fix(map): restore live layer data and small-screen layouts

lib/core/build/demo_flags.dart

@@ -15,13 +15,28 @@ const String _monitorDemoRaw = String.fromEnvironment('DPIP_DEMO_MONITOR');
 const String _monitorDemoSevereRaw = String.fromEnvironment(
   'DPIP_DEMO_MONITOR_SEVERE',
 );
+const String _startupEewDemoRaw = String.fromEnvironment(
+  'DPIP_DEMO_STARTUP_EEW',
+);
 
 /// Whether the 強震監視器 demo feeds are on: debug builds launched with
 /// `--dart-define=DPIP_DEMO_MONITOR=true` (or `=1`). The flag is forced off
 /// outside [kDebugMode] so a release build can never ship the synthetic feeds.
 const bool kMonitorDemoEnabled =
     (_monitorDemoRaw == 'true' || _monitorDemoRaw == '1') && kDebugMode;
 
+/// Temporary startup-only EEW used for visual testing with
+/// `--dart-define=DPIP_DEMO_STARTUP_EEW=true` (or `=1`). It is deliberately
+/// impossible in release builds and yields to the explicit full monitor demo
+/// above.
+///
+/// Remove this flag and the corresponding provider branch when the startup
+/// alert test is finished.
+const bool kStartupEewDemoEnabled =
+    (_startupEewDemoRaw == 'true' || _startupEewDemoRaw == '1') &&
+    kDebugMode &&
+    !kMonitorDemoEnabled;
+
 /// Whether the demo event uses a fixed, severe preset (large magnitude,
 /// shallow depth) instead of the newest real report —
 /// `--dart-define=DPIP_DEMO_MONITOR_SEVERE=true` (or `=1`), alongside

lib/features/changelog/presentation/widgets/update_prompt.dart

@@ -16,6 +16,7 @@ import 'package:dpip/core/version/app_build.dart';
 import 'package:dpip/core/platform/install_source.dart';
 import 'package:dpip/core/settings/setting_keys.dart';
 import 'package:dpip/core/settings/settings_store.dart';
+import 'package:dpip/app/theme/app_spacing.dart';
 import 'package:dpip/features/changelog/domain/changelog_repository.dart';
 import 'package:dpip/features/changelog/domain/release_note.dart';
 import 'package:dpip/features/changelog/domain/update_check.dart';
@@ -102,18 +103,38 @@ class _UpdatePromptState extends State<UpdatePrompt> {
         icon: const Icon(Icons.system_update_outlined),
         title: Text(l10n.updateAvailableTitle),
         content: Text(l10n.updateAvailableBody(version)),
+        // A regular AlertDialog OverflowBar stacks these three buttons at the
+        // trailing edge on a phone, making them look detached from each other.
+        // Keep the two alternatives together and give the primary destination
+        // a stable, full-width row at every supported phone width.
         actions: [
-          TextButton(
-            onPressed: () => Navigator.pop(context, _UpdateAction.skip),
-            child: Text(l10n.updateSkip),
-          ),
-          TextButton(
-            onPressed: () => Navigator.pop(context, _UpdateAction.changelog),
-            child: Text(l10n.updateViewChangelog),
-          ),
-          FilledButton(
-            onPressed: () => Navigator.pop(context, _UpdateAction.update),
-            child: Text(_updateLabel(l10n, source)),
+          Column(
+            crossAxisAlignment: CrossAxisAlignment.stretch,
+            children: [
+              Row(
+                children: [
+                  Expanded(
+                    child: TextButton(
+                      onPressed: () =>
+                          Navigator.pop(context, _UpdateAction.skip),
+                      child: Text(l10n.updateSkip),
+                    ),
+                  ),
+                  Expanded(
+                    child: TextButton(
+                      onPressed: () =>
+                          Navigator.pop(context, _UpdateAction.changelog),
+                      child: Text(l10n.updateViewChangelog),
+                    ),
+                  ),
+                ],
+              ),
+              const SizedBox(height: AppSpacing.sm),
+              FilledButton(
+                onPressed: () => Navigator.pop(context, _UpdateAction.update),
+                child: Text(_updateLabel(l10n, source)),
+              ),
+            ],
           ),
         ],
       ),

lib/features/earthquake/data/monitor_demo.dart

@@ -114,6 +114,52 @@ abstract final class MonitorDemo {
   static DateTime? _origin;
 }
 
