Carry the timeline hours between views (#184)

app/src/main/java/de/jeanlucmakiola/calendula/ui/CalendarHost.kt

@@ -9,6 +9,7 @@ import androidx.compose.animation.fadeIn
 import androidx.compose.animation.slideInHorizontally
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.material3.TopAppBarDefaults
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.LaunchedEffect
@@ -19,6 +20,9 @@ import androidx.compose.runtime.saveable.listSaver
 import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.layout.onGloballyPositioned
+import androidx.compose.ui.layout.positionInWindow
+import androidx.compose.ui.platform.LocalDensity
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.domain.EventForm
@@ -26,6 +30,7 @@ import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.ui.agenda.AgendaScreen
 import de.jeanlucmakiola.calendula.ui.calendars.BackupScreen
 import de.jeanlucmakiola.calendula.ui.calendars.CalendarsScreen
+import de.jeanlucmakiola.calendula.ui.common.BelowTopBarClip
 import de.jeanlucmakiola.floret.identity.fadeThrough
 import de.jeanlucmakiola.floret.identity.predictiveBackExit
 import de.jeanlucmakiola.floret.identity.rememberReduceMotion
@@ -34,8 +39,10 @@ import de.jeanlucmakiola.calendula.ui.common.EventMoveHost
 import de.jeanlucmakiola.calendula.ui.common.EventMoveScope
 import de.jeanlucmakiola.calendula.ui.common.LocalEventMove
 import de.jeanlucmakiola.calendula.ui.common.LocalManageCalendars
+import de.jeanlucmakiola.calendula.ui.common.LocalTimelineScroll
 import de.jeanlucmakiola.calendula.ui.common.LocalViewMorph
 import de.jeanlucmakiola.calendula.ui.common.RescheduleViewModel
+import de.jeanlucmakiola.calendula.ui.common.TimelineScrollMemory
 import de.jeanlucmakiola.calendula.ui.common.ViewMorphScope
 import de.jeanlucmakiola.calendula.ui.common.rememberCalendarFadeSpec
 import de.jeanlucmakiola.calendula.ui.common.rememberViewMorphBoundsTransform
@@ -371,13 +378,23 @@ fun CalendarHost(
         val reduceMotion = rememberReduceMotion()
         val morphBounds = rememberViewMorphBoundsTransform()
         val morphFade = rememberCalendarFadeSpec()
+        val morphClip = remember { BelowTopBarClip() }
+        val density = LocalDensity.current
+        val topBarBottom = TopAppBarDefaults.windowInsets.getTop(density) +
+            with(density) { TopAppBarDefaults.TopAppBarExpandedHeight.toPx() }
+        val timelineScroll = remember { TimelineScrollMemory() }
         CompositionLocalProvider(
             LocalEventMove provides moveScope,
+            LocalTimelineScroll provides timelineScroll,
             // The failure state's way out when every calendar is switched off
             // (#239); nothing else in the calendar surfaces navigates here.
             LocalManageCalendars provides { showCalendars = true },
         ) {
-        SharedTransitionLayout(Modifier.fillMaxSize()) {
+        SharedTransitionLayout(
+            Modifier
+                .fillMaxSize()
+                .onGloballyPositioned { morphClip.top = topBarBottom - it.positionInWindow().y },
+        ) {
         AnimatedContent(
             targetState = view,
             transitionSpec = { viewSwitch },
@@ -385,8 +402,8 @@ fun CalendarHost(
         ) { currentView ->
             val sharedScope = this@SharedTransitionLayout
             val visibilityScope = this@AnimatedContent
-            val viewMorph = remember(reduceMotion, sharedScope, visibilityScope, morphBounds, morphFade) {
+            val viewMorph = remember(reduceMotion, sharedScope, visibilityScope, morphBounds, morphFade, morphClip) {
-                if (reduceMotion) null else ViewMorphScope(sharedScope, visibilityScope, morphBounds, morphFade)
+                if (reduceMotion) null else ViewMorphScope(sharedScope, visibilityScope, morphBounds, morphFade, morphClip)
             }
             CompositionLocalProvider(LocalViewMorph provides viewMorph) {
             when (currentView) {

