diff --git a/src/STPViewer/MainWindow.xaml b/src/STPViewer/MainWindow.xaml
index 9ffc036..aa8172e 100644
--- a/src/STPViewer/MainWindow.xaml
+++ b/src/STPViewer/MainWindow.xaml
@@ -7,7 +7,8 @@
         Title="STPViewer — STP/STEP 3D 檢視器"
         Height="820" Width="1320"
         WindowStartupLocation="CenterScreen"
-        AllowDrop="True" Drop="Window_Drop" DragOver="Window_DragOver">
+        AllowDrop="True" Drop="Window_Drop" DragOver="Window_DragOver"
+        PreviewKeyDown="Window_PreviewKeyDown">
 
     <Window.Resources>
         <conv:EnumToBoolConverter x:Key="ModeConv" />
@@ -25,23 +26,37 @@
             <ToolBar>
                 <Button Command="{Binding ImportCommand}" Padding="8,4" FontSize="13"
                         ToolTip="匯入 STP/STEP/STL/DXF（可複選，也可直接拖放到視窗）">📂 匯入</Button>
+                <Button Click="Recent_Click" Padding="4,4" FontSize="13"
+                        ToolTip="最近開啟的檔案">▾</Button>
                 <Button Command="{Binding ZoomAllCommand}" Padding="8,4" FontSize="13"
                         ToolTip="縮放至全部模型">🔍 全覽</Button>
                 <Separator />
+                <TextBlock Text="視圖：" VerticalAlignment="Center" Margin="4,0,2,0" />
+                <Button Command="{Binding SetStandardViewCommand}" CommandParameter="Iso" Padding="6,4" FontSize="13"
+                        ToolTip="等角視圖">等角</Button>
+                <Button Command="{Binding SetStandardViewCommand}" CommandParameter="Front" Padding="6,4" FontSize="13"
+                        ToolTip="前視圖（-Y 方向看，Z 向上）">前</Button>
+                <Button Command="{Binding SetStandardViewCommand}" CommandParameter="Top" Padding="6,4" FontSize="13"
+                        ToolTip="上視圖（+Z 往下看）">上</Button>
+                <Button Command="{Binding SetStandardViewCommand}" CommandParameter="Right" Padding="6,4" FontSize="13"
+                        ToolTip="右視圖（+X 方向看，Z 向上）">右</Button>
+                <ToggleButton IsChecked="{Binding OrthographicView}" Padding="6,4" FontSize="13" Margin="2,0"
+                              ToolTip="正交投影（平行投影，量尺寸不受透視變形；再按切回透視）">正交</ToggleButton>
+                <Separator />
                 <TextBlock Text="量測：" VerticalAlignment="Center" Margin="4,0,2,0" />
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="量測點座標（吸附頂點）"
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="量測點座標（吸附頂點/圓心）— 快速鍵 P"
                               IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Point}">📍 點</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="兩點距離 + ΔXYZ"
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="兩點距離 + ΔXYZ（點到圓邊會吸圓心 → 可量孔對孔 pitch）— 快速鍵 D"
                               IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Distance}">📏 距離</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="邊長（直線/曲線/圓弧）"
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="邊長（直線/曲線/圓弧）— 快速鍵 E"
                               IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Edge}">📐 邊</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="面積 + 曲面類型/法向量"
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="面積 + 曲面類型/法向量 — 快速鍵 F"
                               IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Face}">⬛ 面</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="圓心/半徑/直徑/周長"
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="圓心/半徑/直徑/周長 — 快速鍵 C"
                               IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Circle}">⭕ 圓</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="兩面/兩邊夾角（點兩個面或靠近直線邊）"
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="兩面/兩邊夾角（點兩個面或靠近直線邊）— 快速鍵 A"
                               IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=Angle}">∠ 角度</ToggleButton>
-                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="面到面最短距離（網格近似）"
+                <ToggleButton Style="{StaticResource ModeButton}" ToolTip="面到面最短距離（網格近似）— 快速鍵 M"
                               IsChecked="{Binding CurrentMode, Converter={StaticResource ModeConv}, ConverterParameter=FaceDistance}">⇔ 面距</ToggleButton>
                 <Separator />
                 <ToggleButton Style="{StaticResource ModeButton}"
@@ -65,10 +80,10 @@
                 <ToggleButton IsChecked="{Binding GizmoEnabled}" Padding="8,4" FontSize="13"
                               ToolTip="三軸操作器：對樹面板選取的檔案顯示 XYZ 箭頭（沿軸移動）與旋轉環（繞軸轉任意角度），每次放開即定位">⊹ 操作器</ToggleButton>
                 <Button Command="{Binding CheckInterferenceCommand}" Padding="8,4" FontSize="13"
-                        ToolTip="干涉檢查：檢查 2 個可見檔案是否相交（match 判定）；無相交時回報最小間隙">🧩 干涉</Button>
+                        ToolTip="干涉檢查：2 個以上可見檔案兩兩檢查是否相交（match 判定）；無相交時回報最小間隙">🧩 干涉</Button>
                 <Separator />
                 <Button Command="{Binding ClearMeasurementsCommand}" Padding="8,4" FontSize="13"
-                        ToolTip="清除全部量測與標記">🧹 清除</Button>
+                        ToolTip="清除全部量測與標記（Esc = 取消進行中量測/退出模式）">🧹 清除</Button>
                 <Separator />
                 <ToggleButton IsChecked="{Binding UseInch}" Padding="8,4" FontSize="13"
                               ToolTip="切換顯示單位 mm ⇄ inch（既有量測即時換算）">mm ⇄ in</ToggleButton>
@@ -77,22 +92,27 @@
                         ToolTip="量測結果匯出 CSV">💾 CSV</Button>
                 <Button Command="{Binding SaveScreenshotCommand}" Padding="8,4" FontSize="13"
                         ToolTip="3D 視圖截圖存 PNG（2x 解析度）">📷 截圖</Button>
+                <Button Command="{Binding ExportStepFileCommand}" Padding="8,4" FontSize="13"
+                        ToolTip="把可見檔案（目前對齊位置）匯出成新 STEP 檔 — 對齊插合結果可交接 CAD；不動原始檔">📤 STEP</Button>
             </ToolBar>
             <ToolBar>
                 <ToggleButton IsChecked="{Binding SectionEnabled}" Padding="8,4" FontSize="13"
                               ToolTip="開啟/關閉剖面檢視">✂ 剖面</ToggleButton>
-                <ComboBox SelectedIndex="{Binding SectionAxisIndex}" Width="52" Margin="4,0"
-                          VerticalAlignment="Center" ToolTip="剖切軸向"
+                <ComboBox SelectedIndex="{Binding SectionAxisIndex}" Width="60" Margin="4,0"
+                          VerticalAlignment="Center" ToolTip="剖切軸向（3點 = 在模型上點 3 點定義任意平面）"
                           IsEnabled="{Binding SectionEnabled}">
                     <ComboBoxItem>X</ComboBoxItem>
                     <ComboBoxItem>Y</ComboBoxItem>
                     <ComboBoxItem>Z</ComboBoxItem>
+                    <ComboBoxItem>3點</ComboBoxItem>
                 </ComboBox>
                 <Slider Value="{Binding SectionPosition}" Minimum="0" Maximum="100" Width="180"
-                        VerticalAlignment="Center" Margin="4,0" ToolTip="剖面位置（沿軸 %）"
+                        VerticalAlignment="Center" Margin="4,0" ToolTip="剖面位置（沿法向 %）"
                         IsEnabled="{Binding SectionEnabled}" />
-                <TextBlock Text="{Binding SectionPosition, StringFormat={}{0:F0}%}" Width="36"
-                           VerticalAlignment="Center" />
+                <TextBox Text="{Binding SectionPosition, StringFormat={}{0:F0}}" Width="34"
+                         VerticalAlignment="Center" ToolTip="剖面位置 %（0–100，可直接輸入，離開欄位生效）"
+                         IsEnabled="{Binding SectionEnabled}" />
+                <TextBlock Text="%" VerticalAlignment="Center" Margin="1,0,0,0" />
                 <CheckBox IsChecked="{Binding SectionFlip}" Content="反向" VerticalAlignment="Center"
                           Margin="4,0" ToolTip="切換保留側" IsEnabled="{Binding SectionEnabled}" />
             </ToolBar>
@@ -111,75 +131,105 @@
 
