AX Agent 스트리밍 중 탭 전환과 새 대화가 멈추는 저장 루프 회귀 수정

원인: 같은 LastActiveTab·LastConversationIds 상태에서도 ChatSessionStateService.Save가 매번 settings.Save를 호출해 SettingsChanged -> UpdateTabUI -> SwitchToTabConversation -> SaveLastConversations 순환이 계속 발생했습니다. 이 때문에 시간 표시가 0초에 머무르고 탭 전환/새 대화가 즉시 덮어써졌습니다.

수정: ChatSessionStateService는 세션 스냅샷이 실제로 바뀐 경우에만 저장하도록 변경했고, 동일 상태 반복 저장 시 Save와 SettingsChanged가 재발화하지 않도록 테스트를 추가했습니다.

검증: dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\verify_streaming_tab_loop_fix\ -p:IntermediateOutputPath=obj\verify_streaming_tab_loop_fix\ (경고 0 / 오류 0), dotnet test src/AxCopilot.Tests/AxCopilot.Tests.csproj -c Release -v minimal --filter ChatSessionStateServiceTests|ChatStreamingUiPolicyTests|AxAgentExecutionEngineTests -p:OutputPath=bin\verify_streaming_tab_loop_fix_tests\ -p:IntermediateOutputPath=obj\verify_streaming_tab_loop_fix_tests\ (통과 51)

src/AxCopilot.Tests/Services/ChatSessionStateServiceTests.cs

@@ -8,6 +8,32 @@ namespace AxCopilot.Tests.Services;
 
 public class ChatSessionStateServiceTests
 {
+    private sealed class TrackingSettingsService : ISettingsService
+    {
+        public AppSettings Settings { get; } = new();
+        public string? MigrationSummary => null;
+        public event EventHandler? SettingsChanged;
+        public int SaveCount { get; private set; }
+        public int SaveAsyncCount { get; private set; }
+
+        public void Load()
+        {
+        }
+
+        public void Save()
+        {
+            SaveCount++;
+            SettingsChanged?.Invoke(this, EventArgs.Empty);
+        }
+
+        public Task SaveAsync()
+        {
+            SaveAsyncCount++;
+            SettingsChanged?.Invoke(this, EventArgs.Empty);
+            return Task.CompletedTask;
+        }
+    }
+
     [Fact]
     public void AppendExecutionEvent_CreatesConversationAndTrimsToLatest400()
     {
@@ -533,6 +559,57 @@ public class ChatSessionStateServiceTests
         session.GetConversationId("Chat").Should().Be("conv-chat-lower");
     }
 
+    [Fact]
+    public void Save_DoesNotPersistOrRaiseEvents_WhenSessionStateIsUnchanged()
+    {
+        var session = new ChatSessionStateService
+        {
+            ActiveTab = "Code",
+        };
+        session.RememberConversation("Code", "conv-code");
+        session.RememberConversation("Chat", "conv-chat");
+
+        var settings = new TrackingSettingsService();
+        settings.Settings.Llm.LastActiveTab = "Code";
+        settings.Settings.Llm.LastConversationIds = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
+        {
+            ["Code"] = "conv-code",
+            ["Chat"] = "conv-chat",
+        };
+
+        var eventCount = 0;
+        settings.SettingsChanged += (_, _) => eventCount++;
+
+        session.Save(settings);
+
+        settings.SaveCount.Should().Be(0);
+        eventCount.Should().Be(0);
+    }
+
+    [Fact]
+    public void Save_PersistsAndRaisesEvents_WhenSessionStateChanges()
+    {
+        var session = new ChatSessionStateService
+        {
+            ActiveTab = "Code",
+        };
+        session.RememberConversation("Code", "conv-code");
+
+        var settings = new TrackingSettingsService();
+        settings.Settings.Llm.LastActiveTab = "Chat";
+        settings.Settings.Llm.LastConversationIds = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+
+        var eventCount = 0;
+        settings.SettingsChanged += (_, _) => eventCount++;
+
+        session.Save(settings);
+
+        settings.SaveCount.Should().Be(1);
+        eventCount.Should().Be(1);
+        settings.Settings.Llm.LastActiveTab.Should().Be("Code");
+        settings.Settings.Llm.LastConversationIds.Should().ContainKey("Code").WhoseValue.Should().Be("conv-code");
+    }
+
     [Fact]
     public void AppendMessage_FirstUserMessageUpdatesConversationTitle()
     {

src/AxCopilot/Services/ChatSessionStateService.cs

@@ -70,16 +70,49 @@ public sealed class ChatSessionStateService
     public void Save(ISettingsService settings)
     {
         var llm = settings.Settings.Llm;
-        llm.LastActiveTab = NormalizeTab(ActiveTab);
+        var normalizedActiveTab = NormalizeTab(ActiveTab);
+        var snapshot = BuildConversationSnapshot();
 
+        if (string.Equals(NormalizeTab(llm.LastActiveTab), normalizedActiveTab, StringComparison.OrdinalIgnoreCase)
+            && ConversationSnapshotEquals(llm.LastConversationIds, snapshot))
+        {
+            return;
+        }
+
+        llm.LastActiveTab = normalizedActiveTab;
+        llm.LastConversationIds = snapshot;
+        settings.Save();
+    }
+
+    private Dictionary<string, string> BuildConversationSnapshot()
+    {
         var snapshot = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
         foreach (var kv in TabConversationIds)
         {
             if (!string.IsNullOrWhiteSpace(kv.Value))
                 snapshot[kv.Key] = kv.Value!;
         }
-        llm.LastConversationIds = snapshot;
-        settings.Save();
+
+        return snapshot;
+    }
+
+    private static bool ConversationSnapshotEquals(
+        IReadOnlyDictionary<string, string> existing,
+        IReadOnlyDictionary<string, string> incoming)
+    {
+        if (existing.Count != incoming.Count)
+            return false;
+
+        foreach (var kv in incoming)
+        {
+            if (!existing.TryGetValue(kv.Key, out var value)
+                || !string.Equals(value, kv.Value, StringComparison.Ordinal))
+            {
+                return false;
+            }
+        }
+
+        return true;
     }
 
     public void RememberConversation(string tab, string? conversationId)