chore: Follow up display read marker in timeline

lib/pages/chat/chat.dart

@@ -102,7 +102,7 @@ class ChatController extends State<ChatPageWithRoom>
 
   Timeline? timeline;
 
-  String? readMarkerEventId;
+  late final String readMarkerEventId;
 
   String get roomId => widget.room.id;
 
@@ -270,6 +270,7 @@ class ChatController extends State<ChatPageWithRoom>
     );
 
     sendingClient = Matrix.of(context).client;
+    readMarkerEventId = room.hasNewMessages ? room.fullyRead : '';
     WidgetsBinding.instance.addObserver(this);
     _tryLoadTimeline();
     if (kIsWeb) {
@@ -284,19 +285,22 @@ class ChatController extends State<ChatPageWithRoom>
       await loadTimelineFuture;
       if (initialEventId != null) scrollToEventId(initialEventId);
 
-      final fullyRead = room.fullyRead;
-      if (fullyRead.isEmpty) {
-        setReadMarker();
-        return;
-      }
-      if (timeline?.events.any((event) => event.eventId == fullyRead) ??
-          false) {
-        Logs().v('Scroll up to visible event', fullyRead);
-        scrollToEventId(fullyRead, highlightEvent: false);
+      final readMarkerEventIndex = readMarkerEventId.isEmpty
+          ? -1
+          : timeline!.events
+              .where((e) => e.isVisibleInGui)
+              .toList()
+              .indexWhere((e) => e.eventId == readMarkerEventId);
+
+      if (readMarkerEventIndex > 1) {
+        Logs().v('Scroll up to visible event', readMarkerEventId);
+        scrollToEventId(readMarkerEventId, highlightEvent: false);
         return;
+      } else if (readMarkerEventId.isNotEmpty && readMarkerEventIndex == -1) {
+        _showScrollUpMaterialBanner(readMarkerEventId);
       }
+
       if (!mounted) return;
-      _showScrollUpMaterialBanner(fullyRead);
     } catch (e, s) {
       ErrorReporter(context, 'Unable to load timeline').onErrorCallback(e, s);
       rethrow;
@@ -323,13 +327,16 @@ class ChatController extends State<ChatPageWithRoom>
   int? animateInEventIndex;
 
   void onInsert(int i) {
+    onChange(i);
+    // setState will be called by updateView() anyway
+    animateInEventIndex = i;
+  }
+
+  void onChange(int i) {
     if (timeline?.events[i].status == EventStatus.synced) {
       final index = timeline!.events.firstIndexWhereNotError;
       if (i == index) setReadMarker(eventId: timeline?.events[i].eventId);
     }
-
-    // setState will be called by updateView() anyway
-    animateInEventIndex = i;
   }
 
   Future<void> _getTimeline({
@@ -347,6 +354,7 @@ class ChatController extends State<ChatPageWithRoom>
         onUpdate: updateView,
         eventContextId: eventContextId,
         onInsert: onInsert,
+        onChange: onChange,
       );
     } catch (e, s) {
       Logs().w('Unable to load timeline on event ID $eventContextId', e, s);
@@ -354,6 +362,7 @@ class ChatController extends State<ChatPageWithRoom>
       timeline = await room.getTimeline(
         onUpdate: updateView,
         onInsert: onInsert,
+        onChange: onChange,
       );
       if (!mounted) return;
       if (e is TimeoutException || e is IOException) {
@@ -380,6 +389,7 @@ class ChatController extends State<ChatPageWithRoom>
     if (_setReadMarkerFuture != null) return;
     if (_scrolledUp) return;
     if (scrollUpBannerEventId != null) return;
+
     if (eventId == null &&
         !room.hasNewMessages &&
         room.notificationCount == 0) {

lib/pages/chat/chat_event_list.dart

@@ -141,8 +141,7 @@ class ChatEventList extends StatelessWidget {
                     .any((e) => e.eventId == event.eventId),
                 timeline: controller.timeline!,
                 displayReadMarker:
-                    controller.readMarkerEventId == event.eventId &&
-                        controller.timeline?.allowNewEvent == false,
+                    i > 0 && controller.readMarkerEventId == event.eventId,
                 nextEvent: i + 1 < events.length ? events[i + 1] : null,
                 previousEvent: i > 0 ? events[i - 1] : null,
                 avatarPresenceBackgroundColor: