AX Agent transcript 호스트를 컬렉션 기반으로 재구성해 코워크·코드 스트리밍 중 UI 부하를 줄임

- 메시지 영역을 ScrollViewer+StackPanel 직접 조작 구조에서 ListBox+ObservableCollection 기반 transcript 호스트로 전환
- ChatWindow.TranscriptHost 도입으로 transcript 요소 추가·교체·삭제·스크롤 접근을 공용 helper로 정리
- 코워크/코드 실행 중 RenderMessages와 라이브 카드가 MessagePanel.Children 직접 조작에 덜 의존하도록 정리
- MessageBubble, AgentEventRendering, Timeline, UserAsk, ConversationManagement 등 transcript 관련 partial을 새 호스트 구조에 맞게 전환
- 향후 claw-code의 VirtualMessageList 수준 가상화를 적용할 수 있는 기반을 마련
- README와 DEVELOPMENT 문서를 2026-04-08 12:52 (KST) 기준으로 갱신
- 검증: dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\\verify\\ -p:IntermediateOutputPath=obj\\verify\\ (경고 0, 오류 0)

src/AxCopilot/Views/ChatWindow.xaml.cs

@@ -218,6 +218,7 @@ public partial class ChatWindow : Window
     public ChatWindow(SettingsService settings)
     {
         InitializeComponent();
+        InitializeTranscriptHost();
         _settings = settings;
         _settings.SettingsChanged += Settings_SettingsChanged;
         _storage = new ChatStorageService();
@@ -377,8 +378,6 @@ public partial class ChatWindow : Window
             UpdateResponsiveChatLayout();
             UpdateInputBoxHeight();
             InputBox.Focus();
-            MessageScroll.ScrollChanged += MessageScroll_ScrollChanged;
-
             // ── 무거운 작업은 유휴 시점에 비동기 실행 ──
             Dispatcher.BeginInvoke(() =>
             {
@@ -637,7 +636,7 @@ public partial class ChatWindow : Window
     private void MessageScroll_ScrollChanged(object sender, ScrollChangedEventArgs e)
     {
         // 스크롤 가능 영역이 없으면(콘텐츠가 짧음) 항상 바닥
-        if (MessageScroll.ScrollableHeight <= 1)
+        if (GetTranscriptScrollableHeight() <= 1)
         {
             _userScrolled = false;
             return;
@@ -647,7 +646,7 @@ public partial class ChatWindow : Window
         if (Math.Abs(e.ExtentHeightChange) > 0.5)
             return;
 
-        var atBottom = MessageScroll.VerticalOffset >= MessageScroll.ScrollableHeight - 40;
+        var atBottom = GetTranscriptVerticalOffset() >= GetTranscriptScrollableHeight() - 40;
         _userScrolled = !atBottom;
     }
 
@@ -667,14 +666,14 @@ public partial class ChatWindow : Window
     /// <summary>부드러운 자동 스크롤 — 하단으로 부드럽게 이동합니다.</summary>
     private void SmoothScrollToEnd()
     {
-        var targetOffset = MessageScroll.ScrollableHeight;
-        var currentOffset = MessageScroll.VerticalOffset;
+        var targetOffset = GetTranscriptScrollableHeight();
+        var currentOffset = GetTranscriptVerticalOffset();
         var diff = targetOffset - currentOffset;
 
         // 스트리밍 중이거나 차이가 작으면 즉시 이동 (UI 부하 최소화)
         if (diff <= 60 || _isStreaming)
         {
-            MessageScroll.ScrollToEnd();
+            ScrollTranscriptToEnd();
             return;
         }
 
@@ -686,7 +685,7 @@ public partial class ChatWindow : Window
             Duration = TimeSpan.FromMilliseconds(200),
             EasingFunction = new CubicEase { EasingMode = EasingMode.EaseOut },
         };
-        animation.Completed += (_, _) => MessageScroll.ScrollToVerticalOffset(targetOffset);
+        animation.Completed += (_, _) => ScrollTranscriptToVerticalOffset(targetOffset);
 
