DateTimeUnit.DAY), zone),
         )
     }
-        MonthWeek(
+    return MonthWeek(
         days = days,
         spans = spans,
         timedByDay = days.associateWith { d ->
@@ -171,9 +189,25 @@ internal fun layoutMonthWeeks(
         },
         countByDay = days.associateWith { d -> weekEvents.count { it.coversDay(d, zone) } },
     )
-    }
 }
 
+/**
+ * Every event touching each of [days], all-day first then by start time. Unlike
+ * [MonthWeek.timedByDay] this keeps multi-day and all-day events on every date
+ * they cover and applies no display cap, so the split style's day pane can list a
+ * date in full without querying the provider again.
+ */
+internal fun instancesByDay(
+    days: List<LocalDate>,
+    instances: List<EventInstance>,
+    zone: TimeZone,
+): Map<LocalDate, List<EventInstance>> =
+    days.associateWith { day ->
+        instances
+            .filter { it.coversDay(day, zone) }
+            .sortedWith(compareByDescending<EventInstance> { it.isAllDay }.thenBy { it.start })
+    }
+
 /**
  * The on-screen grid spans 6 weeks anchored on [weekStart]. Includes the
  * trailing days of the previous month and the leading days of the next month.

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

@@ -0,0 +1,220 @@
+package de.jeanlucmakiola.calendula.ui.month
+
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.calendula.domain.EventInstance
+import kotlinx.datetime.DateTimeUnit
+import kotlinx.datetime.DayOfWeek
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.YearMonth
+import kotlinx.datetime.atTime
+import kotlinx.datetime.plus
+import kotlinx.datetime.toInstant
+import kotlin.time.Instant
+import org.junit.jupiter.api.Test
+
+class MonthLayoutTest {
+
+    private val zone = TimeZone.UTC
+
+    // 2026-06-01 is a Monday, so a Monday-anchored June grid starts on the 1st.
+    private val jun = YearMonth(2026, kotlinx.datetime.Month.JUNE)
+    private val jun1 = LocalDate(2026, 6, 1)
+    private val jun8 = LocalDate(2026, 6, 8)
+    private val weekOf8th = (0..6).map { jun8.plus(it, DateTimeUnit.DAY) }
+
+    private fun at(date: LocalDate, h: Int, m: Int = 0): Instant =
+        date.atTime(h, m).toInstant(zone)
+
+    private fun timed(
+        date: LocalDate,
+        startHour: Int,
+        endHour: Int,
+        id: Long = 1L,
+        title: String = "E",
+    ) = EventInstance(
+        instanceId = id,
+        eventId = id,
+        calendarId = 1L,
+        title = title,
+        start = at(date, startHour),
+        end = at(date, endHour),
+        isAllDay = false,
+        color = 0xFF112233.toInt(),
+        location = null,
+    )
+
+    /** All-day events live at UTC midnights with an *exclusive* end. */
+    private fun allDay(
+        from: LocalDate,
+        toInclusive: LocalDate = from,
+        id: Long = 100L,
+        title: String = "A",
+    ) = EventInstance(
+        instanceId = id,
+        eventId = id,
+        calendarId = 1L,
+        title = title,
+        start = from.atTime(0, 0).toInstant(TimeZone.UTC),
+        end = toInclusive.plus(1, DateTimeUnit.DAY).atTime(0, 0).toInstant(TimeZone.UTC),
+        isAllDay = true,
+        color = 0xFF445566.toInt(),
+        location = null,
+    )
+
+    @Test
+    fun `startOfGridWeek snaps back to the configured week start`() {
+        val wed = LocalDate(2026, 6, 10)
+        assertThat(wed.startOfGridWeek(DayOfWeek.MONDAY)).isEqualTo(jun8)
+        assertThat(jun8.startOfGridWeek(DayOfWeek.MONDAY)).isEqualTo(jun8)
+        // A Sunday-anchored week containing the 10th starts on the 7th.
