feat(ui): consistent motion polish, predictive back & reduced-motion support

Centralise the app's motion vocabulary in CalendarTransitions.kt and route
every surface through it so animation is consistent app-wide:

- Shared expand/collapse, list-item and fade-through helpers; the event-edit
  expand pattern is now the shared one (no duplicate).
- Settings reminder-override rows and the reminder Custom field now expand/
  collapse instead of bare-fading.
- Search and agenda rows animate (fade/relocate) via animateItem.
- Month/week/day slide and the onboarding gates honour the new helpers.
- View switching (month/week/day/agenda) now fades through instead of
  snapping — lateral navigation per M3, while in-view paging keeps its slide.

Add full predictive-back support:

- enableOnBackInvokedCallback in the manifest.
- New Modifier.predictiveBack(onBack) drives the standard preview transform
  (scale/shift/round) following the back gesture; applied to detail, edit,
  search, settings (+ sub-screens & calendar manager via CollapsingScaffold),
  the calendar editor and import — each keeping its existing back semantics.

Reduced-motion guardrail throughout: rememberReduceMotion() (reads the OS
"remove animations" setting, which Compose ignores by default) collapses
spatial motion to a quick fade and skips the back preview.

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

app/src/main/AndroidManifest.xml

@@ -39,6 +39,7 @@
     <application
         android:name=".CalendulaApp"
         android:allowBackup="true"
+        android:enableOnBackInvokedCallback="true"
         android:dataExtractionRules="@xml/data_extraction_rules"
         android:fullBackupContent="@xml/backup_rules"
         android:icon="@mipmap/ic_launcher"

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

@@ -1,6 +1,7 @@
 package de.jeanlucmakiola.calendula.ui
 
 import androidx.activity.compose.BackHandler
+import androidx.compose.animation.AnimatedContent
 import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
@@ -23,6 +24,7 @@ import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.ui.agenda.AgendaScreen
 import de.jeanlucmakiola.calendula.ui.calendars.CalendarsScreen
+import de.jeanlucmakiola.calendula.ui.common.calendarFadeThrough
 import de.jeanlucmakiola.calendula.ui.common.CalendarView
 import de.jeanlucmakiola.calendula.ui.common.drillToDay
 import de.jeanlucmakiola.calendula.ui.common.rememberCalendarSlideSpec
@@ -239,40 +241,50 @@ fun CalendarHost(
     }
 
     Box(modifier = modifier.fillMaxSize()) {
-        when (view) {
+        // Switching between the peer views (month/week/day/agenda) is lateral
-            CalendarView.Week -> WeekScreen(
+        // navigation, so it fades through rather than sliding — paging *within* a
-                selectedView = view,
+        // view keeps the directional slide. AnimatedContent keyed on the view type.
-                onSelectView = onSelectView,
+        val viewSwitch = calendarFadeThrough()
-                onEventClick = onEventClick,
+        AnimatedContent(
-                onOpenSettings = onOpenSettings,
+            targetState = view,
-                onOpenSearch = onOpenSearch,
+            transitionSpec = { viewSwitch },
-                onCreateEvent = onCreateEvent,
+            label = "view-switch",
-            )
+        ) { currentView ->
-            CalendarView.Day -> DayScreen(
+            when (currentView) {
-                selectedView = view,
+                CalendarView.Week -> WeekScreen(
-                onSelectView = onSelectView,
+                    selectedView = currentView,
-                onEventClick = onEventClick,
+                    onSelectView = onSelectView,
-                onOpenSettings = onOpenSettings,
+                    onEventClick = onEventClick,
-                onOpenSearch = onOpenSearch,
+                    onOpenSettings = onOpenSettings,
-                onCreateEvent = onCreateEvent,
+                    onOpenSearch = onOpenSearch,
-                initialDateIso = pendingDayIso,
+                    onCreateEvent = onCreateEvent,
-            )
+                )
-            CalendarView.Month -> MonthScreen(
+                CalendarView.Day -> DayScreen(
-                selectedView = view,
+                    selectedView = currentView,
-                onSelectView = onSelectView,
+                    onSelectView = onSelectView,
-                onOpenDay = onOpenDay,
+                    onEventClick = onEventClick,
-                onOpenSettings = onOpenSettings,
+                    onOpenSettings = onOpenSettings,
-                onOpenSearch = onOpenSearch,
+                    onOpenSearch = onOpenSearch,
-                onCreateEvent = onCreateEvent,
+                    onCreateEvent = onCreateEvent,
-            )
+                    initialDateIso = pendingDayIso,
-            CalendarView.Agenda -> AgendaScreen(
+                )
-                selectedView = view,
+                CalendarView.Month -> MonthScreen(
-                onSelectView = onSelectView,
+                    selectedView = currentView,
-                onEventClick = onEventClick,
+                    onSelectView = onSelectView,
-                onOpenSettings = onOpenSettings,
+                    onOpenDay = onOpenDay,
-                onOpenSearch = onOpenSearch,
+                    onOpenSettings = onOpenSettings,
-                onCreateEvent = onCreateEvent,
+                    onOpenSearch = onOpenSearch,
-            )
+                    onCreateEvent = onCreateEvent,
+                )
+                CalendarView.Agenda -> AgendaScreen(
+                    selectedView = currentView,
+                    onSelectView = onSelectView,
+                    onEventClick = onEventClick,
+                    onOpenSettings = onOpenSettings,
+                    onOpenSearch = onOpenSearch,
+                    onCreateEvent = onCreateEvent,
+                )
+            }
         }
 