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

@@ -57,9 +57,15 @@ internal fun hourCellRadiusPx(cellHeight: Float, cellWidth: Float, maxRadius: Fl
  * drawn across one. Applied to a day column's content, so the cells sit over the
  * column background but beneath the event blocks — blocks stay in a continuous
  * coordinate space and keep spanning cells. [hourHeightPx] is one hour's pixel
- * height; [color] is resolved by the caller from the theme.
+ * height; [color] is resolved by the caller from the theme. [offsetPx] shifts
+ * the cells up, for a fixed window over a scrolled column.
  */
-fun Modifier.hourGridCells(show: Boolean, hourHeightPx: Float, color: Color): Modifier =
+fun Modifier.hourGridCells(
+    show: Boolean,
+    hourHeightPx: Float,
+    color: Color,
+    offsetPx: () -> Float = { 0f },
+): Modifier =
     if (!show) {
         this
     } else {
@@ -71,10 +77,11 @@ fun Modifier.hourGridCells(show: Boolean, hourHeightPx: Float, color: Color): Mo
                 hourCellRadiusPx(cellHeight, size.width, HOUR_CELL_CORNER.toPx()),
             )
             val cellSize = Size(size.width, cellHeight)
+            val top = inset - offsetPx()
             for (hour in 0 until 24) {
                 drawRoundRect(
                     color = color,
-                    topLeft = Offset(0f, hour * hourHeightPx + inset),
+                    topLeft = Offset(0f, hour * hourHeightPx + top),
                     size = cellSize,
                     cornerRadius = radius,
                 )

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

@@ -0,0 +1,54 @@
+package de.jeanlucmakiola.calendula.ui.common
+
+import androidx.compose.foundation.ScrollState
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.rememberUpdatedState
+import androidx.compose.runtime.snapshotFlow
+import androidx.compose.runtime.staticCompositionLocalOf
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.unit.Dp
+import kotlinx.coroutines.flow.first
+import kotlin.math.roundToInt
+
+/**
+ * Where 00:00 sat in the last timeline shown, measured from the top of its
+ * view's content, so the next timeline view opens on the same hours (#184): an
+ * event in both keeps its place and only grows sideways.
+ */
+class TimelineScrollMemory {
+    var midnightY: Float? = null
+}
+
+val LocalTimelineScroll = staticCompositionLocalOf<TimelineScrollMemory?> { null }
+
+/**
+ * The scroll state of a timeline whose scrolling area starts [timelineTop] below
+ * its view's content top. Opens where the last timeline left off, or on noon the
+ * first time.
+ */
+@Composable
+fun rememberTimelineScrollState(timelineTop: Dp): ScrollState {
+    val memory = LocalTimelineScroll.current
+    val topPx = with(LocalDensity.current) { timelineTop.toPx() }
+    val remembered = memory?.midnightY
+    val scrollState = rememberScrollState(
+        initial = remembered?.let { (topPx - it).roundToInt().coerceAtLeast(0) } ?: 0,
+    )
+    val currentTop by rememberUpdatedState(topPx)
+    LaunchedEffect(scrollState) {
+        if (remembered != null) return@LaunchedEffect
+        snapshotFlow { scrollState.maxValue }.first { it > 0 }
+        // Half the scroll range *is* noon: the content spans a full 24 hours, so
+        // centring the range centres midday at whatever hour height is in force.
+        scrollState.scrollTo(scrollState.maxValue / 2)
+    }
+    if (memory != null) {
+        LaunchedEffect(scrollState, memory) {
+            snapshotFlow { currentTop - scrollState.value }.collect { memory.midnightY = it }
+        }
+    }
+    return scrollState
+}

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

@@ -7,6 +7,12 @@ import androidx.compose.animation.SharedTransitionScope
 import androidx.compose.animation.core.FiniteAnimationSpec
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
+import androidx.compose.foundation.ScrollState
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
@@ -14,7 +20,13 @@ import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.compositionLocalOf
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clipToBounds
 import androidx.compose.ui.geometry.Rect
+import androidx.compose.ui.graphics.Path
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.unit.Density
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.LayoutDirection
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import kotlinx.datetime.LocalDate
 
