perf: Background parallel section clip, parallel transform bake, faster gap refine (v0.4.0)

- ApplySection: snapshot on UI thread, clip whole scene with Task.Run +
  Parallel.For, swap once; _sectionApplying/_sectionReapply guard reruns
  with latest params when settings change mid-clip
- TransformRoot: per-face parallel mesh transform (frozen in/out);
  B-rep Modify and visual-tree assignment stay sequential
- InterferenceService.ApproxMinDistance: AABB squared-distance early
  reject + Parallel.For refine with thread-local best
- Stability: global exception handlers in App.xaml.cs (dispatcher/task/
  appdomain -> %LOCALAPPDATA%/STPViewer/error.log); IsBusy CanExecute
  guards on Import/Rotate/Interference; whole-batch busy + reentrancy
  guard in ImportFilesAsync
- Refactor: split MainViewModel into partial classes (Drag/Gizmo/
  Section/Interference/Export); dedupe merged-mesh build and
  ClosestPointOnTriangle
- Bump version to 0.4.0

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/STPViewer/App.xaml.cs

@@ -1,13 +1,60 @@
-using System.Configuration;
+using System;
-using System.Data;
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
 using System.Windows;
 
 namespace STPViewer;
 
 /// <summary>
-/// Interaction logic for App.xaml
+/// 全域例外處理：UI 執行緒未攔截例外 → 記 log + 訊息框後盡量存活（不閃退）；
+/// 背景 Task / 非 UI 執行緒例外 → 記 log。log 位於 %LOCALAPPDATA%\STPViewer\error.log。
 /// </summary>
 public partial class App : Application
 {
-}
+    private static readonly string LogPath = Path.Combine(
+        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+        "STPViewer", "error.log");
 
+    protected override void OnStartup(StartupEventArgs e)
+    {
+        base.OnStartup(e);
+
+        // UI 執行緒（含 async void 回拋）的未攔截例外：記 log、提示、標記 Handled 讓程式存活。
+        // 若後續狀態已壞使用者可自行重啟；至少量測結果 / 已載模型不會直接蒸發。
+        DispatcherUnhandledException += (_, args) =>
+        {
+            LogException("DispatcherUnhandledException", args.Exception);
+            MessageBox.Show(
+                $"發生未預期的錯誤，操作已中止（程式將嘗試繼續運作）。\n\n{args.Exception.Message}\n\n" +
+                $"詳細記錄：{LogPath}",
+                "STPViewer 錯誤", MessageBoxButton.OK, MessageBoxImage.Warning);
+            args.Handled = true;
+        };
+
+        // 沒被 await 的背景 Task 例外（finalizer 階段才浮出）：記 log 並標記已觀察，避免行程終止
+        TaskScheduler.UnobservedTaskException += (_, args) =>
+        {
+            LogException("UnobservedTaskException", args.Exception);
+            args.SetObserved();
+        };
+
+        // 其他非 UI 執行緒的致命例外：無法阻止終止，但至少留下記錄
+        AppDomain.CurrentDomain.UnhandledException += (_, args) =>
+            LogException("AppDomainUnhandledException", args.ExceptionObject as Exception);
+    }
+
+    private static void LogException(string source, Exception? ex)
+    {
+        try
+        {
+            Directory.CreateDirectory(Path.GetDirectoryName(LogPath)!);
+            var sb = new StringBuilder();
+            sb.AppendLine($"[{DateTime.Now:yyyy-MM-dd HH:mm:ss}] {source}");
+            sb.AppendLine(ex?.ToString() ?? "(null exception)");
+            sb.AppendLine(new string('-', 80));
+            File.AppendAllText(LogPath, sb.ToString(), Encoding.UTF8);
+        }
+        catch { /* logging 本身失敗不能再拋 */ }
+    }
+}

src/STPViewer/STPViewer.csproj

@@ -6,7 +6,7 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <UseWPF>true</UseWPF>
-    <Version>0.3.2</Version>   <!-- 單一版號來源：標題與 publish-winapp 打包資料夾都讀這個 -->
+    <Version>0.4.0</Version>   <!-- 單一版號來源：標題與 publish-winapp 打包資料夾都讀這個 -->
   </PropertyGroup>
 
   <ItemGroup>

src/STPViewer/Services/InterferenceService.cs

@@ -237,21 +237,43 @@ public static class InterferenceService
                 if (d < best) { best = d; pa = trisA[i].A; pb = trisB[j].A; }
             }
 
-        // 2) 以最佳點為中心，精修：點 → 對方所有三角形
+        // 2) 以最佳點為中心，精修：點 → 對方所有三角形（AABB 平方距離快速拒絕 + 平行分段，
-        Point3D RefineAgainst(Point3D p, Triangle[] tris, ref double bestD, Point3D current)
+        //    初值來自步驟 1 已相當接近 → 絕大多數三角形被 AABB 直接刷掉）
-        {
+        (pb, best) = ClosestOnTriangles(pa, trisB, pb, best);
-            Point3D bestPt = current;
+        (pa, best) = ClosestOnTriangles(pb, trisA, pa, best);
-            foreach (Triangle t in tris)
+        return (pa, pb, best);
+    }
+
+    /// <summary>點 p 到三角形集的最近點（帶初值；回傳更新後的最近點與距離）</summary>
+    private static (Point3D pt, double d) ClosestOnTriangles(Point3D p, Triangle[] tris, Point3D seedPt, double seedD)
+    {
+        object gate = new();
+        Point3D bestPt = seedPt;
+        double bestD = seedD;
+
+        System.Threading.Tasks.Parallel.For(0, tris.Length,
+            () => (D: seedD, Pt: seedPt, Found: false),
+            (i, _, local) =>
             {
+                Triangle t = tris[i];
+                // AABB 平方距離下界 ≥ 目前最佳 → 不可能更近，略過（絕大多數三角形在此被刷掉）
+                double dx = Math.Max(0, Math.Max(t.Min.X - p.X, p.X - t.Max.X));
+                double dy = Math.Max(0, Math.Max(t.Min.Y - p.Y, p.Y - t.Max.Y));
+                double dz = Math.Max(0, Math.Max(t.Min.Z - p.Z, p.Z - t.Max.Z));
+                if (dx * dx + dy * dy + dz * dz >= local.D * local.D) return local;
+
                 Point3D q = ClosestPointOnTriangle(p, t.A, t.B, t.C);
                 double d = (q - p).Length;
-                if (d < bestD) { bestD = d; bestPt = q; }
+                return d < local.D ? (d, q, true) : local;
-            }
+            },
-            return bestPt;
+            local =>
-        }
+            {
-        pb = RefineAgainst(pa, trisB, ref best, pb);
+                if (!local.Found) return;
-        pa = RefineAgainst(pb, trisA, ref best, pa);
+                lock (gate)
-        return (pa, pb, best);
+                    if (local.D < bestD) { bestD = local.D; bestPt = local.Pt; }
+            });
+
+        return (bestPt, bestD);
     }
 
     /// <summary>點到三角形最近點（Ericson, Real-Time Collision Detection）</summary>

src/STPViewer/Services/MeasurementService.cs

@@ -390,7 +390,7 @@ public class MeasurementService
                 Point3D v = vp[i];
                 for (int t = 0; t + 2 < ti.Count; t += 3)
                 {
-                    Point3D q = ClosestPointOnTriangle(v, tp[ti[t]], tp[ti[t + 1]], tp[ti[t + 2]]);
+                    Point3D q = InterferenceService.ClosestPointOnTriangle(v, tp[ti[t]], tp[ti[t + 1]], tp[ti[t + 2]]);
                     double d = (q - v).Length;
                     if (d < best)
                     {
@@ -406,39 +406,7 @@ public class MeasurementService
         return (pa, pb);
     }
 
-    /// <summary>點到三角形最近點（Ericson, Real-Time Collision Detection）</summary>
+    // 點到三角形最近點：共用 InterferenceService.ClosestPointOnTriangle（v0.4.0 去重複）
-    private static Point3D ClosestPointOnTriangle(Point3D p, Point3D a, Point3D b, Point3D c)
-    {
-        Vector3D ab = b - a, ac = c - a, ap = p - a;
-        double d1 = Vector3D.DotProduct(ab, ap);
-        double d2 = Vector3D.DotProduct(ac, ap);
-        if (d1 <= 0 && d2 <= 0) return a;
-
-        Vector3D bp = p - b;
-        double d3 = Vector3D.DotProduct(ab, bp);
-        double d4 = Vector3D.DotProduct(ac, bp);
-        if (d3 >= 0 && d4 <= d3) return b;
-
-        double vc = d1 * d4 - d3 * d2;
-        if (vc <= 0 && d1 >= 0 && d3 <= 0)
-            return a + ab * (d1 / (d1 - d3));
-
-        Vector3D cp = p - c;
-        double d5 = Vector3D.DotProduct(ab, cp);
-        double d6 = Vector3D.DotProduct(ac, cp);
-        if (d6 >= 0 && d5 <= d6) return c;
-
-        double vb = d5 * d2 - d1 * d6;
-        if (vb <= 0 && d2 >= 0 && d6 <= 0)
-            return a + ac * (d2 / (d2 - d6));
-
-        double va = d3 * d6 - d5 * d4;
-        if (va <= 0 && d4 - d3 >= 0 && d5 - d6 >= 0)
-            return b + (c - b) * ((d4 - d3) / ((d4 - d3) + (d5 - d6)));
-
-        double denom = 1 / (va + vb + vc);
-        return a + ab * (vb * denom) + ac * (vc * denom);
-    }
 