         // Search overlay — below detail/edit in the Box so a tapped result's

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

@@ -2,6 +2,9 @@ package de.jeanlucmakiola.calendula.ui
 
 import android.Manifest
 import android.content.pm.PackageManager
+import androidx.compose.animation.Crossfade
+import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
+import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.mutableStateOf
@@ -20,6 +23,7 @@ import de.jeanlucmakiola.calendula.ui.permission.PermissionScreen
 import de.jeanlucmakiola.calendula.ui.permission.ReminderOnboardingScreen
 import de.jeanlucmakiola.calendula.ui.permission.ReminderOnboardingViewModel
 
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
 @Composable
 fun RootScreen(
     modifier: Modifier = Modifier,
@@ -51,32 +55,40 @@ fun RootScreen(
         onDispose { lifecycle.removeObserver(obs) }
     }
 
-    if (hasPermission) {
+    // Cross-fade the one-time onboarding gates so granting permission / finishing
-        // Second onboarding gate (v1.4, one-time): reminder notifications.
+    // onboarding eases into the next screen instead of snapping. A fade carries no
-        // Null until DataStore's first emission — render nothing for that
+    // spatial motion, so it stays appropriate under "remove animations" too.
-        // frame instead of flashing the wrong screen.
+    val gateSpec = MaterialTheme.motionScheme.fastEffectsSpec<Float>()
-        val reminderOnboarding: ReminderOnboardingViewModel = hiltViewModel()
+    Crossfade(targetState = hasPermission, animationSpec = gateSpec, label = "permissionGate") { granted ->
-        val onboardingDone by reminderOnboarding.onboardingDone.collectAsStateWithLifecycle()
+        if (granted) {
-        when (onboardingDone) {
+            // Second onboarding gate (v1.4, one-time): reminder notifications.
-            true -> CalendarHost(
+            // Null until DataStore's first emission — render nothing for that
-                modifier = modifier,
+            // frame instead of flashing the wrong screen.
-                requestedDetailKey = requestedDetailKey,
+            val reminderOnboarding: ReminderOnboardingViewModel = hiltViewModel()
-                onDetailKeyConsumed = onDetailKeyConsumed,
+            val onboardingDone by reminderOnboarding.onboardingDone.collectAsStateWithLifecycle()
-                widgetNavRequest = widgetNavRequest,
+            Crossfade(targetState = onboardingDone, animationSpec = gateSpec, label = "onboardingGate") { done ->
-                onWidgetNavConsumed = onWidgetNavConsumed,
+                when (done) {
-                requestedImportUri = requestedImportUri,
+                    true -> CalendarHost(
-                onImportConsumed = onImportConsumed,
+                        modifier = modifier,
-            )
+                        requestedDetailKey = requestedDetailKey,
-            false -> ReminderOnboardingScreen(
+                        onDetailKeyConsumed = onDetailKeyConsumed,
-                onFinished = reminderOnboarding::finish,
+                        widgetNavRequest = widgetNavRequest,
+                        onWidgetNavConsumed = onWidgetNavConsumed,
+                        requestedImportUri = requestedImportUri,
+                        onImportConsumed = onImportConsumed,
+                    )
+                    false -> ReminderOnboardingScreen(
+                        onFinished = reminderOnboarding::finish,
+                        modifier = modifier,
+                    )
+                    null -> {}
+                }
+            }
+        } else {
+            PermissionScreen(
+                onGranted = { hasPermission = true },
                 modifier = modifier,
             )
-            null -> {}
         }
-    } else {
-        PermissionScreen(
-            onGranted = { hasPermission = true },
-            modifier = modifier,
-        )
     }
 }

