TASK 9.4: live chat wiring — right panel with Super Chat + membership badges

- YouTubeStreamService: added GetBroadcastLiveChatIdAsync to fetch liveChatId from broadcast contentDetails
- YouTubeChatService.Poll(): parse snippet.type to handle textMessageEvent, superChatEvent, newSponsorEvent
- MainViewModel: wire _youtubeChat.Start(liveChatId) in PrepareAndStartLiveAsync after broadcast creation
- MainViewModel: wire _youtubeChat.Stop() in StopStream before encoder stop
- MainViewModel: wire _youtubeChat.Dispose() in Shutdown
- MainWindow.xaml: updated chat DataTemplate with member badge (⭐), Super Chat highlight (💰 + gold border), timestamps (HH:mm)
- MainWindow.xaml.cs: auto-scroll ChatListBox on new messages via CollectionChanged
- Chat lifecycle is non-fatal: failures log and the stream continues without on-panel chat

MainWindow.xaml

@@ -980,16 +980,90 @@
                              ItemsSource="{Binding ChatMessages}"
                              ItemContainerStyle="{StaticResource YtListBoxItem}"
                              Visibility="{Binding ShowChatInactiveMessage, Converter={StaticResource InverseBoolToVis}}"
-                             Foreground="#e0e0e0" FontSize="12">
+                             Foreground="#e0e0e0" FontSize="12"
+                             ScrollViewer.HorizontalScrollBarVisibility="Disabled"
+                             x:Name="ChatListBox">
                         <ListBox.ItemTemplate>
                             <DataTemplate>
-                                <StackPanel Margin="0,2">
+                                <Border x:Name="MessageBorder" Padding="6,4" CornerRadius="4" Margin="0,1">
-                                    <TextBlock>
+                                    <Border.Style>
-                                        <Run Text="{Binding AuthorName, Mode=OneWay}" FontWeight="Bold" Foreground="#e94560"/>
+                                        <Style TargetType="Border">
-                                        <Run Text=": "/>
+                                            <Setter Property="Background" Value="Transparent"/>
-                                        <Run Text="{Binding Message, Mode=OneWay}" Foreground="#e0e0e0"/>
+                                            <Style.Triggers>
+                                                <DataTrigger Binding="{Binding IsSuperChat}" Value="True">
+                                                    <Setter Property="Background" Value="#2a1a0a"/>
+                                                    <Setter Property="BorderBrush" Value="#eab308"/>
+                                                    <Setter Property="BorderThickness" Value="1,0,1,0"/>
+                                                </DataTrigger>
+                                            </Style.Triggers>
+                                        </Style>
+                                    </Border.Style>
+                                    <StackPanel>
+                                        <StackPanel Orientation="Horizontal">
+                                            <!-- Member badge -->
+                                            <TextBlock Text="⭐" FontSize="10" Margin="0,0,3,0"
+                                                       VerticalAlignment="Center">
+                                                <TextBlock.Style>
+                                                    <Style TargetType="TextBlock">
+                                                        <Setter Property="Visibility" Value="Collapsed"/>
+                                                        <Style.Triggers>
+                                                            <DataTrigger Binding="{Binding IsMember}" Value="True">
+                                                                <Setter Property="Visibility" Value="Visible"/>
+                                                            </DataTrigger>
+                                                        </Style.Triggers>
+                                                    </Style>
+                                                </TextBlock.Style>
+                                            </TextBlock>
+
+                                            <!-- Author name -->
+                                            <TextBlock FontWeight="Bold" Foreground="#e94560"
+                                                       Text="{Binding AuthorName, Mode=OneWay}"
+                                                       VerticalAlignment="Center"/>
+
+                                            <!-- Super Chat amount -->
+                                            <TextBlock Foreground="#eab308" FontWeight="Bold"
+                                                       FontSize="11" Margin="6,0,0,0"
+                                                       VerticalAlignment="Center">
+                                                <TextBlock.Style>
+                                                    <Style TargetType="TextBlock">
+                                                        <Setter Property="Visibility" Value="Collapsed"/>
+                                                        <Style.Triggers>
+                                                            <DataTrigger Binding="{Binding IsSuperChat}" Value="True">
+                                                                <Setter Property="Visibility" Value="Visible"/>
+                                                            </DataTrigger>
+                                                        </Style.Triggers>
+                                                    </Style>
+                                                </TextBlock.Style>
+                                                <Run Text="💰 $"/>
+                                                <Run Text="{Binding SuperChatAmount, Mode=OneWay, StringFormat=F2}"/>
+                                                <Run Text="{Binding SuperChatCurrency, Mode=OneWay}"/>
+                                            </TextBlock>
+
+                                            <!-- Timestamp -->
+                                            <TextBlock Foreground="#555" FontSize="10"
+                                                       Margin="6,0,0,0" VerticalAlignment="Center">
+                                                <TextBlock.Style>
+                                                    <Style TargetType="TextBlock">
+                                                        <Setter Property="Visibility" Value="Collapsed"/>
+                                                        <Style.Triggers>
+                                                            <DataTrigger Binding="{Binding Timestamp}" Value="{x:Null}">
+                                                                <Setter Property="Visibility" Value="Visible"/>
+                                                            </DataTrigger>
+                                                        </Style.Triggers>
+                                                    </Style>
+                                                </TextBlock.Style>
+                                                <TextBlock.Text>
+                                                    <Binding Path="Timestamp" StringFormat="{}{0:HH:mm}"/>
+                                                </TextBlock.Text>
                                             </TextBlock>
                                         </StackPanel>
+
+                                        <!-- Message -->
+                                        <TextBlock Text="{Binding Message, Mode=OneWay}"
+                                                   Foreground="#e0e0e0" TextWrapping="Wrap"
+                                                   Margin="0,2,0,0"/>
+                                    </StackPanel>
+                                </Border>
                             </DataTemplate>
                         </ListBox.ItemTemplate>
                     </ListBox>