+/// A single, stable EEW inserted on debug startup for visual testing.
+///
+/// [RealtimeChannel] continues polling at its normal safety-critical cadence,
+/// but every fetch returns this same immutable alert. Its collection equality
+/// therefore suppresses every later poll and consumers observe exactly one
+/// alert rather than a new serial every second.
+class StartupEewDemoSource extends RealtimeSource<List<Eew>> {
+  StartupEewDemoSource({DateTime Function()? clock})
+    : _alerts = [
+        Eew(
+          agency: 'DEMO',
+          id: 'startup-demo',
+          serial: 1,
+          status: 0,
+          isFinal: false,
+          info: EewInfo(
+            time: (clock ?? DateTime.now)().toUtc().millisecondsSinceEpoch,
+            longitude: 121.7,
+            latitude: 23.9,
+            depth: 10,
+            magnitude: 6.5,
+            location: '花蓮縣近海',
+            max: 7,
+          ),
+        ),
+      ];
+
+  final List<Eew> _alerts;
+
+  @override
+  Future<Result<List<Eew>>> fetch() async => Ok(_alerts);
+
+  @override
+  DateTime? timestampOf(List<Eew> value) => null;
+
+  @override
+  bool sameData(List<Eew>? a, List<Eew>? b) {
+    if (a == null || b == null) return a == b;
+    if (a.length != b.length) return false;
+    for (var i = 0; i < a.length; i++) {
+      if (a[i] != b[i]) return false;
+    }
+    return true;
+  }
+}
+
 /// Polls as an always-live EEW alert for [MonitorDemo]'s event, bumping the
 /// serial every couple of seconds so the feed visibly updates and the monitor
 /// cards re-render while the wavefront keeps expanding.

lib/features/earthquake/earthquake_providers.dart

@@ -56,6 +56,8 @@ List<SingleChildWidget> earthquakeProviders(SharedDeps deps) {
   // without waiting for a live event.
   final eewSource = kMonitorDemoEnabled
       ? DemoEewSource(reports) as RealtimeSource<List<Eew>>
+      : kStartupEewDemoEnabled
+      ? StartupEewDemoSource() as RealtimeSource<List<Eew>>
       : EewRealtimeSource(api.openEewSse, cwaOnly: () => eewCwaOnly.enabled)
             as RealtimeSource<List<Eew>>;
   final eewChannel = RealtimeChannel<List<Eew>>(

lib/features/home/presentation/widgets/home_content.dart

@@ -164,6 +164,12 @@ class HomeContent extends StatelessWidget {
   /// distance.
   static const double _forecastExpandExtent = 200;
 
+  /// Minimum room for the header + the hero's bottom weather card. A short
+  /// phone can provide less than this after the region-bar inset; making that
+  /// extra height part of the outer list keeps both the loading/rain card and
+  /// the fully expanded dry forecast scrollable instead of clipping them.
+  static const double _minimumWeatherHeroHeight = 760;
+
   /// Current growth of the hero forecast card for [offset].
   static double _forecastExpansion(double offset) =>
       (offset / _forecastExpandExtent).clamp(0.0, 1.0);
@@ -260,6 +266,12 @@ class HomeContent extends StatelessWidget {
                   // sky-tuned ink is exactly what makes scrolled content hard
                   // to read, no matter how dimmed the backdrop behind it is.
                   final reveal = this.reveal * (1 - _focus(offset));
+                  final forecastExpansion = _forecastExpansion(offset);
+                  final heroLayoutHeight = heroHeight == null
+                      ? null
+                      : heroHeight < _minimumWeatherHeroHeight
+                      ? _minimumWeatherHeroHeight
+                      : heroHeight;
                   return Column(
                     key: ValueKey(areaIndex),
                     crossAxisAlignment: CrossAxisAlignment.stretch,
@@ -274,7 +286,7 @@ class HomeContent extends StatelessWidget {
                       // changes shape, so it never needs to be torn down and
                       // rebuilt when the sheet opens or closes.
                       SizedBox(
-                        height: heroHeight,
+                        height: heroLayoutHeight,
                         // Only the trailing gap depends on scroll offset, so
                         // that is all this block's Padding re-reads per tick.
                         child: Padding(
@@ -340,7 +352,7 @@ class HomeContent extends StatelessWidget {
                                     opacity: reveal,
                                     child: HomeForecastSection(
                                       key: ValueKey('forecast-hero-$areaIndex'),
-                                      expansion: _forecastExpansion(offset),
+                                      expansion: forecastExpansion,
                                       reveal: reveal,
                                       sky: sky,
                                       weatherMode: weatherMode,