@@ -27,12 +39,17 @@ import kotlinx.datetime.LocalDate
  * multi-day event is drawn once per day, per week row or per timeline column,
  * and only one element per key may take part. The segment that starts on the
  * same day in both views is the one that travels; the rest fade where they are.
+ *
+ * A day's ground — its month cell, its timeline column — travels too, so the
+ * events never arrive ahead of what they sit on.
  */
 sealed interface ViewMorphKey {
     data class Event(val eventId: Long, val beginMillis: Long, val day: LocalDate) : ViewMorphKey
 
     data class Day(val date: LocalDate) : ViewMorphKey
 
+    data class Ground(val date: LocalDate) : ViewMorphKey
+
     companion object {
         /** [event]'s occurrence as drawn from [day]. */
         fun event(event: EventInstance, day: LocalDate): Event =
@@ -47,8 +64,30 @@ class ViewMorphScope(
     val visibility: AnimatedVisibilityScope,
     val boundsTransform: BoundsTransform,
     val fadeSpec: FiniteAnimationSpec<Float>,
+    val clip: SharedTransitionScope.OverlayClip,
 )
 
+/**
+ * Keeps what travels below the top bar, which every view has at the same height:
+ * the overlay draws above the whole screen, so an event scrolled under the bar
+ * would otherwise cross it. [top] is the bar's bottom edge in the shared layout.
+ */
+@OptIn(ExperimentalSharedTransitionApi::class)
+class BelowTopBarClip : SharedTransitionScope.OverlayClip {
+    var top = 0f
+
+    override fun getClipPath(
+        sharedContentState: SharedTransitionScope.SharedContentState,
+        bounds: Rect,
+        layoutDirection: LayoutDirection,
+        density: Density,
+    ): Path = Path().apply { addRect(Rect(-FAR, top, FAR, FAR)) }
+
+    private companion object {
+        const val FAR = 1e6f
+    }
+}
+
 val LocalViewMorph = compositionLocalOf<ViewMorphScope?> { null }
 
 /**
@@ -84,6 +123,7 @@ fun Modifier.morphEvent(key: ViewMorphKey.Event): Modifier {
             enter = fadeIn(morph.fadeSpec),
             exit = fadeOut(morph.fadeSpec),
             boundsTransform = morph.boundsTransform,
+            clipInOverlayDuringTransition = morph.clip,
             resizeMode = SharedTransitionScope.ResizeMode.RemeasureToBounds,
             zIndexInOverlay = 1f,
         )
@@ -102,10 +142,64 @@ fun Modifier.morphDay(date: LocalDate): Modifier {
             enter = fadeIn(morph.fadeSpec),
             exit = fadeOut(morph.fadeSpec),
             boundsTransform = morph.boundsTransform,
+            clipInOverlayDuringTransition = morph.clip,
+            // Over the grounds, which a month cell's number sits inside.
+            zIndexInOverlay = 1f,
         )
     }
 }
 
+/** Tags a day's ground, under the events and numbers that travel with it. */
+@OptIn(ExperimentalSharedTransitionApi::class)
+@Composable
+fun Modifier.morphGround(date: LocalDate): Modifier {
+    val morph = LocalViewMorph.current ?: return this
+    return with(morph.shared) {
+        this@morphGround.sharedBounds(
+            sharedContentState = rememberSharedContentState(ViewMorphKey.Ground(date)),
+            animatedVisibilityScope = morph.visibility,
+            enter = fadeIn(morph.fadeSpec),
+            exit = fadeOut(morph.fadeSpec),
+            boundsTransform = morph.boundsTransform,
+            clipInOverlayDuringTransition = morph.clip,
+            resizeMode = SharedTransitionScope.ResizeMode.RemeasureToBounds,
+        )
+    }
+}
+
+/**
+ * The on-screen window of each day's timeline column, painted like the column
+ * behind the scrolling one: a whole 24-hour column can't travel, its window can.
+ * Nothing is drawn while there is no morph to take part in.
+ */
+@Composable
+fun TimelineGrounds(
+    days: List<LocalDate>,
+    scrollState: ScrollState,
+    hourHeight: Dp,
+    columnGap: Dp,
+    modifier: Modifier = Modifier,
+) {
+    if (LocalViewMorph.current == null) return
+    val showHourGrid = LocalShowHourGrid.current
+    val hourPx = with(LocalDensity.current) { hourHeight.toPx() }
+    val cell = MaterialTheme.colorScheme.surfaceContainer
+    val ground = if (showHourGrid) MaterialTheme.colorScheme.surface else cell
+    Row(modifier = modifier, horizontalArrangement = Arrangement.spacedBy(columnGap)) {
+        days.forEach { day ->
+            Box(
+                Modifier
+                    .weight(1f)
+                    .fillMaxHeight()
+                    .morphGround(day)
+                    .clipToBounds()
+                    .background(ground)
+                    .hourGridCells(showHourGrid, hourPx, cell) { scrollState.value.toFloat() },
+            )
+        }
+    }
+}
+
 /** The view switch's travel: the M3 Expressive default spatial spring, as the pagers settle. */
 @OptIn(ExperimentalSharedTransitionApi::class, ExperimentalMaterial3ExpressiveApi::class)
 @Composable