         <Grid>
             <Grid.ColumnDefinitions>
-                <ColumnDefinition Width="280" />
-                <ColumnDefinition Width="*" />
-                <ColumnDefinition Width="300" />
+                <ColumnDefinition Width="280" MinWidth="160" />
+                <ColumnDefinition Width="Auto" />
+                <ColumnDefinition Width="*" MinWidth="300" />
+                <ColumnDefinition Width="Auto" />
+                <ColumnDefinition Width="300" MinWidth="160" />
             </Grid.ColumnDefinitions>
 
             <!-- ─── 裝配樹面板 ─── -->
             <GroupBox Grid.Column="0" Header="模型 / 裝配樹" Margin="4">
-                <TreeView ItemsSource="{Binding Roots}"
-                          ScrollViewer.HorizontalScrollBarVisibility="Disabled"
-                          VirtualizingPanel.IsVirtualizing="True"
-                          SelectedItemChanged="Tree_SelectedItemChanged">
-                    <TreeView.ItemContainerStyle>
-                        <Style TargetType="TreeViewItem">
-                            <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
-                        </Style>
-                    </TreeView.ItemContainerStyle>
-                    <TreeView.ItemTemplate>
-                        <HierarchicalDataTemplate DataType="{x:Type vm:ModelNodeViewModel}"
-                                                  ItemsSource="{Binding Children}">
-                            <StackPanel Orientation="Horizontal" Margin="0,1"
-                                        ToolTip="{Binding ToolTipText}">
-                                <CheckBox IsChecked="{Binding IsVisible}" VerticalAlignment="Center"
-                                          ToolTip="顯示 / 隱藏（含子節點）" />
-                                <Button Width="14" Height="14" Margin="3,0"
-                                        VerticalAlignment="Center" ToolTip="點擊換色（含子節點）"
-                                        Command="{Binding CycleColorCommand}">
-                                    <Button.Template>
-                                        <ControlTemplate TargetType="Button">
-                                            <Border BorderBrush="Gray" BorderThickness="1" CornerRadius="2">
-                                                <Border.Background>
-                                                    <SolidColorBrush Color="{Binding Color}" />
-                                                </Border.Background>
-                                            </Border>
-                                        </ControlTemplate>
-                                    </Button.Template>
-                                </Button>
-                                <TextBlock Text="{Binding Name}" VerticalAlignment="Center"
-                                           MaxWidth="130" TextTrimming="CharacterEllipsis">
-                                    <TextBlock.Style>
-                                        <Style TargetType="TextBlock">
-                                            <Style.Triggers>
-                                                <DataTrigger Binding="{Binding IsRoot}" Value="True">
-                                                    <Setter Property="FontWeight" Value="SemiBold" />
-                                                </DataTrigger>
-                                            </Style.Triggers>
-                                        </Style>
-                                    </TextBlock.Style>
-                                </TextBlock>
-                                <CheckBox IsChecked="{Binding ShowEdges}" Content="邊" FontSize="10"
-                                          VerticalAlignment="Center" Margin="4,0,0,0"
-                                          Visibility="{Binding IsRoot, Converter={StaticResource BoolToVis}}"
-                                          ToolTip="顯示輪廓邊線（邊線量大時轉動視角會變慢）" />
-                                <Button Content="🔍" Width="20" Margin="3,0,0,0" Padding="0"
-                                        VerticalAlignment="Center" ToolTip="縮放至此節點"
-                                        Command="{Binding DataContext.ZoomNodeCommand, RelativeSource={RelativeSource AncestorType=Window}}"
-                                        CommandParameter="{Binding}" />
-                                <Button Content="✕" Width="20" Padding="0" Margin="2,0,0,0"
-                                        VerticalAlignment="Center" ToolTip="移除此檔案"
-                                        Visibility="{Binding IsRoot, Converter={StaticResource BoolToVis}}"
-                                        Command="{Binding DataContext.RemoveRootCommand, RelativeSource={RelativeSource AncestorType=Window}}"
-                                        CommandParameter="{Binding}" />
-                            </StackPanel>
-                        </HierarchicalDataTemplate>
-                    </TreeView.ItemTemplate>
-                </TreeView>
+                <DockPanel>
+                    <TextBox DockPanel.Dock="Top" Margin="0,2,0,4"
+                             Text="{Binding TreeFilter, UpdateSourceTrigger=PropertyChanged}"
+                             ToolTip="輸入名稱過濾裝配樹（只影響樹面板顯示，不影響 3D 可見性；清空 = 全顯）" />
+                    <TreeView ItemsSource="{Binding Roots}"
+                              ScrollViewer.HorizontalScrollBarVisibility="Disabled"
+                              VirtualizingPanel.IsVirtualizing="True"
+                              SelectedItemChanged="Tree_SelectedItemChanged">
+                        <TreeView.ItemContainerStyle>
+                            <Style TargetType="TreeViewItem">
+                                <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
+                                <Setter Property="Visibility"
+                                        Value="{Binding IsFilterVisible, Converter={StaticResource BoolToVis}}" />
+                            </Style>
+                        </TreeView.ItemContainerStyle>
+                        <TreeView.ItemTemplate>
+                            <HierarchicalDataTemplate DataType="{x:Type vm:ModelNodeViewModel}"
+                                                      ItemsSource="{Binding Children}">
+                                <StackPanel Orientation="Horizontal" Margin="0,1"
+                                            Background="Transparent"
+                                            ToolTip="{Binding ToolTipText}"
+                                            Tag="{Binding DataContext, RelativeSource={RelativeSource AncestorType=Window}}">
+                                    <StackPanel.ContextMenu>
+                                        <ContextMenu>
+                                            <MenuItem Header="👁 只顯示此節點"
+                                                      Command="{Binding PlacementTarget.Tag.IsolateNodeCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
+                                                      CommandParameter="{Binding}" />
+                                            <MenuItem Header="🔄 反轉顯示"
+                                                      Command="{Binding PlacementTarget.Tag.InvertVisibilityCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}" />
+                                            <MenuItem Header="☀ 全部顯示"
+                                                      Command="{Binding PlacementTarget.Tag.ShowAllCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}" />
+                                            <Separator />
+                                            <MenuItem Header="⚖ 量體積 / 質心"
+                                                      Command="{Binding PlacementTarget.Tag.MeasureVolumeCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"
+                                                      CommandParameter="{Binding}" />
+                                        </ContextMenu>
+                                    </StackPanel.ContextMenu>
+                                    <CheckBox IsChecked="{Binding IsVisible}" VerticalAlignment="Center"
+                                              ToolTip="顯示 / 隱藏（含子節點）" />
+                                    <Button Width="14" Height="14" Margin="3,0"
+                                            VerticalAlignment="Center" ToolTip="點擊換色（含子節點）"
+                                            Command="{Binding CycleColorCommand}">
+                                        <Button.Template>
+                                            <ControlTemplate TargetType="Button">
+                                                <Border BorderBrush="Gray" BorderThickness="1" CornerRadius="2">
+                                                    <Border.Background>
+                                                        <SolidColorBrush Color="{Binding Color}" />
+                                                    </Border.Background>
+                                                </Border>
+                                            </ControlTemplate>
+                                        </Button.Template>
+                                    </Button>
+                                    <TextBlock Text="{Binding Name}" VerticalAlignment="Center"
+                                               MaxWidth="130" TextTrimming="CharacterEllipsis">
+                                        <TextBlock.Style>
+                                            <Style TargetType="TextBlock">
+                                                <Style.Triggers>
+                                                    <DataTrigger Binding="{Binding IsRoot}" Value="True">
+                                                        <Setter Property="FontWeight" Value="SemiBold" />
+                                                    </DataTrigger>
+                                                </Style.Triggers>
+                                            </Style>
+                                        </TextBlock.Style>
+                                    </TextBlock>
+                                    <CheckBox IsChecked="{Binding ShowEdges}" Content="邊" FontSize="10"
+                                              VerticalAlignment="Center" Margin="4,0,0,0"
+                                              Visibility="{Binding IsRoot, Converter={StaticResource BoolToVis}}"
+                                              ToolTip="顯示輪廓邊線（邊線量大時轉動視角會變慢）" />
+                                    <Button Content="🔍" Width="20" Margin="3,0,0,0" Padding="0"
+                                            VerticalAlignment="Center" ToolTip="縮放至此節點"
+                                            Command="{Binding DataContext.ZoomNodeCommand, RelativeSource={RelativeSource AncestorType=Window}}"
+                                            CommandParameter="{Binding}" />
+                                    <Button Content="✕" Width="20" Padding="0" Margin="2,0,0,0"
+                                            VerticalAlignment="Center" ToolTip="移除此檔案"
+                                            Visibility="{Binding IsRoot, Converter={StaticResource BoolToVis}}"
+                                            Command="{Binding DataContext.RemoveRootCommand, RelativeSource={RelativeSource AncestorType=Window}}"
+                                            CommandParameter="{Binding}" />
+                                </StackPanel>
+                            </HierarchicalDataTemplate>
+                        </TreeView.ItemTemplate>
+                    </TreeView>
+                </DockPanel>
             </GroupBox>
 