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

@@ -47,6 +47,7 @@ import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.EventInstance
+import de.jeanlucmakiola.calendula.ui.common.calendarAnimateItem
 import de.jeanlucmakiola.calendula.ui.common.CalendarDrawer
 import de.jeanlucmakiola.calendula.ui.common.CalendarFabColumn
 import de.jeanlucmakiola.calendula.ui.common.CalendarFailure
@@ -190,6 +191,7 @@ private fun AgendaList(
                 AgendaEventRow(
                     event = event,
                     position = positionOf(index, day.events.size),
+                    modifier = calendarAnimateItem(),
                     onClick = { onEventClick(event) },
                 )
             }
@@ -221,11 +223,13 @@ private fun AgendaDayHeader(date: LocalDate, today: LocalDate) {
 private fun AgendaEventRow(
     event: EventInstance,
     position: Position,
+    modifier: Modifier = Modifier,
     onClick: () -> Unit,
 ) {
     val dark = isSystemInDarkTheme()
     val title = event.title.ifBlank { stringResource(R.string.event_untitled) }
     GroupedRow(
+        modifier = modifier,
         title = title,
         summary = agendaTimeSummary(event),
         position = position,

app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsScreen.kt

@@ -4,7 +4,6 @@ import android.accounts.AccountManager
 import android.content.Context
 import android.content.Intent
 import android.provider.Settings
-import androidx.activity.compose.BackHandler
 import androidx.activity.compose.rememberLauncherForActivityResult
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.foundation.background
@@ -73,6 +72,7 @@ import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.ui.common.CALENDAR_COLOR_PALETTE
 import de.jeanlucmakiola.calendula.ui.common.CalendarColorChip
+import de.jeanlucmakiola.calendula.ui.common.predictiveBack
 import de.jeanlucmakiola.calendula.ui.common.CollapsingScaffold
 import de.jeanlucmakiola.calendula.ui.common.ColorSwatchRow
 import de.jeanlucmakiola.calendula.ui.common.GroupedRow
@@ -295,10 +295,9 @@ private fun CalendarEditor(
     var confirmDelete by remember { mutableStateOf(false) }
     val dark = isSystemInDarkTheme()
 
-    BackHandler(onBack = onClose)
-
     Scaffold(
         modifier = Modifier
+            .predictiveBack(onBack = onClose)
             .fillMaxSize()
             .background(MaterialTheme.colorScheme.surface),
         topBar = {

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

@@ -1,14 +1,56 @@
 package de.jeanlucmakiola.calendula.ui.common
 
+import android.provider.Settings
+import androidx.activity.BackEventCompat
+import androidx.activity.compose.PredictiveBackHandler
 import androidx.compose.animation.ContentTransform
+import androidx.compose.animation.EnterTransition
+import androidx.compose.animation.ExitTransition
+import androidx.compose.animation.core.Animatable
+import androidx.compose.animation.core.FastOutSlowInEasing
 import androidx.compose.animation.core.FiniteAnimationSpec
+import androidx.compose.animation.expandVertically
+import androidx.compose.animation.fadeIn
+import androidx.compose.animation.fadeOut
+import androidx.compose.animation.shrinkVertically
 import androidx.compose.animation.slideInHorizontally
+import androidx.compose.animation.slideInVertically
 import androidx.compose.animation.slideOutHorizontally
 import androidx.compose.animation.togetherWith
+import androidx.compose.foundation.lazy.LazyItemScope
+import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.unit.IntOffset
+import androidx.compose.ui.unit.dp
+import kotlin.coroutines.cancellation.CancellationException
+
+/**
+ * Whether the user has asked the system to remove animations (Settings →
+ * Accessibility → "Remove animations", which sets the global animator duration
+ * scale to 0). Compose animations do *not* honour this platform flag on their
+ * own, so the shared motion helpers in this file check it and fall back to a
+ * quick cross-fade — opacity only, no spatial movement — to respect the
+ * vestibular intent of the setting while keeping state changes legible.
+ *
+ * Read once at composition; the scale changes rarely and only takes full effect
+ * after a process restart anyway.
+ */
+@Composable
+fun rememberReduceMotion(): Boolean {
+    val resolver = LocalContext.current.contentResolver
+    return remember(resolver) {
+        Settings.Global.getFloat(resolver, Settings.Global.ANIMATOR_DURATION_SCALE, 1f) == 0f
+    }
+}
 