app/src/main/java/de/jeanlucmakiola/calendula/ui/day/DayScreen.kt

@@ -12,10 +12,12 @@ import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.mutableStateMapOf
 import de.jeanlucmakiola.calendula.ui.common.jumpToPage
+import de.jeanlucmakiola.calendula.ui.common.TimelineGrounds
 import de.jeanlucmakiola.calendula.ui.common.ViewMorphKey
 import de.jeanlucmakiola.calendula.ui.common.ViewMorphPage
 import de.jeanlucmakiola.calendula.ui.common.morphEvent
 import de.jeanlucmakiola.calendula.ui.common.morphPageActive
+import de.jeanlucmakiola.calendula.ui.common.rememberTimelineScrollState
 import de.jeanlucmakiola.calendula.ui.common.pagedHeight
 import de.jeanlucmakiola.calendula.ui.common.rememberCalendarPageSpec
 import de.jeanlucmakiola.calendula.ui.common.rememberCurrentMinute
@@ -146,7 +148,7 @@ import de.jeanlucmakiola.calendula.ui.common.hourCellBlockInset
 import de.jeanlucmakiola.calendula.ui.common.hourGridCells
 import de.jeanlucmakiola.calendula.ui.common.tappedMinuteOfDay
 import de.jeanlucmakiola.calendula.ui.week.TimedBlock
-import kotlinx.coroutines.flow.first
+import de.jeanlucmakiola.calendula.ui.week.weekDayHeaderHeight
 import kotlinx.coroutines.launch
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
@@ -307,15 +309,10 @@ private fun DayContent(
     val fadeSpec = rememberCalendarFadeSpec()
 
     // Shared by every page and the gutter, so the vertical scroll position
-    // survives day-to-day swipes. We only centre on noon once, on first entry
+    // survives day-to-day swipes, and carried over from the timeline view
-    // into the day view (i.e. when arriving from the month/week view).
+    // before this one.
-    val scrollState = rememberScrollState()
+    val stripHeight = (state as? DayUiState.Success)?.allDayStripHeight() ?: 0.dp
-    LaunchedEffect(Unit) {
+    val scrollState = rememberTimelineScrollState(stripHeight + TIMELINE_TOP_GAP)
-        snapshotFlow { scrollState.maxValue }.first { it > 0 }
-        // Half the scroll range *is* noon: the content spans a full 24 hours, so
-        // centring the range centres midday at whatever hour height is in force.
-        scrollState.scrollTo(scrollState.maxValue / 2)
-    }
 
     // Above the pager: a page change mid-drag would strand the floating block
     // inside the outgoing page.
@@ -444,14 +441,15 @@ private fun DayFrame(
             // timelines have, so labels and column agree.
             BoxWithConstraints(modifier = Modifier.fillMaxSize()) {
                 val zoom = LocalTimelineZoom.current
-                val hourHeight = zoom.scale.hourHeight(maxHeight)
+                val fitHeight = maxHeight + allDayHeight - weekDayHeaderHeight()
+                val hourHeight = zoom.scale.hourHeight(fitHeight)
                 // Start inset so the labels centre on the top bar hamburger,
                 // matching the week view.
                 HourGutter(
                     scrollState = scrollState,
                     hourHeight = hourHeight,
                     dragController = dragController,
-                    modifier = rememberTimelinePinchZoom(scrollState, maxHeight, hourHeight, zoom),
+                    modifier = rememberTimelinePinchZoom(scrollState, fitHeight, hourHeight, zoom),
                 )
             }
         }
@@ -521,6 +519,7 @@ private fun DayPage(
         Spacer(Modifier.height(TIMELINE_TOP_GAP))
         Timeline(
             state = state,
+            allDayHeight = allDayHeight,
             scrollState = scrollState,
             dragController = dragController,
             active = active,
@@ -672,6 +671,7 @@ private fun AllDayBar(
 @Composable
 private fun Timeline(
     state: DayUiState.Success,
+    allDayHeight: Dp,
     scrollState: ScrollState,
     dragController: TimelineDragController,
     active: Boolean,
@@ -692,14 +692,27 @@ private fun Timeline(
 