     // ─── overlay helpers ─────────────────────────────────────────
 

src/STPViewer/ViewModels/MainViewModel.Drag.cs

@@ -0,0 +1,90 @@
+using System.Windows;
+using System.Windows.Media.Media3D;
+using HelixToolkit.Wpf;
+using STPViewer.Models;
+
+namespace STPViewer.ViewModels;
+
+// ─── 拖曳模式（左鍵按住零件沿螢幕平面拖；放開才烘進 B-rep）──────────
+public partial class MainViewModel
+{
+    // 拖曳模式：暫時 Transform 跟著滑鼠，放開才一次性烘進 B-rep（TranslateRoot）
+    private ModelNodeViewModel? _dragRoot;
+    private Point3D _dragAnchor;              // 命中點（世界座標），拖曳平面的錨點
+    private Vector3D _dragApplied;            // 目前累計位移
+    private TranslateTransform3D? _dragTransform;
+
+    /// <summary>左鍵按下：命中零件則開始拖曳（回傳 true 表示要捕捉滑鼠）</summary>
+    public bool OnDragStart(Point position)
+    {
+        if (_viewport is null || IsBusy || CurrentMode != MeasureMode.Drag || _dragRoot is not null)
+            return false;
+
+        // 兩種渲染內容都可能在場：合併網格查 _mergedMap、逐面（剖面時）查 _faceMap
+        ModelNodeViewModel? leaf = null;
+        Point3D anchor = default;
+        foreach (var h in _viewport.Viewport.FindHits(position))
+        {
+            if (h.Model is null) continue;
+            if (_faceMap.TryGetValue(h.Model, out FaceInfo? fi)) { leaf = fi.Owner; anchor = h.Position; break; }
+            if (_mergedMap.TryGetValue(h.Model, out ModelNodeViewModel? ml)) { leaf = ml; anchor = h.Position; break; }
+        }
+        if (leaf is null) return false;
+        ModelNodeViewModel? root = FindRootOf(leaf) ?? RootContaining(leaf);
+        if (root is null) return false;
+
+        _dragRoot = root;
+        _dragAnchor = anchor;
+        _dragApplied = default;
+        _dragTransform = new TranslateTransform3D();
+        foreach (ModelNodeViewModel l in root.Leaves())
+            if (l.BodyVisual is not null)
+                l.BodyVisual.Transform = _dragTransform;
+
+        // 拖曳中隱藏邊線（LinesVisual3D 隨 Transform 變更逐幀重建會卡）
+        _edgesSuspended = true;
+        SetEdgesActive(false);
+        StatusText = $"拖曳「{root.Name}」中…（放開定位）";
+        return true;
+    }
+
+    /// <summary>滑鼠移動：把 2D 位移投影到「過錨點、面向相機」的平面上 → 暫時 Transform</summary>
+    public void OnDragMove(Point position)
+    {
+        if (_viewport?.Camera is not System.Windows.Media.Media3D.ProjectionCamera cam ||
+            _dragRoot is null || _dragTransform is null) return;
+
+        Point3D? p = _viewport.Viewport.UnProject(position, _dragAnchor, cam.LookDirection);
+        if (p is null) return;
+        _dragApplied = p.Value - _dragAnchor;
+        _dragTransform.OffsetX = _dragApplied.X;
+        _dragTransform.OffsetY = _dragApplied.Y;
+        _dragTransform.OffsetZ = _dragApplied.Z;
+    }
+
+    /// <summary>放開：移除暫時 Transform，一次性烘進 B-rep（量測精度不受拖曳影響）</summary>
+    public bool OnDragEnd()
+    {
+        if (_dragRoot is null) return false;
+        ModelNodeViewModel root = _dragRoot;
+        Vector3D delta = _dragApplied;
+
+        // 清除暫時位移：必須用 Identity，不可用 null —— HelixToolkit GetTransform 對 child.Transform
+        // 不做 null 檢查（Children.Add(null) 會拋「無法新增空值到集合中」），下次 FindHits 即 crash
+        foreach (ModelNodeViewModel l in root.Leaves())
+            if (l.BodyVisual is not null)
+                l.BodyVisual.Transform = Transform3D.Identity;
+        _dragRoot = null;
+        _dragTransform = null;
+        _dragApplied = default;
+        _edgesSuspended = false;
+        SetEdgesActive(true); // 恢復所有檔案的邊線（被拖檔案的點隨後由 TranslateRoot 更新，期間不會渲染）
+
+        if (delta.LengthSquared > 1e-12)
+        {
+            TranslateRoot(root, delta); // 烘進 B-rep + 網格 + 邊線 + 邊界（量測清空）
+            StatusText = $"已拖曳「{root.Name}」 Δ({delta.X:F2}, {delta.Y:F2}, {delta.Z:F2}) mm（可用 🧩干涉 驗證）";
+        }
+        return true;
+    }
+}

src/STPViewer/ViewModels/MainViewModel.Export.cs

@@ -0,0 +1,65 @@
+using System;
+using System.IO;
+using System.Text;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using CommunityToolkit.Mvvm.Input;
+using Microsoft.Win32;
+using STPViewer.Models;
+
+namespace STPViewer.ViewModels;
+
+// ─── 匯出（量測 CSV / 視圖 PNG 截圖）────────────────────────────────
+public partial class MainViewModel
+{
+    [RelayCommand]
+    private void ExportCsv()
+    {
+        if (Measurements.Count == 0)
+        {
+            StatusText = "沒有量測結果可匯出";
+            return;
+        }
+        var dlg = new SaveFileDialog
+        {
+            Title = "匯出量測結果",
+            Filter = "CSV 檔案 (*.csv)|*.csv",
+            FileName = $"measurements_{DateTime.Now:yyyyMMdd_HHmmss}.csv",
+        };
+        if (dlg.ShowDialog() != true) return;
+
+        var sb = new StringBuilder();
+        sb.AppendLine("標籤,類型,明細");
+        foreach (MeasurementResult m in Measurements)
+        {
+            static string Esc(string s) => $"\"{s.Replace("\"", "\"\"")}\"";
+            sb.AppendLine($"{Esc(m.Title)},{m.Kind},{Esc(m.Detail.Replace("\n", " | "))}");
+        }
+        File.WriteAllText(dlg.FileName, sb.ToString(), new UTF8Encoding(true)); // BOM：Excel 中文不亂碼
+        StatusText = $"已匯出 {Measurements.Count} 筆量測 → {Path.GetFileName(dlg.FileName)}";
+    }
+
+    [RelayCommand]
+    private void SaveScreenshot()
+    {
+        if (_viewport is null || _viewport.ActualWidth < 1) return;
+        var dlg = new SaveFileDialog
+        {
+            Title = "儲存視圖截圖",
+            Filter = "PNG 圖片 (*.png)|*.png",
+            FileName = $"stpviewer_{DateTime.Now:yyyyMMdd_HHmmss}.png",
+        };
+        if (dlg.ShowDialog() != true) return;
+
+        const double scale = 2.0; // 2x 解析度
+        var rtb = new RenderTargetBitmap(
+            (int)(_viewport.ActualWidth * scale), (int)(_viewport.ActualHeight * scale),
+            96 * scale, 96 * scale, PixelFormats.Pbgra32);
+        rtb.Render(_viewport);
+        var encoder = new PngBitmapEncoder();
+        encoder.Frames.Add(BitmapFrame.Create(rtb));
+        using FileStream fs = File.Create(dlg.FileName);
+        encoder.Save(fs);
+        StatusText = $"已儲存截圖 → {Path.GetFileName(dlg.FileName)}";
+    }
+}

