fix(navigation): slide departing chat routes across the full viewport

lib/app/app_navigator.dart

@@ -199,15 +199,27 @@ class AppChatPageRoute<T> extends PageRoute<T>
     if (AppMotion.isReduced(context) && !_fullPageBackSwipeActive) {
       return child;
     }
-    final leaving = _fullPageBackSwipeActive;
+    final leaving =
+        _fullPageBackSwipeActive ||
+        animation.status == AnimationStatus.reverse ||
+        animation.status == AnimationStatus.dismissed;
     if (leaving) {
       final effectiveAnimation = popGestureInProgress
           ? animation
           : CurvedAnimation(
               parent: animation,
               curve: AppMotion.standard,
-              reverseCurve: AppMotion.accelerate,
+              reverseCurve: AppMotion.standard.flipped,
             );
+      final slide = SlideTransition(
+        position: Tween<Offset>(
+          begin: const Offset(1, 0),
+          end: Offset.zero,
+        ).animate(effectiveAnimation),
+        transformHitTests: false,
+        child: child,
+      );
+      if (!_fullPageBackSwipeActive) return slide;
       return Stack(
         fit: StackFit.expand,
         children: [
@@ -220,14 +232,7 @@ class AppChatPageRoute<T> extends PageRoute<T>
               child: ColoredBox(color: Color(0xFF000000)),
             ),
           ),
-          SlideTransition(
-            position: Tween<Offset>(
-              begin: const Offset(1, 0),
-              end: Offset.zero,
-            ).animate(effectiveAnimation),
-            transformHitTests: false,
-            child: child,
-          ),
+          slide,
         ],
       );
     }

test/full_page_back_swipe_test.dart

@@ -392,7 +392,7 @@ void main() {
     expect(tester.takeException(), isNull);
   });
 
-  testWidgets('ordinary pop keeps the compact non-interactive transition', (
+  testWidgets('ordinary pop slides the conversation across the full viewport', (
     tester,
   ) async {
     final harness = await _pumpRouteHarness(tester);
@@ -402,8 +402,14 @@ void main() {
     await tester.pump(const Duration(milliseconds: 90));
 
     final chatLeft = tester.getTopLeft(find.byKey(_chatKey)).dx;
-    expect(chatLeft, greaterThan(0));
-    expect(chatLeft, lessThan(30));
+    expect(chatLeft, greaterThan(180));
+    expect(chatLeft, lessThan(390));
+    final revealedColor = await _pixelAt(
+      tester,
+      harness,
+      const Offset(24, 420),
+    );
+    _expectColorClose(revealedColor, _previousColor);
 
     await tester.pumpAndSettle();
     expect(harness.observer.popCount, 1);

test/main_tab_motion_test.dart

@@ -19,6 +19,7 @@ import 'package:mithka/chat/chat_view.dart';
 import 'package:mithka/chats/archived_chats_view.dart';
 import 'package:mithka/chats/chat_list_view.dart';
 import 'package:mithka/chats/search_view.dart';
+import 'package:mithka/components/app_icons.dart';
 import 'package:mithka/components/drawer_controller.dart' as dc;
 import 'package:mithka/contacts/contacts_view.dart';
 import 'package:mithka/l10n/app_locale_controller.dart';
@@ -598,6 +599,51 @@ void main() {
       debugDefaultTargetPlatformOverride = null;
     }
   });
+
+  testWidgets(
+    'phone chat back button slides the conversation out across the viewport',
+    (tester) async {
+      debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+      try {
+        await _setSurfaceSize(tester, const Size(390, 844));
+        await _pumpMainShell(tester);
+        final deepLinks = ChatDeepLinkController.shared;
+
+        deepLinks.openChat(chatId: 41, title: 'Mobile chat', messageId: 410);
+        await tester.pump();
+        await tester.pump();
+        await tester.pump(const Duration(milliseconds: 350));
+        _discardMissingTdlibErrors(tester);
+
+        final chatView = find.byType(ChatView);
+        expect(chatView, findsOneWidget);
+        expect(tester.getTopLeft(chatView).dx, closeTo(0, 0.5));
+
+        final backButton = find.descendant(
+          of: chatView,
+          matching: find.byIcon(HeroAppIcons.chevronLeft.data),
+        );
+        expect(backButton, findsOneWidget);
+        await tester.tap(backButton);
+        await tester.pump();
+        await tester.pump(const Duration(milliseconds: 90));
+        _discardMissingTdlibErrors(tester);
+
+        final midPopLeft = tester.getTopLeft(chatView).dx;
+        expect(midPopLeft, greaterThan(180));
+        expect(midPopLeft, lessThan(390));
+
+        await tester.pump(const Duration(milliseconds: 240));
+        await tester.pump();
+        _discardMissingTdlibErrors(tester);
+        expect(chatView, findsNothing);
+        expect(find.byType(ChatListView), findsOneWidget);
+        await _disposeShell(tester);
+      } finally {
+        debugDefaultTargetPlatformOverride = null;
+      }
+    },
+  );
 }
 
 void _discardMissingTdlibErrors(WidgetTester tester) {