         // ScrollViewer에 직접 애니메이션을 적용할 수 없으므로 타이머 기반으로 보간
         var startTime = DateTime.UtcNow;
@@ -698,7 +697,7 @@ public partial class ChatWindow : Window
             var progress = Math.Min(elapsed / 200.0, 1.0);
             var eased = 1.0 - Math.Pow(1.0 - progress, 3);
             var offset = currentOffset + diff * eased;
-            MessageScroll.ScrollToVerticalOffset(offset);
+            ScrollTranscriptToVerticalOffset(offset);
 
             if (progress >= 1.0)
             {
@@ -1505,7 +1504,7 @@ public partial class ChatWindow : Window
             lock (_convLock) _currentConversation = conv;
             SyncTabConversationIdsFromSession();
             SaveLastConversations();
-            MessagePanel.Children.Clear();
+            ClearTranscriptElements();
             RenderMessages();
             EmptyState.Visibility = conv.Messages.Count > 0 ? Visibility.Collapsed : Visibility.Visible;
             UpdateChatTitle();
@@ -1520,7 +1519,7 @@ public partial class ChatWindow : Window
             _currentConversation = ChatSession?.CreateFreshConversation(_activeTab, _settings)
                 ?? new ChatConversation { Tab = _activeTab };
         }
-        MessagePanel.Children.Clear();
+        ClearTranscriptElements();
         EmptyState.Visibility = Visibility.Visible;
         _attachedFiles.Clear();
         RefreshAttachedFilesUI();
@@ -2298,8 +2297,8 @@ public partial class ChatWindow : Window
 
     private void RenderMessages(bool preserveViewport = false)
     {
-        var previousScrollableHeight = MessageScroll?.ScrollableHeight ?? 0;
-        var previousVerticalOffset = MessageScroll?.VerticalOffset ?? 0;
+        var previousScrollableHeight = GetTranscriptScrollableHeight();
+        var previousVerticalOffset = GetTranscriptVerticalOffset();
 
         ChatConversation? conv;
         lock (_convLock) conv = _currentConversation;
@@ -2318,7 +2317,7 @@ public partial class ChatWindow : Window
 
         if (conv == null || (visibleMessages.Count == 0 && visibleEvents.Count == 0))
         {
-            MessagePanel.Children.Clear();
+            ClearTranscriptElements();
             _runBannerAnchors.Clear();
             _lastRenderedTimelineKeys.Clear();
             _lastRenderedMessageCount = 0;
@@ -2355,13 +2354,13 @@ public partial class ChatWindow : Window
 
         // ── 증분 렌더링: 이전 키 목록과 비교하여 변경 최소화 ──
         // agent live card가 존재하면 Children과 키 불일치 가능 → 전체 재빌드
-        var hasExternalChildren = _agentLiveContainer != null && MessagePanel.Children.Contains(_agentLiveContainer);
+        var hasExternalChildren = _agentLiveContainer != null && ContainsTranscriptElement(_agentLiveContainer);
         var expectedChildCount = _lastRenderedTimelineKeys.Count + (_lastRenderedHiddenCount > 0 ? 1 : 0);
         var canIncremental = !hasExternalChildren
             && _lastRenderedTimelineKeys.Count > 0
             && newKeys.Count >= _lastRenderedTimelineKeys.Count
             && _lastRenderedHiddenCount == hiddenCount
-            && MessagePanel.Children.Count == expectedChildCount;
+            && GetTranscriptElementCount() == expectedChildCount;
 
         if (canIncremental)
         {
@@ -2392,8 +2391,8 @@ public partial class ChatWindow : Window
                 try
                 {
                     // 이전 live 요소를 Children 끝에서 제거
-                    for (int r = 0; r < prevLiveCount && MessagePanel.Children.Count > 0; r++)
-                        MessagePanel.Children.RemoveAt(MessagePanel.Children.Count - 1);
+                    for (int r = 0; r < prevLiveCount && GetTranscriptElementCount() > 0; r++)
+                        RemoveTranscriptElementAt(GetTranscriptElementCount() - 1);
 