src/STPViewer/ViewModels/MainViewModel.Gizmo.cs

@@ -0,0 +1,191 @@
+using System;
+using System.Collections.Generic;
+using System.Windows.Media;
+using System.Windows.Media.Media3D;
+using CommunityToolkit.Mvvm.ComponentModel;
+using HelixToolkit.Wpf;
+
+namespace STPViewer.ViewModels;
+
+// ─── Gizmo 三軸操作器（XYZ 箭頭 + 旋轉環；每次放開滑鼠烘進 B-rep）──────
+public partial class MainViewModel
+{
+    [ObservableProperty]
+    private bool gizmoEnabled;
+
+    private readonly List<HelixToolkit.Wpf.Manipulator> _gizmoParts = new();
+    private ModelVisual3D? _gizmoProxy;        // 操作器綁定的代理 visual（其 Transform = 使用者拖出的變換）
+    private ModelNodeViewModel? _gizmoTarget;
+    private bool _gizmoDragActive;             // 拖動中（邊線已暫停）
+    private bool _gizmoBaking;                 // 烘焙中，忽略 Transform 變更回呼
+    private bool _gizmoBakePending;            // 已排程烘焙，防同一次放開重複觸發
+
+    // 操作器疊圖層：另一個透明 Viewport3D 疊在主視窗上、相機同步、只放操作器 →
+    // 操作器不在主場景，永不被實體遮擋（always-on-top）；空白處滑鼠穿透回主視窗
+    private System.Windows.Controls.Viewport3D? _overlayViewport;
+    private PerspectiveCamera? _overlayCamera;
+
+    /// <summary>注入操作器疊圖層（透明 Viewport3D，疊在主視窗上、永遠最上層）</summary>
+    public void AttachOverlay(System.Windows.Controls.Viewport3D overlay)
+    {
+        _overlayViewport = overlay;
+        _overlayCamera = new PerspectiveCamera();
+        overlay.Camera = _overlayCamera;
+        // 操作器材質需打光（manipulator 用 DiffuseMaterial）
+        overlay.Children.Add(new ModelVisual3D { Content = new AmbientLight(Color.FromRgb(0x80, 0x80, 0x80)) });
+        overlay.Children.Add(new ModelVisual3D { Content = new DirectionalLight(Colors.White, new Vector3D(-1, -1, -3)) });
+        SyncOverlayCamera();
+    }
+
+    /// <summary>疊圖層相機跟隨主相機（每次主相機變更時呼叫，讓操作器疊在正確螢幕位置）</summary>
+    private void SyncOverlayCamera()
+    {
+        if (_overlayCamera is null || _viewport?.Camera is not ProjectionCamera src) return;
+        _overlayCamera.Position = src.Position;
+        _overlayCamera.LookDirection = src.LookDirection;
+        _overlayCamera.UpDirection = src.UpDirection;
+        _overlayCamera.NearPlaneDistance = src.NearPlaneDistance;
+        _overlayCamera.FarPlaneDistance = src.FarPlaneDistance;
+        if (src is PerspectiveCamera p) _overlayCamera.FieldOfView = p.FieldOfView;
+    }
+
+    partial void OnGizmoEnabledChanged(bool value) => UpdateGizmo();
+
+    partial void OnSelectedNodeChanged(ModelNodeViewModel? value)
+    {
+        if (GizmoEnabled) UpdateGizmo(); // 換選取 → 操作器跟著換目標
+    }
+
+    private void UpdateGizmo()
+    {
+        RemoveGizmo();
+        if (!GizmoEnabled || _viewport is null || _overlayViewport is null) return;
+
+        ModelNodeViewModel? root = SelectedNode is not null ? RootContaining(SelectedNode)
+            : Roots.Count == 1 ? Roots[0] : null;
+        if (root is null || root.Bounds.IsEmpty)
+        {
+            StatusText = "操作器：請先在樹面板點選要操作的檔案";
+            GizmoEnabled = false;
+            return;
+        }
+        _gizmoTarget = root;
+        SyncOverlayCamera(); // 操作器出現前先對齊相機
+
+        Rect3D b = root.Bounds;
+        var center = new Point3D(b.X + b.SizeX / 2, b.Y + b.SizeY / 2, b.Z + b.SizeZ / 2);
+        double diag = new Vector3D(b.SizeX, b.SizeY, b.SizeZ).Length;
+
+        _gizmoProxy = new ModelVisual3D();
+        _overlayViewport.Children.Add(_gizmoProxy);
+        System.ComponentModel.DependencyPropertyDescriptor
+            .FromProperty(Visual3D.TransformProperty, typeof(Visual3D))
+            .AddValueChanged(_gizmoProxy, GizmoTransformChanged);
+
+        void AddPart(HelixToolkit.Wpf.Manipulator man)
+        {
+            man.Position = center;
+            man.Bind(_gizmoProxy);
+            _gizmoParts.Add(man);
+            _overlayViewport!.Children.Add(man); // 放疊圖層 → 永不被實體遮擋
+        }
+        // 平移箭頭（X 紅 / Y 綠 / Z 藍 — 業界慣例）
+        AddPart(new TranslateManipulator { Direction = new Vector3D(1, 0, 0), Color = Colors.Red,   Length = diag * 0.22, Diameter = diag * 0.016 });
+        AddPart(new TranslateManipulator { Direction = new Vector3D(0, 1, 0), Color = Colors.Green, Length = diag * 0.22, Diameter = diag * 0.016 });
+        AddPart(new TranslateManipulator { Direction = new Vector3D(0, 0, 1), Color = Colors.Blue,  Length = diag * 0.22, Diameter = diag * 0.016 });
+        // 旋轉環
+        AddPart(new RotateManipulator { Axis = new Vector3D(1, 0, 0), Color = Colors.Red,   Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
+        AddPart(new RotateManipulator { Axis = new Vector3D(0, 1, 0), Color = Colors.Green, Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
+        AddPart(new RotateManipulator { Axis = new Vector3D(0, 0, 1), Color = Colors.Blue,  Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
+
+        StatusText = $"操作器：拖箭頭沿軸移動「{root.Name}」、拖環繞軸旋轉；放開即定位";
+    }
+
+    private void RemoveGizmo()
+    {
+        if (_gizmoProxy is not null)
+        {
+            System.ComponentModel.DependencyPropertyDescriptor
+                .FromProperty(Visual3D.TransformProperty, typeof(Visual3D))
+                .RemoveValueChanged(_gizmoProxy, GizmoTransformChanged);
+            _overlayViewport?.Children.Remove(_gizmoProxy);
+        }
+        foreach (HelixToolkit.Wpf.Manipulator man in _gizmoParts)
+        {
+            man.UnBind();
+            _overlayViewport?.Children.Remove(man);
+        }
+        _gizmoParts.Clear();
+        _gizmoProxy = null;
+
+        if (_gizmoTarget is not null) // 清掉殘留的暫時 Transform（用 Identity，不可 null → 否則 FindHits crash）
+            foreach (ModelNodeViewModel l in _gizmoTarget.Leaves())
+                if (l.BodyVisual is not null)
+                    l.BodyVisual.Transform = Transform3D.Identity;
+        _gizmoTarget = null;
+        if (_gizmoDragActive)
+        {
+            _gizmoDragActive = false;
+            _edgesSuspended = false;
+            SetEdgesActive(true);
+        }
+    }
+
+    /// <summary>操作器拖動中：把代理的 Transform 套到目標檔案的所有 BodyVisual（暫時、GPU 端）</summary>
+    private void GizmoTransformChanged(object? sender, EventArgs e)
+    {
+        if (_gizmoBaking || _gizmoTarget is null || _gizmoProxy is null) return;
+        Transform3D t = _gizmoProxy.Transform;
+        if (!_gizmoDragActive && t is not null && !t.Value.IsIdentity)
+        {
+            _gizmoDragActive = true;
+            _edgesSuspended = true;
+            SetEdgesActive(false); // 邊線逐幀重建會卡，拖動中暫停
+        }
+        foreach (ModelNodeViewModel l in _gizmoTarget.Leaves())
+            if (l.BodyVisual is not null)
+                l.BodyVisual.Transform = t;
+    }
+
+    /// <summary>滑鼠放開（MainWindow 轉發，handledEventsToo）：把累積變換烘進 B-rep 並重置操作器</summary>
+    public void OnGizmoMouseUp()
+    {
+        if (_gizmoTarget is null || _gizmoProxy is null || _gizmoBakePending) return;
+        Matrix3D m = _gizmoProxy.Transform?.Value ?? Matrix3D.Identity;
+        if (m.IsIdentity) return; // 只是點一下、沒拖操作器 → 不烘焙
+
+        // 延後到 manipulator 自身的 mouse-up 處理（釋放捕捉等）完成後再烘焙，避免在其事件中改動視覺樹造成 reentrancy
+        _gizmoBakePending = true;
+        _viewport?.Dispatcher.BeginInvoke(new Action(() => BakeGizmo(m)),
+            System.Windows.Threading.DispatcherPriority.Background);
+    }
+
+    private void BakeGizmo(Matrix3D m)
+    {
+        _gizmoBakePending = false;
+        if (_gizmoTarget is null) return;
+        ModelNodeViewModel root = _gizmoTarget;
+
+        _gizmoBaking = true; // 防 proxy 歸零觸發 GizmoTransformChanged 重入
+        foreach (ModelNodeViewModel l in root.Leaves())
+            if (l.BodyVisual is not null)
+                l.BodyVisual.Transform = Transform3D.Identity; // 清暫時位移（用 Identity，不可 null）
+        if (_gizmoProxy is not null) _gizmoProxy.Transform = Transform3D.Identity; // 綁定 → 操作器歸零
+        _gizmoBaking = false;
+        _gizmoDragActive = false;
+        _edgesSuspended = false;
+        SetEdgesActive(true);
+
+        TransformRoot(root, Services.RigidAlign.ToModOp(m), m); // 烘進 B-rep（量測精度不受影響）
+
+        // 操作器移到變換後的新中心
+        Rect3D b = root.Bounds;
+        if (!b.IsEmpty)
+        {
+            var center = new Point3D(b.X + b.SizeX / 2, b.Y + b.SizeY / 2, b.Z + b.SizeZ / 2);
+            foreach (HelixToolkit.Wpf.Manipulator man in _gizmoParts)
+                man.Position = center;
+        }
+        StatusText = $"已套用操作器變換「{root.Name}」（可用 🧩干涉 驗證）";
+    }
+}