+            <GridSplitter Grid.Column="1" Width="5" HorizontalAlignment="Stretch"
+                          VerticalAlignment="Stretch" Background="#FFD8D8D8"
+                          ToolTip="拖曳調整面板寬度" />
+
             <!-- ─── 3D 視圖 ─── -->
-            <h:HelixViewport3D x:Name="viewport" Grid.Column="1"
+            <h:HelixViewport3D x:Name="viewport" Grid.Column="2"
                                ShowViewCube="True" ShowCoordinateSystem="True"
                                ShowFrameRate="False" ZoomExtentsWhenLoaded="True"
                                PanGesture="MiddleClick" PanGesture2="Shift+LeftClick"
@@ -208,11 +258,15 @@
 
             <!-- 操作器疊圖層：透明 Viewport3D 疊在主視窗上、永遠最上層。
                  只在操作器開啟時 IsHitTestVisible（否則空白處滑鼠才會穿透回主視窗） -->
-            <Viewport3D x:Name="gizmoOverlay" Grid.Column="1"
+            <Viewport3D x:Name="gizmoOverlay" Grid.Column="2"
                         IsHitTestVisible="{Binding GizmoEnabled}" />
 
+            <GridSplitter Grid.Column="3" Width="5" HorizontalAlignment="Stretch"
+                          VerticalAlignment="Stretch" Background="#FFD8D8D8"
+                          ToolTip="拖曳調整面板寬度" />
+
             <!-- ─── 量測結果面板 ─── -->
-            <GroupBox Grid.Column="2" Header="量測結果" Margin="4">
+            <GroupBox Grid.Column="4" Header="量測結果" Margin="4">
                 <ListBox ItemsSource="{Binding Measurements}" HorizontalContentAlignment="Stretch"
                          ScrollViewer.HorizontalScrollBarVisibility="Disabled">
                     <ListBox.ItemTemplate>
diff --git a/src/STPViewer/MainWindow.xaml.cs b/src/STPViewer/MainWindow.xaml.cs
index ae92dcd..8036ebc 100644
--- a/src/STPViewer/MainWindow.xaml.cs
+++ b/src/STPViewer/MainWindow.xaml.cs
@@ -1,6 +1,9 @@
+using System.ComponentModel;
 using System.Linq;
 using System.Reflection;
 using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Controls.Primitives;
 using System.Windows.Input;
 using STPViewer.Services;
 using STPViewer.ViewModels;
@@ -10,6 +13,7 @@ namespace STPViewer;
 public partial class MainWindow : Window
 {
     private readonly MainViewModel _vm = new();
+    private readonly AppSettings _settings;
 
     public MainWindow()
     {
@@ -21,12 +25,54 @@ public partial class MainWindow : Window
         _vm.Attach(viewport);
         _vm.AttachOverlay(gizmoOverlay);
         Loaded += MainWindow_Loaded;
+        Closing += MainWindow_Closing;
+
+        // 使用者設定：視窗位置大小（View 職責）+ 單位/MRU（VM 職責）
+        _settings = SettingsService.Load();
+        ApplyWindowSettings();
+        _vm.LoadSettings(_settings);
 
         // Gizmo 操作器放在疊圖層；manipulator 會把 MouseUp 標 handled，需 handledEventsToo 才收得到
         gizmoOverlay.AddHandler(MouseLeftButtonUpEvent,
             new MouseButtonEventHandler((_, _) => _vm.OnGizmoMouseUp()), handledEventsToo: true);
     }
 
+    private void ApplyWindowSettings()
+    {
+        if (_settings.WindowWidth >= 400 && _settings.WindowHeight >= 300)
+        {
+            Width = _settings.WindowWidth;
+            Height = _settings.WindowHeight;
+        }
+        // 位置要落在目前虛擬桌面內才還原（避免拔掉外接螢幕後視窗開在螢幕外）
+        if (!double.IsNaN(_settings.WindowLeft) && !double.IsNaN(_settings.WindowTop) &&
+            _settings.WindowLeft >= SystemParameters.VirtualScreenLeft - 50 &&
+            _settings.WindowTop >= SystemParameters.VirtualScreenTop - 50 &&
+            _settings.WindowLeft <= SystemParameters.VirtualScreenLeft + SystemParameters.VirtualScreenWidth - 200 &&
+            _settings.WindowTop <= SystemParameters.VirtualScreenTop + SystemParameters.VirtualScreenHeight - 200)
+        {
+            WindowStartupLocation = WindowStartupLocation.Manual;
+            Left = _settings.WindowLeft;
+            Top = _settings.WindowTop;
+        }
+        if (_settings.WindowMaximized)
+            WindowState = WindowState.Maximized;
+    }
+
+    private void MainWindow_Closing(object? sender, CancelEventArgs e)
+    {
+        Rect r = WindowState == WindowState.Normal
+            ? new Rect(Left, Top, Width, Height)
+            : RestoreBounds;
+        _settings.WindowLeft = r.Left;
+        _settings.WindowTop = r.Top;
+        _settings.WindowWidth = r.Width;
+        _settings.WindowHeight = r.Height;
+        _settings.WindowMaximized = WindowState == WindowState.Maximized;
+        _vm.SaveSettingsInto(_settings);
+        SettingsService.Save(_settings);
+    }
+
     /// <summary>支援命令列帶檔開啟：STPViewer.exe a.stp b.stl …</summary>
     private async void MainWindow_Loaded(object sender, RoutedEventArgs e)
     {
@@ -36,6 +82,47 @@ public partial class MainWindow : Window
             await _vm.ImportFilesAsync(files);
     }
 
+    /// <summary>Esc / 量測模式快速鍵（焦點在輸入框時不攔截，樹搜尋、剖面數值可正常打字）</summary>
+    private void Window_PreviewKeyDown(object sender, KeyEventArgs e)
+    {
+        if (Keyboard.FocusedElement is TextBoxBase or ComboBox) return;
+        if (e.Key == Key.Escape)
+        {
+            _vm.OnEscape();
+            e.Handled = true;
+            return;
+        }
+        if (Keyboard.Modifiers != ModifierKeys.None) return;
+        if (_vm.OnHotKey(e.Key))
+            e.Handled = true;
+    }
+
+    /// <summary>最近檔案下拉（▾）：即時從 VM 的 MRU 清單組選單</summary>
+    private void Recent_Click(object sender, RoutedEventArgs e)
+    {
+        var menu = new ContextMenu
+        {
+            PlacementTarget = (UIElement)sender,
+            Placement = PlacementMode.Bottom,
+        };
+        if (_vm.RecentFiles.Count == 0)
+        {
+            menu.Items.Add(new MenuItem { Header = "（沒有最近開啟的檔案）", IsEnabled = false });
+        }
+        else
+        {
+            foreach (string f in _vm.RecentFiles)
+                menu.Items.Add(new MenuItem
+                {
+                    Header = System.IO.Path.GetFileName(f),
+                    ToolTip = f,
+                    Command = _vm.ImportRecentCommand,
+                    CommandParameter = f,
+                });
+        }
+        menu.IsOpen = true;
+    }
+
     private void Tree_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e) =>
         _vm.SelectedNode = e.NewValue as ModelNodeViewModel;
 
diff --git a/src/STPViewer/Models/MeasureMode.cs b/src/STPViewer/Models/MeasureMode.cs
index 1884c25..6c49cb2 100644
--- a/src/STPViewer/Models/MeasureMode.cs
+++ b/src/STPViewer/Models/MeasureMode.cs
@@ -15,4 +15,5 @@ public enum MeasureMode
     Align3,       // 三點對齊：旋轉+平移（來源 3 點 → 目標 3 點）
     Drag,         // 拖曳模式：左鍵按住零件沿螢幕平面拖動（放開才烘進 B-rep）
     Interference, // 干涉檢查結果（非點擊模式，僅作為結果類型）
+    Volume,       // 體積/質心（樹右鍵選單觸發，非點擊模式，僅作為結果類型）
 }
diff --git a/src/STPViewer/Models/UnitSystem.cs b/src/STPViewer/Models/UnitSystem.cs
index dffcf4a..0c08b56 100644
--- a/src/STPViewer/Models/UnitSystem.cs
+++ b/src/STPViewer/Models/UnitSystem.cs
@@ -21,6 +21,10 @@ public static class Units
     public static string A(double mm2, UnitSystem u) =>
         u == UnitSystem.Millimeter ? $"{mm2:N3} mm²" : $"{mm2 / (MmPerInch * MmPerInch):N4} in²";
 