                     // 안정 접두사 이후의 새 아이템 렌더링 (새 stable + 새 live 포함)
                     for (int i = prevStableCount; i < visibleTimeline.Count; i++)
@@ -2418,18 +2417,18 @@ public partial class ChatWindow : Window
         if (!incremented)
         {
             // ── 전체 재빌드 (대화 전환, 접기/펴기, 중간 변경 등) ──
-            MessagePanel.Children.Clear();
+            ClearTranscriptElements();
             _runBannerAnchors.Clear();
 
             if (hiddenCount > 0)
-                MessagePanel.Children.Add(CreateTimelineLoadMoreCard(hiddenCount));
+                AddTranscriptElement(CreateTimelineLoadMoreCard(hiddenCount));
 
             foreach (var item in visibleTimeline)
                 item.Render();
 
             // 전체 재빌드로 Children이 초기화되었으므로 agent live card 복원
-            if (_agentLiveContainer != null && !MessagePanel.Children.Contains(_agentLiveContainer))
-                MessagePanel.Children.Add(_agentLiveContainer);
+            if (_agentLiveContainer != null && !ContainsTranscriptElement(_agentLiveContainer))
+                AddTranscriptElement(_agentLiveContainer);
 
             _lastRenderedTimelineKeys = newKeys;
             _lastRenderedHiddenCount = hiddenCount;
@@ -2443,21 +2442,20 @@ public partial class ChatWindow : Window
         {
             _ = Dispatcher.InvokeAsync(() =>
             {
-                if (MessageScroll != null)
-                    MessageScroll.ScrollToEnd();
+                ScrollTranscriptToEnd();
             }, DispatcherPriority.Background);
             return;
         }
 
         _ = Dispatcher.InvokeAsync(() =>
         {
-            if (MessageScroll == null)
+            if (_transcriptScrollViewer == null)
                 return;
 
-            var newScrollableHeight = MessageScroll.ScrollableHeight;
+            var newScrollableHeight = GetTranscriptScrollableHeight();
             var delta = newScrollableHeight - previousScrollableHeight;
             var targetOffset = Math.Max(0, previousVerticalOffset + Math.Max(0, delta));
-            MessageScroll.ScrollToVerticalOffset(targetOffset);
+            ScrollTranscriptToVerticalOffset(targetOffset);
         }, DispatcherPriority.Background);
     }
 
@@ -2598,7 +2596,7 @@ public partial class ChatWindow : Window
             if (now - _lastScrollTick >= 150)
             {
                 _lastScrollTick = now;
-                MessageScroll.ScrollToVerticalOffset(MessageScroll.ScrollableHeight);
+                ScrollTranscriptToVerticalOffset(GetTranscriptScrollableHeight());
             }
         }
     }
@@ -2636,7 +2634,7 @@ public partial class ChatWindow : Window
         // 탭 기억 초기화 (새 대화이므로)
         _tabConversationId[_activeTab] = null;
         SyncTabConversationIdsToSession();
-        MessagePanel.Children.Clear();
+        ClearTranscriptElements();
         _attachedFiles.Clear();
         RefreshAttachedFilesUI();
         LoadConversationSettings();
@@ -2688,7 +2686,7 @@ public partial class ChatWindow : Window
         {
             var conv = session.LoadOrCreateConversation(_activeTab, _storage, _settings);
             lock (_convLock) _currentConversation = conv;
-            MessagePanel.Children.Clear();
+            ClearTranscriptElements();
             RenderMessages();
             EmptyState.Visibility = conv.Messages.Count > 0 ? Visibility.Collapsed : Visibility.Visible;
             UpdateChatTitle();
@@ -5910,7 +5908,7 @@ public partial class ChatWindow : Window
                 _cachedStreamContent = "";
                 _displayedLength = 0;
                 _cursorVisible = true;
-                MessagePanel.Children.Add(streamingContainer);
+                AddTranscriptElement(streamingContainer);
                 ForceScrollToEnd();
                 _cursorTimer.Start();
                 _typingTimer.Start();
@@ -6028,7 +6026,7 @@ public partial class ChatWindow : Window
 
     private async Task ShowTypedAssistantPreviewAsync(string finalContent, CancellationToken ct)
     {
-        if (string.IsNullOrWhiteSpace(finalContent) || MessagePanel == null)
+        if (string.IsNullOrWhiteSpace(finalContent))
             return;
 