src/STPViewer/ViewModels/MainViewModel.Interference.cs

@@ -0,0 +1,125 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Media;
+using System.Windows.Media.Media3D;
+using CommunityToolkit.Mvvm.Input;
+using HelixToolkit.Wpf;
+using STPViewer.Models;
+using STPViewer.Services;
+
+namespace STPViewer.ViewModels;
+
+// ─── 干涉檢查 ────────────────────────────────────────────────────────
+public partial class MainViewModel
+{
+    [RelayCommand(CanExecute = nameof(IsIdle))]
+    private async Task CheckInterferenceAsync()
+    {
+        if (_viewport is null) return;
+        var visibleRoots = Roots.Where(r => r.IsVisible).ToList();
+        if (visibleRoots.Count != 2)
+        {
+            StatusText = $"干涉檢查需要剛好 2 個可見檔案（目前 {visibleRoots.Count} 個）— 用樹面板勾選";
+            return;
+        }
+
+        List<MeshGeometry3D> MeshesOf(ModelNodeViewModel root) =>
+            root.Leaves().Where(l => l.IsVisible && l.FacesContent is not null)
+                .SelectMany(l => l.FacesContent!.Children)
+                .Where(m => m is GeometryModel3D gm && _faceMap.ContainsKey(gm))
+                .Select(m => _faceMap[(GeometryModel3D)m].Mesh)
+                .ToList();
+
+        var a = MeshesOf(visibleRoots[0]);
+        var b = MeshesOf(visibleRoots[1]);
+        string nameA = visibleRoots[0].Name, nameB = visibleRoots[1].Name;
+
+        IsBusy = true;
+        StatusText = $"干涉檢查中：{nameA} ⟷ {nameB} …";
+        try
+        {
+            InterferenceResult result = await Task.Run(() => InterferenceService.Check(a, b));
+            AddInterferenceResult(result, nameA, nameB);
+        }
+        catch (Exception ex)
+        {
+            StatusText = $"干涉檢查失敗：{ex.Message}";
+        }
+        finally
+        {
+            IsBusy = false;
+        }
+    }
+
+    private void AddInterferenceResult(InterferenceResult result, string nameA, string nameB)
+    {
+        double diag = SceneDiagonal();
+        double markerR = Math.Clamp(diag * 0.004, 0.01, 5.0);
+        MeasurementResult m;
+
+        if (result.Intersects)
+        {
+            int pairs = result.PairCount;
+            int segCount = result.Segments.Count;
+            m = new MeasurementResult
+            {
+                Kind = MeasureMode.Interference,
+                TitleFor = _ => $"🧩 干涉！{nameA} ⟷ {nameB}",
+                DetailFor = _ => $"兩零件相交（不 match）\n相交三角形對 = {pairs:N0}\n" +
+                                 $"紅色線 = 干涉交線（{segCount:N0} 段）\n（共面貼合不會被算為干涉）",
+            };
+            var pts = new Point3DCollection(Math.Min(result.Segments.Count, 20000) * 2);
+            foreach ((Point3D s0, Point3D s1) in result.Segments) { pts.Add(s0); pts.Add(s1); }
+            m.Overlays.Add(new LinesVisual3D { Points = pts, Color = Colors.Red, Thickness = 3 });
+            if (result.Segments.Count > 0)
+            {
+                Point3D at = result.Segments[0].A;
+                m.Overlays.Add(new BillboardTextVisual3D
+                {
+                    Position = at + new Vector3D(0, 0, markerR * 3),
+                    Text = "干涉",
+                    Foreground = Brushes.White,
+                    Background = Brushes.Red,
+                    Padding = new Thickness(5, 2, 5, 2),
+                    FontSize = 14,
+                });
+            }
+        }
+        else
+        {
+            Point3D ga = result.GapA, gb = result.GapB;
+            Vector3D d = gb - ga;
+            double gap = result.GapDistance;
+            m = new MeasurementResult
+            {
+                Kind = MeasureMode.Interference,
+                TitleFor = u => $"🧩 無干涉  gap ≈ {Units.L(gap, u)}",
+                DetailFor = u => $"{nameA} ⟷ {nameB} 無相交\n最小間隙 ≈ {Units.L(gap, u)}（網格近似）\n" +
+                                 $"gap ≈ 0 即為貼合（match）\n點 1 {Units.P(ga, u)}\n點 2 {Units.P(gb, u)}",
+            };
+            m.Overlays.Add(new SphereVisual3D { Center = ga, Radius = markerR, Fill = Brushes.OrangeRed });
+            m.Overlays.Add(new SphereVisual3D { Center = gb, Radius = markerR, Fill = Brushes.OrangeRed });
+            m.Overlays.Add(new LinesVisual3D
+            {
+                Points = new Point3DCollection { ga, gb },
+                Color = Colors.OrangeRed,
+                Thickness = 2,
+            });
+            var label = new BillboardTextVisual3D
+            {
+                Position = ga + d / 2 + new Vector3D(0, 0, markerR * 2),
+                Text = $"gap {Units.L(gap, UnitSystem.Millimeter)}",
+                Foreground = Brushes.Black,
+                Background = new SolidColorBrush(Color.FromArgb(200, 255, 255, 210)),
+                Padding = new Thickness(4, 2, 4, 2),
+                FontSize = 14,
+            };
+            m.Overlays.Add(label);
+            m.DynamicLabels.Add((label, u => $"gap {Units.L(gap, u)}"));
+        }
+        AddMeasurement(m);
+    }
+}

src/STPViewer/ViewModels/MainViewModel.Section.cs

@@ -0,0 +1,171 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using System.Windows.Media;
+using System.Windows.Media.Media3D;
+using System.Windows.Threading;
+using CommunityToolkit.Mvvm.ComponentModel;
+using HelixToolkit.Wpf;
+using STPViewer.Models;
+using STPViewer.Services;
+
+namespace STPViewer.ViewModels;
+
+// ─── 剖面（CPU 網格裁切；v0.4.0 起裁切在背景執行緒平行計算，UI 不凍結）──
+public partial class MainViewModel
+{
+    private readonly DispatcherTimer _sectionTimer;
+    private RectangleVisual3D? _sectionPlaneVisual;
+    private Point3D _sectionPlanePoint;   // SectionEnabled 時的剖切平面（合併邊線重建用）
+    private Vector3D _sectionNormal;
+
+    // 背景裁切 guard：進行中又有新變更（拉滑桿/換軸/零件平移）→ 完成後用最新參數重跑一輪。
+    // 不要改回同步呼叫 ClipMesh —— 大檔（64k 面）整場景裁切會凍結 UI 數秒
+    private bool _sectionApplying;
+    private bool _sectionReapply;
+
+    [ObservableProperty]
+    private bool sectionEnabled;
+
+    /// <summary>0=X 1=Y 2=Z</summary>
+    [ObservableProperty]
+    private int sectionAxisIndex;
+
+    /// <summary>剖面位置（沿軸 0~100%）</summary>
+    [ObservableProperty]
+    private double sectionPosition = 50;
+
+    [ObservableProperty]
+    private bool sectionFlip;
+
+    partial void OnSectionEnabledChanged(bool value) => ScheduleSection();
+    partial void OnSectionAxisIndexChanged(int value) => ScheduleSection();
+    partial void OnSectionPositionChanged(double value) => ScheduleSection();
+    partial void OnSectionFlipChanged(bool value) => ScheduleSection();
+
+    private void ScheduleSection()
+    {
+        _sectionTimer.Stop();
+        _sectionTimer.Start();
+    }
+
+    private async void ApplySection()
+    {
+        if (_viewport is null) return;
+
+        if (!SectionEnabled)
+        {
+            // 還原原始幾何（換回 fi.Mesh 參照，便宜、同步即可）。
+            // 若背景裁切還在跑，其 await 之後會看到 SectionEnabled=false 而放棄套用
+            foreach ((Model3D model, FaceInfo fi) in _faceMap)
+                if (model is GeometryModel3D gm && !ReferenceEquals(gm.Geometry, fi.Mesh))
+                    gm.Geometry = fi.Mesh;
+            foreach (ModelNodeViewModel root in Roots) RefreshRootEdges(root);
+            if (_sectionPlaneVisual is not null)
+            {
+                _viewport.Children.Remove(_sectionPlaneVisual);
+                _sectionPlaneVisual = null;
+            }
+            ApplyRenderMode(); // 剖面關閉 → 瀏覽模式可切回合併網格
+            StatusText = "剖面已關閉";
+            return;
+        }
+
+        if (_sectionApplying) { _sectionReapply = true; return; }
+        _sectionApplying = true;
+        try
+        {
+            do
+            {
+                _sectionReapply = false;
+
+                Rect3D bounds = UnionBounds();
+                if (bounds.IsEmpty) return;
+
+                Vector3D axis = SectionAxisIndex switch
+                {
+                    0 => new Vector3D(1, 0, 0),
+                    1 => new Vector3D(0, 1, 0),
+                    _ => new Vector3D(0, 0, 1),
+                };
+                double t = SectionPosition / 100.0;
+                Point3D min = bounds.Location;
+                var size = new Vector3D(bounds.SizeX, bounds.SizeY, bounds.SizeZ);
+                double planeCoord = SectionAxisIndex switch
+                {
+                    0 => min.X + size.X * t,
+                    1 => min.Y + size.Y * t,
+                    _ => min.Z + size.Z * t,
+                };
+                Point3D center = min + size / 2;
+                Point3D planePoint = SectionAxisIndex switch
+                {
+                    0 => new Point3D(planeCoord, center.Y, center.Z),
+                    1 => new Point3D(center.X, planeCoord, center.Z),
+                    _ => new Point3D(center.X, center.Y, planeCoord),
+                };
+                Vector3D normal = SectionFlip ? -axis : axis;
+
+                // UI 執行緒快照（原始 mesh 皆已 Freeze，可跨執行緒），背景平行裁切，回 UI 一次換上。
+                // 裁切期間若參數又變 / 零件被平移（TransformRoot 會呼叫 ApplySection）→
+                // _sectionReapply 讓迴圈用最新的 fi.Mesh 與平面重跑，最終狀態必為最新
+                var models = new List<GeometryModel3D>(_faceMap.Count);
+                var sources = new List<MeshGeometry3D>(_faceMap.Count);
+                foreach ((Model3D model, FaceInfo fi) in _faceMap)
+                    if (model is GeometryModel3D gm)
+                    {
+                        models.Add(gm);
+                        sources.Add(fi.Mesh);
+                    }
+
+                MeshGeometry3D[] clipped = await Task.Run(() =>
+                {
+                    var result = new MeshGeometry3D[sources.Count];
+                    Parallel.For(0, sources.Count, i =>
+                        result[i] = SectionService.ClipMesh(sources[i], planePoint, normal));
+                    return result;
+                });
+
+                if (!SectionEnabled) return; // 裁切期間被關掉 → 還原分支已處理，丟棄結果
+
+                for (int i = 0; i < models.Count; i++)
+                    models[i].Geometry = clipped[i]; // 已移除檔案的殘留 model 賦值無害（不在視覺樹上）
+
+                _sectionPlanePoint = planePoint;
+                _sectionNormal = normal;
+                foreach (ModelNodeViewModel root in Roots) RefreshRootEdges(root);
+
+                ApplyRenderMode(); // 剖面開啟 → 改用逐面（裁切後幾何）
+                UpdateSectionPlaneVisual(planePoint, axis, size);
+                StatusText = $"剖面：{"XYZ"[SectionAxisIndex]} 軸 {SectionPosition:F0}%" + (SectionFlip ? "（反向）" : "");
+            } while (_sectionReapply);
+        }
+        finally
+        {
+            _sectionApplying = false;
+        }
+    }
+
+    private void UpdateSectionPlaneVisual(Point3D planePoint, Vector3D axis, Vector3D size)
+    {
+        if (_sectionPlaneVisual is not null)
+            _viewport!.Children.Remove(_sectionPlaneVisual);
+
+        (Vector3D lenDir, double len, double wid) = SectionAxisIndex switch
+        {
+            0 => (new Vector3D(0, 1, 0), size.Y, size.Z),
+            1 => (new Vector3D(1, 0, 0), size.X, size.Z),
+            _ => (new Vector3D(1, 0, 0), size.X, size.Y),
+        };
+        _sectionPlaneVisual = new RectangleVisual3D
+        {
+            Origin = planePoint,
+            Normal = axis,
+            LengthDirection = lenDir,
+            Length = len * 1.05,
+            Width = wid * 1.05,
+            Fill = new SolidColorBrush(Color.FromArgb(40, 30, 120, 255)),
+        };
+        _viewport!.Children.Add(_sectionPlaneVisual);
+    }
+}

src/STPViewer/ViewModels/MainViewModel.cs

@@ -3,11 +3,9 @@ using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.IO;
 using System.Linq;
-using System.Text;
 using System.Threading.Tasks;
 using System.Windows;
 using System.Windows.Media;
-using System.Windows.Media.Imaging;
 using System.Windows.Media.Media3D;
 using System.Windows.Threading;
 using CommunityToolkit.Mvvm.ComponentModel;
@@ -35,12 +33,6 @@ public partial class MainViewModel : ObservableObject
     /// 邊界由匯入時依面序串接而成，與 BuildMergedMesh 串接順序一致；平移不改各面頂點數，故邊界永久有效。</summary>
     private readonly Dictionary<Model3D, (int[] Starts, FaceInfo[] Faces)> _mergedFaceRanges = new();
 
