에이전트 선택적 탐색 구조 개선과 경고 정리 반영

- claude-code 선택적 탐색 흐름을 참고해 Cowork/Code 시스템 프롬프트에서 folder_map 상시 선행 지시를 완화하고 glob/grep 기반 좁은 탐색을 우선하도록 조정함

- FolderMapTool 기본 depth를 2로, include_files 기본값을 false로 낮추고 MultiReadTool 최대 파일 수를 8개로 줄여 초기 과탐색 폭을 보수적으로 조정함

- AgentLoopExplorationPolicy partial을 추가해 탐색 범위 분류, broad-scan corrective hint, exploration_breadth 성능 로그를 연결함

- AgentLoopService에 탐색 범위 가이드 주입과 실행 중 탐색 폭 추적을 추가하고, 좁은 질문에서 반복적인 folder_map/대량 multi_read를 교정하도록 정리함

- DocxToHtmlConverter nullable 경고를 수정해 Release 빌드 경고 0 / 오류 0 기준을 다시 충족함

- README와 docs/DEVELOPMENT.md에 2026-04-09 10:36 (KST) 기준 개발 이력을 반영함

src/AxCopilot/Services/Agent/PptxSkill.cs

@@ -298,12 +298,12 @@ public class PptxSkill : IAgentTool
 
     public async Task<ToolResult> ExecuteAsync(JsonElement args, AgentContext context, CancellationToken ct)
     {
-        var presTitle = args.TryGetProperty("title", out var tt) ? tt.GetString() ?? "Presentation" : "Presentation";
+        var presTitle = args.SafeTryGetProperty("title", out var tt) ? tt.SafeGetString() ?? "Presentation" : "Presentation";
         string path;
-        if (args.TryGetProperty("path", out var pathEl) && pathEl.ValueKind == JsonValueKind.String
-            && !string.IsNullOrWhiteSpace(pathEl.GetString()))
+        if (args.SafeTryGetProperty("path", out var pathEl) && pathEl.ValueKind == JsonValueKind.String
+            && !string.IsNullOrWhiteSpace(pathEl.SafeGetString()))
         {
-            path = pathEl.GetString()!;
+            path = pathEl.SafeGetString()!;
         }
         else
         {
@@ -311,10 +311,10 @@ public class PptxSkill : IAgentTool
             if (safe.Length > 60) safe = safe[..60].TrimEnd();
             path = (string.IsNullOrWhiteSpace(safe) ? "presentation" : safe) + ".pptx";
         }
-        var theme     = args.TryGetProperty("theme",  out var th)  ? th.GetString()  ?? "professional"  : "professional";
-        var aspect    = args.TryGetProperty("aspect", out var asp) ? asp.GetString() ?? "widescreen"    : "widescreen";
+        var theme     = args.SafeTryGetProperty("theme",  out var th)  ? th.SafeGetString()  ?? "professional"  : "professional";
+        var aspect    = args.SafeTryGetProperty("aspect", out var asp) ? asp.SafeGetString() ?? "widescreen"    : "widescreen";
 
-        if (!args.TryGetProperty("slides", out var slidesEl) || slidesEl.ValueKind != JsonValueKind.Array)
+        if (!args.SafeTryGetProperty("slides", out var slidesEl) || slidesEl.ValueKind != JsonValueKind.Array)
             return ToolResult.Fail("slides 배열이 필요합니다.");
 
         var fullPath = FileReadTool.ResolvePath(path, context.WorkFolder);
@@ -333,10 +333,10 @@ public class PptxSkill : IAgentTool
         // ── 테마 결정 우선순위: theme_file > custom_colors > theme 이름 ──────
         FullTheme fullTheme;
 
-        if (args.TryGetProperty("theme_file", out var tfEl) && !string.IsNullOrEmpty(tfEl.GetString()))
+        if (args.SafeTryGetProperty("theme_file", out var tfEl) && !string.IsNullOrEmpty(tfEl.SafeGetString()))
         {
             // 기존 PPTX에서 테마 색상 추출 → default layout (professional)
-            var tfPath = FileReadTool.ResolvePath(tfEl.GetString()!, context.WorkFolder);
+            var tfPath = FileReadTool.ResolvePath(tfEl.SafeGetString()!, context.WorkFolder);
             var extracted = ExtractThemeFromPptx(tfPath);
             var baseLayout = FullThemes["professional"].Layout;
             fullTheme = extracted != null
@@ -344,12 +344,12 @@ public class PptxSkill : IAgentTool
                 : FullThemes["professional"];
         }
         else if (string.Equals(theme, "custom", StringComparison.OrdinalIgnoreCase)
-                 && args.TryGetProperty("custom_colors", out var ccEl)
+                 && args.SafeTryGetProperty("custom_colors", out var ccEl)
                  && ccEl.ValueKind == JsonValueKind.Object)
         {
             // 사용자 지정 색상 → default layout (professional)
             static string Hex(JsonElement obj, string key, string fallback) =>
-                obj.TryGetProperty(key, out var v) ? (v.GetString() ?? fallback).TrimStart('#') : fallback;
+                obj.SafeTryGetProperty(key, out var v) ? (v.SafeGetString() ?? fallback).TrimStart('#') : fallback;
             var customColors = new ThemeColors(
                 Primary:    Hex(ccEl, "primary",     "1F4E79"),
                 Accent:     Hex(ccEl, "accent",      "2E75B6"),
@@ -441,7 +441,7 @@ public class PptxSkill : IAgentTool
 
             foreach (var slideEl in slidesEl.EnumerateArray())
             {
-                var layout    = slideEl.TryGetProperty("layout", out var lay) ? lay.GetString() ?? "content" : "content";
+                var layout    = slideEl.SafeTryGetProperty("layout", out var lay) ? lay.SafeGetString() ?? "content" : "content";
                 var slidePart = presPart.AddNewPart<SlidePart>();
                 slidePart.AddPart(layoutPart);
 
@@ -480,11 +480,11 @@ public class PptxSkill : IAgentTool
                 }
 
                 // 발표자 노트
-                if (slideEl.TryGetProperty("notes", out var notesEl) &&
+                if (slideEl.SafeTryGetProperty("notes", out var notesEl) &&
                     notesEl.ValueKind == JsonValueKind.String &&
-                    !string.IsNullOrWhiteSpace(notesEl.GetString()))
+                    !string.IsNullOrWhiteSpace(notesEl.SafeGetString()))
                 {
-                    AddNotesSlide(slidePart, notesEl.GetString()!);
+                    AddNotesSlide(slidePart, notesEl.SafeGetString()!);
                 }
 
                 slidePart.Slide.Save();
@@ -928,11 +928,11 @@ public class PptxSkill : IAgentTool
     private static void BuildTableSlide(ShapeTree t, JsonElement s, ThemeColors c, long W, long H, ref uint id)
     {
         var title   = Str(s, "title");
-        var headers = s.TryGetProperty("headers", out var hEl)
-            ? hEl.EnumerateArray().Select(x => x.GetString() ?? "").ToList()
+        var headers = s.SafeTryGetProperty("headers", out var hEl)
+            ? hEl.EnumerateArray().Select(x => x.SafeGetString() ?? "").ToList()
             : new List<string>();
-        var rows = s.TryGetProperty("rows", out var rEl)
-            ? rEl.EnumerateArray().Select(r => r.EnumerateArray().Select(c2 => c2.GetString() ?? "").ToList()).ToList()
+        var rows = s.SafeTryGetProperty("rows", out var rEl)
+            ? rEl.EnumerateArray().Select(r => r.EnumerateArray().Select(c2 => c2.SafeGetString() ?? "").ToList()).ToList()
             : new List<List<string>>();
         const long M = 450000;
 
@@ -1233,8 +1233,8 @@ public class PptxSkill : IAgentTool
     // ══════════════════════════════════════════════════════════════════════════
 
     private static string Str(JsonElement e, string key)
-        => e.TryGetProperty(key, out var v) && v.ValueKind == JsonValueKind.String
-            ? v.GetString() ?? ""
+        => e.SafeTryGetProperty(key, out var v) && v.ValueKind == JsonValueKind.String
+            ? v.SafeGetString() ?? ""
             : "";
 
     private static void AddNotesSlide(SlidePart slidePart, string notes)