     // BoxWithConstraints rather than Box: the fit-the-whole-day scale needs the
     // timeline's own viewport height, which is only known here — below the top
-    // bar, date header and all-day strip.
+    // bar and all-day strip. It fits the week view's timeline instead, so an
+    // hour is as tall here as there (#184).
+    val weekHeader = weekDayHeaderHeight()
     BoxWithConstraints(modifier = Modifier.fillMaxSize()) {
-        val hourHeight = zoom.scale.hourHeight(maxHeight)
+        val fitHeight = maxHeight + allDayHeight - weekHeader
+        val hourHeight = zoom.scale.hourHeight(fitHeight)
         val totalHeight = hourHeight * 24
         // The pinch sits above the scroll viewport: it has to outrank the
         // vertical scroll, and it does that by watching the initial pass, which
         // only reaches it if it is the viewport's ancestor.
-        val pinch = rememberTimelinePinchZoom(scrollState, maxHeight, hourHeight, zoom)
+        val pinch = rememberTimelinePinchZoom(scrollState, fitHeight, hourHeight, zoom)
+        TimelineGrounds(
+            days = listOf(state.date),
+            scrollState = scrollState,
+            hourHeight = hourHeight,
+            columnGap = 0.dp,
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(end = TIMELINE_CONTENT_END_INSET)
+                .clip(RoundedCornerShape(16.dp)),
+        )
         // Scrolls on the same state as the gutter and the other pages, so they
         // all stay aligned. A static, rounded-clipped window — the content
         // scrolls inside it, so the soft corners are permanent at any scroll
@@ -975,10 +988,11 @@ private fun EventBlock(
 private fun DayLoading() {
     val scale = LocalTimelineZoom.current.scale
     val scrollState = rememberScrollState()
+    val weekHeader = weekDayHeaderHeight()
     BoxWithConstraints(modifier = Modifier.fillMaxSize()) {
         // Same scale resolution as the loaded timeline, so the skeleton's column
         // doesn't resize the moment the real day arrives.
-        val hourHeight = scale.hourHeight(maxHeight)
+        val hourHeight = scale.hourHeight(maxHeight - weekHeader - TIMELINE_TOP_GAP)
         val totalHeight = hourHeight * 24
         // The skeleton wears the loaded column's own ground, so the arrival of
         // the real day doesn't flash a solid block into a gapped grid.

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

@@ -14,6 +14,7 @@ import de.jeanlucmakiola.calendula.ui.common.LocalViewMorph
 import de.jeanlucmakiola.calendula.ui.common.ViewMorphKey
 import de.jeanlucmakiola.calendula.ui.common.morphDay
 import de.jeanlucmakiola.calendula.ui.common.morphEvent
+import de.jeanlucmakiola.calendula.ui.common.morphGround
 import de.jeanlucmakiola.calendula.ui.common.morphPageActive
 import de.jeanlucmakiola.calendula.ui.common.jumpToPage
 import de.jeanlucmakiola.calendula.ui.common.pagedHeight
@@ -2185,6 +2186,7 @@ private fun MonthWeekRow(
                             .fillMaxHeight()
                             .padding(horizontal = CELL_GAP, vertical = 1.dp)
                             .morphElement(MonthMorphKey.Cell(d))
+                            .morphGround(d)
                             .background(
                                 color = when {
                                     inMonth(d) -> MaterialTheme.colorScheme.surfaceContainer

