AX Agent 실행 선택 분기를 엔진으로 이관

- AxAgentExecutionEngine에 ExecutePreparedAsync를 추가해 AgentLoop와 일반 LLM 호출 선택을 엔진이 담당하도록 정리함

- SendMessageAsync와 SendRegenerateAsync가 공통 실행 진입점을 사용하도록 바꿔 창 코드의 중복 분기를 줄임

- 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

@@ -74,6 +74,17 @@ public sealed class AxAgentExecutionEngine
         return new PreparedExecution(mode, promptStack, preparedTurn.Messages);
     }
 
+    public Task<string> ExecutePreparedAsync(
+        PreparedExecution prepared,
+        Func<IReadOnlyList<ChatMessage>, CancellationToken, Task<string>> agentLoopRunner,
+        Func<IReadOnlyList<ChatMessage>, CancellationToken, Task<string>> llmRunner,
+        CancellationToken cancellationToken)
+    {
+        return prepared.Mode.UseAgentLoop
+            ? agentLoopRunner(prepared.Messages, cancellationToken)
+            : llmRunner(prepared.Messages, cancellationToken);
+    }
+
     public PreparedTurn PrepareTurn(
         ChatConversation conversation,
         IEnumerable<string?> systemPrompts,

src/AxCopilot/Views/ChatWindow.xaml.cs

@@ -8408,20 +8408,14 @@ public partial class ChatWindow : Window
                 }
             }
 
-            if (executionMode.UseAgentLoop)
-            {
-                var response = await RunAgentLoopAsync(runTab, originTab, conv, sendMessages, _streamCts!.Token);
-                assistantContent = response;
-                StopAiIconPulse();
-                _cachedStreamContent = response;
-            }
-            else
-            {
-                var response = await _llm.SendAsync(sendMessages, _streamCts.Token);
-                assistantContent = response;
-                StopAiIconPulse();
-                _cachedStreamContent = response;
-            }
+            var response = await _chatEngine.ExecutePreparedAsync(
+                preparedExecution,
+                (messages, token) => RunAgentLoopAsync(runTab, originTab, conv, messages, token),
+                (messages, token) => _llm.SendAsync(messages.ToList(), token),
+                _streamCts.Token);
+            assistantContent = response;
+            StopAiIconPulse();
+            _cachedStreamContent = response;
 
             draftSucceeded = true;
         }
@@ -10981,9 +10975,11 @@ public partial class ChatWindow : Window
             var executionMode = preparedExecution.Mode;
             sendMessages = preparedExecution.Messages;
 
-            var response = executionMode.UseAgentLoop
-                ? await RunAgentLoopAsync(runTab, runTab, conv, sendMessages, _streamCts.Token)
-                : await _llm.SendAsync(sendMessages, _streamCts.Token);
+            var response = await _chatEngine.ExecutePreparedAsync(
+                preparedExecution,
+                (messages, token) => RunAgentLoopAsync(runTab, runTab, conv, messages, token),
+                (messages, token) => _llm.SendAsync(messages.ToList(), token),
+                _streamCts.Token);
             assistantContent = response;
             StopAiIconPulse();
             _cachedStreamContent = response;