what the hell

src/cascadia/CascadiaPackage/Package-Dev.appxmanifest

@@ -85,7 +85,7 @@
                 <uap3:Name>com.microsoft.windows.terminal.settings</uap3:Name>
               </uap3:AppExtensionHost>
         </uap3:Extension>
-        <uap3:Extension Category="windows.appExtension">
+        <!-- <uap3:Extension Category="windows.appExtension">
             <uap3:AppExtension Name="com.microsoft.windows.console.host"
                 Id="OpenConsole-Dev"
                 DisplayName="OpenConsole Dev"
@@ -111,7 +111,7 @@
             <com:ComInterface>
                 <com:ProxyStub Id="DEC4804D-56D1-4F73-9FBE-6828E7C85C56" DisplayName="OpenConsoleHandoffProxy" Path="OpenConsoleProxy.dll"/>
                 <com:Interface Id="E686C757-9A35-4A1C-B3CE-0BCC8B5C69F4" ProxyStubClsid="DEC4804D-56D1-4F73-9FBE-6828E7C85C56"/>
-                <com:Interface Id="6F23DA90-15C5-4203-9DB0-64E73F1B1B00" ProxyStubClsid="DEC4804D-56D1-4F73-9FBE-6828E7C85C56"/> <!-- ITerminalHandoff3 -->
+                <com:Interface Id="6F23DA90-15C5-4203-9DB0-64E73F1B1B00" ProxyStubClsid="DEC4804D-56D1-4F73-9FBE-6828E7C85C56"/> 
                 <com:Interface Id="746E6BC0-AB05-4E38-AB14-71E86763141F" ProxyStubClsid="DEC4804D-56D1-4F73-9FBE-6828E7C85C56"/>
             </com:ComInterface>
         </com:Extension>
@@ -137,7 +137,7 @@
                   <desktop5:Verb Id="OpenTerminalDev" Clsid="52065414-e077-47ec-a3ac-1cc5455e1b54" />
                 </desktop5:ItemType>
             </desktop4:FileExplorerContextMenus>
-        </desktop4:Extension>
+        </desktop4:Extension> -->
 
       </Extensions>
 

src/cascadia/TerminalApp/App.xaml

@@ -245,6 +245,7 @@
                 </ResourceDictionary>
 
                 <ResourceDictionary Source="ms-resource:///Files/TerminalApp/HighlightedTextControlStyle.xaml" />
+                <ResourceDictionary Source="ms-resource:///Files/TerminalApp/VerticalTabViewStyle.xaml" />
             </ResourceDictionary.MergedDictionaries>
         </ResourceDictionary>
 

src/cascadia/TerminalApp/Resources/en-US/Resources.resw

@@ -442,6 +442,10 @@
   <data name="NewTabRun.Text" xml:space="preserve">
     <value>Open a new tab</value>
   </data>
+  <data name="TabNewButtonText" xml:space="preserve">
+    <value>New tab</value>
+    <comment>Label for the new tab button in vertical tab strip mode.</comment>
+  </data>
   <data name="NewPaneRun.Text" xml:space="preserve">
     <value>Alt+Click to split the current window</value>
   </data>

src/cascadia/TerminalApp/TabManagement.cpp

@@ -255,9 +255,38 @@ namespace winrt::TerminalApp::implementation
         }
         if (_tabRow)
         {
-            // collapse/show the row that the tabs are in.
-            // NaN is the special value XAML uses for "Auto" sizing.
-            _tabRow.Height(isVisible ? NAN : 0);
+            if (_tabPosition == Settings::Model::TabPosition::Left ||
+                _tabPosition == Settings::Model::TabPosition::Right)
+            {
+                // For left/right positions, collapse the column width instead of row height.
+                // Also hide the splitter.
+                _tabRow.Width(isVisible ? std::numeric_limits<double>::quiet_NaN() : 0);
+                if (_tabStripSplitter)
+                {
+                    _tabStripSplitter.Visibility(isVisible ? Visibility::Visible : Visibility::Collapsed);
+                }
+                // Collapse or restore the tab strip column
+                auto tabStripColIdx = (_tabPosition == Settings::Model::TabPosition::Left) ? 0u : 2u;
+                auto root = this->Root();
+                if (root.ColumnDefinitions().Size() > tabStripColIdx)
+                {
+                    auto col = root.ColumnDefinitions().GetAt(tabStripColIdx);
+                    if (isVisible)
+                    {
+                        col.Width(WUX::GridLengthHelper::FromPixels(200));
+                    }
+                    else
+                    {
+                        col.Width(WUX::GridLengthHelper::FromPixels(0));
+                    }
+                }
+            }
+            else
+            {
+                // Top/Bottom: collapse/show the row that the tabs are in.
+                // NaN is the special value XAML uses for "Auto" sizing.
+                _tabRow.Height(isVisible ? NAN : 0);
+            }
         }
     }
 

src/cascadia/TerminalApp/TerminalAppLib.vcxproj

@@ -65,6 +65,10 @@
       <Type>DefaultStyle</Type>
       <SubType>Designer</SubType>
     </Page>
+    <Page Include="VerticalTabViewStyle.xaml">
+      <Type>DefaultStyle</Type>
+      <SubType>Designer</SubType>
+    </Page>
     <Page Include="ColorPickupFlyout.xaml">
       <SubType>Designer</SubType>
     </Page>

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -315,6 +315,307 @@ namespace winrt::TerminalApp::implementation
         return true;
     }
 