 /**
  * The M3 Expressive spatial spring used for the month/week slide: the *fast*
@@ -24,17 +66,160 @@ fun rememberCalendarSlideSpec(): FiniteAnimationSpec<IntOffset> =
     MaterialTheme.motionScheme.fastSpatialSpec()
 
 /**
- * Horizontal slide for navigating between adjacent months/weeks.
+ * The fast effects spec from the active motion scheme, for opacity (fade)
+ * transitions. Captured in composable scope alongside [rememberCalendarSlideSpec]
+ * for use in non-composable transition lambdas and as the reduced-motion fallback.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun rememberCalendarFadeSpec(): FiniteAnimationSpec<Float> =
+    MaterialTheme.motionScheme.fastEffectsSpec()
+
+/**
+ * Horizontal slide for navigating between adjacent months/weeks/days.
  *
- * @param slideDir +1 = forward (incoming from the right), -1 = back, 0 = jump
+ * @param slideDir     +1 = forward (incoming from the right), -1 = back, 0 = jump
- *                 (e.g. "today"); a jump reuses the forward direction.
+ *                     (e.g. "today"); a jump reuses the forward direction.
- * @param spec     spatial animation spec, typically [rememberCalendarSlideSpec].
+ * @param spec         spatial animation spec, typically [rememberCalendarSlideSpec].
+ * @param fadeSpec     effects spec for the reduced-motion fade, typically
+ *                     [rememberCalendarFadeSpec].
+ * @param reduceMotion when true, swap the directional slide for a plain cross-fade.
  */
 fun calendarSlideTransition(
     slideDir: Int,
     spec: FiniteAnimationSpec<IntOffset>,
+    fadeSpec: FiniteAnimationSpec<Float>,
+    reduceMotion: Boolean,
 ): ContentTransform {
+    if (reduceMotion) {
+        return fadeIn(fadeSpec).togetherWith(fadeOut(fadeSpec))
+    }
     val dir = if (slideDir == 0) 1 else slideDir
     return slideInHorizontally(spec) { w -> dir * w }
         .togetherWith(slideOutHorizontally(spec) { w -> -dir * w })
 }
+
+/**
+ * Cross-fade [ContentTransform] for swapping whole screens or content blocks
+ * where there is no meaningful spatial direction (e.g. onboarding gates). Pure
+ * opacity, so it doubles as its own reduced-motion form.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun calendarFadeThrough(): ContentTransform {
+    val fade = MaterialTheme.motionScheme.fastEffectsSpec<Float>()
+    return fadeIn(fade).togetherWith(fadeOut(fade))
+}
+
+/**
+ * Enter transition for a vertically-revealed section (expandable rows, inline
+ * fields): height grows from the top while fading in. Under reduced motion the
+ * height growth is dropped, leaving a quick fade.
+ *
+ * Pair with [calendarCollapseExit]. This is the promoted form of the pattern
+ * originally inlined in the event edit form, so every expandable surface in the
+ * app reveals the same way.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun calendarExpandEnter(reduceMotion: Boolean = rememberReduceMotion()): EnterTransition {
+    val fade = fadeIn(MaterialTheme.motionScheme.fastEffectsSpec())
+    return if (reduceMotion) {
+        fade
+    } else {
+        expandVertically(MaterialTheme.motionScheme.fastSpatialSpec()) + fade
+    }
+}
+
+/** Exit counterpart to [calendarExpandEnter]: shrink + fade, or fade only under reduced motion. */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun calendarCollapseExit(reduceMotion: Boolean = rememberReduceMotion()): ExitTransition {
+    val fade = fadeOut(MaterialTheme.motionScheme.fastEffectsSpec())
+    return if (reduceMotion) {
+        fade
+    } else {
+        shrinkVertically(MaterialTheme.motionScheme.fastSpatialSpec()) + fade
+    }
+}
+
+/**
+ * Enter transition for content revealed by an `AnimatedContent`/`AnimatedVisibility`
+ * (e.g. search results once a query resolves): a gentle rise + fade. Reduced
+ * motion keeps the fade only.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun calendarItemEnter(reduceMotion: Boolean = rememberReduceMotion()): EnterTransition {
+    val fade = fadeIn(MaterialTheme.motionScheme.fastEffectsSpec())
+    return if (reduceMotion) {
+        fade
+    } else {
+        fade + slideInVertically(MaterialTheme.motionScheme.fastSpatialSpec()) { h -> h / 6 }
+    }
+}
+
+/**
+ * Shared [LazyItemScope.animateItem] wiring so list rows fade/relocate with the
+ * app's motion scheme instead of Compose's default spring. Returns a bare
+ * [Modifier] under reduced motion so rows snap into place. Requires the list to
+ * supply stable item keys.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun LazyItemScope.calendarAnimateItem(reduceMotion: Boolean = rememberReduceMotion()): Modifier =
+    if (reduceMotion) {
+        Modifier
+    } else {
+        Modifier.animateItem(
+            fadeInSpec = MaterialTheme.motionScheme.fastEffectsSpec(),
+            placementSpec = MaterialTheme.motionScheme.fastSpatialSpec(),
+            fadeOutSpec = MaterialTheme.motionScheme.fastEffectsSpec(),
+        )
+    }
+
+/**
+ * Standard Android predictive-back transform for a full-screen overlay: as the
+ * back gesture is dragged, the surface scales toward ~90%, shifts toward the
+ * swiped edge and rounds its corners, previewing what's behind. Completing the
+ * gesture invokes [onBack]; cancelling springs it back.
+ *
+ * A drop-in replacement for a screen's own `BackHandler(onBack)` — register it
+ * once and apply the returned [Modifier] to that screen's root so the preview
+ * respects the same back semantics. Under reduced motion the visual preview is
+ * skipped (the back still works); on API < 34 the system delivers no progress,
+ * so it degrades to a plain back.
+ */
+@Composable
+fun Modifier.predictiveBack(
+    onBack: () -> Unit,
+    enabled: Boolean = true,
+    reduceMotion: Boolean = rememberReduceMotion(),
+): Modifier {
+    val progress = remember { Animatable(0f) }
+    var fromLeftEdge by remember { mutableStateOf(true) }
+
+    PredictiveBackHandler(enabled = enabled) { events ->
+        try {
+            events.collect { event ->
+                fromLeftEdge = event.swipeEdge == BackEventCompat.EDGE_LEFT
+                progress.snapTo(FastOutSlowInEasing.transform(event.progress))
+            }
+            onBack()
+            progress.snapTo(0f)
+        } catch (_: CancellationException) {
+            progress.animateTo(0f)
+        }
+    }
+
+    if (reduceMotion) return this
+    return this.graphicsLayer {
+        val p = progress.value
+        val scale = 1f - 0.1f * p
+        scaleX = scale
+        scaleY = scale
+        translationX = (if (fromLeftEdge) 1f else -1f) * 24.dp.toPx() * p
+        shape = RoundedCornerShape(32.dp.toPx() * p)
+        clip = p > 0f
+    }
+}

