feat: add FailureReason to FaceInferResult for specific error messages

- FaceInferToolPlugin now returns specific reasons: '未命中模型' or '表面过窄'
- ViewModel handlers show FailureReason instead of generic '未命中有效表面'
- Catch exceptions still pass through BuildFromFaceNormal error messages

src/Core/FaceInferResult.cs

@@ -3,22 +3,15 @@ using Autodesk.Navisworks.Api;
 namespace NavisworksTransport
 {
     /// <summary>
-    /// 快速取面结果。
-    /// 所有坐标为宿主坐标系。
+    /// 快速取面结果。所有坐标为宿主坐标系。
     /// </summary>
     public class FaceInferResult
     {
-        /// <summary>点击命中点（宿主坐标系）</summary>
         public Point3D HitPoint { get; }
-
-        /// <summary>面法向量（已归一化，朝向相机）</summary>
         public Vector3D Normal { get; }
-
-        /// <summary>命中的 ModelItem</summary>
         public ModelItem ModelItem { get; }
-
-        /// <summary>推断是否成功</summary>
         public bool IsValid { get; }
+        public string FailureReason { get; }
 
         public FaceInferResult(Point3D hitPoint, Vector3D normal, ModelItem modelItem)
         {
@@ -26,10 +19,20 @@ namespace NavisworksTransport
             Normal = normal;
             ModelItem = modelItem;
             IsValid = modelItem != null;
+            FailureReason = null;
         }
 
-        /// <summary>创建失败结果</summary>
-        public static FaceInferResult Invalid { get; } = new FaceInferResult(
-            new Point3D(), new Vector3D(), null);
+        private FaceInferResult(string failureReason)
+        {
+            HitPoint = new Point3D();
+            Normal = new Vector3D();
+            ModelItem = null;
+            IsValid = false;
+            FailureReason = failureReason;
+        }
+
+        public static FaceInferResult Invalid { get; } = new FaceInferResult(new Point3D(), new Vector3D(), null);
+
+        public static FaceInferResult Failure(string reason) => new FaceInferResult(reason);
     }
 }

src/Core/FaceInferToolPlugin.cs

@@ -99,7 +99,7 @@ namespace NavisworksTransport
             // 拾取中心点
             var centerPick = view.PickItemFromPoint(x, y);
             if (centerPick == null)
-                return FaceInferResult.Invalid;
+                return FaceInferResult.Failure("未命中任何模型，请点击模型表面。");
 
             var p0 = centerPick.Point;
 
@@ -145,7 +145,7 @@ namespace NavisworksTransport
             }
 
             LogManager.Debug("[FaceInferTool] 所有偏移量均无法推断平面");
-            return FaceInferResult.Invalid;
+            return FaceInferResult.Failure("点击位置表面过窄或不平整，无法推断平面。\n请点击较大的平整表面。");
         }
 
         // ---- Vector3D 辅助方法（避免依赖 Navisworks Vector3D 静态方法在不同版本的可用性差异）----

src/UI/WPF/ViewModels/PathEditingViewModel.cs

@@ -2434,12 +2434,8 @@ namespace NavisworksTransport.UI.WPF.ViewModels
             if (!result.IsValid)
             {
                 CleanupAssemblyEndFaceSelection(clearVisuals: false);
-                DialogHelper.ShowStatusAndDialog(
-                    "未命中有效表面。",
-                    "取端面失败",
-                    "未命中有效表面。\n请在终点箱体端面上点击。",
-                    UpdateMainStatus,
-                    System.Windows.MessageBoxImage.Warning);
+                var reason = result.FailureReason ?? "未命中有效表面。";
+                DialogHelper.ShowStatusAndDialog(reason, "取端面失败", reason, UpdateMainStatus, System.Windows.MessageBoxImage.Warning);
                 return;
             }
 
@@ -2567,12 +2563,8 @@ namespace NavisworksTransport.UI.WPF.ViewModels
             if (!result.IsValid)
             {
                 CleanupAssemblyInstallationSelection();
-                DialogHelper.ShowStatusAndDialog(
-                    "未命中有效表面。",
-                    "选安装面失败",
-                    "未命中有效表面。",
-                    UpdateMainStatus,
-                    System.Windows.MessageBoxImage.Warning);
+                var reason = result.FailureReason ?? "未命中有效表面。";
+                DialogHelper.ShowStatusAndDialog(reason, "选安装面失败", reason, UpdateMainStatus, System.Windows.MessageBoxImage.Warning);
                 return;
             }