AX Agent: 실행 이벤트 세션 변이 경로 엔진으로 통합

- ChatWindow에 중복돼 있던 실행 이벤트/Agent run 교차 탭 복원 로직을 AxAgentExecutionEngine helper로 이동함

- AppendExecutionEvent, AppendAgentRun이 공통 session mutation 경로를 사용하도록 정리해 이후 runtime state 공통화 기반을 마련함

- README와 DEVELOPMENT 문서에 2026-04-05 15:42 (KST) 기준 변경 이력 반영

- 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/Services/Agent/AxAgentExecutionEngine.cs

@@ -16,6 +16,9 @@ public sealed class AxAgentExecutionEngine
         ExecutionMode Mode,
         IReadOnlyList<string> PromptStack,
         List<ChatMessage> Messages);
+    public sealed record SessionMutationResult(
+        ChatConversation CurrentConversation,
+        ChatConversation UpdatedConversation);
 
     public IReadOnlyList<string> BuildPromptStack(
         string? conversationSystem,
@@ -159,6 +162,42 @@ public sealed class AxAgentExecutionEngine
         return normalized;
     }
 
+    public SessionMutationResult AppendExecutionEvent(
+        ChatSessionStateService session,
+        ChatStorageService storage,
+        ChatConversation? activeConversation,
+        string activeTab,
+        string targetTab,
+        AgentEvent evt)
+    {
+        return ApplyConversationMutation(
+            session,
+            storage,
+            activeConversation,
+            activeTab,
+            targetTab,
+            normalizedTarget => session.AppendExecutionEvent(normalizedTarget, evt, null));
+    }
+
+    public SessionMutationResult AppendAgentRun(
+        ChatSessionStateService session,
+        ChatStorageService storage,
+        ChatConversation? activeConversation,
+        string activeTab,
+        string targetTab,
+        AgentEvent evt,
+        string status,
+        string summary)
+    {
+        return ApplyConversationMutation(
+            session,
+            storage,
+            activeConversation,
+            activeTab,
+            targetTab,
+            normalizedTarget => session.AppendAgentRun(normalizedTarget, evt, status, summary, null));
+    }
+
     public string NormalizeAssistantContent(
         ChatConversation conversation,
         string runTab,
@@ -208,4 +247,86 @@ public sealed class AxAgentExecutionEngine
             FileName = source.FileName,
         };
     }
+
+    private static SessionMutationResult ApplyConversationMutation(
+        ChatSessionStateService session,
+        ChatStorageService storage,
+        ChatConversation? activeConversation,
+        string activeTab,
+        string targetTab,
+        Func<string, ChatConversation> mutate)
+    {
+        var normalizedTarget = NormalizeTabName(targetTab);
+        var normalizedActive = NormalizeTabName(activeTab);
+        ChatConversation updatedConversation;
+
+        if (string.Equals(normalizedTarget, normalizedActive, StringComparison.OrdinalIgnoreCase))
+        {
+            session.CurrentConversation = updatedConversation = mutate(normalizedTarget);
+            return new SessionMutationResult(updatedConversation, updatedConversation);
+        }
+
+        var activeSnapshot = activeConversation;
+        var previousSessionConversation = session.CurrentConversation;
+        updatedConversation = mutate(normalizedTarget);
+
+        if (activeSnapshot != null
+            && string.Equals(NormalizeTabName(activeSnapshot.Tab), normalizedActive, StringComparison.OrdinalIgnoreCase))
+        {
+            session.CurrentConversation = activeSnapshot;
+            return new SessionMutationResult(activeSnapshot, updatedConversation);
+        }
+
+        if (previousSessionConversation != null
+            && string.Equals(NormalizeTabName(previousSessionConversation.Tab), normalizedActive, StringComparison.OrdinalIgnoreCase))
+        {
+            session.CurrentConversation = previousSessionConversation;
+            return new SessionMutationResult(previousSessionConversation, updatedConversation);
+        }
+
+        var activeId = session.GetConversationId(normalizedActive);
+        var restoredConversation = string.IsNullOrWhiteSpace(activeId)
+            ? null
+            : storage.Load(activeId);
+
+        if (restoredConversation != null)
+        {
+            session.CurrentConversation = restoredConversation;
+            return new SessionMutationResult(restoredConversation, updatedConversation);
+        }
+
+        var fallbackConversation = session.LoadOrCreateConversation(normalizedActive, storage, GetFallbackSettings());
+        session.CurrentConversation = fallbackConversation;
+        return new SessionMutationResult(fallbackConversation, updatedConversation);
+    }
+
+    private static SettingsService GetFallbackSettings()
+    {
+        return (System.Windows.Application.Current as App)?.SettingsService
+            ?? new SettingsService();
+    }
+
+    private static string NormalizeTabName(string? tab)
+    {
+        var normalized = (tab ?? "").Trim();
+        if (string.IsNullOrEmpty(normalized))
+            return "Chat";
+
+        if (normalized.Contains("코워크", StringComparison.OrdinalIgnoreCase))
+            return "Cowork";
+
+        var canonical = new string(normalized
+            .Where(char.IsLetterOrDigit)
+            .ToArray())
+            .ToLowerInvariant();
+
+        if (canonical is "cowork" or "coworkcode" or "coworkcodetab")
+            return "Cowork";
+
+        if (normalized.Contains("코드", StringComparison.OrdinalIgnoreCase)
+            || canonical is "code" or "codetab")
+            return "Code";
+
+        return "Chat";
+    }
 }