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

@@ -1,6 +1,5 @@
 package de.jeanlucmakiola.calendula.ui.common
 
-import androidx.activity.compose.BackHandler
 import androidx.compose.animation.core.animateDpAsState
 import androidx.compose.foundation.background
 import androidx.compose.foundation.interaction.MutableInteractionSource
@@ -73,11 +72,11 @@ fun CollapsingScaffold(
     actions: @Composable RowScope.() -> Unit = {},
     content: @Composable ColumnScope.() -> Unit,
 ) {
-    BackHandler(onBack = onBack)
     val scrollBehavior =
         TopAppBarDefaults.exitUntilCollapsedScrollBehavior(rememberTopAppBarState())
     Scaffold(
         modifier = modifier
+            .predictiveBack(onBack = onBack)
             .fillMaxSize()
             .background(MaterialTheme.colorScheme.surface)
             .nestedScroll(scrollBehavior.nestedScrollConnection),

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

@@ -173,7 +173,11 @@ fun ReminderDefaultPicker(
             },
             onClick = { customExpanded = !customExpanded },
         )
-        AnimatedVisibility(visible = customExpanded) {
+        AnimatedVisibility(
+            visible = customExpanded,
+            enter = calendarExpandEnter(),
+            exit = calendarCollapseExit(),
+        ) {
             CustomReminderEditor(
                 amountText = amountText,
                 onAmountChange = { amountText = it },