+        assertThat(wed.startOfGridWeek(DayOfWeek.SUNDAY)).isEqualTo(LocalDate(2026, 6, 7))
+    }
+
+    @Test
+    fun `monthGridRange always covers 42 days from the grid start`() {
+        val range = monthGridRange(jun, DayOfWeek.MONDAY, zone)
+        assertThat(range.start).isEqualTo(at(jun1, 0))
+        // 42 days inclusive → the last second of 2026-07-12.
+        assertThat(range.endInclusive)
+            .isEqualTo(LocalDate(2026, 7, 12).atTime(23, 59, 59).toInstant(zone))
+    }
+
+    @Test
+    fun `week count follows the month's shape rather than a fixed six rows`() {
+        // June 2026: starts Monday, 30 days → 5 rows.
+        assertThat(layoutMonthWeeks(jun, DayOfWeek.MONDAY, emptyList(), zone)).hasSize(5)
+        // August 2026: starts Saturday, 31 days → spills to 6 rows.
+        val aug = YearMonth(2026, kotlinx.datetime.Month.AUGUST)
+        assertThat(layoutMonthWeeks(aug, DayOfWeek.MONDAY, emptyList(), zone)).hasSize(6)
+        // February 2021: starts Monday, 28 days → exactly 4 rows.
+        val feb = YearMonth(2021, kotlinx.datetime.Month.FEBRUARY)
+        assertThat(layoutMonthWeeks(feb, DayOfWeek.MONDAY, emptyList(), zone)).hasSize(4)
+    }
+
+    @Test
+    fun `layoutMonthWeeks rows are contiguous and seven days wide`() {
+        val weeks = layoutMonthWeeks(jun, DayOfWeek.MONDAY, emptyList(), zone)
+        assertThat(weeks.first().days.first()).isEqualTo(jun1)
+        weeks.forEach { assertThat(it.days).hasSize(7) }
+        val allDays = weeks.flatMap { it.days }
+        allDays.zipWithNext { a, b -> assertThat(b).isEqualTo(a.plus(1, DateTimeUnit.DAY)) }
+    }
+
+    @Test
+    fun `a multi-day event becomes one span across its columns`() {
+        val ev = allDay(LocalDate(2026, 6, 10), LocalDate(2026, 6, 12))
+        val week = layoutCalendarWeek(weekOf8th, listOf(ev), zone)
+
+        assertThat(week.spans).hasSize(1)
+        val span = week.spans.single()
+        assertThat(span.startCol).isEqualTo(2) // Wednesday the 10th
+        assertThat(span.endCol).isEqualTo(4) // Friday the 12th
+        assertThat(span.lane).isEqualTo(0)
+        assertThat(span.continuesLeft).isFalse()
+        assertThat(span.continuesRight).isFalse()
+    }
+
+    @Test
+    fun `a span running past the row end is flagged as continuing`() {
+        // Saturday the 13th through Tuesday the 16th straddles the row boundary.
+        val ev = allDay(LocalDate(2026, 6, 13), LocalDate(2026, 6, 16))
+        val week = layoutCalendarWeek(weekOf8th, listOf(ev), zone)
+
+        val span = week.spans.single()
+        assertThat(span.startCol).isEqualTo(5)
+        assertThat(span.endCol).isEqualTo(6)
+        assertThat(span.continuesLeft).isFalse()
+        assertThat(span.continuesRight).isTrue()
+
+        // The following row picks it up with the flags mirrored.