-    // 拖曳模式：暫時 Transform 跟著滑鼠，放開才一次性烘進 B-rep（TranslateRoot）
-    private ModelNodeViewModel? _dragRoot;
-    private Point3D _dragAnchor;              // 命中點（世界座標），拖曳平面的錨點
-    private Vector3D _dragApplied;            // 目前累計位移
-    private TranslateTransform3D? _dragTransform;
-
     private HelixViewport3D? _viewport;
     private int _paletteIndex;
     private readonly Dictionary<MeasureMode, int> _counters = new();
@@ -57,12 +49,6 @@ public partial class MainViewModel : ObservableObject
     [ObservableProperty]
     private ModelNodeViewModel? selectedNode;
 
-    // 剖面
-    private readonly DispatcherTimer _sectionTimer;
-    private RectangleVisual3D? _sectionPlaneVisual;
-    private Point3D _sectionPlanePoint;   // SectionEnabled 時的剖切平面（合併邊線重建用）
-    private Vector3D _sectionNormal;
-
     // 互動中暫停邊線：轉動/縮放/平移時隱藏 LinesVisual3D，停下再顯示 → 大組件流暢
     private readonly DispatcherTimer _interactionTimer;
     private bool _edgesSuspended;
@@ -74,25 +60,14 @@ public partial class MainViewModel : ObservableObject
     private string statusText = "就緒 — 匯入 STP/STEP/STL/DXF（拖放亦可）。右鍵旋轉、滾輪縮放、中鍵或 Shift+左鍵平移";
 
     [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(ImportCommand))]
+    [NotifyCanExecuteChangedFor(nameof(RotateRootCommand))]
+    [NotifyCanExecuteChangedFor(nameof(CheckInterferenceCommand))]
     private bool isBusy;
 
     [ObservableProperty]
     private bool useInch;
 
-    [ObservableProperty]
-    private bool sectionEnabled;
-
-    /// <summary>0=X 1=Y 2=Z</summary>
-    [ObservableProperty]
-    private int sectionAxisIndex;
-
-    /// <summary>剖面位置（沿軸 0~100%）</summary>
-    [ObservableProperty]
-    private double sectionPosition = 50;
-
-    [ObservableProperty]
-    private bool sectionFlip;
-
     public ObservableCollection<ModelNodeViewModel> Roots { get; } = new();
     public ObservableCollection<MeasurementResult> Measurements { get; } = new();
 
@@ -123,30 +98,6 @@ public partial class MainViewModel : ObservableObject
             viewport.Camera.Changed += (_, _) => OnCameraMoved();
     }
 
-    /// <summary>注入操作器疊圖層（透明 Viewport3D，疊在主視窗上、永遠最上層）</summary>
-    public void AttachOverlay(System.Windows.Controls.Viewport3D overlay)
-    {
-        _overlayViewport = overlay;
-        _overlayCamera = new PerspectiveCamera();
-        overlay.Camera = _overlayCamera;
-        // 操作器材質需打光（manipulator 用 DiffuseMaterial）
-        overlay.Children.Add(new ModelVisual3D { Content = new AmbientLight(Color.FromRgb(0x80, 0x80, 0x80)) });
-        overlay.Children.Add(new ModelVisual3D { Content = new DirectionalLight(Colors.White, new Vector3D(-1, -1, -3)) });
-        SyncOverlayCamera();
-    }
-
-    /// <summary>疊圖層相機跟隨主相機（每次主相機變更時呼叫，讓操作器疊在正確螢幕位置）</summary>
-    private void SyncOverlayCamera()
-    {
-        if (_overlayCamera is null || _viewport?.Camera is not ProjectionCamera src) return;
-        _overlayCamera.Position = src.Position;
-        _overlayCamera.LookDirection = src.LookDirection;
-        _overlayCamera.UpDirection = src.UpDirection;
-        _overlayCamera.NearPlaneDistance = src.NearPlaneDistance;
-        _overlayCamera.FarPlaneDistance = src.FarPlaneDistance;
-        if (src is PerspectiveCamera p) _overlayCamera.FieldOfView = p.FieldOfView;
-    }
-
     private void OnCameraMoved()
     {
         SyncOverlayCamera(); // 操作器疊圖層跟著主相機
@@ -170,9 +121,12 @@ public partial class MainViewModel : ObservableObject
                 SyncVisual(root.EdgeVisual, active && root.EdgeVisual.Points.Count > 0);
     }
 
+    /// <summary>IsBusy 時停用會改動幾何/場景的指令（匯入、旋轉、干涉），避免背景運算期間狀態被改走造成結果錯位</summary>
+    private bool IsIdle() => !IsBusy;
+
     // ─── 匯入 ────────────────────────────────────────────────────
 
-    [RelayCommand]
+    [RelayCommand(CanExecute = nameof(IsIdle))]
     private async Task ImportAsync()
     {
         var dlg = new OpenFileDialog
@@ -189,34 +143,40 @@ public partial class MainViewModel : ObservableObject
     public async Task ImportFilesAsync(IEnumerable<string> paths)
     {
         if (_viewport is null) return;
+        // 拖放/命令列可繞過指令 CanExecute 直接進來 → 匯入或背景運算期間直接擋掉，
+        // 避免兩批匯入交錯（StepImportService 有共享狀態，非重入安全）
+        if (IsBusy) { StatusText = "忙碌中（匯入或運算進行中），請稍候再匯入"; return; }
         int ok = 0, fail = 0;
-        foreach (string path in paths)
+        IsBusy = true; // 整批匯入期間維持 busy（v0.4.0：不再逐檔開關，杜絕檔案之間的重入空窗）
+        try
         {
-            string name = Path.GetFileNameWithoutExtension(path);
+            foreach (string path in paths)
-            IsBusy = true;
-            StatusText = $"匯入中：{name} …";
-            // 匯入階段回報（從背景執行緒來 → 切回 UI 執行緒）
-            _importService.Progress = msg =>
-                System.Windows.Application.Current?.Dispatcher.BeginInvoke(
-                    () => StatusText = $"匯入 {name}：{msg}");
-            try
             {
-                ImportedFileData data = await Task.Run(() => _importService.Import(path));
+                string name = Path.GetFileNameWithoutExtension(path);
-                BuildRoot(data);
+                StatusText = $"匯入中：{name} …";
-                ok++;
+                // 匯入階段回報（從背景執行緒來 → 切回 UI 執行緒）
-            }
+                _importService.Progress = msg =>
-            catch (Exception ex)
+                    System.Windows.Application.Current?.Dispatcher.BeginInvoke(
-            {
+                        () => StatusText = $"匯入 {name}：{msg}");
-                fail++;
+                try
-                StatusText = $"匯入失敗：{name} — {ex.Message}";
+                {
-                MessageBox.Show($"{path}\n\n{ex.Message}", "匯入失敗",
+                    ImportedFileData data = await Task.Run(() => _importService.Import(path));
-                    MessageBoxButton.OK, MessageBoxImage.Warning);
+                    BuildRoot(data);
-            }
+                    ok++;
-            finally
+                }
-            {
+                catch (Exception ex)
-                IsBusy = false;
+                {
+                    fail++;
+                    StatusText = $"匯入失敗：{name} — {ex.Message}";
+                    MessageBox.Show($"{path}\n\n{ex.Message}", "匯入失敗",
+                        MessageBoxButton.OK, MessageBoxImage.Warning);
+                }
             }
         }
+        finally
+        {
+            IsBusy = false;
+        }
         if (ok > 0)
         {
             if (SectionEnabled) ApplySection();
@@ -373,20 +333,19 @@ public partial class MainViewModel : ObservableObject
 
     // ─── 合併網格（瀏覽模式降 draw call）────────────────────────
 
-    /// <summary>把一個零件的所有面網格併成單一 MeshGeometry3D（索引位移後串接）</summary>
+    /// <summary>把多個面網格依序併成單一 MeshGeometry3D（索引位移後串接；順序 = 呼叫端給的面序）</summary>
-    private static MeshGeometry3D BuildMergedMesh(IReadOnlyList<ImportedFace> faces)
+    private static MeshGeometry3D MergeMeshes(IReadOnlyList<MeshGeometry3D> meshes)
     {
         int nv = 0, nt = 0;
-        foreach (ImportedFace f in faces) { nv += f.Mesh.Positions.Count; nt += f.Mesh.TriangleIndices.Count; }
+        foreach (MeshGeometry3D m in meshes) { nv += m.Positions.Count; nt += m.TriangleIndices.Count; }
 
         var pos = new Point3DCollection(nv);
         var nrm = new Vector3DCollection(nv);
         var idx = new Int32Collection(nt);
         int baseIdx = 0;
         bool hasNormals = true;
-        foreach (ImportedFace f in faces)
+        foreach (MeshGeometry3D m in meshes)
         {
-            MeshGeometry3D m = f.Mesh;
             foreach (Point3D p in m.Positions) pos.Add(p);
             if (m.Normals.Count == m.Positions.Count)
                 foreach (Vector3D v in m.Normals) nrm.Add(v);
@@ -401,33 +360,24 @@ public partial class MainViewModel : ObservableObject
         return mesh;
     }
 