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

@@ -75,6 +75,8 @@ import de.jeanlucmakiola.calendula.ui.common.CalendarView
 import de.jeanlucmakiola.calendula.ui.common.NowLine
 import de.jeanlucmakiola.calendula.ui.common.ViewSwitcherPill
 import de.jeanlucmakiola.calendula.ui.common.calendarSlideTransition
+import de.jeanlucmakiola.calendula.ui.common.rememberCalendarFadeSpec
+import de.jeanlucmakiola.calendula.ui.common.rememberReduceMotion
 import de.jeanlucmakiola.calendula.ui.common.next
 import de.jeanlucmakiola.calendula.ui.common.pastelize
 import de.jeanlucmakiola.calendula.ui.common.rememberCalendarSlideSpec
@@ -237,6 +239,8 @@ private fun DayContent(
     val threshold = with(density) { 24.dp.toPx() }
     var dragAccum by remember { mutableFloatStateOf(0f) }
     val slideSpec = rememberCalendarSlideSpec()
+    val fadeSpec = rememberCalendarFadeSpec()
+    val reduceMotion = rememberReduceMotion()
 
     // Hoisted above the per-day AnimatedContent so the vertical scroll position
     // survives day-to-day swipes. We only centre on noon once, on first entry
@@ -287,7 +291,7 @@ private fun DayContent(
                 DayUiState.Loading -> "loading"
             }
         },
-        transitionSpec = { calendarSlideTransition(slideDir, slideSpec) },
+        transitionSpec = { calendarSlideTransition(slideDir, slideSpec, fadeSpec, reduceMotion) },
         label = "day-transition",
     ) { s ->
         when (s) {

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

@@ -6,7 +6,6 @@ import android.content.Context
 import android.content.Intent
 import android.content.pm.PackageManager
 import android.net.Uri
-import androidx.activity.compose.BackHandler
 import androidx.activity.compose.rememberLauncherForActivityResult
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.foundation.background
@@ -92,6 +91,7 @@ import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.EventStatus
 import de.jeanlucmakiola.calendula.domain.RecurringWriteScope
 import de.jeanlucmakiola.calendula.domain.Reminder
+import de.jeanlucmakiola.calendula.ui.common.predictiveBack
 import de.jeanlucmakiola.calendula.ui.common.CalendarFailure
 import de.jeanlucmakiola.calendula.ui.common.OptionCard
 import de.jeanlucmakiola.calendula.ui.common.currentLocale
@@ -132,8 +132,6 @@ fun EventDetailScreen(
     val state by viewModel.state.collectAsStateWithLifecycle()
     val deleteState by viewModel.deleteState.collectAsStateWithLifecycle()
 
-    BackHandler(onBack = onBack)
-
     val context = LocalContext.current
     val scope = rememberCoroutineScope()
     val snackbarHostState = remember { SnackbarHostState() }
@@ -214,6 +212,7 @@ fun EventDetailScreen(
     }
 
     Scaffold(
+        modifier = Modifier.predictiveBack(onBack = onBack),
         snackbarHost = { SnackbarHost(snackbarHostState) },
         topBar = {
             TopAppBar(

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

@@ -8,14 +8,9 @@ import android.content.pm.PackageManager
 import android.net.Uri
 import android.provider.ContactsContract
 import android.util.Patterns
-import androidx.activity.compose.BackHandler
 import androidx.activity.compose.rememberLauncherForActivityResult
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.animation.AnimatedVisibility
-import androidx.compose.animation.expandVertically
-import androidx.compose.animation.fadeIn
-import androidx.compose.animation.fadeOut
-import androidx.compose.animation.shrinkVertically
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.isSystemInDarkTheme
@@ -63,7 +58,6 @@ import androidx.compose.material3.DropdownMenu
 import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.FilterChip
-import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
@@ -121,6 +115,9 @@ import de.jeanlucmakiola.calendula.domain.RecurringWriteScope
 import de.jeanlucmakiola.calendula.domain.SimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.parseSimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.toRRule
+import de.jeanlucmakiola.calendula.ui.common.calendarCollapseExit
+import de.jeanlucmakiola.calendula.ui.common.calendarExpandEnter
+import de.jeanlucmakiola.calendula.ui.common.predictiveBack
 import de.jeanlucmakiola.calendula.ui.common.CALENDAR_COLOR_PALETTE
 import de.jeanlucmakiola.calendula.ui.common.CalendarDatePickerDialog
 import de.jeanlucmakiola.calendula.ui.common.ColorSwatchRow
@@ -202,8 +199,6 @@ fun EventEditScreen(
         viewModel.reset()
         onClose()
     }
-    BackHandler(onBack = close)
-
     // The event vanished between the detail screen and the edit tap — fall
     // back to the detail screen, which shows its own failure state.
     LaunchedEffect(loadFailed) {
@@ -253,6 +248,7 @@ fun EventEditScreen(
     }
 