+    /// <summary>體積</summary>
+    public static string V(double mm3, UnitSystem u) =>
+        u == UnitSystem.Millimeter ? $"{mm3:N2} mm³" : $"{mm3 / (MmPerInch * MmPerInch * MmPerInch):N4} in³";
+
     /// <summary>座標分量（無單位字尾）</summary>
     public static string C(double mm, UnitSystem u) =>
         u == UnitSystem.Millimeter ? $"{mm:F3}" : $"{mm / MmPerInch:F4}";
diff --git a/src/STPViewer/STPViewer.csproj b/src/STPViewer/STPViewer.csproj
index 258685a..3a24a7f 100644
--- a/src/STPViewer/STPViewer.csproj
+++ b/src/STPViewer/STPViewer.csproj
@@ -6,7 +6,7 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <UseWPF>true</UseWPF>
-    <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 -->
+    <Version>0.5.0</Version>   <!-- 單一版號來源：標題與 publish-winapp 打包資料夾都讀這個 -->
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/STPViewer/Services/MeasurementService.cs b/src/STPViewer/Services/MeasurementService.cs
index c280218..1c86b35 100644
--- a/src/STPViewer/Services/MeasurementService.cs
+++ b/src/STPViewer/Services/MeasurementService.cs
@@ -31,7 +31,12 @@ public class MeasurementService
 
     // ─── 拾取輔助 ────────────────────────────────────────────────
 
-    /// <summary>命中點吸附到最近的 B-rep 頂點（容差內），否則回傳原始表面點</summary>
+    /// <summary>
+    /// 命中點吸附：點到圓形邊附近（容差內）→ 吸附**圓心**（量兩孔 pitch 的關鍵，v0.5.0）；
+    /// 否則吸附最近的 B-rep 頂點（容差內）；都沒有 → 回傳原始表面點。
+    /// 圓心與頂點都在容差內時，比「命中點到圓形邊」與「命中點到頂點」誰近（圓弧端點常與圓重疊，
+    /// 點在圓邊上時圓心優先勝出才符合直覺）。
+    /// </summary>
     public Point3D Snap(FaceInfo fi, Point3D hit, double tolerance)
     {
         if (fi.BrepFace is null) return hit;
@@ -47,6 +52,22 @@ public class MeasurementService
             }
         }
         catch { /* 頂點存取失敗則不吸附 */ }
+
+        // 圓形邊：以「命中點到邊曲線」的距離參與比較，勝出時吸附到圓心
+        try
+        {
+            foreach (Edge e in fi.BrepFace.AllEdges)
+            {
+                if (e.Curve3D is not Ellipse { IsCircle: true } el) continue;
+                double pos;
+                try { pos = el.PositionOf(ToGeo(hit)); } catch { continue; }
+                if (double.IsNaN(pos)) continue;
+                Point3D onCurve = ToP3(el.PointAt(Math.Clamp(pos, 0, 1)));
+                double d = (onCurve - hit).Length;
+                if (d < bestD) { bestD = d; best = ToP3(el.Center); }
+            }
+        }
+        catch { /* 邊存取失敗則維持頂點吸附結果 */ }
         return best;
     }
 
@@ -406,6 +427,47 @@ public class MeasurementService
         return (pa, pb);
     }
 
+    // ─── 體積 / 質心（封閉網格 signed volume）────────────────────
+
+    /// <summary>
+    /// 網格體積與質心：各三角形與原點構成的四面體有向體積加總（divergence theorem）。
+    /// 只對「封閉」網格有意義（開放殼會得到不可靠的值 → IsClosedReliable=false 供呼叫端提示）。
+    /// 多個 mesh（多實體）直接加總。
+    /// </summary>
+    public static (double VolumeMm3, Point3D Centroid, bool Reliable) MeshVolume(
+        System.Collections.Generic.IEnumerable<MeshGeometry3D> meshes)
+    {
+        double vol6 = 0;                       // Σ 6×有向體積
+        double absVol6 = 0;                    // Σ |6×有向體積|（封閉性 sanity check 用）
+        double cx = 0, cy = 0, cz = 0;         // Σ 四面體質心 × 6×有向體積
+        foreach (MeshGeometry3D mesh in meshes)
+        {
+            Point3DCollection pos = mesh.Positions;
+            Int32Collection idx = mesh.TriangleIndices;
+            for (int i = 0; i + 2 < idx.Count; i += 3)
+            {
+                Point3D a = pos[idx[i]], b = pos[idx[i + 1]], c = pos[idx[i + 2]];
+                // 6V = a · (b × c)
+                double v = a.X * (b.Y * c.Z - b.Z * c.Y)
+                         + a.Y * (b.Z * c.X - b.X * c.Z)
+                         + a.Z * (b.X * c.Y - b.Y * c.X);
+                vol6 += v;
+                absVol6 += Math.Abs(v);
+                // 四面體（a,b,c,原點）質心 = (a+b+c)/4
+                cx += (a.X + b.X + c.X) / 4 * v;
+                cy += (a.Y + b.Y + c.Y) / 4 * v;
+                cz += (a.Z + b.Z + c.Z) / 4 * v;
+            }
+        }
+        double volume = Math.Abs(vol6) / 6;
+        // 有向體積相對正負抵銷比例過高 → 可能是開放殼/法向不一致，數值不可靠
+        bool reliable = absVol6 > 0 && Math.Abs(vol6) / absVol6 > 0.01 && volume > 1e-9;
+        Point3D centroid = Math.Abs(vol6) > 1e-12
+            ? new Point3D(cx / vol6, cy / vol6, cz / vol6)
+            : default;
+        return (volume, centroid, reliable);
+    }
+
     // 點到三角形最近點：共用 InterferenceService.ClosestPointOnTriangle（v0.4.0 去重複）
 
     // ─── overlay helpers ─────────────────────────────────────────
diff --git a/src/STPViewer/Services/SettingsService.cs b/src/STPViewer/Services/SettingsService.cs
new file mode 100644
index 0000000..245cc1d
--- /dev/null
+++ b/src/STPViewer/Services/SettingsService.cs
@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text.Json;
+
+namespace STPViewer.Services;
+
+/// <summary>使用者設定（%LOCALAPPDATA%\STPViewer\settings.json）</summary>
+public class AppSettings
+{
+    public double WindowWidth { get; set; } = double.NaN;
+    public double WindowHeight { get; set; } = double.NaN;
+    public double WindowLeft { get; set; } = double.NaN;
+    public double WindowTop { get; set; } = double.NaN;
+    public bool WindowMaximized { get; set; }
+    public bool UseInch { get; set; }
+    public List<string> RecentFiles { get; set; } = new();
+}
+
+/// <summary>設定讀寫：壞檔/缺檔一律回預設值，儲存失敗靜默（設定不值得讓程式閃退）</summary>
+public static class SettingsService
+{
+    public const int MaxRecentFiles = 10;
+
+    private static readonly string SettingsPath = Path.Combine(
+        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+        "STPViewer", "settings.json");
+
+    public static AppSettings Load()
+    {
+        try
+        {
+            if (File.Exists(SettingsPath))
+                return JsonSerializer.Deserialize<AppSettings>(File.ReadAllText(SettingsPath)) ?? new AppSettings();
+        }
+        catch { /* 壞檔回預設 */ }
+        return new AppSettings();
+    }
+
+    public static void Save(AppSettings settings)
+    {
+        try
+        {
+            Directory.CreateDirectory(Path.GetDirectoryName(SettingsPath)!);
+            File.WriteAllText(SettingsPath,
+                JsonSerializer.Serialize(settings, new JsonSerializerOptions { WriteIndented = true }));
+        }
+        catch { /* 儲存失敗靜默 */ }
+    }
+}
diff --git a/src/STPViewer/ViewModels/MainViewModel.Export.cs b/src/STPViewer/ViewModels/MainViewModel.Export.cs
index 9a70c7c..3fdeeb4 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Export.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Export.cs
@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using System.Text;
 using System.Windows.Media;
 using System.Windows.Media.Imaging;
@@ -39,6 +40,48 @@ public partial class MainViewModel
         StatusText = $"已匯出 {Measurements.Count} 筆量測 → {Path.GetFileName(dlg.FileName)}";
     }
 