+        val nextRow = layoutCalendarWeek(
+            weekOf8th.map { it.plus(7, DateTimeUnit.DAY) },
+            listOf(ev),
+            zone,
+        )
+        val tail = nextRow.spans.single()
+        assertThat(tail.startCol).isEqualTo(0)
+        assertThat(tail.endCol).isEqualTo(1)
+        assertThat(tail.continuesLeft).isTrue()
+        assertThat(tail.continuesRight).isFalse()
+    }
+
+    @Test
+    fun `overlapping spans are stacked on separate lanes`() {
+        val a = allDay(LocalDate(2026, 6, 9), LocalDate(2026, 6, 11), id = 1L)
+        val b = allDay(LocalDate(2026, 6, 10), LocalDate(2026, 6, 12), id = 2L)
+        val week = layoutCalendarWeek(weekOf8th, listOf(a, b), zone)
+
+        assertThat(week.spans.map { it.lane }).containsExactly(0, 1)
+    }
+
+    @Test
+    fun `single-day timed events stay pills and sort by start`() {
+        val late = timed(LocalDate(2026, 6, 10), 14, 15, id = 1L)
+        val early = timed(LocalDate(2026, 6, 10), 9, 10, id = 2L)
+        val week = layoutCalendarWeek(weekOf8th, listOf(late, early), zone)
+
+        assertThat(week.spans).isEmpty()
+        assertThat(week.timedByDay[LocalDate(2026, 6, 10)]?.map { it.instanceId })
+            .containsExactly(2L, 1L)
+            .inOrder()
+        assertThat(week.timedByDay[LocalDate(2026, 6, 11)]).isEmpty()
+    }
+
+    @Test
+    fun `countByDay totals bars and pills on each date`() {
+        val span = allDay(LocalDate(2026, 6, 10), LocalDate(2026, 6, 12), id = 1L)
+        val pill = timed(LocalDate(2026, 6, 10), 9, 10, id = 2L)
+        val week = layoutCalendarWeek(weekOf8th, listOf(span, pill), zone)
+
+        assertThat(week.countByDay[LocalDate(2026, 6, 10)]).isEqualTo(2)
+        assertThat(week.countByDay[LocalDate(2026, 6, 11)]).isEqualTo(1)
+        assertThat(week.countByDay[LocalDate(2026, 6, 13)]).isEqualTo(0)
+    }
+
+    @Test
+    fun `layoutMonthWeeks agrees with laying each row out on its own`() {
+        val events = listOf(
+            allDay(LocalDate(2026, 6, 10), LocalDate(2026, 6, 12), id = 1L),
+            timed(LocalDate(2026, 6, 18), 9, 10, id = 2L),
+        )
+        val weeks = layoutMonthWeeks(jun, DayOfWeek.MONDAY, events, zone)
+
+        weeks.forEach { row ->
+            assertThat(row).isEqualTo(layoutCalendarWeek(row.days, events, zone))
+        }
+    }
+
+    @Test
+    fun `instancesByDay puts all-day events first then orders by start`() {
+        val allDayEv = allDay(LocalDate(2026, 6, 10), id = 1L)
+        val late = timed(LocalDate(2026, 6, 10), 14, 15, id = 2L)
+        val early = timed(LocalDate(2026, 6, 10), 9, 10, id = 3L)
+
+        val byDay = instancesByDay(weekOf8th, listOf(late, early, allDayEv), zone)
+
+        assertThat(byDay.getValue(LocalDate(2026, 6, 10)).map { it.instanceId })
+            .containsExactly(1L, 3L, 2L)
+            .inOrder()
+    }
+
+    @Test
+    fun `instancesByDay repeats a multi-day event on every date it covers`() {
+        val ev = allDay(LocalDate(2026, 6, 10), LocalDate(2026, 6, 12))
+        val byDay = instancesByDay(weekOf8th, listOf(ev), zone)
+
+        assertThat(byDay.getValue(LocalDate(2026, 6, 9))).isEmpty()
+        assertThat(byDay.getValue(LocalDate(2026, 6, 10))).hasSize(1)
+        assertThat(byDay.getValue(LocalDate(2026, 6, 11))).hasSize(1)
+        assertThat(byDay.getValue(LocalDate(2026, 6, 12))).hasSize(1)
+        assertThat(byDay.getValue(LocalDate(2026, 6, 13))).isEmpty()
+    }
+
+    @Test
+    fun `instancesByDay covers every date in the grid, empty ones included`() {
+        val byDay = instancesByDay(weekOf8th, emptyList(), zone)
+        assertThat(byDay.keys).containsExactlyElementsIn(weekOf8th)
+        assertThat(byDay.values.flatten()).isEmpty()
+    }
+}