     Scaffold(
+        modifier = Modifier.predictiveBack(onBack = close),
         snackbarHost = { SnackbarHost(snackbarHostState) },
         topBar = {
             TopAppBar(
@@ -410,7 +406,6 @@ private enum class PickerTarget { StartDate, StartTime, EndDate, EndTime }
  * spring open with the expressive spatial spec instead of popping in.
  * (Initially-visible sections render without animating.)
  */
-@OptIn(ExperimentalMaterial3ExpressiveApi::class)
 @Composable
 private fun OptionalFormSection(
     visible: Boolean,
@@ -418,10 +413,8 @@ private fun OptionalFormSection(
 ) {
     AnimatedVisibility(
         visible = visible,
-        enter = expandVertically(MaterialTheme.motionScheme.fastSpatialSpec()) +
+        enter = calendarExpandEnter(),
-            fadeIn(MaterialTheme.motionScheme.fastEffectsSpec()),
+        exit = calendarCollapseExit(),
-        exit = shrinkVertically(MaterialTheme.motionScheme.fastSpatialSpec()) +
-            fadeOut(MaterialTheme.motionScheme.fastEffectsSpec()),
     ) {
         Column(modifier = Modifier.fillMaxWidth(), content = content)
     }

app/src/main/java/de/jeanlucmakiola/calendula/ui/imports/ImportScreen.kt

@@ -1,7 +1,6 @@
 package de.jeanlucmakiola.calendula.ui.imports
 
 import android.net.Uri
-import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -39,6 +38,7 @@ import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.ics.IcsParseWarning
+import de.jeanlucmakiola.calendula.ui.common.predictiveBack
 import de.jeanlucmakiola.calendula.ui.common.OptionCard
 
 /**
@@ -57,7 +57,6 @@ fun ImportScreen(
 ) {
     LaunchedEffect(uri) { viewModel.load(uri) }
     val state by viewModel.state.collectAsStateWithLifecycle()
-    BackHandler(onBack = onClose)
 
     // A single event isn't shown here — it opens the create form for review.
     LaunchedEffect(state) {
@@ -65,7 +64,9 @@ fun ImportScreen(
     }
 
     Scaffold(
-        modifier = Modifier.fillMaxSize(),
+        modifier = Modifier
+            .predictiveBack(onBack = onClose)
+            .fillMaxSize(),
         topBar = {
             TopAppBar(
                 title = { Text(stringResource(R.string.import_title)) },

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

@@ -66,6 +66,8 @@ import de.jeanlucmakiola.calendula.ui.common.CalendarFailure
 import de.jeanlucmakiola.calendula.ui.common.CalendarView
 import de.jeanlucmakiola.calendula.ui.common.ViewSwitcherPill
 import de.jeanlucmakiola.calendula.ui.common.calendarSlideTransition
+import de.jeanlucmakiola.calendula.ui.common.rememberCalendarFadeSpec
+import de.jeanlucmakiola.calendula.ui.common.rememberReduceMotion
 import de.jeanlucmakiola.calendula.ui.common.currentLocale
 import de.jeanlucmakiola.calendula.ui.common.rememberCalendarSlideSpec
 import de.jeanlucmakiola.calendula.ui.common.next
@@ -217,6 +219,8 @@ private fun MonthContent(
     val threshold = with(density) { 6.dp.toPx() }
     var dragAccum by remember { mutableFloatStateOf(0f) }
     val slideSpec = rememberCalendarSlideSpec()
+    val fadeSpec = rememberCalendarFadeSpec()
+    val reduceMotion = rememberReduceMotion()
 
     val swipeModifier = Modifier.pointerInput(Unit) {
         detectHorizontalDragGestures(
@@ -243,7 +247,7 @@ private fun MonthContent(
                 MonthUiState.Loading -> "loading"
             }
         },
-        transitionSpec = { calendarSlideTransition(slideDir, slideSpec) },
+        transitionSpec = { calendarSlideTransition(slideDir, slideSpec, fadeSpec, reduceMotion) },
         label = "month-transition",
     ) { s ->
         when (s) {

app/src/main/java/de/jeanlucmakiola/calendula/ui/search/SearchScreen.kt

@@ -1,6 +1,5 @@
 package de.jeanlucmakiola.calendula.ui.search
 
-import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.background
 import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.foundation.layout.Arrangement
@@ -49,6 +48,8 @@ import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.EventInstance
+import de.jeanlucmakiola.calendula.ui.common.calendarAnimateItem
+import de.jeanlucmakiola.calendula.ui.common.predictiveBack
 import de.jeanlucmakiola.calendula.ui.common.GroupedRow
 import de.jeanlucmakiola.calendula.ui.common.InlineTextField
 import de.jeanlucmakiola.calendula.ui.common.Position
@@ -88,10 +89,8 @@ fun SearchScreen(
         focusRequester.requestFocus()
         keyboard?.show()
     }
-    BackHandler(onBack = onBack)
-
     Scaffold(
-        modifier = modifier,
+        modifier = modifier.predictiveBack(onBack = onBack),
         containerColor = MaterialTheme.colorScheme.surface,
         topBar = {
             TopAppBar(
@@ -174,6 +173,7 @@ private fun SearchResults(
             SearchResultRow(
                 event = event,
                 position = positionOf(index, events.size),
+                modifier = calendarAnimateItem(),
                 onClick = { onEventClick(event) },
             )
         }
@@ -184,10 +184,12 @@ private fun SearchResults(
 private fun SearchResultRow(
     event: EventInstance,
     position: Position,
+    modifier: Modifier = Modifier,
     onClick: () -> Unit,
 ) {
     val dark = isSystemInDarkTheme()
     GroupedRow(
+        modifier = modifier,
         title = event.title,
         summary = searchSummary(event),
         position = position,

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

@@ -88,6 +88,8 @@ import de.jeanlucmakiola.calendula.qs.NewEventTileService
 import de.jeanlucmakiola.calendula.ui.crash.CrashReportDialog
 import de.jeanlucmakiola.calendula.ui.crash.openIssueTracker
 import de.jeanlucmakiola.calendula.ui.crash.submitCrashReport
+import de.jeanlucmakiola.calendula.ui.common.calendarCollapseExit
+import de.jeanlucmakiola.calendula.ui.common.calendarExpandEnter
 import de.jeanlucmakiola.calendula.ui.common.CollapsingScaffold
 import de.jeanlucmakiola.calendula.ui.common.GroupedRow
 import de.jeanlucmakiola.calendula.ui.common.IMPLEMENTED_VIEWS
@@ -674,7 +676,11 @@ private fun NotificationsScreen(
                         }
                     },
                 )
-                AnimatedVisibility(visible = expanded) {
+                AnimatedVisibility(
+                    visible = expanded,
+                    enter = calendarExpandEnter(),
+                    exit = calendarCollapseExit(),
+                ) {
                     Column {
                         val timed = state.perCalendarReminderOverride.choiceFor(calendar.id)
                         GroupedRow(

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

@@ -80,6 +80,8 @@ import de.jeanlucmakiola.calendula.ui.common.CalendarView
 import de.jeanlucmakiola.calendula.ui.common.NowLine
 import de.jeanlucmakiola.calendula.ui.common.ViewSwitcherPill
 import de.jeanlucmakiola.calendula.ui.common.calendarSlideTransition
+import de.jeanlucmakiola.calendula.ui.common.rememberCalendarFadeSpec
+import de.jeanlucmakiola.calendula.ui.common.rememberReduceMotion
 import de.jeanlucmakiola.calendula.ui.common.currentLocale
 import de.jeanlucmakiola.calendula.ui.common.rememberCalendarSlideSpec
 import de.jeanlucmakiola.calendula.ui.common.next
@@ -247,6 +249,8 @@ private fun WeekContent(
     val threshold = with(density) { 24.dp.toPx() }
     var dragAccum by remember { mutableFloatStateOf(0f) }
     val slideSpec = rememberCalendarSlideSpec()
+    val fadeSpec = rememberCalendarFadeSpec()
+    val reduceMotion = rememberReduceMotion()
 
     // Hoisted above the per-week AnimatedContent so the vertical scroll position
     // survives week-to-week swipes (e.g. 18:00 stays centred). We only centre on
@@ -300,7 +304,7 @@ private fun WeekContent(
                 WeekUiState.Loading -> "loading"
             }
         },
-        transitionSpec = { calendarSlideTransition(slideDir, slideSpec) },
+        transitionSpec = { calendarSlideTransition(slideDir, slideSpec, fadeSpec, reduceMotion) },
         label = "week-transition",
     ) { s ->
         when (s) {