AX Agent 탭 내 대화 선택 복귀 회귀 수정

- 같은 탭 안에서 다른 대화를 선택할 때 SaveLastConversations로 발생한 SettingsChanged가 UI 전체 갱신을 다시 태우며 현재 선택을 스트리밍 대화로 덮어쓰던 흐름을 차단함
- ChatStreamingUiPolicy에 스트리밍 대화 우선 노출 정책을 분리하고, 사용자가 명시적으로 선택한 대화가 있으면 탭 복귀 후에도 해당 선택을 유지하도록 SwitchToTabConversation 분기를 조정함
- README.md와 docs/DEVELOPMENT.md에 2026-04-15 22:07 (KST) 기준 회귀 원인과 검증 결과를 반영함

검증 결과
- dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\verify_conversation_selection_persist\ -p:IntermediateOutputPath=obj\verify_conversation_selection_persist\ : 경고 0 / 오류 0
- dotnet test src/AxCopilot.Tests/AxCopilot.Tests.csproj -c Release -v minimal --filter ChatStreamingUiPolicyTests|ChatSessionStateServiceTests -p:OutputPath=bin\verify_conversation_selection_persist_tests\ -p:IntermediateOutputPath=obj\verify_conversation_selection_persist_tests\ : 통과 55

src/AxCopilot.Tests/Views/ChatStreamingUiPolicyTests.cs

@@ -51,4 +51,22 @@ public class ChatStreamingUiPolicyTests
 
         result.Should().Be(expected);
     }
+
+    [Theory]
+    [InlineData(null, null, false)]
+    [InlineData("run-1", null, true)]
+    [InlineData("run-1", "", true)]
+    [InlineData("run-1", "run-1", true)]
+    [InlineData("run-1", "other-conversation", false)]
+    public void ShouldPreferStreamingConversation_ShouldKeepExplicitConversationSelection(
+        string? streamingConversationId,
+        string? rememberedConversationId,
+        bool expected)
+    {
+        var result = ChatStreamingUiPolicy.ShouldPreferStreamingConversation(
+            streamingConversationId,
+            rememberedConversationId);
+
+        result.Should().Be(expected);
+    }
 }

src/AxCopilot/Views/ChatStreamingUiPolicy.cs

@@ -1,5 +1,7 @@
 namespace AxCopilot.Views;
 
+using System;
+
 internal enum StreamingGuideVisibility
 {
     Hidden,
@@ -26,4 +28,15 @@ internal static class ChatStreamingUiPolicy
 
     internal static bool ShouldRenderConversationBoundContent(StreamingGuideVisibility visibility)
         => visibility == StreamingGuideVisibility.ActiveConversation;
+
+    internal static bool ShouldPreferStreamingConversation(
+        string? streamingConversationId,
+        string? rememberedConversationId)
+    {
+        if (string.IsNullOrWhiteSpace(streamingConversationId))
+            return false;
+
+        return string.IsNullOrWhiteSpace(rememberedConversationId)
+            || string.Equals(streamingConversationId, rememberedConversationId, StringComparison.Ordinal);
+    }
 }

src/AxCopilot/Views/ChatWindow.xaml.cs

@@ -151,6 +151,7 @@ public partial class ChatWindow : Window
     private StackPanel? _selectedMessageActionBar;
     private Border? _selectedMessageBorder;
     private bool _isRefreshingFromSettings;
+    private bool _suppressSettingsRefreshForSessionSave;
     private int? _lastCompactionBeforeTokens;
     private int? _lastCompactionAfterTokens;
     private DateTime? _lastCompactionAt;
@@ -600,7 +601,7 @@ public partial class ChatWindow : Window
 
     private void Settings_SettingsChanged(object? sender, EventArgs e)
     {
-        if (_forceClose || !IsLoaded || _isRefreshingFromSettings)
+        if (_forceClose || !IsLoaded || _isRefreshingFromSettings || _suppressSettingsRefreshForSessionSave)
             return;
 
         Dispatcher.BeginInvoke(new Action(() =>
@@ -1899,13 +1900,20 @@ public partial class ChatWindow : Window
 
         Services.LogService.Info($"[SwitchTab] START tab={_activeTab}, emptyState={EmptyState.Visibility}, streaming={_isStreaming}");
 
-        // 현재 탭에 실행 중인 대화가 있으면 차단하지 않고 해당 대화를 그대로 보여줍니다.
+        // 현재 탭에 실행 중인 대화가 있더라도, 사용자가 같은 탭 안에서 다른 대화를 선택한 상태라면
+        // 해당 선택을 유지하고 상단 가이드만 background conversation 모드로 보여줍니다.
+        var session = ChatSession;
         var streamingConversation = GetStreamingConversation(_activeTab);
-        if (_streamingTabs.Contains(_activeTab) && streamingConversation != null)
+        var rememberedConversationId = session?.GetConversationId(_activeTab);
+        var shouldPreferStreamingConversation = _streamingTabs.Contains(_activeTab)
+            && ChatStreamingUiPolicy.ShouldPreferStreamingConversation(
+                streamingConversation?.Id,
+                rememberedConversationId);
+        if (shouldPreferStreamingConversation && streamingConversation != null)
         {
             Services.LogService.Info($"[SwitchTab] STREAMING_CONV path: tab={_activeTab}, convId={streamingConversation.Id[..Math.Min(8, streamingConversation.Id.Length)]}");
             lock (_convLock)
-                _currentConversation = ChatSession?.SetCurrentConversation(_activeTab, streamingConversation, _storage) ?? streamingConversation;
+                _currentConversation = session?.SetCurrentConversation(_activeTab, streamingConversation, _storage) ?? streamingConversation;
             SyncTabConversationIdsFromSession();
             SaveLastConversations();
             ClearTranscriptElements();
@@ -1919,7 +1927,6 @@ public partial class ChatWindow : Window
             return;
         }
 
-        var session = ChatSession;
         if (session != null)
         {
             var conv = session.LoadOrCreateConversation(_activeTab, _storage, _settings);
@@ -3391,7 +3398,15 @@ public partial class ChatWindow : Window
         {
             SyncTabConversationIdsToSession();
             session.ActiveTab = _activeTab;
-            session.Save(_settings);
+            _suppressSettingsRefreshForSessionSave = true;
+            try
+            {
+                session.Save(_settings);
+            }
+            finally
+            {
+                _suppressSettingsRefreshForSessionSave = false;
+            }
             SyncTabConversationIdsFromSession();
             return;
         }