-    /// <summary>重建合併網格（位置變更後，如零件平移）。由 leaf 逐面 fi.Mesh（未剖切原始）串接。</summary>
+    /// <summary>匯入時建合併網格（依 faces 面序串接，與 _mergedFaceRanges 的頂點邊界對齊）</summary>
+    private static MeshGeometry3D BuildMergedMesh(IReadOnlyList<ImportedFace> faces)
+    {
+        var meshes = new List<MeshGeometry3D>(faces.Count);
+        foreach (ImportedFace f in faces) meshes.Add(f.Mesh);
+        return MergeMeshes(meshes);
+    }
+
+    /// <summary>重建合併網格（位置變更後，如零件平移）。由 leaf 逐面 fi.Mesh（未剖切原始）依 FacesContent 子序串接，
+    /// 與匯入時 BuildMergedMesh 的面序一致 → _mergedFaceRanges 頂點邊界維持有效。</summary>
     private void RebuildMerged(ModelNodeViewModel leaf)
     {
         if (leaf.MergedContent is null || leaf.FacesContent is null) return;
-        int nv = 0, nt = 0;
+        var meshes = new List<MeshGeometry3D>(leaf.FacesContent.Children.Count);
         foreach (Model3D mm in leaf.FacesContent.Children)
             if (mm is GeometryModel3D g && _faceMap.TryGetValue(g, out FaceInfo? fi))
-            { nv += fi.Mesh.Positions.Count; nt += fi.Mesh.TriangleIndices.Count; }
+                meshes.Add(fi.Mesh);
-
+        ((GeometryModel3D)leaf.MergedContent.Children[0]).Geometry = MergeMeshes(meshes);
-        var pos = new Point3DCollection(nv);
-        var nrm = new Vector3DCollection(nv);
-        var idx = new Int32Collection(nt);
-        int baseIdx = 0; bool hasNormals = true;
-        foreach (Model3D mm in leaf.FacesContent.Children)
-        {
-            if (mm is not GeometryModel3D g || !_faceMap.TryGetValue(g, out FaceInfo? fi)) continue;
-            MeshGeometry3D m = fi.Mesh;
-            foreach (Point3D p in m.Positions) pos.Add(p);
-            if (m.Normals.Count == m.Positions.Count) foreach (Vector3D v in m.Normals) nrm.Add(v);
-            else hasNormals = false;
-            foreach (int ti in m.TriangleIndices) idx.Add(ti + baseIdx);
-            baseIdx += m.Positions.Count;
-        }
-        var mesh = new MeshGeometry3D { Positions = pos, TriangleIndices = idx };
-        if (hasNormals && nrm.Count == pos.Count) mesh.Normals = nrm;
-        mesh.Freeze();
-        ((GeometryModel3D)leaf.MergedContent.Children[0]).Geometry = mesh;
     }
 
     /// <summary>
@@ -849,27 +799,37 @@ public partial class MainViewModel : ObservableObject
         if (_viewport is null) return;
         ClearMeasurements(); // 量測標記位置已失效
 
-        foreach (ModelNodeViewModel leaf in root.Leaves())
+        var leaves = root.Leaves().ToList();
-        {
+
-            // B-rep：對 Solid/Shell 整體 Modify（避免共用邊被逐面重複變換）
+        // B-rep：對 Solid/Shell 整體 Modify（避免共用邊被逐面重複變換）。
+        // CADability 物件非執行緒安全 → 維持循序
+        foreach (ModelNodeViewModel leaf in leaves)
             foreach (CADability.GeoObject.IGeoObject g in leaf.SourceGeos)
             {
                 try { g.Modify(op); }
                 catch { /* 個別物件變換失敗不中斷 */ }
             }
 
-            // 渲染網格（逐面，與目前顯示哪種內容無關）
+        // 渲染網格：面級平行變換（來源/輸出皆 frozen、各面獨立 → 安全；大檔 64k 面吃滿多核）
+        var faceItems = new List<(GeometryModel3D Gm, FaceInfo Fi)>();
+        foreach (ModelNodeViewModel leaf in leaves)
             if (leaf.FacesContent is not null)
-            {
                 foreach (Model3D mm in leaf.FacesContent.Children)
-                {
+                    if (mm is GeometryModel3D gm && _faceMap.TryGetValue(gm, out FaceInfo? fi))
-                    if (mm is not GeometryModel3D gm || !_faceMap.TryGetValue(gm, out FaceInfo? fi)) continue;
+                        faceItems.Add((gm, fi));
-                    MeshGeometry3D moved = TransformMesh(fi.Mesh, m);
+
-                    fi.Mesh = moved;
+        var moved = new MeshGeometry3D[faceItems.Count];
-                    gm.Geometry = moved;
+        Parallel.For(0, faceItems.Count, i => moved[i] = TransformMesh(faceItems[i].Fi.Mesh, m));
-                }
+        for (int i = 0; i < faceItems.Count; i++) // 視覺樹賦值回 UI 執行緒循序做
+        {
+            faceItems[i].Fi.Mesh = moved[i];
+            faceItems[i].Gm.Geometry = moved[i];
+        }
+
+        foreach (ModelNodeViewModel leaf in leaves)
+        {
+            if (leaf.FacesContent is not null)
                 RebuildMerged(leaf); // 合併網格同步
-            }
 
             // 邊線端點（資料）；實際合併線於迴圈後重建
             if (leaf.OriginalEdgePoints is not null)
@@ -926,7 +886,7 @@ public partial class MainViewModel : ObservableObject
 
     // ─── 旋轉 90°（樹面板選取的檔案，繞其中心）──────────────────
 
-    [RelayCommand]
+    [RelayCommand(CanExecute = nameof(IsIdle))]
     private void RotateRoot(string axisName)
     {
         ModelNodeViewModel? root = SelectedNode is not null ? RootContaining(SelectedNode)
@@ -960,499 +920,6 @@ public partial class MainViewModel : ObservableObject
 
