AX Agent transcript 렌더 계획/적용 구조를 분리해 유지보수성을 높이고 문서를 갱신한다

- ChatWindow transcript 렌더를 planner/execution 단계로 분리해 RenderMessages 오케스트레이션을 단순화함
- TranscriptRenderPlanner/TranscriptRenderExecution partial을 추가해 planning과 host 적용 책임을 나눔
- README와 DEVELOPMENT 문서에 2026-04-09 09:37 (KST) 기준 구조 개선 이력을 반영함
- dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\\verify\\ -p:IntermediateOutputPath=obj\\verify\\ 검증 결과 경고 0개 오류 0개

src/AxCopilot/Views/ChatWindow.TranscriptRenderExecution.cs

@@ -0,0 +1,60 @@
+namespace AxCopilot.Views;
+
+public partial class ChatWindow
+{
+    private bool TryApplyIncrementalTranscriptRender(TranscriptRenderPlan renderPlan)
+    {
+        if (!renderPlan.CanIncremental)
+            return false;
+
+        var prefixMatch = true;
+        for (var i = 0; i < renderPlan.PreviousStableCount; i++)
+        {
+            if (i >= renderPlan.NewKeys.Count || !string.Equals(_lastRenderedTimelineKeys[i], renderPlan.NewKeys[i], StringComparison.Ordinal))
+            {
+                prefixMatch = false;
+                break;
+            }
+        }
+
+        if (!prefixMatch)
+            return false;
+
+        try
+        {
+            for (var removeIndex = 0; removeIndex < renderPlan.PreviousLiveCount && GetTranscriptElementCount() > 0; removeIndex++)
+                RemoveTranscriptElementAt(GetTranscriptElementCount() - 1);
+
+            for (var i = renderPlan.PreviousStableCount; i < renderPlan.VisibleTimeline.Count; i++)
+                renderPlan.VisibleTimeline[i].Render();
+
+            _lastRenderedTimelineKeys = renderPlan.NewKeys;
+            _lastRenderedHiddenCount = renderPlan.HiddenCount;
+            return true;
+        }
+        catch (Exception ex)
+        {
+            Services.LogService.Warn($"증분 transcript 렌더 실패, 전체 렌더로 전환: {ex.Message}");
+            _lastRenderedTimelineKeys.Clear();
+            return false;
+        }
+    }
+
+    private void ApplyFullTranscriptRender(TranscriptRenderPlan renderPlan)
+    {
+        ClearTranscriptElements();
+        _runBannerAnchors.Clear();
+
+        if (renderPlan.HiddenCount > 0)
+            AddTranscriptElement(CreateTimelineLoadMoreCard(renderPlan.HiddenCount));
+
+        foreach (var item in renderPlan.VisibleTimeline)
+            item.Render();
+
+        if (_agentLiveContainer != null && !ContainsTranscriptElement(_agentLiveContainer))
+            AddTranscriptElement(_agentLiveContainer);
+
+        _lastRenderedTimelineKeys = renderPlan.NewKeys;
+        _lastRenderedHiddenCount = renderPlan.HiddenCount;
+    }
+}