+    /// <summary>
+    /// 把可見檔案（目前位置，含對齊/旋轉/拖曳結果）匯出成「新的」STEP 檔 —
+    /// 對齊插合後的配合結果可交接給 CAD；不動任何原始檔（唯讀原則不變）。
+    /// 只含 B-rep Solid/Shell（STL 網格、DXF 線架構無法進 STEP B-rep）。
+    /// </summary>
+    [RelayCommand(CanExecute = nameof(IsIdle))]
+    private void ExportStepFile()
+    {
+        var geos = Roots.Where(r => r.IsVisible)
+            .SelectMany(r => r.Leaves()).Where(l => l.IsVisible)
+            .SelectMany(l => l.SourceGeos)
+            .Where(g => g is CADability.GeoObject.Solid or CADability.GeoObject.Shell)
+            .ToList();
+        if (geos.Count == 0)
+        {
+            StatusText = "沒有可匯出的 B-rep 幾何（STEP 匯出僅含 Solid/Shell；請勾選要匯出的 STEP 檔案）";
+            return;
+        }
+
+        var dlg = new SaveFileDialog
+        {
+            Title = "匯出目前場景為 STEP（零件在目前對齊位置）",
+            Filter = "STEP 檔案 (*.stp)|*.stp|STEP 檔案 (*.step)|*.step",
+            FileName = $"assembly_{DateTime.Now:yyyyMMdd_HHmmss}.stp",
+        };
+        if (dlg.ShowDialog() != true) return;
+
+        try
+        {
+            // B-rep 已含目前位置（TransformRoot 對 Solid/Shell 整體 Modify）→ 直接寫出
+            CADability.Project project = CADability.Project.CreateSimpleProject();
+            CADability.Model model = project.GetActiveModel();
+            foreach (CADability.GeoObject.IGeoObject g in geos) model.Add(g);
+            new CADability.ExportStep().WriteToFile(dlg.FileName, project);
+            StatusText = $"已匯出 STEP（{geos.Count} 個實體，目前位置）→ {Path.GetFileName(dlg.FileName)}";
+        }
+        catch (Exception ex)
+        {
+            StatusText = $"STEP 匯出失敗：{ex.Message}";
+        }
+    }
+
     [RelayCommand]
     private void SaveScreenshot()
     {
diff --git a/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs b/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs
index bb79902..63df8a9 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Gizmo.cs
@@ -23,7 +23,7 @@ public partial class MainViewModel
     // 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;
+    private ProjectionCamera? _overlayCamera; // 型別跟隨主相機（透視/正交切換，v0.5.0）
 
     /// <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)
@@ -37,16 +37,41 @@ public partial class MainViewModel
         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>
+    /// <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）。
+    /// 主相機可能在透視/正交間切換（Orthographic 屬性）→ 疊圖層相機「型別」也要跟著換，投影才一致。
+    /// </summary>
     private void SyncOverlayCamera()
     {
-        if (_overlayCamera is null || _viewport?.Camera is not ProjectionCamera src) return;
+        if (_overlayViewport is null || _viewport?.Camera is not ProjectionCamera src) return;
+
+        if (src is PerspectiveCamera p)
+        {
+            if (_overlayCamera is not PerspectiveCamera op)
+            {
+                op = new PerspectiveCamera();
+                _overlayCamera = op;
+                _overlayViewport.Camera = op;
+            }
+            op.FieldOfView = p.FieldOfView;
+        }
+        else if (src is OrthographicCamera o)
+        {
+            if (_overlayCamera is not OrthographicCamera oo)
+            {
+                oo = new OrthographicCamera();
+                _overlayCamera = oo;
+                _overlayViewport.Camera = oo;
+            }
+            oo.Width = o.Width;
+        }
+        if (_overlayCamera is null) 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();
diff --git a/src/STPViewer/ViewModels/MainViewModel.Interference.cs b/src/STPViewer/ViewModels/MainViewModel.Interference.cs
index 2e6700e..24b8a67 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Interference.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Interference.cs
@@ -20,9 +20,9 @@ public partial class MainViewModel
     {
         if (_viewport is null) return;
         var visibleRoots = Roots.Where(r => r.IsVisible).ToList();
-        if (visibleRoots.Count != 2)
+        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";
+            StatusText = $"干涉檢查需要至少 2 個可見檔案（目前 {visibleRoots.Count} 個）— 用樹面板勾選";
             return;
         }
 
@@ -33,16 +33,27 @@ public partial class MainViewModel
                 .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;
+        // 網格快照（開跑後零件被改走也不會半途換料；v0.4.0 起運算期間指令已鎖，這裡是雙保險）
+        var meshes = visibleRoots.ToDictionary(r => r, MeshesOf);
 
         IsBusy = true;
-        StatusText = $"干涉檢查中：{nameA} ⟷ {nameB} …";
         try
         {
-            InterferenceResult result = await Task.Run(() => InterferenceService.Check(a, b));
-            AddInterferenceResult(result, nameA, nameB);
+            int pairs = 0, intersecting = 0;
+            for (int i = 0; i < visibleRoots.Count; i++)
+                for (int j = i + 1; j < visibleRoots.Count; j++)
+                {
+                    pairs++;
+                    string nameA = visibleRoots[i].Name, nameB = visibleRoots[j].Name;
+                    StatusText = $"干涉檢查中（第 {pairs} 組）：{nameA} ⟷ {nameB} …";
+                    var a = meshes[visibleRoots[i]];
+                    var b = meshes[visibleRoots[j]];
+                    InterferenceResult result = await Task.Run(() => InterferenceService.Check(a, b));
+                    AddInterferenceResult(result, nameA, nameB);
+                    if (result.Intersects) intersecting++;
+                }
+            if (pairs > 1)
+                StatusText = $"干涉檢查完成：{pairs} 組配對、{intersecting} 組相交";
         }
         catch (Exception ex)
         {
diff --git a/src/STPViewer/ViewModels/MainViewModel.Section.cs b/src/STPViewer/ViewModels/MainViewModel.Section.cs
index 8cadeb9..95311cb 100644
--- a/src/STPViewer/ViewModels/MainViewModel.Section.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.Section.cs
@@ -38,11 +38,116 @@ public partial class MainViewModel
     [ObservableProperty]
     private bool sectionFlip;
 
-    partial void OnSectionEnabledChanged(bool value) => ScheduleSection();
-    partial void OnSectionAxisIndexChanged(int value) => ScheduleSection();
-    partial void OnSectionPositionChanged(double value) => ScheduleSection();
+    // ── 3點自訂剖切平面（SectionAxisIndex == 3，v0.5.0）──
+    private const int CustomAxisIndex = 3;
+    private Vector3D? _customNormal;                                  // null = 尚未定義（等使用者點 3 點）
+    private readonly List<Point3D> _sectionPicks = new();
+    private readonly List<Visual3D> _sectionPickOverlays = new();
+
+    partial void OnSectionEnabledChanged(bool value)
+    {
+        if (!value) CancelSectionPickIfActive(quiet: true);
+        ScheduleSection();
+    }
+
+    partial void OnSectionAxisIndexChanged(int value)
+    {
+        if (value == CustomAxisIndex)
+        {
+            if (_customNormal is null)
+                StatusText = "3點剖面：請在模型上點 3 個點定義剖切平面（Esc 取消）";
+        }
+        else
+        {
+            // 離開自訂平面 → 丟棄舊平面（再選「3點」即重新定義）
+            _customNormal = null;
+            ClearSectionPicks();
+        }
+        ScheduleSection();
+    }
+
+    partial void OnSectionPositionChanged(double value)
+    {
+        if (value < 0) { SectionPosition = 0; return; }   // 位置數值輸入框防呆
+        if (value > 100) { SectionPosition = 100; return; }
+        ScheduleSection();
+    }
+
     partial void OnSectionFlipChanged(bool value) => ScheduleSection();
 
