feat(chat): load older messages on scroll-to-top (history pagination) (v1.11.0+15)

Repository keeps one live Timeline per room and re-yields on its
onUpdate callback (fires for both live events AND requestHistory),
not just onSync which never fires for pagination. loadMoreMessages
now paginates that same instance; added canLoadMore.

Timeline widget requests older history when scrolled within 400px of
the oldest end, guarded against re-entry, with a top loading spinner.

Verified: widget test drives a drag-to-top and asserts loadMoreMessages
fires; live smoke test confirms the onUpdate delivery path (reused by
history) still shows new messages after the refactor.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/core/config/app_config.dart

@@ -11,7 +11,7 @@ abstract final class AppConfig {
     'turns:matrix.m8chat.au:5349',
   ];
   static const String appName = 'M8Chat';
-  static const String appVersion = '1.10.0';
+  static const String appVersion = '1.11.0';
 
   // Jitsi conferencing
   static const String jitsiDomain = 'conf.m8chat.au';

lib/features/chat/data/chat_repository.dart

@@ -1,6 +1,12 @@
-// Version: 1.4.0 | Created: 2026-04-01 | Updated: 2026-07-04
+// Version: 1.5.0 | Created: 2026-04-01 | Updated: 2026-07-04
 // Chat repository — bridges Matrix SDK timeline to app domain models.
 // Phase 2 additions: sendFile, sendReaction, redactEvent, reply support.
+// v1.5.0: keep one live Timeline per room so scroll-back history pagination
+// (requestHistory) acts on the same instance the stream is watching, and
+// re-yield on the timeline's own onUpdate (fires for both live events and
+// history) rather than only on onSync (which does not fire for pagination).
+
+import 'dart:async';
 
 import 'package:matrix/matrix.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
@@ -22,6 +28,10 @@ class ChatRepository {
 
   final Client _client;
 
+  /// Live timelines keyed by room id, so [loadMoreMessages] paginates the
+  /// same instance the active [watchTimeline] stream is mapping.
+  final Map<String, Timeline> _timelines = {};
+
   Room? _getRoom(String roomId) => _client.getRoomById(roomId);
 
   /// Returns a stream of message lists for [roomId].
@@ -29,20 +39,32 @@ class ChatRepository {
     final room = _getRoom(roomId);
     if (room == null) return;
 
-    final timeline = await room.getTimeline();
+    final signal = StreamController<void>();
+    final timeline = await room.getTimeline(
+      onUpdate: () {
+        if (!signal.isClosed) signal.add(null);
+      },
+    );
+    _timelines[roomId] = timeline;
 
-    yield await _mapTimeline(timeline, room);
-
-    await for (final update in _client.onSync.stream) {
-      final updatesThisRoom = update.rooms?.join?.containsKey(roomId) ?? false;
-      if (updatesThisRoom) {
+    try {
+      yield await _mapTimeline(timeline, room);
+      await for (final _ in signal.stream) {
         yield await _mapTimeline(timeline, room);
       }
+    } finally {
+      timeline.cancelSubscriptions();
+      if (identical(_timelines[roomId], timeline)) {
+        _timelines.remove(roomId);
+      }
+      await signal.close();
     }
-
-    timeline.cancelSubscriptions();
   }
 
+  /// Whether [roomId] has older messages that can still be paginated in.
+  bool canLoadMore(String roomId) =>
+      _timelines[roomId]?.canRequestHistory ?? false;
+
   /// Sends a plain text message. Supports replies via [inReplyToEventId].
   Future<void> sendTextMessage(
     String roomId,
@@ -107,11 +129,12 @@ class ChatRepository {
     await room.setReadMarker(lastEventId, mRead: lastEventId);
   }
 
-  /// Requests older messages (pagination).
+  /// Requests older messages (pagination) on the active timeline for [roomId].
+  /// No-op if there is no live timeline or no more history to fetch.
   Future<void> loadMoreMessages(String roomId) async {
-    final room = _getRoom(roomId);
-    if (room == null) return;
-    await room.requestHistory();
+    final timeline = _timelines[roomId];
+    if (timeline == null || !timeline.canRequestHistory) return;
+    await timeline.requestHistory();
   }
 
   /// Event types that should never appear in the chat timeline.

lib/features/chat/presentation/chat_screen.dart

@@ -1,4 +1,4 @@
-// Version: 1.6.0 | Created: 2026-04-01 | Updated: 2026-07-04
+// Version: 1.7.0 | Created: 2026-04-01 | Updated: 2026-07-04
 // Full chat screen — timeline + input + typing indicators + read receipts
 // + long-press context menu (quick reactions, reply, react, copy, edit,
 // delete) + day separators + same-sender message grouping + room options.
@@ -17,6 +17,7 @@ import '../../../shared/utils/matrix_id.dart';
 import '../../../shared/utils/mxc_url.dart';
 import '../../../shared/widgets/matrix_avatar.dart';
 import '../../rooms/presentation/user_search_dialog.dart';
+import '../data/chat_repository.dart';
 import '../domain/message_model.dart';
 import 'chat_controller.dart';
 import 'message_bubble.dart';
@@ -144,7 +145,12 @@ class _TimelineState extends ConsumerState<_Timeline> {
   /// The list is reverse:true, so the newest message sits at offset 0.
   /// Show the jump-to-latest button once the user scrolls up past this.
   static const _showButtonThreshold = 400.0;
+
+  /// How close to the oldest (top of a reverse list) before we prefetch more.
+  static const _loadMoreThreshold = 400.0;
+
   bool _showScrollToLatest = false;
+  bool _loadingMore = false;
 
   @override
   void initState() {
@@ -161,10 +167,30 @@ class _TimelineState extends ConsumerState<_Timeline> {
 
   void _onScroll() {
     if (!_scrollController.hasClients) return;
-    final show = _scrollController.offset > _showButtonThreshold;
+    final pos = _scrollController.position;
+
+    final show = pos.pixels > _showButtonThreshold;
     if (show != _showScrollToLatest) {
       setState(() => _showScrollToLatest = show);
     }
+
+    // Near the oldest end (top of a reverse list) → load older history.
+    if (pos.hasContentDimensions &&
+        pos.pixels >= pos.maxScrollExtent - _loadMoreThreshold) {
+      _loadOlder();
+    }
+  }
+
+  Future<void> _loadOlder() async {
+    if (_loadingMore) return;
+    final repo = ref.read(chatRepositoryProvider);
+    if (!repo.canLoadMore(widget.roomId)) return;
+    setState(() => _loadingMore = true);
+    try {
+      await repo.loadMoreMessages(widget.roomId);
+    } finally {
+      if (mounted) setState(() => _loadingMore = false);
+    }
   }
 
   void _scrollToLatest() {
@@ -249,6 +275,20 @@ class _TimelineState extends ConsumerState<_Timeline> {
                 );
               },
             ),
+            // Loading older history (top of a reverse list).
+            if (_loadingMore)
+              const Positioned(
+                top: 8,
+                left: 0,
+                right: 0,
+                child: Center(
+                  child: SizedBox(
+                    width: 22,
+                    height: 22,
+                    child: CircularProgressIndicator(strokeWidth: 2),
+                  ),
+                ),
+              ),
             Positioned(
               right: 12,
               bottom: 12,