fix(month): seat the split style's dots by lane (#53)

The dots gathered a day's *distinct colours*, which meant dot i stood for
no particular event and two events sharing a calendar collapsed into one —
undercounting the day.

Seat them off the same lane assignment the paged grid draws from, so a dot
and the bar in that lane are the same event. That fixes the count, and it
is what will let one morph into the other when the grid expands.

The cap is now MAX_EVENT_ROWS rather than a constant of its own: the two
have to agree or a dot would have no bar to become.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -0,0 +1,129 @@
+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.Month
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.YearMonth
+import kotlinx.datetime.atTime
+import kotlinx.datetime.plus
+import kotlinx.datetime.toInstant
+import org.junit.jupiter.api.Test
+
+/**
+ * What lets the split style's dots morph into the paged style's bars (#53): both
+ * read a day off the *same* lane seating, so dot _i_ and lane _i_ are one event.
+ */
+class LaneEventsTest {
+
+    private val zone = TimeZone.UTC
+    private val jul26 = YearMonth(2026, Month.JULY)
+
+    /** July 2026 starts on a Wednesday, so this row — Jul 6–12 — sits wholly inside it. */
+    private fun rowOfJuly6(events: List<EventInstance>) =
+        layoutMonthWeeks(jul26, DayOfWeek.MONDAY, events, zone)[1]
+
+    private fun allDay(from: LocalDate, toInclusive: LocalDate, id: Long, color: Int = BLUE) =
+        EventInstance(
+            instanceId = id,
+            eventId = id,
+            calendarId = 1L,
+            title = "A$id",
+            start = from.atTime(0, 0).toInstant(zone),
+            end = toInclusive.plus(1, DateTimeUnit.DAY).atTime(0, 0).toInstant(zone),
+            isAllDay = true,
+            color = color,
+            location = null,
+        )
+
+    private fun timed(date: LocalDate, hour: Int, id: Long, color: Int = RED) = EventInstance(
+        instanceId = id,
+        eventId = id,
+        calendarId = 1L,
+        title = "T$id",
+        start = date.atTime(hour, 0).toInstant(zone),
+        end = date.atTime(hour + 1, 0).toInstant(zone),
+        isAllDay = false,
+        color = color,
+        location = null,
+    )
+
+    @Test
+    fun `a bar keeps its lane and the day's timed events fill what's left`() {
+        val bar = allDay(LocalDate(2026, 7, 7), LocalDate(2026, 7, 9), id = 1L)
+        val meeting = timed(LocalDate(2026, 7, 7), hour = 9, id = 2L)
+        val week = rowOfJuly6(listOf(bar, meeting))
+
+        // Jul 7 is column 1 of a Monday-anchored row starting Jul 6.
+        assertThat(week.laneEvents(col = 1, day = LocalDate(2026, 7, 7), laneCap = 3))
+            .containsExactly(bar, meeting)
+            .inOrder()
+    }
+
+    @Test
+    fun `a day the bar misses seats its own events from lane zero`() {
+        val bar = allDay(LocalDate(2026, 7, 7), LocalDate(2026, 7, 9), id = 1L)
+        val monday = timed(LocalDate(2026, 7, 6), hour = 9, id = 2L)
+        val week = rowOfJuly6(listOf(bar, monday))
+
+        assertThat(week.laneEvents(col = 0, day = LocalDate(2026, 7, 6), laneCap = 3))
+            .containsExactly(monday)
+    }
+
+    @Test
+    fun `a multi-day bar is seated on every day it covers`() {
+        val bar = allDay(LocalDate(2026, 7, 7), LocalDate(2026, 7, 9), id = 1L)
+        val week = rowOfJuly6(listOf(bar))
+
+        (1..3).forEach { col ->
+            val day = LocalDate(2026, 7, 6 + col)
+            assertThat(week.laneEvents(col, day, laneCap = 3)).containsExactly(bar)
+        }
+        assertThat(week.laneEvents(col = 4, day = LocalDate(2026, 7, 10), laneCap = 3)).isEmpty()
+    }
+
+    /** The bug the colour-gathered dots had: one dot for two events on one calendar. */
+    @Test
+    fun `events sharing a colour each keep their own lane`() {
+        val first = timed(LocalDate(2026, 7, 6), hour = 9, id = 1L, color = RED)
+        val second = timed(LocalDate(2026, 7, 6), hour = 14, id = 2L, color = RED)
+        val week = rowOfJuly6(listOf(first, second))
+
+        assertThat(week.laneEvents(col = 0, day = LocalDate(2026, 7, 6), laneCap = 3))
+            .containsExactly(first, second)
+            .inOrder()
+    }
+
+    @Test
+    fun `seating stops at the cap and leaves the rest to the overflow count`() {
+        val events = (0 until 5).map { timed(LocalDate(2026, 7, 6), hour = 8 + it, id = it + 1L) }
+        val week = rowOfJuly6(events)
+
+        val seated = week.laneEvents(col = 0, day = LocalDate(2026, 7, 6), laneCap = 3)
+        assertThat(seated).hasSize(3)
+        assertThat(seated).containsExactlyElementsIn(events.take(3)).inOrder()
+        assertThat(week.countByDay[LocalDate(2026, 7, 6)]!! - seated.size).isEqualTo(2)
+    }
+
+    /** A bar parked below the cap is out of view, so it takes no dot with it. */
+    @Test
+    fun `a bar beyond the cap is left out`() {
+        val bars = (0 until 4).map {
+            allDay(LocalDate(2026, 7, 6), LocalDate(2026, 7, 8), id = it + 1L)
+        }
+        val week = rowOfJuly6(bars)
+
+        val seated = week.laneEvents(col = 0, day = LocalDate(2026, 7, 6), laneCap = 3)
+        assertThat(seated).hasSize(3)
+        assertThat(week.spans.filter { it.lane >= 3 }.map { it.event })
+            .containsNoneIn(seated)
+    }
+
+    private companion object {
+        const val BLUE = 0xFF3366CC.toInt()
+        const val RED = 0xFFCC3333.toInt()
+    }
+}