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

@@ -135,10 +135,12 @@ import de.jeanlucmakiola.calendula.ui.common.NowLine
 import de.jeanlucmakiola.calendula.ui.common.rememberCurrentMinute
 import de.jeanlucmakiola.calendula.ui.common.ViewSwitcherPill
 import de.jeanlucmakiola.calendula.ui.common.rememberCalendarFadeSpec
+import de.jeanlucmakiola.calendula.ui.common.TimelineGrounds
 import de.jeanlucmakiola.calendula.ui.common.ViewMorphKey
 import de.jeanlucmakiola.calendula.ui.common.ViewMorphPage
 import de.jeanlucmakiola.calendula.ui.common.morphDay
 import de.jeanlucmakiola.calendula.ui.common.morphEvent
+import de.jeanlucmakiola.calendula.ui.common.rememberTimelineScrollState
 import de.jeanlucmakiola.calendula.ui.common.morphPageActive
 import de.jeanlucmakiola.calendula.ui.common.withTitleWeight
 import de.jeanlucmakiola.floret.identity.rememberReduceMotion
@@ -159,7 +161,6 @@ import de.jeanlucmakiola.calendula.ui.common.hourGridCells
 import de.jeanlucmakiola.calendula.ui.common.tappedMinuteOfDay
 import de.jeanlucmakiola.calendula.ui.common.next
 import de.jeanlucmakiola.floret.time.isoWeekNumber
-import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.launch
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
@@ -183,6 +184,15 @@ private val HEADER_BOTTOM_PADDING = 8.dp
 /** The header's date slot, reserved whether or not it holds today's circle. */
 private val DATE_SLOT_SIZE = 28.dp
 
+/** The weekday header's height, which the day view takes off to fit the week's hours (#184). */
+@Composable
+internal fun weekDayHeaderHeight(): Dp {
+    val label = MaterialTheme.typography.labelSmall
+    val line = label.lineHeight.takeIf { it.isSp } ?: label.fontSize
+    return HEADER_TOP_PADDING + with(LocalDensity.current) { line.toDp() } + 2.dp +
+        DATE_SLOT_SIZE + HEADER_BOTTOM_PADDING
+}
+
 /** Total all-day strip height for a week (0 when there are no all-day events). */
 internal fun WeekUiState.Success.allDayStripHeight(): Dp {
     if (allDaySpans.isEmpty()) return 0.dp
@@ -419,16 +429,10 @@ private fun WeekContent(
     val fadeSpec = rememberCalendarFadeSpec()
 
     // Shared by every page and the gutter, so the vertical scroll position
-    // survives week-to-week swipes (e.g. 18:00 stays centred). We only centre on
+    // survives week-to-week swipes (e.g. 18:00 stays centred), and carried over
-    // noon once, on first entry into the week view (i.e. when arriving from the
+    // from the timeline view before this one.
-    // month/day view), not on every swipe.
+    val stripHeight = (state as? WeekUiState.Success)?.allDayStripHeight() ?: 0.dp
-    val scrollState = rememberScrollState()
+    val scrollState = rememberTimelineScrollState(weekDayHeaderHeight() + stripHeight + TIMELINE_TOP_GAP)
-    LaunchedEffect(Unit) {
-        snapshotFlow { scrollState.maxValue }.first { it > 0 }
-        // Half the scroll range *is* noon: the content spans a full 24 hours, so
-        // centring the range centres midday at whatever hour height is in force.
-        scrollState.scrollTo(scrollState.maxValue / 2)
-    }
 