+    /// <summary>3點剖面定義模式中的點擊（OnViewportClick 轉入）。回傳 true = 已消費此點擊。</summary>
+    public bool HandleSectionPlanePick(System.Windows.Point position)
+    {
+        if (!SectionEnabled || SectionAxisIndex != CustomAxisIndex || _customNormal is not null) return false;
+        if (_viewport is null) return true;
+
+        Point3D? hit = null;
+        foreach (var h in _viewport.Viewport.FindHits(position))
+        {
+            if (h.Model is null) continue;
+            if (_faceMap.ContainsKey(h.Model) || _mergedFaceRanges.ContainsKey(h.Model))
+            {
+                hit = h.Position;
+                break;
+            }
+        }
+        if (hit is null)
+        {
+            StatusText = $"3點剖面：未命中模型表面（已選 {_sectionPicks.Count}/3 點，Esc 取消）";
+            return true;
+        }
+        if (_sectionPicks.Count == 2 &&
+            Vector3D.CrossProduct(_sectionPicks[1] - _sectionPicks[0], hit.Value - _sectionPicks[0]).LengthSquared < 1e-12)
+        {
+            StatusText = "3點剖面：三點共線，請改選不共線的第 3 點";
+            return true;
+        }
+
+        _sectionPicks.Add(hit.Value);
+        double markerR = Math.Clamp(SceneDiagonal() * 0.004, 0.01, 5.0);
+        var marker = new SphereVisual3D { Center = hit.Value, Radius = markerR, Fill = System.Windows.Media.Brushes.DodgerBlue };
+        _sectionPickOverlays.Add(marker);
+        _viewport.Children.Add(marker);
+
+        if (_sectionPicks.Count < 3)
+        {
+            StatusText = $"3點剖面：已選 {_sectionPicks.Count}/3 點";
+            return true;
+        }
+
+        Vector3D n = Vector3D.CrossProduct(_sectionPicks[1] - _sectionPicks[0], _sectionPicks[2] - _sectionPicks[0]);
+        ClearSectionPicks();
+        if (n.LengthSquared < 1e-12)
+        {
+            StatusText = "3點剖面：三點退化（共線），請重新點選";
+            return true;
+        }
+        n.Normalize();
+        _customNormal = n;
+        StatusText = $"3點剖面：平面已定義（法向 {n.X:F2}, {n.Y:F2}, {n.Z:F2}）— 用位置滑桿掃剖面";
+        ApplySection();
+        return true;
+    }
+
+    /// <summary>取消 3 點平面定義（Esc / 關剖面）。回傳 true = 有取消動作。</summary>
+    private bool CancelSectionPickIfActive(bool quiet = false)
+    {
+        bool picking = SectionEnabled && SectionAxisIndex == CustomAxisIndex && _customNormal is null;
+        if (_sectionPicks.Count == 0 && !picking) return false;
+        ClearSectionPicks();
+        if (SectionAxisIndex == CustomAxisIndex && _customNormal is null)
+            SectionAxisIndex = 0; // 回 X 軸
+        if (!quiet) StatusText = "已取消 3 點剖面定義";
+        return true;
+    }
+
+    private void ClearSectionPicks()
+    {
+        foreach (Visual3D v in _sectionPickOverlays) _viewport?.Children.Remove(v);
+        _sectionPickOverlays.Clear();
+        _sectionPicks.Clear();
+    }
+
     private void ScheduleSection()
     {
         _sectionTimer.Stop();
@@ -82,28 +187,40 @@ public partial class MainViewModel
                 Rect3D bounds = UnionBounds();
                 if (bounds.IsEmpty) return;
 
-                Vector3D axis = SectionAxisIndex switch
+                Vector3D axis;
+                if (SectionAxisIndex == CustomAxisIndex)
                 {
-                    0 => new Vector3D(1, 0, 0),
-                    1 => new Vector3D(0, 1, 0),
-                    _ => new Vector3D(0, 0, 1),
-                };
+                    if (_customNormal is null) return; // 平面尚未定義（等使用者點 3 點）
+                    axis = _customNormal.Value;
+                }
+                else
+                {
+                    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
+                // 平面位置：場景 AABB 8 個角投影到法向的 [dmin, dmax]，滑桿 t 內插
+                //（軸向法向 = 與舊版逐軸計算等價；任意法向也成立）
+                double dmin = double.MaxValue, dmax = double.MinValue;
+                for (int ci = 0; ci < 8; ci++)
                 {
-                    0 => new Point3D(planeCoord, center.Y, center.Z),
-                    1 => new Point3D(center.X, planeCoord, center.Z),
-                    _ => new Point3D(center.X, center.Y, planeCoord),
-                };
+                    var corner = new Point3D(
+                        (ci & 1) == 0 ? min.X : min.X + size.X,
+                        (ci & 2) == 0 ? min.Y : min.Y + size.Y,
+                        (ci & 4) == 0 ? min.Z : min.Z + size.Z);
+                    double d = Vector3D.DotProduct((Vector3D)corner, axis);
+                    if (d < dmin) dmin = d;
+                    if (d > dmax) dmax = d;
+                }
+                double dStar = dmin + (dmax - dmin) * t;
+                Point3D planePoint = center + axis * (dStar - Vector3D.DotProduct((Vector3D)center, axis));
                 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。
@@ -137,7 +254,8 @@ public partial class MainViewModel
 
                 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）" : "");
+                string axisName = SectionAxisIndex == CustomAxisIndex ? "自訂平面" : $"{"XYZ"[SectionAxisIndex]} 軸";
+                StatusText = $"剖面：{axisName} {SectionPosition:F0}%" + (SectionFlip ? "（反向）" : "");
             } while (_sectionReapply);
         }
         finally
@@ -155,8 +273,10 @@ public partial class MainViewModel
         {
             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),
+            2 => (new Vector3D(1, 0, 0), size.X, size.Y),
+            _ => (AnyPerpendicular(axis), size.Length * 0.8, size.Length * 0.8), // 自訂平面
         };
+        lenDir.Normalize();
         _sectionPlaneVisual = new RectangleVisual3D
         {
             Origin = planePoint,
@@ -168,4 +288,14 @@ public partial class MainViewModel
         };
         _viewport!.Children.Add(_sectionPlaneVisual);
     }
+
+    /// <summary>取任一與 n 垂直的單位向量（自訂平面的指示矩形方向用）</summary>
+    private static Vector3D AnyPerpendicular(Vector3D n)
+    {
+        Vector3D v = Math.Abs(n.Z) < 0.9
+            ? Vector3D.CrossProduct(n, new Vector3D(0, 0, 1))
+            : Vector3D.CrossProduct(n, new Vector3D(1, 0, 0));
+        v.Normalize();
+        return v;
+    }
 }
diff --git a/src/STPViewer/ViewModels/MainViewModel.cs b/src/STPViewer/ViewModels/MainViewModel.cs
index e06dd14..1f64d0d 100644
--- a/src/STPViewer/ViewModels/MainViewModel.cs
+++ b/src/STPViewer/ViewModels/MainViewModel.cs
@@ -61,16 +61,55 @@ public partial class MainViewModel : ObservableObject
 
     [ObservableProperty]
     [NotifyCanExecuteChangedFor(nameof(ImportCommand))]
+    [NotifyCanExecuteChangedFor(nameof(ImportRecentCommand))]
     [NotifyCanExecuteChangedFor(nameof(RotateRootCommand))]
     [NotifyCanExecuteChangedFor(nameof(CheckInterferenceCommand))]
+    [NotifyCanExecuteChangedFor(nameof(ExportStepFileCommand))]
     private bool isBusy;
 
     [ObservableProperty]
     private bool useInch;
 
+    /// <summary>樹面板名稱過濾字串（只影響樹顯示，不影響 3D 可見性）</summary>
+    [ObservableProperty]
+    private string? treeFilter;
+
+    partial void OnTreeFilterChanged(string? value)
+    {
+        foreach (ModelNodeViewModel root in Roots) root.ApplyFilter(value);
+    }
+
+    /// <summary>最近開啟檔案（MRU，最多 10 筆；隨 settings.json 保存）</summary>
+    public ObservableCollection<string> RecentFiles { get; } = new();
+
     public ObservableCollection<ModelNodeViewModel> Roots { get; } = new();
     public ObservableCollection<MeasurementResult> Measurements { get; } = new();
 
+    // ─── 使用者設定（視窗由 MainWindow 處理；VM 管單位 + MRU）─────
+
+    public void LoadSettings(AppSettings s)
+    {
+        UseInch = s.UseInch;
+        RecentFiles.Clear();
+        foreach (string f in s.RecentFiles.Where(File.Exists).Take(SettingsService.MaxRecentFiles))
+            RecentFiles.Add(f);
+    }
+
+    public void SaveSettingsInto(AppSettings s)
+    {
+        s.UseInch = UseInch;
+        s.RecentFiles = RecentFiles.ToList();
+    }
+
+    private void TouchRecent(string path)
+    {
+        string full = Path.GetFullPath(path);
+        RecentFiles.Remove(full);
+        RecentFiles.Insert(0, full);
+        while (RecentFiles.Count > SettingsService.MaxRecentFiles)
+            RecentFiles.RemoveAt(RecentFiles.Count - 1);
+    }
+
     public MainViewModel()
     {
         _sectionTimer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(100) };
@@ -140,6 +179,10 @@ public partial class MainViewModel : ObservableObject
             await ImportFilesAsync(dlg.FileNames);
     }
 
