perf(mobile): avoid redundant history-row work during navigation

Signed-off-by: Tom Brow <tomb@block.xyz>

mobile/test/features/channels/date_formatters_test.dart

@@ -5,6 +5,26 @@ import 'package:buzz/features/channels/date_formatters.dart';
 int _ts(DateTime local) => local.millisecondsSinceEpoch ~/ 1000;
 
 void main() {
+  test('timeline calendar grouping matches uncached local-day comparisons', () {
+    final days = TimelineCalendarDays();
+    final timestamps = [
+      DateTime(2025, 12, 31, 23, 59),
+      DateTime(2026, 1, 1),
+      DateTime(2026, 3, 8, 1, 30),
+      DateTime(2026, 3, 8, 3, 30),
+      DateTime(2026, 11, 1, 1, 30),
+      DateTime(2026, 11, 1, 3, 30),
+      DateTime(2026, 11, 2),
+    ].map(_ts).toList();
+    for (var repeat = 0; repeat < 3; repeat++) {
+      for (final a in timestamps) {
+        for (final b in timestamps) {
+          expect(days.isSameDay(a, b), isSameDay(a, b));
+        }
+      }
+    }
+  });
+
   group('formatDayHeading', () {
     // Fix "now" so tests are deterministic.
     final now = DateTime(2026, 4, 23, 14, 30); // Apr 23 2026, 2:30 PM local

mobile/test/features/channels/local_message_send_transition_test.dart

@@ -64,6 +64,43 @@ void main() {
       isFalse,
     );
   });
+  testWidgets('loaded history has no send animation or row layout', (
+    tester,
+  ) async {
+    await tester.pumpWidget(_testable(animate: false));
+    final history = find.byType(LocalMessageSendTransition);
+    expect(
+      find.descendant(of: history, matching: find.byType(AnimatedBuilder)),
+      findsNothing,
+    );
+    expect(find.byType(LocalSendRow), findsNothing);
+    expect(tester.getSize(history).height, 80);
+    expect(
+      tester.getSize(find.byKey(const ValueKey('avatar'))),
+      const Size(40, 40),
+    );
+  });
+
+  testWidgets('enabling motion does not replay a settled entrance', (
+    tester,
+  ) async {
+    await tester.pumpWidget(_testable(animate: true, reduceMotion: true));
+    final avatar = tester.element(find.byKey(const ValueKey('avatar')));
+    await tester.pumpWidget(_testable(animate: true, reduceMotion: false));
+    expect(tester.element(find.byKey(const ValueKey('avatar'))), same(avatar));
+    expect(tester.getSize(find.byType(LocalMessageSendTransition)).height, 80);
+    expect(find.byType(LocalSendRow), findsNothing);
+  });
+
+  testWidgets('expiring a send claim retains message state', (tester) async {
+    await tester.pumpWidget(_testable());
+    await tester.pumpAndSettle();
+    final avatar = tester.element(find.byKey(const ValueKey('avatar')));
+    await tester.pumpWidget(_testable(animate: false));
+    expect(tester.element(find.byKey(const ValueKey('avatar'))), same(avatar));
+    expect(tester.getSize(find.byType(LocalMessageSendTransition)).height, 80);
+  });
+
   testWidgets('history moves up while the avatar remains anchored', (
     tester,
   ) async {
@@ -85,7 +122,7 @@ void main() {
       ),
     );
     await tester.pumpAndSettle();
-    expect(tester.getSize(find.byType(LocalSendRow)).height, 80);
+    expect(tester.getSize(find.byType(LocalMessageSendTransition)).height, 80);
     expect(tester.getRect(find.byKey(const ValueKey('avatar'))), avatar);
     expect(
       tester.getTopLeft(find.byKey(const ValueKey('history'))).dy,
@@ -130,7 +167,10 @@ void main() {
       await tester.pumpWidget(
         _testable(animate: reduced, reduceMotion: reduced),
       );
-      expect(tester.getSize(find.byType(LocalSendRow)).height, 80);
+      expect(
+        tester.getSize(find.byType(LocalMessageSendTransition)).height,
+        80,
+      );
       expect(
         tester
             .widget<LocalSendProgress>(find.byType(LocalSendProgress))
@@ -138,7 +178,10 @@ void main() {
         1,
       );
       await tester.pump(const Duration(milliseconds: 100));
-      expect(tester.getSize(find.byType(LocalSendRow)).height, 80);
+      expect(
+        tester.getSize(find.byType(LocalMessageSendTransition)).height,
+        80,
+      );
     });
   }
 }

mobile/test/features/channels/message_footer_layout_test.dart

@@ -1,8 +1,47 @@
 import 'package:buzz/features/channels/message_footer_layout.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
+  testWidgets('unchanged footer geometry does not relayout its timeline row', (
+    tester,
+  ) async {
+    var layouts = 0;
+    final overlap = ValueNotifier(8.0);
+    addTearDown(overlap.dispose);
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Align(
+          alignment: Alignment.topLeft,
+          child: _LayoutCounter(
+            onLayout: () => layouts++,
+            child: ValueListenableBuilder(
+              valueListenable: overlap,
+              builder: (context, value, child) => MessageFooterLayout(
+                overlap: value,
+                footer: const SizedBox(width: 100, height: 32),
+                child: const SizedBox(width: 200, height: 60),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    final initialLayouts = layouts;
+    tester.element(find.byType(MessageFooterLayout)).markNeedsBuild();
+    await tester.pump();
+    expect(
+      layouts,
+      initialLayouts,
+      reason: 'Rebuilding unchanged reactions must not dirty the row layout',
+    );
+    overlap.value = 12;
+    await tester.pump();
+    expect(layouts, greaterThan(initialLayouts));
+    expect(tester.getSize(find.byType(MessageFooterLayout)).height, 80);
+  });
+
   testWidgets('footer global transforms and semantics include overlap offset', (
     tester,
   ) async {
@@ -118,3 +157,21 @@ void main() {
     },
   );
 }
+
+class _LayoutCounter extends SingleChildRenderObjectWidget {
+  const _LayoutCounter({required this.onLayout, required super.child});
+  final VoidCallback onLayout;
+  @override
+  RenderObject createRenderObject(BuildContext context) =>
+      _CountLayouts(onLayout);
+}
+
+class _CountLayouts extends RenderProxyBox {
+  _CountLayouts(this.onLayout);
+  final VoidCallback onLayout;
+  @override
+  void performLayout() {
+    onLayout();
+    super.performLayout();
+  }
+}