     // 三點對齊的剛體變換數學在 Services/RigidAlign.cs（SmokeTest --align-test 驗證）
 
-    // ─── 拖曳模式（左鍵按住零件沿螢幕平面拖；放開才烘進 B-rep）──
-
-    /// <summary>左鍵按下：命中零件則開始拖曳（回傳 true 表示要捕捉滑鼠）</summary>
-    public bool OnDragStart(Point position)
-    {
-        if (_viewport is null || IsBusy || CurrentMode != MeasureMode.Drag || _dragRoot is not null)
-            return false;
-
-        // 兩種渲染內容都可能在場：合併網格查 _mergedMap、逐面（剖面時）查 _faceMap
-        ModelNodeViewModel? leaf = null;
-        Point3D anchor = default;
-        foreach (var h in _viewport.Viewport.FindHits(position))
-        {
-            if (h.Model is null) continue;
-            if (_faceMap.TryGetValue(h.Model, out FaceInfo? fi)) { leaf = fi.Owner; anchor = h.Position; break; }
-            if (_mergedMap.TryGetValue(h.Model, out ModelNodeViewModel? ml)) { leaf = ml; anchor = h.Position; break; }
-        }
-        if (leaf is null) return false;
-        ModelNodeViewModel? root = FindRootOf(leaf) ?? RootContaining(leaf);
-        if (root is null) return false;
-
-        _dragRoot = root;
-        _dragAnchor = anchor;
-        _dragApplied = default;
-        _dragTransform = new TranslateTransform3D();
-        foreach (ModelNodeViewModel l in root.Leaves())
-            if (l.BodyVisual is not null)
-                l.BodyVisual.Transform = _dragTransform;
-
-        // 拖曳中隱藏邊線（LinesVisual3D 隨 Transform 變更逐幀重建會卡）
-        _edgesSuspended = true;
-        SetEdgesActive(false);
-        StatusText = $"拖曳「{root.Name}」中…（放開定位）";
-        return true;
-    }
-
-    /// <summary>滑鼠移動：把 2D 位移投影到「過錨點、面向相機」的平面上 → 暫時 Transform</summary>
-    public void OnDragMove(Point position)
-    {
-        if (_viewport?.Camera is not System.Windows.Media.Media3D.ProjectionCamera cam ||
-            _dragRoot is null || _dragTransform is null) return;
-
-        Point3D? p = _viewport.Viewport.UnProject(position, _dragAnchor, cam.LookDirection);
-        if (p is null) return;
-        _dragApplied = p.Value - _dragAnchor;
-        _dragTransform.OffsetX = _dragApplied.X;
-        _dragTransform.OffsetY = _dragApplied.Y;
-        _dragTransform.OffsetZ = _dragApplied.Z;
-    }
-
-    /// <summary>放開：移除暫時 Transform，一次性烘進 B-rep（量測精度不受拖曳影響）</summary>
-    public bool OnDragEnd()
-    {
-        if (_dragRoot is null) return false;
-        ModelNodeViewModel root = _dragRoot;
-        Vector3D delta = _dragApplied;
-
-        // 清除暫時位移：必須用 Identity，不可用 null —— HelixToolkit GetTransform 對 child.Transform
-        // 不做 null 檢查（Children.Add(null) 會拋「無法新增空值到集合中」），下次 FindHits 即 crash
-        foreach (ModelNodeViewModel l in root.Leaves())
-            if (l.BodyVisual is not null)
-                l.BodyVisual.Transform = Transform3D.Identity;
-        _dragRoot = null;
-        _dragTransform = null;
-        _dragApplied = default;
-        _edgesSuspended = false;
-        SetEdgesActive(true); // 恢復所有檔案的邊線（被拖檔案的點隨後由 TranslateRoot 更新，期間不會渲染）
-
-        if (delta.LengthSquared > 1e-12)
-        {
-            TranslateRoot(root, delta); // 烘進 B-rep + 網格 + 邊線 + 邊界（量測清空）
-            StatusText = $"已拖曳「{root.Name}」 Δ({delta.X:F2}, {delta.Y:F2}, {delta.Z:F2}) mm（可用 🧩干涉 驗證）";
-        }
-        return true;
-    }
-
-    // ─── Gizmo 三軸操作器（XYZ 箭頭 + 旋轉環；每次放開滑鼠烘進 B-rep）──
-
-    [ObservableProperty]
-    private bool gizmoEnabled;
-
-    private readonly List<HelixToolkit.Wpf.Manipulator> _gizmoParts = new();
-    private ModelVisual3D? _gizmoProxy;        // 操作器綁定的代理 visual（其 Transform = 使用者拖出的變換）
-    private ModelNodeViewModel? _gizmoTarget;
-    private bool _gizmoDragActive;             // 拖動中（邊線已暫停）
-    private bool _gizmoBaking;                 // 烘焙中，忽略 Transform 變更回呼
-    private bool _gizmoBakePending;            // 已排程烘焙，防同一次放開重複觸發
-
-    // 操作器疊圖層：另一個透明 Viewport3D 疊在主視窗上、相機同步、只放操作器 →
-    // 操作器不在主場景，永不被實體遮擋（always-on-top）；空白處滑鼠穿透回主視窗
-    private System.Windows.Controls.Viewport3D? _overlayViewport;
-    private PerspectiveCamera? _overlayCamera;
-
-    partial void OnGizmoEnabledChanged(bool value) => UpdateGizmo();
-
-    partial void OnSelectedNodeChanged(ModelNodeViewModel? value)
-    {
-        if (GizmoEnabled) UpdateGizmo(); // 換選取 → 操作器跟著換目標
-    }
-
-    private void UpdateGizmo()
-    {
-        RemoveGizmo();
-        if (!GizmoEnabled || _viewport is null || _overlayViewport is null) return;
-
-        ModelNodeViewModel? root = SelectedNode is not null ? RootContaining(SelectedNode)
-            : Roots.Count == 1 ? Roots[0] : null;
-        if (root is null || root.Bounds.IsEmpty)
-        {
-            StatusText = "操作器：請先在樹面板點選要操作的檔案";
-            GizmoEnabled = false;
-            return;
-        }
-        _gizmoTarget = root;
-        SyncOverlayCamera(); // 操作器出現前先對齊相機
-
-        Rect3D b = root.Bounds;
-        var center = new Point3D(b.X + b.SizeX / 2, b.Y + b.SizeY / 2, b.Z + b.SizeZ / 2);
-        double diag = new Vector3D(b.SizeX, b.SizeY, b.SizeZ).Length;
-
-        _gizmoProxy = new ModelVisual3D();
-        _overlayViewport.Children.Add(_gizmoProxy);
-        System.ComponentModel.DependencyPropertyDescriptor
-            .FromProperty(Visual3D.TransformProperty, typeof(Visual3D))
-            .AddValueChanged(_gizmoProxy, GizmoTransformChanged);
-
-        void AddPart(HelixToolkit.Wpf.Manipulator man)
-        {
-            man.Position = center;
-            man.Bind(_gizmoProxy);
-            _gizmoParts.Add(man);
-            _overlayViewport!.Children.Add(man); // 放疊圖層 → 永不被實體遮擋
-        }
-        // 平移箭頭（X 紅 / Y 綠 / Z 藍 — 業界慣例）
-        AddPart(new TranslateManipulator { Direction = new Vector3D(1, 0, 0), Color = Colors.Red,   Length = diag * 0.22, Diameter = diag * 0.016 });
-        AddPart(new TranslateManipulator { Direction = new Vector3D(0, 1, 0), Color = Colors.Green, Length = diag * 0.22, Diameter = diag * 0.016 });
-        AddPart(new TranslateManipulator { Direction = new Vector3D(0, 0, 1), Color = Colors.Blue,  Length = diag * 0.22, Diameter = diag * 0.016 });
-        // 旋轉環
-        AddPart(new RotateManipulator { Axis = new Vector3D(1, 0, 0), Color = Colors.Red,   Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
-        AddPart(new RotateManipulator { Axis = new Vector3D(0, 1, 0), Color = Colors.Green, Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
-        AddPart(new RotateManipulator { Axis = new Vector3D(0, 0, 1), Color = Colors.Blue,  Diameter = diag * 0.34, InnerDiameter = diag * 0.30, Length = diag * 0.012 });
-
-        StatusText = $"操作器：拖箭頭沿軸移動「{root.Name}」、拖環繞軸旋轉；放開即定位";
-    }
-
-    private void RemoveGizmo()
-    {
-        if (_gizmoProxy is not null)
-        {
-            System.ComponentModel.DependencyPropertyDescriptor
-                .FromProperty(Visual3D.TransformProperty, typeof(Visual3D))
-                .RemoveValueChanged(_gizmoProxy, GizmoTransformChanged);
-            _overlayViewport?.Children.Remove(_gizmoProxy);
-        }
-        foreach (HelixToolkit.Wpf.Manipulator man in _gizmoParts)
-        {
-            man.UnBind();
-            _overlayViewport?.Children.Remove(man);
-        }
-        _gizmoParts.Clear();
-        _gizmoProxy = null;
-
-        if (_gizmoTarget is not null) // 清掉殘留的暫時 Transform（用 Identity，不可 null → 否則 FindHits crash）
-            foreach (ModelNodeViewModel l in _gizmoTarget.Leaves())
-                if (l.BodyVisual is not null)
-                    l.BodyVisual.Transform = Transform3D.Identity;
-        _gizmoTarget = null;
-        if (_gizmoDragActive)
-        {
-            _gizmoDragActive = false;
-            _edgesSuspended = false;
-            SetEdgesActive(true);
-        }
-    }
-
-    /// <summary>操作器拖動中：把代理的 Transform 套到目標檔案的所有 BodyVisual（暫時、GPU 端）</summary>
-    private void GizmoTransformChanged(object? sender, EventArgs e)
-    {
-        if (_gizmoBaking || _gizmoTarget is null || _gizmoProxy is null) return;
-        Transform3D t = _gizmoProxy.Transform;
-        if (!_gizmoDragActive && t is not null && !t.Value.IsIdentity)
-        {
-            _gizmoDragActive = true;
-            _edgesSuspended = true;
-            SetEdgesActive(false); // 邊線逐幀重建會卡，拖動中暫停
-        }
-        foreach (ModelNodeViewModel l in _gizmoTarget.Leaves())
-            if (l.BodyVisual is not null)
-                l.BodyVisual.Transform = t;
-    }
-
-    /// <summary>滑鼠放開（MainWindow 轉發，handledEventsToo）：把累積變換烘進 B-rep 並重置操作器</summary>
-    public void OnGizmoMouseUp()
-    {
-        if (_gizmoTarget is null || _gizmoProxy is null || _gizmoBakePending) return;
-        Matrix3D m = _gizmoProxy.Transform?.Value ?? Matrix3D.Identity;
-        if (m.IsIdentity) return; // 只是點一下、沒拖操作器 → 不烘焙
-
-        // 延後到 manipulator 自身的 mouse-up 處理（釋放捕捉等）完成後再烘焙，避免在其事件中改動視覺樹造成 reentrancy
-        _gizmoBakePending = true;
-        _viewport?.Dispatcher.BeginInvoke(new Action(() => BakeGizmo(m)),
-            System.Windows.Threading.DispatcherPriority.Background);
-    }
-
-    private void BakeGizmo(Matrix3D m)
-    {
-        _gizmoBakePending = false;
-        if (_gizmoTarget is null) return;
-        ModelNodeViewModel root = _gizmoTarget;
-
-        _gizmoBaking = true; // 防 proxy 歸零觸發 GizmoTransformChanged 重入
-        foreach (ModelNodeViewModel l in root.Leaves())
-            if (l.BodyVisual is not null)
-                l.BodyVisual.Transform = Transform3D.Identity; // 清暫時位移（用 Identity，不可 null）
-        if (_gizmoProxy is not null) _gizmoProxy.Transform = Transform3D.Identity; // 綁定 → 操作器歸零
-        _gizmoBaking = false;
-        _gizmoDragActive = false;
-        _edgesSuspended = false;
-        SetEdgesActive(true);
-
-        TransformRoot(root, RigidAlign.ToModOp(m), m); // 烘進 B-rep（量測精度不受影響）
-
-        // 操作器移到變換後的新中心
-        Rect3D b = root.Bounds;
-        if (!b.IsEmpty)
-        {
-            var center = new Point3D(b.X + b.SizeX / 2, b.Y + b.SizeY / 2, b.Z + b.SizeZ / 2);
-            foreach (HelixToolkit.Wpf.Manipulator man in _gizmoParts)
-                man.Position = center;
-        }
-        StatusText = $"已套用操作器變換「{root.Name}」（可用 🧩干涉 驗證）";
-    }
-
-    // ─── 干涉檢查 ────────────────────────────────────────────────
-
-    [RelayCommand]