MainWindow.xaml.cs

@@ -21,6 +21,7 @@ public partial class MainWindow : Window
         AppLog.Write("MainWindow ctor: after InitializeComponent");
         _viewModel = (MainViewModel)DataContext;
         _viewModel.PropertyChanged += OnViewModelPropertyChanged;
+        _viewModel.ChatMessages.CollectionChanged += OnChatMessagesChanged;
         // When a focused scene is deleted, never land focus on a hidden scene.
         SceneList.IsSelectable = item => item is Scene { IsHidden: false };
         UpdateTaskbarOverlay();
@@ -232,6 +233,14 @@ public partial class MainWindow : Window
         TakeSnapshot();
     }
 
+    private void OnChatMessagesChanged(object? sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
+    {
+        if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
+        {
+            ChatListBox.ScrollIntoView(ChatListBox.Items[^1]);
+        }
+    }
+
     // Static images and the webcam share the move/resize/selection behavior.
     private static bool IsDraggableElement(SceneElement element)
         => element.IsDraggable;

Services/YouTubeChatService.cs

@@ -73,6 +73,7 @@ public class YouTubeChatService : IDisposable
             {
                 var snippet = item.GetProperty("snippet");
                 var author = item.GetProperty("authorDetails");
+                var type = snippet.GetProperty("type").GetString() ?? "textMessageEvent";
 
                 var message = new ChatMessage
                 {
@@ -80,11 +81,50 @@ public class YouTubeChatService : IDisposable
                     AuthorName = author.GetProperty("displayName").GetString()!,
                     AuthorChannelId = author.GetProperty("channelId").GetString()!,
                     AuthorImageUrl = author.GetProperty("profileImageUrl").GetString()!,
-                    Message = snippet.GetProperty("textMessageDetails").GetProperty("messageText").GetString()!,
                     Timestamp = DateTime.Parse(snippet.GetProperty("publishedAt").GetString()!),
-                    IsMember = author.GetProperty("isChatSponsor").GetBoolean()
+                    IsMember = author.GetProperty("isChatSponsor").GetBoolean(),
+                    MembershipLevel = author.TryGetProperty("badgeText", out var badgeText)
+                        ? badgeText.GetString()
+                        : null
                 };
 