lib/shared/map/map_layer.dart

@@ -254,6 +254,22 @@ abstract interface class MapLayer {
   void onStyleReset();
 }
 
+/// Transfers the hosting surface's visibility when its active layer changes.
+///
+/// Inactive realtime layers may retain `visible = false` from an earlier tab
+/// switch. Merely calling [MapLayer.render] when selecting one again does not
+/// repair that state, so its guarded map pushes remain disabled even though the
+/// user is looking at it. Every selection therefore hides the outgoing layer
+/// and explicitly gives the incoming one the surface's current visibility.
+void handoffMapLayerVisibility({
+  required MapLayer previous,
+  required MapLayer next,
+  required bool surfaceVisible,
+}) {
+  previous.onSurfaceVisibility(false);
+  next.onSurfaceVisibility(surfaceVisible);
+}
+
 /// No-op bodies for the [MapLayer] members a given layer type doesn't use.
 ///
 /// Timeline layers (radar, satellite, QPESUMS) draw nothing in [MapLayer.render]

lib/shared/map/map_scaffold.dart

@@ -1142,6 +1142,16 @@ class _MapScaffoldState extends State<MapScaffold> with WidgetsBindingObserver {
     if (layer.id == _active.id) return;
     final controller = _controller;
     final previous = _active;
+    // A layer can have retained `visible = false` since it was active when the
+    // map tab was hidden. Rendering it again is not enough: realtime layers
+    // gate their source updates on that flag, leaving their freshly-created
+    // sources empty. Transfer visibility on every selection so switching back
+    // to the monitor immediately replays the current EEW snapshot.
+    handoffMapLayerVisibility(
+      previous: previous,
+      next: layer,
+      surfaceVisible: _isVisible,
+    );
     // Invalidate in-flight loads/renders of the previous layer.
     _generation++;
     setState(() {

test/features/changelog/update_prompt_test.dart

@@ -137,6 +137,26 @@ void main() {
     expect(find.text('App Store'), findsOneWidget);
   });
 
+  testWidgets('keeps phone-width actions in two intentional rows', (
+    tester,
+  ) async {
+    tester.view.physicalSize = const Size(371, 667);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+
+    await _pump(tester, version: '3.2.0');
+
+    final skip = tester.getRect(find.text('Skip this one'));
+    final changes = tester.getRect(find.text('View changes'));
+    final store = tester.getRect(
+      find.widgetWithText(FilledButton, 'App Store'),
+    );
+    expect(skip.center.dy, changes.center.dy);
+    expect(store.top, greaterThan(skip.bottom));
+    expect(store.width, greaterThan(skip.width + changes.width));
+  });
+
   testWidgets('a TestFlight build is sent to TestFlight', (tester) async {
     await _pump(
       tester,

test/features/earthquake/startup_eew_demo_test.dart

@@ -0,0 +1,19 @@
+import 'package:dpip/features/earthquake/data/monitor_demo.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  test('startup demo always exposes the same single EEW', () async {
+    final source = StartupEewDemoSource(
+      clock: () => DateTime.utc(2026, 8, 28, 10),
+    );
+
+    final first = (await source.fetch()).valueOrNull!;
+    final second = (await source.fetch()).valueOrNull!;
+
+    expect(first, hasLength(1));
+    expect(first.single.id, 'startup-demo');
+    expect(first.single.serial, 1);
+    expect(second, hasLength(1));
+    expect(source.sameData(first, second), isTrue);
+  });
+}