-    private async Task CheckInterferenceAsync()
-    {
-        if (_viewport is null) return;
-        var visibleRoots = Roots.Where(r => r.IsVisible).ToList();
-        if (visibleRoots.Count != 2)
-        {
-            StatusText = $"干涉檢查需要剛好 2 個可見檔案（目前 {visibleRoots.Count} 個）— 用樹面板勾選";
-            return;
-        }
-
-        List<MeshGeometry3D> MeshesOf(ModelNodeViewModel root) =>
-            root.Leaves().Where(l => l.IsVisible && l.FacesContent is not null)
-                .SelectMany(l => l.FacesContent!.Children)
-                .Where(m => m is GeometryModel3D gm && _faceMap.ContainsKey(gm))
-                .Select(m => _faceMap[(GeometryModel3D)m].Mesh)
-                .ToList();
-
-        var a = MeshesOf(visibleRoots[0]);
-        var b = MeshesOf(visibleRoots[1]);
-        string nameA = visibleRoots[0].Name, nameB = visibleRoots[1].Name;
-
-        IsBusy = true;
-        StatusText = $"干涉檢查中：{nameA} ⟷ {nameB} …";
-        try
-        {
-            InterferenceResult result = await Task.Run(() => InterferenceService.Check(a, b));
-            AddInterferenceResult(result, nameA, nameB);
-        }
-        catch (Exception ex)
-        {
-            StatusText = $"干涉檢查失敗：{ex.Message}";
-        }
-        finally
-        {
-            IsBusy = false;
-        }
-    }
-
-    private void AddInterferenceResult(InterferenceResult result, string nameA, string nameB)
-    {
-        double diag = SceneDiagonal();
-        double markerR = Math.Clamp(diag * 0.004, 0.01, 5.0);
-        MeasurementResult m;
-
-        if (result.Intersects)
-        {
-            int pairs = result.PairCount;
-            int segCount = result.Segments.Count;
-            m = new MeasurementResult
-            {
-                Kind = MeasureMode.Interference,
-                TitleFor = _ => $"🧩 干涉！{nameA} ⟷ {nameB}",
-                DetailFor = _ => $"兩零件相交（不 match）\n相交三角形對 = {pairs:N0}\n" +
-                                 $"紅色線 = 干涉交線（{segCount:N0} 段）\n（共面貼合不會被算為干涉）",
-            };
-            var pts = new Point3DCollection(Math.Min(result.Segments.Count, 20000) * 2);
-            foreach ((Point3D s0, Point3D s1) in result.Segments) { pts.Add(s0); pts.Add(s1); }
-            m.Overlays.Add(new LinesVisual3D { Points = pts, Color = Colors.Red, Thickness = 3 });
-            if (result.Segments.Count > 0)
-            {
-                Point3D at = result.Segments[0].A;
-                m.Overlays.Add(new BillboardTextVisual3D
-                {
-                    Position = at + new Vector3D(0, 0, markerR * 3),
-                    Text = "干涉",
-                    Foreground = Brushes.White,
-                    Background = Brushes.Red,
-                    Padding = new Thickness(5, 2, 5, 2),
-                    FontSize = 14,
-                });
-            }
-        }
-        else
-        {
-            Point3D ga = result.GapA, gb = result.GapB;
-            Vector3D d = gb - ga;
-            double gap = result.GapDistance;
-            m = new MeasurementResult
-            {
-                Kind = MeasureMode.Interference,
-                TitleFor = u => $"🧩 無干涉  gap ≈ {Units.L(gap, u)}",
-                DetailFor = u => $"{nameA} ⟷ {nameB} 無相交\n最小間隙 ≈ {Units.L(gap, u)}（網格近似）\n" +
-                                 $"gap ≈ 0 即為貼合（match）\n點 1 {Units.P(ga, u)}\n點 2 {Units.P(gb, u)}",
-            };
-            m.Overlays.Add(new SphereVisual3D { Center = ga, Radius = markerR, Fill = Brushes.OrangeRed });
-            m.Overlays.Add(new SphereVisual3D { Center = gb, Radius = markerR, Fill = Brushes.OrangeRed });
-            m.Overlays.Add(new LinesVisual3D
-            {
-                Points = new Point3DCollection { ga, gb },
-                Color = Colors.OrangeRed,
-                Thickness = 2,
-            });
-            var label = new BillboardTextVisual3D
-            {
-                Position = ga + d / 2 + new Vector3D(0, 0, markerR * 2),
-                Text = $"gap {Units.L(gap, UnitSystem.Millimeter)}",
-                Foreground = Brushes.Black,
-                Background = new SolidColorBrush(Color.FromArgb(200, 255, 255, 210)),
-                Padding = new Thickness(4, 2, 4, 2),
-                FontSize = 14,
-            };
-            m.Overlays.Add(label);
-            m.DynamicLabels.Add((label, u => $"gap {Units.L(gap, u)}"));
-        }
-        AddMeasurement(m);
-    }
-
-    // ─── 剖面 ────────────────────────────────────────────────────
-
-    partial void OnSectionEnabledChanged(bool value) => ScheduleSection();
-    partial void OnSectionAxisIndexChanged(int value) => ScheduleSection();
-    partial void OnSectionPositionChanged(double value) => ScheduleSection();
-    partial void OnSectionFlipChanged(bool value) => ScheduleSection();
-
-    private void ScheduleSection()
-    {
-        _sectionTimer.Stop();
-        _sectionTimer.Start();
-    }
-
-    private void ApplySection()
-    {
-        if (_viewport is null) return;
-
-        if (!SectionEnabled)
-        {
-            // 還原原始幾何
-            foreach ((Model3D model, FaceInfo fi) in _faceMap)
-                if (model is GeometryModel3D gm && !ReferenceEquals(gm.Geometry, fi.Mesh))
-                    gm.Geometry = fi.Mesh;
-            foreach (ModelNodeViewModel root in Roots) RefreshRootEdges(root);
-            if (_sectionPlaneVisual is not null)
-            {
-                _viewport.Children.Remove(_sectionPlaneVisual);
-                _sectionPlaneVisual = null;
-            }
-            ApplyRenderMode(); // 剖面關閉 → 瀏覽模式可切回合併網格
-            StatusText = "剖面已關閉";
-            return;
-        }
-
-        Rect3D bounds = UnionBounds();
-        if (bounds.IsEmpty) return;
-
-        Vector3D axis = SectionAxisIndex switch
-        {
-            0 => new Vector3D(1, 0, 0),
-            1 => new Vector3D(0, 1, 0),
-            _ => new Vector3D(0, 0, 1),
-        };
-        double t = SectionPosition / 100.0;
-        Point3D min = bounds.Location;
-        var size = new Vector3D(bounds.SizeX, bounds.SizeY, bounds.SizeZ);
-        double planeCoord = SectionAxisIndex switch
-        {
-            0 => min.X + size.X * t,
-            1 => min.Y + size.Y * t,
-            _ => min.Z + size.Z * t,
-        };
-        Point3D center = min + size / 2;
-        Point3D planePoint = SectionAxisIndex switch
-        {
-            0 => new Point3D(planeCoord, center.Y, center.Z),
-            1 => new Point3D(center.X, planeCoord, center.Z),
-            _ => new Point3D(center.X, center.Y, planeCoord),
-        };
-        Vector3D normal = SectionFlip ? -axis : axis;
-
-        foreach ((Model3D model, FaceInfo fi) in _faceMap)
-            if (model is GeometryModel3D gm)
-                gm.Geometry = SectionService.ClipMesh(fi.Mesh, planePoint, normal);
-
-        _sectionPlanePoint = planePoint;
-        _sectionNormal = normal;
-        foreach (ModelNodeViewModel root in Roots) RefreshRootEdges(root);
-
-        ApplyRenderMode(); // 剖面開啟 → 改用逐面（裁切後幾何）
-        UpdateSectionPlaneVisual(planePoint, axis, size);
-        StatusText = $"剖面：{"XYZ"[SectionAxisIndex]} 軸 {SectionPosition:F0}%" + (SectionFlip ? "（反向）" : "");
-    }
-
-    private void UpdateSectionPlaneVisual(Point3D planePoint, Vector3D axis, Vector3D size)
-    {
-        if (_sectionPlaneVisual is not null)
-            _viewport!.Children.Remove(_sectionPlaneVisual);
-
-        (Vector3D lenDir, double len, double wid) = SectionAxisIndex switch
-        {
-            0 => (new Vector3D(0, 1, 0), size.Y, size.Z),
-            1 => (new Vector3D(1, 0, 0), size.X, size.Z),
-            _ => (new Vector3D(1, 0, 0), size.X, size.Y),
-        };
-        _sectionPlaneVisual = new RectangleVisual3D
-        {
-            Origin = planePoint,
-            Normal = axis,
-            LengthDirection = lenDir,
-            Length = len * 1.05,
-            Width = wid * 1.05,
-            Fill = new SolidColorBrush(Color.FromArgb(40, 30, 120, 255)),
-        };
-        _viewport!.Children.Add(_sectionPlaneVisual);
-    }
-
-    // ─── 匯出 ────────────────────────────────────────────────────
-
-    [RelayCommand]
-    private void ExportCsv()
-    {
-        if (Measurements.Count == 0)
-        {
-            StatusText = "沒有量測結果可匯出";
-            return;
-        }
-        var dlg = new SaveFileDialog
-        {
-            Title = "匯出量測結果",
-            Filter = "CSV 檔案 (*.csv)|*.csv",
-            FileName = $"measurements_{DateTime.Now:yyyyMMdd_HHmmss}.csv",
-        };
-        if (dlg.ShowDialog() != true) return;
-
-        var sb = new StringBuilder();
-        sb.AppendLine("標籤,類型,明細");
-        foreach (MeasurementResult m in Measurements)
-        {
-            static string Esc(string s) => $"\"{s.Replace("\"", "\"\"")}\"";
-            sb.AppendLine($"{Esc(m.Title)},{m.Kind},{Esc(m.Detail.Replace("\n", " | "))}");
-        }
-        File.WriteAllText(dlg.FileName, sb.ToString(), new UTF8Encoding(true)); // BOM：Excel 中文不亂碼
-        StatusText = $"已匯出 {Measurements.Count} 筆量測 → {Path.GetFileName(dlg.FileName)}";
-    }
-
-    [RelayCommand]
-    private void SaveScreenshot()
-    {
-        if (_viewport is null || _viewport.ActualWidth < 1) return;
-        var dlg = new SaveFileDialog
-        {
-            Title = "儲存視圖截圖",
-            Filter = "PNG 圖片 (*.png)|*.png",
-            FileName = $"stpviewer_{DateTime.Now:yyyyMMdd_HHmmss}.png",
-        };
-        if (dlg.ShowDialog() != true) return;
-
-        const double scale = 2.0; // 2x 解析度
-        var rtb = new RenderTargetBitmap(
-            (int)(_viewport.ActualWidth * scale), (int)(_viewport.ActualHeight * scale),
-            96 * scale, 96 * scale, PixelFormats.Pbgra32);
-        rtb.Render(_viewport);
-        var encoder = new PngBitmapEncoder();
-        encoder.Frames.Add(BitmapFrame.Create(rtb));
-        using FileStream fs = File.Create(dlg.FileName);
-        encoder.Save(fs);
-        StatusText = $"已儲存截圖 → {Path.GetFileName(dlg.FileName)}";
-    }
-
     // ─── 共用 ────────────────────────────────────────────────────
 
     private Rect3D UnionBounds()