+    /// <summary>MRU 下拉點選（檔案可能已被移走 → ImportFilesAsync 會報匯入失敗）</summary>
+    [RelayCommand(CanExecute = nameof(IsIdle))]
+    private Task ImportRecentAsync(string path) => ImportFilesAsync(new[] { path });
+
     public async Task ImportFilesAsync(IEnumerable<string> paths)
     {
         if (_viewport is null) return;
@@ -162,6 +205,7 @@ public partial class MainViewModel : ObservableObject
                 {
                     ImportedFileData data = await Task.Run(() => _importService.Import(path));
                     BuildRoot(data);
+                    TouchRecent(path);
                     ok++;
                 }
                 catch (Exception ex)
@@ -200,6 +244,7 @@ public partial class MainViewModel : ObservableObject
             root.ShowEdges = false;
 
         Roots.Add(root);
+        if (!string.IsNullOrWhiteSpace(TreeFilter)) root.ApplyFilter(TreeFilter); // 新檔套用目前過濾
         foreach (ModelNodeViewModel leaf in root.Leaves())
         {
             leaf.VisualStateChanged += _ => SyncLeafVisuals(root);
@@ -410,6 +455,44 @@ public partial class MainViewModel : ObservableObject
     [RelayCommand]
     private void ZoomAll() => _viewport?.ZoomExtents(400);
 
+    /// <summary>標準視圖（機構慣例 Z 向上）：Iso / Front / Back / Top / Bottom / Left / Right</summary>
+    [RelayCommand]
+    private void SetStandardView(string name)
+    {
+        if (_viewport?.Camera is not ProjectionCamera cam) return;
+        (Vector3D dir, Vector3D up) = name switch
+        {
+            "Front"  => (new Vector3D(0, 1, 0),  new Vector3D(0, 0, 1)),  // 從 -Y 往 +Y 看
+            "Back"   => (new Vector3D(0, -1, 0), new Vector3D(0, 0, 1)),
+            "Top"    => (new Vector3D(0, 0, -1), new Vector3D(0, 1, 0)),
+            "Bottom" => (new Vector3D(0, 0, 1),  new Vector3D(0, -1, 0)),
+            "Right"  => (new Vector3D(-1, 0, 0), new Vector3D(0, 0, 1)),
+            "Left"   => (new Vector3D(1, 0, 0),  new Vector3D(0, 0, 1)),
+            _        => (new Vector3D(-1, -1, -1), new Vector3D(0, 0, 1)), // Iso
+        };
+        dir.Normalize();
+        Rect3D b = UnionBounds();
+        Point3D center = b.IsEmpty ? new Point3D()
+            : new Point3D(b.X + b.SizeX / 2, b.Y + b.SizeY / 2, b.Z + b.SizeZ / 2);
+        double dist = Math.Max(SceneDiagonal() * 1.8, 10);
+        cam.Position = center - dir * dist;
+        cam.LookDirection = dir * dist; // 目標點 = Position + LookDirection = 場景中心
+        cam.UpDirection = up;
+        _viewport.ZoomExtents(400);
+        StatusText = $"視圖：{name}";
+    }
+
+    /// <summary>正交投影切換（平行投影，量尺寸不受透視變形；Helix 保持視角換相機型別）</summary>
+    [ObservableProperty]
+    private bool orthographicView;
+
+    partial void OnOrthographicViewChanged(bool value)
+    {
+        if (_viewport is null) return;
+        _viewport.Orthographic = value;
+        StatusText = value ? "正交投影（平行投影，適合尺寸確認）" : "透視投影";
+    }
+
     [RelayCommand]
     private void RemoveRoot(ModelNodeViewModel root)
     {
@@ -440,6 +523,92 @@ public partial class MainViewModel : ObservableObject
         StatusText = $"已移除：{root.Name}";
     }
 
+    // ─── 顯示控制 / 體積（樹右鍵選單）────────────────────────────
+
+    /// <summary>只顯示此節點（其餘全部隱藏；「全部顯示」復原）</summary>
+    [RelayCommand]
+    private void IsolateNode(ModelNodeViewModel node)
+    {
+        foreach (ModelNodeViewModel r in Roots) SetVisibleRecursive(r, false);
+        SetVisibleRecursive(node, true);
+        StatusText = $"只顯示「{node.Name}」（樹右鍵 → 全部顯示 復原）";
+    }
+
+    [RelayCommand]
+    private void InvertVisibility()
+    {
+        foreach (ModelNodeViewModel l in Roots.SelectMany(r => r.Leaves()))
+            l.IsVisible = !l.IsVisible;
+        StatusText = "已反轉顯示";
+    }
+
+    [RelayCommand]
+    private void ShowAll()
+    {
+        foreach (ModelNodeViewModel r in Roots) SetVisibleRecursive(r, true);
+        StatusText = "已全部顯示";
+    }
+
+    /// <summary>逐節點顯式遞迴設定可見性。不能只設 root（setter 同值不觸發 cascade，
+    /// 之前的隔離操作可能留下「父關子開」的混合狀態）</summary>
+    private static void SetVisibleRecursive(ModelNodeViewModel node, bool visible)
+    {
+        node.IsVisible = visible;
+        foreach (ModelNodeViewModel c in node.Children) SetVisibleRecursive(c, visible);
+    }
+
+    /// <summary>體積/質心（網格 signed volume，封閉實體才可靠）→ 加進量測結果 + 質心標記</summary>
+    [RelayCommand]
+    private void MeasureVolume(ModelNodeViewModel node)
+    {
+        var meshes = node.Leaves()
+            .Where(l => l.FacesContent is not null)
+            .SelectMany(l => l.FacesContent!.Children)
+            .OfType<GeometryModel3D>()
+            .Where(g => _faceMap.ContainsKey(g))
+            .Select(g => _faceMap[g].Mesh)
+            .ToList();
+        if (meshes.Count == 0)
+        {
+            StatusText = $"「{node.Name}」沒有可計算的面網格（線架構無體積）";
+            return;
+        }
+
+        (double vol, Point3D centroid, bool reliable) = MeasurementService.MeshVolume(meshes);
+        if (!reliable)
+        {
+            StatusText = $"「{node.Name}」非封閉網格（開放殼），無法可靠計算體積";
+            return;
+        }
+
+        double diag = SceneDiagonal();
+        double markerR = Math.Clamp(diag * 0.004, 0.01, 5.0);
+        string label = NextLabel(MeasureMode.Volume, "V");
+        string name = node.Name;
+        Rect3D b = node.Bounds;
+        var m = new MeasurementResult
+        {
+            Kind = MeasureMode.Volume,
+            TitleFor = u => $"{label}  {name}  V ≈ {Units.V(vol, u)}",
+            DetailFor = u => $"體積 ≈ {Units.V(vol, u)}（網格近似）\n質心 {Units.P(centroid, u)}\n" +
+                             $"外形（AABB）{Units.C(b.SizeX, u)} × {Units.C(b.SizeY, u)} × {Units.C(b.SizeZ, u)} " +
+                             (u == UnitSystem.Millimeter ? "mm" : "in"),
+        };
+        m.Overlays.Add(new SphereVisual3D { Center = centroid, Radius = markerR, Fill = Brushes.OrangeRed });
+        var volLabel = new BillboardTextVisual3D
+        {
+            Position = centroid + new Vector3D(0, 0, markerR * 2),
+            Text = $"{label} {Units.V(vol, 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(volLabel);
+        m.DynamicLabels.Add((volLabel, u => $"{label} {Units.V(vol, u)}"));
+        AddMeasurement(m);
+    }
+
     // ─── 量測 ────────────────────────────────────────────────────
 
     partial void OnCurrentModeChanged(MeasureMode value)
@@ -470,10 +639,52 @@ public partial class MainViewModel : ObservableObject
         StatusText = value ? "顯示單位：inch" : "顯示單位：mm";
     }
 