+                switch (type)
+                {
+                    case "superChatEvent":
+                        message.IsSuperChat = true;
+                        if (snippet.TryGetProperty("superChatDetails", out var scDetails))
+                        {
+                            message.SuperChatAmount = scDetails.TryGetProperty("amountMicros", out var amt)
+                                ? amt.GetDouble() / 1_000_000.0
+                                : 0;
+                            message.SuperChatCurrency = scDetails.TryGetProperty("currency", out var cur)
+                                ? cur.GetString()
+                                : null;
+                            message.Message = scDetails.TryGetProperty("userComment", out var comment)
+                                ? comment.GetString() ?? string.Empty
+                                : string.Empty;
+                        }
+                        break;
+
+                    case "newSponsorEvent":
+                        message.Message = $"🎉 {message.AuthorName} became a member!";
+                        if (snippet.TryGetProperty("membershipDetails", out var memDetails))
+                        {
+                            message.MembershipLevel = memDetails.TryGetProperty("memberLevelName", out var level)
+                                ? level.GetString()
+                                : message.MembershipLevel;
+                        }
+                        break;
+
+                    default: // textMessageEvent
+                        message.Message = snippet.TryGetProperty("textMessageDetails", out var textDetails)
+                            ? textDetails.TryGetProperty("messageText", out var text)
+                                ? text.GetString() ?? string.Empty
+                                : string.Empty
+                            : string.Empty;
+                        break;
+                }
+
                 MessageReceived?.Invoke(message);
             }
         }

Services/YouTubeStreamService.cs

@@ -190,4 +190,28 @@ public class YouTubeStreamService
         }
         return health;
     }
+
+    /// <summary>Returns the liveChatId for a broadcast by fetching its contentDetails.
+    /// The liveChatId is needed to poll chat messages. Called after broadcast creation
+    /// in PrepareAndStartLiveAsync.</summary>
+    public async Task<string?> GetBroadcastLiveChatIdAsync(string broadcastId)
+    {
+        if (!await EnsureToken()) return null;
+
+        _http.DefaultRequestHeaders.Authorization = new("Bearer", _auth.CurrentChannel!.AccessToken);
+        var response = await _http.GetAsync(
+            $"{ApiBase}/liveBroadcasts?part=contentDetails&id={broadcastId}");
+        if (!response.IsSuccessStatusCode) return null;
+
+        var json = await response.Content.ReadAsStringAsync();
+        var data = JsonSerializer.Deserialize<JsonElement>(json);
+        var items = data.GetProperty("items");
+        if (items.GetArrayLength() == 0) return null;
+
+        var contentDetails = items[0].GetProperty("contentDetails");
+        if (contentDetails.TryGetProperty("liveChatId", out var liveChatId))
+            return liveChatId.GetString();
+
+        return null;
+    }
 }

ViewModels/MainViewModel.cs

@@ -1605,6 +1605,7 @@ public class MainViewModel : ViewModelBase
         _screenCaptureManager.Dispose();
         _layoutStore.Dispose();
         _musicPlayer.Dispose();
+        _youtubeChat.Dispose();
     }
 
     public void SaveLayoutNow()
@@ -2236,6 +2237,27 @@ public class MainViewModel : ViewModelBase
                 return;
             }
             AppLog.Write($"Broadcast created: {_currentBroadcastId}");
+
+            // Start chat polling (TASK 9.4): fetch the liveChatId from the broadcast's
+            // contentDetails, then start the poll loop. Chat is non-fatal — if it fails,
+            // the stream continues without on-panel chat.
+            try
+            {
+                var liveChatId = await _youtubeStream.GetBroadcastLiveChatIdAsync(_currentBroadcastId);
+                if (liveChatId != null)
+                {
+                    _youtubeChat.Start(liveChatId);
+                    AppLog.Write($"Chat polling started: {liveChatId}");
+                }
+                else
+                {
+                    AppLog.Write("Could not retrieve liveChatId; chat polling disabled");
+                }
+            }
+            catch (Exception chatEx)
+            {
+                AppLog.Write($"Chat start failed (non-fatal): {chatEx.Message}");
+            }
         }
         catch (Exception ex)
         {
@@ -2302,6 +2324,9 @@ public class MainViewModel : ViewModelBase
         StreamStatus = StreamStatus.Offline;
         WindowTitle = "ytLlive";
         ResetHealth(StreamStatus.Offline);
+        // Stop chat polling first (TASK 9.4) — no more messages arriving while
+        // we're tearing down the stream.
+        _youtubeChat.Stop();
         // Close the audio pipe FIRST so ffmpeg sees EOF on the audio input,
         // then stop the pump (stdin EOF) — both inputs end and the encoder
         // finalizes the FLV. Audio capture itself is always-on (preview