         // 라이브 카드 제거 (최종 메시지 버블 표시 전)
@@ -6043,7 +6041,7 @@ public partial class ChatWindow : Window
         // 모든 상태를 로컬 변수로 관리하고 await Task.Delay로 UI 스레드 양보
         var displayedLength = 0;
         var cursorVisible = true;
-        MessagePanel.Children.Add(container);
+        AddTranscriptElement(container);
         ForceScrollToEnd();
         streamText.Text = "\u258c";
 
@@ -7019,7 +7017,7 @@ public partial class ChatWindow : Window
 
     private void ShowAgentLiveCard(string runTab)
     {
-        if (MessagePanel == null) return;
+        if (MessageList == null) return;
         if (!string.Equals(runTab, _activeTab, StringComparison.OrdinalIgnoreCase)) return;
 
         RemoveAgentLiveCard(animated: false); // 기존 카드 즉시 제거
@@ -7127,7 +7125,7 @@ public partial class ChatWindow : Window
         container.Children.Add(card);
 
         _agentLiveContainer = container;
-        MessagePanel.Children.Add(container);
+        AddTranscriptElement(container);
         ForceScrollToEnd();
 
         // 경과 시간 타이머
@@ -7199,15 +7197,15 @@ public partial class ChatWindow : Window
         _agentLiveSubItemTexts.Clear();
         _agentLiveCurrentCategory = null;
 
-        if (animated && MessagePanel != null && MessagePanel.Children.Contains(toRemove) && !IsLightweightLiveProgressMode())
+        if (animated && ContainsTranscriptElement(toRemove) && !IsLightweightLiveProgressMode())
         {
             var anim = new DoubleAnimation(toRemove.Opacity, 0, TimeSpan.FromMilliseconds(160));
-            anim.Completed += (_, _) => MessagePanel?.Children.Remove(toRemove);
+            anim.Completed += (_, _) => RemoveTranscriptElement(toRemove);
             toRemove.BeginAnimation(UIElement.OpacityProperty, anim);
         }
         else
         {
-            MessagePanel?.Children.Remove(toRemove);
+            RemoveTranscriptElement(toRemove);
         }
     }
 
@@ -7505,7 +7503,7 @@ public partial class ChatWindow : Window
             };
 
         var runTab = string.IsNullOrWhiteSpace(_streamRunTab) ? _activeTab : _streamRunTab!;
-        if (MessagePanel != null
+        if (MessageList != null
             && string.Equals(runTab, _activeTab, StringComparison.OrdinalIgnoreCase)
             && !IsLightweightLiveProgressMode(runTab))
             ScheduleExecutionHistoryRender(autoScroll: false);
@@ -7882,7 +7880,7 @@ public partial class ChatWindow : Window
         card.BeginAnimation(UIElement.OpacityProperty,
             new DoubleAnimation(0, 1, TimeSpan.FromMilliseconds(300)));
 
-        MessagePanel.Children.Add(card);
+        AddTranscriptElement(card);
     }
 
     /// <summary>계획 카드 아래에 승인/수정/취소 의사결정 버튼을 추가합니다.</summary>
@@ -8138,7 +8136,7 @@ public partial class ChatWindow : Window
 
         // 슬라이드 + 페이드 등장 애니메이션
         ApplyMessageEntryAnimation(container);
-        MessagePanel.Children.Add(container);
+        AddTranscriptElement(container);
         ForceScrollToEnd(); // 의사결정 버튼 표시 시 강제 하단 이동
 