test/features/home/presentation/widgets/home_content_test.dart

@@ -36,13 +36,17 @@ import 'package:provider/provider.dart';
 /// Stub weather: home content resolves no towns from an empty directory, so
 /// neither endpoint is invoked in the switch tests.
 class _FakeWeatherRepository implements MeteorWeatherRepository {
+  const _FakeWeatherRepository({this.forecastValue});
+
+  final WeatherForecast? forecastValue;
+
   @override
   Future<Result<WeatherRealtime?>> realtime(double lat, double lng) async =>
       const Ok(null);
 
   @override
   Future<Result<WeatherForecast>> forecast(String code) async =>
-      Ok(WeatherForecast(updateTime: 0, forecast: const []));
+      Ok(forecastValue ?? WeatherForecast(updateTime: 0, forecast: const []));
 
   @override
   dynamic noSuchMethod(Invocation invocation) => throw UnimplementedError();
@@ -115,7 +119,9 @@ class _StaticEewSource extends RealtimeSource<List<Eew>> {
 Widget _wrap(
   RegionStore store, {
   bool expanded = false,
+  double topInset = 0,
   RainHourTrendRepository? hourTrend,
+  WeatherForecast? forecast,
   TownDirectory directory = const TownDirectory(<String, Town>{}),
 }) {
   final events = _FakeEventRepository();
@@ -130,7 +136,7 @@ Widget _wrap(
         Provider<EventRepository>.value(value: events),
         ChangeNotifierProvider<HomeWeatherController>(
           create: (_) => HomeWeatherController(
-            _FakeWeatherRepository(),
+            _FakeWeatherRepository(forecastValue: forecast),
             hourTrend ?? _FakeHourTrendRepository(),
             store,
             directory,
@@ -156,6 +162,7 @@ Widget _wrap(
         body: HomeContent(
           scrollController: ScrollController(),
           expanded: expanded,
+          topInset: topInset,
         ),
       ),
     ),
@@ -397,6 +404,68 @@ void main() {
     },
   );
 
+  testWidgets('a short phone can scroll to the full forecast detail band', (
+    tester,
+  ) async {
+    tester.view.physicalSize = const Size(320, 568);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+
+    final store = await _store();
+    store
+      ..select(1)
+      ..setCurrentCode('100');
+    const directory = TownDirectory({
+      '100': Town(
+        code: '100',
+        city: 'Test',
+        town: 'North',
+        lat: 25.0,
+        lng: 121.5,
+        cityLevel: 'City',
+        townLevel: 'District',
+      ),
+    });
+    const point = WeatherForecastPoint(
+      time: '14:00',
+      temperature: 30,
+      apparentTemp: 33,
+      humidity: 70,
+      weather: 'Clear',
+      weatherCode: 100,
+      pop: 0,
+      wind: ForecastWind(direction: 'NE', speed: 2, beaufort: 2),
+    );
+    await tester.pumpWidget(
+      _wrap(
+        store,
+        expanded: true,
+        topInset: 88,
+        hourTrend: _FakeHourTrendRepository(dry: true),
+        forecast: const WeatherForecast(
+          updateTime: 0,
+          forecast: [point, point, point],
+        ),
+        directory: directory,
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(tester.takeException(), isNull, reason: 'initial short layout');
+
+    final details = find.text('Feels like 33°');
+    await tester.scrollUntilVisible(
+      details,
+      120,
+      scrollable: find.byType(Scrollable).first,
+    );
+    await tester.pumpAndSettle();
+
+    expect(details, findsOneWidget);
+    expect(details.hitTestable(), findsOneWidget);
+    expect(tester.takeException(), isNull);
+  });
+
   testWidgets('全國 keeps its events card (it is not a missing location)', (
     tester,
   ) async {