     // Above the pager: a page change mid-drag would strand the floating block
     // inside the outgoing page.
@@ -587,12 +591,13 @@ private fun WeekFrame(
             // timelines have, so labels and columns agree.
             BoxWithConstraints(modifier = Modifier.fillMaxSize()) {
                 val zoom = LocalTimelineZoom.current
-                val hourHeight = zoom.scale.hourHeight(maxHeight)
+                val fitHeight = maxHeight + allDayHeight
+                val hourHeight = zoom.scale.hourHeight(fitHeight)
                 HourGutter(
                     scrollState = scrollState,
                     hourHeight = hourHeight,
                     dragController = dragController,
-                    modifier = rememberTimelinePinchZoom(scrollState, maxHeight, hourHeight, zoom),
+                    modifier = rememberTimelinePinchZoom(scrollState, fitHeight, hourHeight, zoom),
                 )
             }
         }
@@ -670,6 +675,7 @@ private fun WeekPage(
         Spacer(Modifier.height(TIMELINE_TOP_GAP))
         Timeline(
             state = state,
+            allDayHeight = allDayHeight,
             scrollState = scrollState,
             dragController = dragController,
             active = active,
@@ -940,6 +946,7 @@ private fun AllDayBar(
 @Composable
 private fun Timeline(
     state: WeekUiState.Success,
+    allDayHeight: Dp,
     scrollState: ScrollState,
     dragController: TimelineDragController,
     active: Boolean,
@@ -960,14 +967,26 @@ private fun Timeline(
 
     // BoxWithConstraints rather than Box: the fit-the-whole-day scale needs the
     // timeline's own viewport height, which is only known here — below the top
-    // bar, day header and all-day strip.
+    // bar, day header and all-day strip. The strip is given back, so the scale
+    // holds while paging and matches the day view's (#184).
     BoxWithConstraints(modifier = Modifier.fillMaxSize()) {
-        val hourHeight = zoom.scale.hourHeight(maxHeight)
+        val fitHeight = maxHeight + allDayHeight
+        val hourHeight = zoom.scale.hourHeight(fitHeight)
         val totalHeight = hourHeight * 24
         // The pinch sits above the scroll viewport: it has to outrank the
         // vertical scroll, and it does that by watching the initial pass, which
         // only reaches it if it is the viewport's ancestor.
-        val pinch = rememberTimelinePinchZoom(scrollState, maxHeight, hourHeight, zoom)
+        val pinch = rememberTimelinePinchZoom(scrollState, fitHeight, hourHeight, zoom)
+        TimelineGrounds(
+            days = state.days,
+            scrollState = scrollState,
+            hourHeight = hourHeight,
+            columnGap = COLUMN_GAP,
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(end = TIMELINE_CONTENT_END_INSET)
+                .clip(RoundedCornerShape(16.dp)),
+        )
         // Scrolls on the same state as the gutter and the other pages, so they
         // all stay aligned. A static, rounded-clipped window — the content
         // scrolls inside it, so the soft corners are permanent at any scroll
@@ -1267,20 +1286,24 @@ private fun EventBlock(
     }
 }
 
+private val SKELETON_HEADER_HEIGHT = 36.dp
+private val SKELETON_HEADER_PADDING = 8.dp
+
 @Composable
 private fun WeekLoading(dayCount: Int) {
     val scale = LocalTimelineZoom.current.scale
     val scrollState = rememberScrollState()
+    val headerHeight = weekDayHeaderHeight()
     Column(modifier = Modifier.fillMaxSize()) {
         // Header skeleton
-        Row(modifier = Modifier.fillMaxWidth().padding(8.dp)) {
+        Row(modifier = Modifier.fillMaxWidth().padding(SKELETON_HEADER_PADDING)) {
             Spacer(Modifier.width(GUTTER_WIDTH))
             repeat(dayCount) {
                 Box(
                     modifier = Modifier
                         .weight(1f)
                         .padding(horizontal = 2.dp)
-                        .height(36.dp)
+                        .height(SKELETON_HEADER_HEIGHT)
                         .background(
                             MaterialTheme.colorScheme.surfaceContainer,
                             RoundedCornerShape(8.dp),
@@ -1291,7 +1314,9 @@ private fun WeekLoading(dayCount: Int) {
         BoxWithConstraints(modifier = Modifier.fillMaxSize()) {
             // Same scale resolution as the loaded timeline, so the skeleton's
             // columns don't resize the moment the real week arrives.
-            val hourHeight = scale.hourHeight(maxHeight)
+            val fitHeight = maxHeight + SKELETON_HEADER_HEIGHT + SKELETON_HEADER_PADDING * 2 -
+                headerHeight - TIMELINE_TOP_GAP
+            val hourHeight = scale.hourHeight(fitHeight)
             val totalHeight = hourHeight * 24
             // The skeleton wears the loaded columns' own ground, so the arrival
             // of the real week doesn't flash solid blocks into a gapped grid.