         // PlanViewerWindow 등 외부에서 TCS가 완료되면 인라인 버튼도 자동 접기
@@ -8726,7 +8724,7 @@ public partial class ChatWindow : Window
         {
             var feedback = textBox.Text.Trim();
             if (string.IsNullOrEmpty(feedback)) return;
-            MessagePanel.Children.Remove(container);
+            RemoveTranscriptElement(container);
             _ = RetryWithFeedbackAsync(feedback);
         };
 
@@ -8738,7 +8736,7 @@ public partial class ChatWindow : Window
             Cursor = Cursors.Hand,
         };
         cancelBtn.Child = new TextBlock { Text = "취소", FontSize = 12, Foreground = secondaryText };
-        cancelBtn.MouseLeftButtonUp += (_, _) => MessagePanel.Children.Remove(container);
+        cancelBtn.MouseLeftButtonUp += (_, _) => RemoveTranscriptElement(container);
 
         btnRow.Children.Add(cancelBtn);
         btnRow.Children.Add(sendBtn);
@@ -8746,7 +8744,7 @@ public partial class ChatWindow : Window
         container.Child = stack;
 
         ApplyMessageEntryAnimation(container);
-        MessagePanel.Children.Add(container);
+        AddTranscriptElement(container);
         ForceScrollToEnd();
         textBox.Focus();
     }
@@ -8827,7 +8825,7 @@ public partial class ChatWindow : Window
         if (hostWidth < 100)
             hostWidth = ComposerShell?.ActualWidth ?? 0;
         if (hostWidth < 100)
-            hostWidth = MessageScroll?.ActualWidth ?? 0;
+            hostWidth = MessageList?.ActualWidth ?? 0;
         if (hostWidth < 100)
             hostWidth = 1120;
 
@@ -8837,7 +8835,7 @@ public partial class ChatWindow : Window
 
     private bool UpdateResponsiveChatLayout()
     {
-        var viewportWidth = MessageScroll?.ActualWidth ?? 0;
+        var viewportWidth = MessageList?.ActualWidth ?? 0;
         if (viewportWidth < 200)
             viewportWidth = ActualWidth;
         if (viewportWidth < 200)
@@ -8859,8 +8857,8 @@ public partial class ChatWindow : Window
         if (Math.Abs(_lastResponsiveMessageWidth - messageWidth) > 1)
         {
             _lastResponsiveMessageWidth = messageWidth;
-            if (MessagePanel != null)
-                MessagePanel.MaxWidth = messageWidth;
+            if (MessageList != null)
+                MessageList.MaxWidth = messageWidth + 48;
             if (EmptyState != null)
                 EmptyState.MaxWidth = messageWidth;
             changed = true;
@@ -9646,15 +9644,15 @@ public partial class ChatWindow : Window
         // MessagePanel에서 해당 메시지 인덱스의 자식 요소를 찾아 스크롤
         // 메시지 패널의 자식 수가 대화 메시지 수와 정확히 일치하지 않을 수 있으므로
         // (배너, 계획카드 등 섞임) BringIntoView로 대략적 위치 이동
-        if (msgIndex < MessagePanel.Children.Count)
+        if (msgIndex < GetTranscriptElementCount())
         {
-            var element = MessagePanel.Children[msgIndex] as FrameworkElement;
+            var element = GetTranscriptElementAt(msgIndex) as FrameworkElement;
             element?.BringIntoView();
         }
-        else if (MessagePanel.Children.Count > 0)
+        else if (GetTranscriptElementCount() > 0)
         {
             // 범위 밖이면 마지막 자식으로 이동
-            (MessagePanel.Children[^1] as FrameworkElement)?.BringIntoView();
+            (GetTranscriptElementAt(GetTranscriptElementCount() - 1) as FrameworkElement)?.BringIntoView();
         }
     }
 
@@ -14604,7 +14602,7 @@ public partial class ChatWindow : Window
             _currentConversation = null;
             SyncTabConversationIdsFromSession();
         }
-        MessagePanel.Children.Clear();
+        ClearTranscriptElements();
         EmptyState.Visibility = Visibility.Visible;
         UpdateChatTitle();
         RefreshConversationList();