fix(mobile): keep latest messages above composer (#4981)

**Category:** fix
**User Impact:** Mobile users who jump to Latest now see the newest
message fully above the composer instead of partially hidden behind it.

**Problem:** The channel message list treated the raw viewport bottom as
the latest boundary even though the composer occupies part of that
viewport. Latest jumps and follow-mode corrections could therefore place
the newest message underneath the composer.

**Solution:** Derive the latest alignment from the measured composer
inset and use that same boundary for scrolling, follow detection, and
layout correction.

<img width="498" height="1008" alt="Screen Recording 2026-08-05 at 5 18
19 PM"
src="https://github.com/user-attachments/assets/a7fc1a94-3ffb-4c34-908d-9bf4f3f082b4"
/>


<details>
<summary>File changes</summary>

**mobile/lib/features/channels/channel_detail_page/message_list.dart**
Aligns Latest navigation and follow-mode correction with the visible
bottom edge above the composer, and evaluates boundary state against the
same geometry.

**mobile/test/features/channels/channel_detail_page_test.dart**
Adds a regression assertion that the newest live message clears the
composer and that the Latest control disappears after navigation.

</details>

## Reproduction steps

1. Open a mobile channel with enough messages to scroll away from the
newest message.
2. Tap **Latest**.
3. Confirm the newest message is fully visible immediately above the
composer and the **Latest** control disappears.
4. Resize the composer or keyboard while following latest and confirm
the newest message remains above the composer.

## Tested fix

The newest message remains fully visible above the composer after
jumping to **Latest**.

![Tested fix: latest message remains above the
composer](https://d24qwcpro867f5.cloudfront.net/repos/buzz/prs/4981/latest-above-composer-tested.gif)

## Validation

- `flutter analyze` — no issues
- `flutter test` — 1,243 passed

---------

Signed-off-by: Taylor Ho <taylorkmho@gmail.com>

mobile/lib/features/channels/channel_detail_page/message_list.dart

@@ -155,6 +155,13 @@ class _MessageList extends HookConsumerWidget {
           : displayEntries.length - 1 - chronologicalIndex;
     }
 
+    double latestAlignment() {
+      final viewportHeight = context.size?.height ?? 0;
+      return viewportHeight > 0
+          ? (composerBottomInset / viewportHeight).clamp(0.0, 1.0).toDouble()
+          : 0.0;
+    }
+
     Future<void> scrollToLatest() async {
       if (!itemScrollController.isAttached || isAutoScrolling.value) return;
       followsLatest.value = true;
@@ -163,6 +170,7 @@ class _MessageList extends HookConsumerWidget {
       try {
         await itemScrollController.scrollTo(
           index: 0,
+          alignment: latestAlignment(),
           duration: const Duration(milliseconds: 220),
           curve: Curves.easeOutCubic,
         );
@@ -199,12 +207,15 @@ class _MessageList extends HookConsumerWidget {
     }
 
     bool latestIsAtBoundary() {
-      // In this reversed list, item 0's leading edge is the bottom boundary.
-      // Being merely visible is not enough: a user who has pulled a tall
-      // newest row away from the boundary must not snap back on live updates.
+      // In this reversed list, item 0's leading edge is the visible bottom
+      // boundary above the composer. Being merely visible is not enough: a
+      // user who has pulled a tall newest row away from that boundary must not
+      // snap back on live updates.
+      final boundary = latestAlignment();
       return itemPositionsListener.itemPositions.value.any(
         (position) =>
-            position.index == 0 && position.itemLeadingEdge.abs() < 0.01,
+            position.index == 0 &&
+            (position.itemLeadingEdge - boundary).abs() < 0.01,
       );
     }
 

mobile/test/features/channels/channel_detail_page_test.dart

@@ -2053,7 +2053,7 @@ void main() {
         expect(latestMessage, findsOneWidget);
         expect(
           tester.getBottomLeft(latestMessage).dy,
-          lessThanOrEqualTo(tester.getTopLeft(composerDock).dy + 1),
+          closeTo(tester.getTopLeft(composerDock).dy, 1),
         );
 
         await tester.tap(find.text('Message #general'));
@@ -2065,7 +2065,7 @@ void main() {
         );
         expect(
           tester.getBottomLeft(latestMessage).dy,
-          lessThanOrEqualTo(tester.getTopLeft(composerDock).dy + 1),
+          closeTo(tester.getTopLeft(composerDock).dy, 1),
         );
         expect(
           find.byKey(const ValueKey('channel-jump-to-latest')),
@@ -2078,7 +2078,7 @@ void main() {
         expect(latestMessage, findsOneWidget);
         expect(
           tester.getBottomLeft(latestMessage).dy,
-          lessThanOrEqualTo(tester.getTopLeft(composerDock).dy + 1),
+          closeTo(tester.getTopLeft(composerDock).dy, 1),
         );
         expect(
           find.byKey(const ValueKey('channel-jump-to-latest')),
@@ -2087,6 +2087,53 @@ void main() {
       },
     );
 
+    testWidgets('keeps a short followed tail flush through composer resize', (
+      tester,
+    ) async {
+      tester.view.physicalSize = const Size(400, 800);
+      tester.view.devicePixelRatio = 1;
+      addTearDown(tester.view.resetPhysicalSize);
+      addTearDown(tester.view.resetDevicePixelRatio);
+      addTearDown(tester.view.reset);
+
+      final messages = [
+        for (var i = 0; i < 3; i++)
+          _textMsg(
+            id: 'msg$i',
+            pubkey: 'alice',
+            content: 'Message $i',
+            createdAt: 1000 + i,
+          ),
+      ];
+
+      await tester.pumpWidget(
+        _buildTestable(
+          messages: messages,
+          users: const {
+            'alice': UserProfile(pubkey: 'alice', displayName: 'Alice'),
+          },
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      final latestMessage = find.byKey(
+        const ValueKey('channel-message-group-msg2'),
+      );
+      final composerDock = find.byKey(const ValueKey('channel-composer-dock'));
+
+      await tester.tap(find.text('Message #general'));
+      await tester.pumpAndSettle();
+
+      expect(
+        tester.getBottomLeft(latestMessage).dy,
+        closeTo(tester.getTopLeft(composerDock).dy, 1),
+      );
+      expect(
+        find.byKey(const ValueKey('channel-jump-to-latest')),
+        findsNothing,
+      );
+    });
+
     testWidgets(
       'does not realign a user-detached timeline on keyboard resize',
       (tester) async {
@@ -2232,6 +2279,18 @@ void main() {
       await tester.pumpAndSettle();
 
       expect(findRichText('Newest live update'), findsOneWidget);
+      final latestMessage = find.byKey(
+        const ValueKey('channel-message-group-newest'),
+      );
+      final composerDock = find.byKey(const ValueKey('channel-composer-dock'));
+      expect(
+        tester.getBottomLeft(latestMessage).dy,
+        closeTo(tester.getTopLeft(composerDock).dy, 1),
+      );
+      expect(
+        find.byKey(const ValueKey('channel-jump-to-latest')),
+        findsNothing,
+      );
     });
 
     testWidgets(