AX Agent loop 정책을 분리하고 transcript 가상화·성능 계측 구조를 강화한다

- AgentLoop 검증/문서/compact 정책 메서드를 partial 파일로 분리해 loop 본문의 책임을 줄임
- transcript 렌더에 cache pruning과 deferred scrolling을 적용해 긴 세션의 UI 부담을 낮춤
- AgentPerformanceLogService를 추가해 transcript 렌더와 agent loop 실행 요약을 perf 로그로 남김
- README와 DEVELOPMENT 문서에 2026-04-09 10:08 (KST) 기준 구조 개선 및 계측 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/Services/AgentPerformanceLogService.cs

@@ -0,0 +1,72 @@
+using System.Text;
+using System.Text.Json;
+using System.IO;
+
+namespace AxCopilot.Services;
+
+public static class AgentPerformanceLogService
+{
+    private static readonly string PerfDir;
+    private static readonly object _lock = new();
+    private static readonly JsonSerializerOptions _jsonOptions = new()
+    {
+        WriteIndented = false,
+        Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
+    };
+
+    static AgentPerformanceLogService()
+    {
+        PerfDir = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+            "AxCopilot",
+            "perf");
+        try { Directory.CreateDirectory(PerfDir); } catch { }
+    }
+
+    public static void LogMetric(
+        string area,
+        string name,
+        string conversationId,
+        string tab,
+        long durationMs,
+        object? detail = null)
+    {
+        try
+        {
+            var fileName = $"performance-{DateTime.Now:yyyy-MM-dd}.json";
+            var filePath = Path.Combine(PerfDir, fileName);
+            var json = JsonSerializer.Serialize(new AgentPerformanceEntry
+            {
+                Timestamp = DateTime.Now,
+                Area = area,
+                Name = name,
+                ConversationId = conversationId ?? "",
+                Tab = tab ?? "",
+                DurationMs = durationMs,
+                Detail = detail == null ? "" : JsonSerializer.Serialize(detail, _jsonOptions),
+            }, _jsonOptions);
+
+            lock (_lock)
+            {
+                File.AppendAllText(filePath, json + Environment.NewLine, Encoding.UTF8);
+            }
+        }
+        catch
+        {
+            // 성능 로그 실패는 런타임에 영향 주지 않음
+        }
+    }
+
+    public static string GetPerformanceFolder() => PerfDir;
+}
+
+public sealed class AgentPerformanceEntry
+{
+    public DateTime Timestamp { get; init; }
+    public string Area { get; init; } = "";
+    public string Name { get; init; } = "";
+    public string ConversationId { get; init; } = "";
+    public string Tab { get; init; } = "";
+    public long DurationMs { get; init; }
+    public string Detail { get; init; } = "";
+}