+    /// <summary>Esc（MainWindow 轉發）：先取消進行中的多段量測（保留模式），再按退回瀏覽模式；再退操作器</summary>
+    public void OnEscape()
+    {
+        if (CancelSectionPickIfActive()) return; // 3點剖面定義中 → 先取消定義
+        bool hadPending = _pendingPoint is not null || _pendingDirection is not null ||
+                          _pendingFace is not null || _pendingAlign is not null || _align3.Count > 0;
+        if (hadPending)
+        {
+            CancelPending();
+            StatusText = "已取消目前量測起點（再按 Esc 退出量測模式）";
+        }
+        else if (CurrentMode != MeasureMode.None)
+        {
+            CurrentMode = MeasureMode.None;
+        }
+        else if (GizmoEnabled)
+        {
+            GizmoEnabled = false;
+        }
+    }
+
+    /// <summary>量測模式快速鍵（MainWindow 轉發；無修飾鍵）。同鍵再按 = 退回瀏覽。回傳 false 表示非快速鍵。</summary>
+    public bool OnHotKey(System.Windows.Input.Key key)
+    {
+        MeasureMode? m = key switch
+        {
+            System.Windows.Input.Key.P => MeasureMode.Point,
+            System.Windows.Input.Key.D => MeasureMode.Distance,
+            System.Windows.Input.Key.E => MeasureMode.Edge,
+            System.Windows.Input.Key.F => MeasureMode.Face,
+            System.Windows.Input.Key.C => MeasureMode.Circle,
+            System.Windows.Input.Key.A => MeasureMode.Angle,
+            System.Windows.Input.Key.M => MeasureMode.FaceDistance,
+            _ => null,
+        };
+        if (m is null) return false;
+        CurrentMode = CurrentMode == m ? MeasureMode.None : m.Value;
+        return true;
+    }
+
     /// <summary>MainWindow 滑鼠左鍵點擊轉發進來</summary>
     public void OnViewportClick(Point position)
     {
-        if (_viewport is null || IsBusy || CurrentMode is MeasureMode.None or MeasureMode.Drag) return;
+        if (_viewport is null || IsBusy) return;
+        if (HandleSectionPlanePick(position)) return; // 3點剖面定義模式優先吃點擊（v0.5.0）
+        if (CurrentMode is MeasureMode.None or MeasureMode.Drag) return;
 
         var hits = _viewport.Viewport.FindHits(position);
         FaceInfo? fi = null;
diff --git a/src/STPViewer/ViewModels/ModelNodeViewModel.cs b/src/STPViewer/ViewModels/ModelNodeViewModel.cs
index 935a5da..711e640 100644
--- a/src/STPViewer/ViewModels/ModelNodeViewModel.cs
+++ b/src/STPViewer/ViewModels/ModelNodeViewModel.cs
@@ -57,8 +57,24 @@ public partial class ModelNodeViewModel : ObservableObject
     public int FaceCount { get; init; }
     public int TriangleCount { get; init; }
 
-    /// <summary>世界座標邊界（零件平移後同步位移）</summary>
-    public Rect3D Bounds { get; set; }
+    /// <summary>世界座標邊界（零件平移/旋轉後由 RecomputeBounds 更新；連動 Stats/Tooltip 的外形尺寸）</summary>
+    public Rect3D Bounds
+    {
+        get => _bounds;
+        set
+        {
+            if (_bounds == value) return;
+            _bounds = value;
+            OnPropertyChanged(nameof(Stats));
+            OnPropertyChanged(nameof(ToolTipText));
+        }
+    }
+    private Rect3D _bounds = Rect3D.Empty;
+
+    /// <summary>外形尺寸 L×W×H（AABB，mm）</summary>
+    public string SizeText => Bounds.IsEmpty
+        ? ""
+        : $"{Bounds.SizeX:F1} × {Bounds.SizeY:F1} × {Bounds.SizeZ:F1} mm";
 
     /// <summary>來源 B-rep 物件（零件平移時整體 Modify，避免共用邊被重複位移）</summary>
     public List<CADability.GeoObject.IGeoObject> SourceGeos { get; } = new();
@@ -67,10 +83,32 @@ public partial class ModelNodeViewModel : ObservableObject
     public bool HasBrep { get; init; } = true;
 
     public string Stats =>
-        $"{SolidCount} 實體 · {FaceCount} 面 · {TriangleCount:N0} △" + (HasBrep ? "" : " · 無B-rep");
+        $"{SolidCount} 實體 · {FaceCount} 面 · {TriangleCount:N0} △" + (HasBrep ? "" : " · 無B-rep") +
+        (Bounds.IsEmpty ? "" : $"\n外形 {SizeText}");
 
     public string ToolTipText => (FilePath is not null ? FilePath + "\n" : "") + Stats;
 
+    // ── 樹搜尋/過濾（只影響樹面板顯示，不影響 3D 可見性）──
+
+    [ObservableProperty]
+    private bool isFilterVisible = true;
+
+    /// <summary>
+    /// 套用名稱過濾：符合者 + 其祖先 + 其子樹 顯示。空字串 = 全顯。
+    /// 過濾中有符合的子孫時自動展開。回傳此節點是否顯示。
+    /// </summary>
+    public bool ApplyFilter(string? filter, bool ancestorMatched = false)
+    {
+        bool empty = string.IsNullOrWhiteSpace(filter);
+        bool selfMatch = !empty && Name.Contains(filter!, StringComparison.OrdinalIgnoreCase);
+        bool anyChild = false;
+        foreach (ModelNodeViewModel c in Children)
+            anyChild |= c.ApplyFilter(filter, ancestorMatched || selfMatch);
+        IsFilterVisible = empty || selfMatch || ancestorMatched || anyChild;
+        if (!empty && anyChild) IsExpanded = true;
+        return IsFilterVisible;
+    }
+
     // ── 視覺物件 ──
     public ModelVisual3D? BodyVisual { get; set; }          // leaf：面網格容器（內容在兩種模式間切換）
     public Model3DGroup? FacesContent { get; set; }         // leaf：逐面 GeometryModel3D（量測拾取用）
diff --git a/tools/SmokeTest/ExportTest.cs b/tools/SmokeTest/ExportTest.cs
new file mode 100644
index 0000000..5ec0a6b
--- /dev/null
+++ b/tools/SmokeTest/ExportTest.cs
@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using CADability;
+using CADability.GeoObject;
+using STPViewer.Services;
+using IOPath = System.IO.Path; // CADability.GeoObject.Path（曲線）撞名
+
+namespace SmokeTest;
+
+/// <summary>
+/// STEP 匯出往返驗證（v0.5.0 匯出 STEP 功能的無 UI 驗證）：
+/// 匯入來源 STEP → 走與 MainViewModel.ExportStepFile 相同路徑寫出新檔 → 重新匯入比對實體數。
+/// </summary>
+public static class ExportTest
+{
+    public static int Run(string sourcePath, string outPath)
+    {
+        Console.WriteLine($"=== ExportTest: {IOPath.GetFileName(sourcePath)} → {IOPath.GetFileName(outPath)} ===");
+        ImportedFileData data = new StepImportService().Import(sourcePath);
+        var geos = Collect(data.Root).Where(g => g is Solid or Shell).ToList();
+        Console.WriteLine($"  來源 Solid/Shell 物件 = {geos.Count}（Solids = {data.Root.SolidCount}）");
+
+        Project project = Project.CreateSimpleProject();
+        Model model = project.GetActiveModel();
+        foreach (IGeoObject g in geos) model.Add(g);
+        new ExportStep().WriteToFile(outPath, project);
+        var fi = new FileInfo(outPath);
+        Console.WriteLine($"  已寫出（{fi.Length:N0} bytes）");
+        if (fi.Length < 100)
+        {
+            Console.WriteLine("ExportTest: FAIL（輸出檔近乎空白）");
+            return 1;
+        }
+
+        ImportedFileData back = new StepImportService().Import(outPath);
+        Console.WriteLine($"  回讀 Solids = {back.Root.SolidCount}, Faces = {back.Root.FaceCount}");
+        bool ok = back.Root.SolidCount == data.Root.SolidCount && back.Root.FaceCount > 0;
+        Console.WriteLine(ok
+            ? "ExportTest: PASS（實體數一致）"
+            : $"ExportTest: FAIL（來源 Solids {data.Root.SolidCount} ↔ 回讀 {back.Root.SolidCount}）");
+        return ok ? 0 : 1;
+    }
+
+    private static IEnumerable<IGeoObject> Collect(ImportedNode n)
+    {
+        foreach (IGeoObject g in n.SourceGeos) yield return g;
+        foreach (ImportedNode c in n.Children)
+            foreach (IGeoObject g in Collect(c))
+                yield return g;
+    }
+}
diff --git a/tools/SmokeTest/Program.cs b/tools/SmokeTest/Program.cs
index 7960ce9..646c0b4 100644
--- a/tools/SmokeTest/Program.cs
+++ b/tools/SmokeTest/Program.cs
@@ -35,6 +35,9 @@ if (args[0] == "--align-test")
 if (args[0] == "--bbox")
     return SmokeTest.BBoxDump.Run(args[1]);
 
+if (args[0] == "--export-test")
+    return SmokeTest.ExportTest.Run(args[1], args[2]) == 0 ? 0 : 2;
+
 var service = new StepImportService { Progress = s => Console.WriteLine($"  [階段] {s}") };
 int failed = 0;