+    // Method Description:
+    // - Rearranges the TerminalPage's root grid to place the tab strip at the
+    //   position indicated by the current theme's TabPosition property. For Top,
+    //   the existing behavior is preserved (tabs in titlebar or Row 0). For
+    //   Bottom, the tab row goes in the last row. For Left/Right, an outer
+    //   3-column grid is created with a resizable splitter between the tab strip
+    //   and the content area.
+    void TerminalPage::_ApplyTabPosition()
+    {
+        // Read the tab position from the theme
+        if (const auto theme = _settings.GlobalSettings().CurrentTheme())
+        {
+            if (const auto window = theme.Window())
+            {
+                _tabPosition = window.TabPosition();
+            }
+        }
+
+        auto root = this->Root();
+        auto infoBarPanel = this->InfoBarPanel();
+
+        switch (_tabPosition)
+        {
+        case TabPosition::Top:
+        {
+            // Default XAML layout: Row 0=TabRow(Auto), Row 1=InfoBars(Auto), Row 2=TabContent(*)
+            // If ShowTabsInTitlebar, remove the tab row from the grid and raise SetTitleBarContent
+            if (_settings.GlobalSettings().ShowTabsInTitlebar())
+            {
+                uint32_t index = 0;
+                if (root.Children().IndexOf(_tabRow, index))
+                {
+                    root.Children().RemoveAt(index);
+                }
+                SetTitleBarContent.raise(*this, _tabRow);
+
+                const auto transparent = Media::SolidColorBrush();
+                transparent.Color(Windows::UI::Colors::Transparent());
+                _tabRow.Background(transparent);
+            }
+            break;
+        }
+        case TabPosition::Bottom:
+        {
+            // Rearrange to: Row 0=InfoBars(Auto), Row 1=TabContent(*), Row 2=TabRow(Auto)
+            // Remove only the three layout elements; leave deferred-load stubs
+            // (CommandPalette, SuggestionsControl, dialogs, etc.) in the tree
+            // so that FindName() can still locate them later.
+            uint32_t idx;
+            if (root.Children().IndexOf(_tabRow, idx))
+                root.Children().RemoveAt(idx);
+            if (root.Children().IndexOf(infoBarPanel, idx))
+                root.Children().RemoveAt(idx);
+            if (root.Children().IndexOf(_tabContent, idx))
+                root.Children().RemoveAt(idx);
+
+            root.RowDefinitions().Clear();
+
+            WUX::Controls::RowDefinition row0;
+            row0.Height(WUX::GridLengthHelper::FromValueAndType(1, WUX::GridUnitType::Auto));
+            WUX::Controls::RowDefinition row1;
+            row1.Height(WUX::GridLengthHelper::FromValueAndType(1, WUX::GridUnitType::Star));
+            WUX::Controls::RowDefinition row2;
+            row2.Height(WUX::GridLengthHelper::FromValueAndType(1, WUX::GridUnitType::Auto));
+            root.RowDefinitions().Append(row0);
+            root.RowDefinitions().Append(row1);
+            root.RowDefinitions().Append(row2);
+
+            WUX::Controls::Grid::SetRow(infoBarPanel, 0);
+            WUX::Controls::Grid::SetRow(_tabContent, 1);
+            WUX::Controls::Grid::SetRow(_tabRow, 2);
+
+            // Insert layout elements at the front so overlay elements
+            // (command palette, dialogs) remain on top in z-order.
+            root.Children().InsertAt(0, infoBarPanel);
+            root.Children().InsertAt(1, _tabContent);
+            root.Children().InsertAt(2, _tabRow);
+
+            // Update overlay elements: the ones that had Grid.Row="2" in XAML
+            // should now target Row 1 (the content area) instead of Row 2
+            // (which is the tab row in this layout). Iterate the remaining
+            // children (index 3+) and reassign any that were on row 2.
+            for (uint32_t i = 3; i < root.Children().Size(); ++i)
+            {
+                auto child = root.Children().GetAt(i);
+                if (const auto& fwe { child.try_as<WUX::FrameworkElement>() })
+                {
+                    if (WUX::Controls::Grid::GetRow(fwe) == 2)
+                    {
+                        WUX::Controls::Grid::SetRow(fwe, 1);
+                    }
+                }
+            }
+            break;
+        }
+        case TabPosition::Left:
+        case TabPosition::Right:
+        {
+            // Build a 3-column layout: [tabstrip | splitter | content] or reversed.
+            // Remove only the three layout elements; leave deferred-load stubs
+            // (CommandPalette, SuggestionsControl, dialogs, etc.) in the tree
+            // so that FindName() can still locate them later.
+            uint32_t removeIdx;
+            if (root.Children().IndexOf(_tabRow, removeIdx))
+                root.Children().RemoveAt(removeIdx);
+            if (root.Children().IndexOf(infoBarPanel, removeIdx))
+                root.Children().RemoveAt(removeIdx);
+            if (root.Children().IndexOf(_tabContent, removeIdx))
+                root.Children().RemoveAt(removeIdx);
+
+            root.RowDefinitions().Clear();
+
+            // Create column definitions
+            WUX::Controls::ColumnDefinition tabStripCol;
+            tabStripCol.Width(WUX::GridLengthHelper::FromPixels(200));
+            tabStripCol.MinWidth(100);
+            tabStripCol.MaxWidth(400);
+
+            WUX::Controls::ColumnDefinition splitterCol;
+            splitterCol.Width(WUX::GridLengthHelper::FromValueAndType(1, WUX::GridUnitType::Auto));
+
+            WUX::Controls::ColumnDefinition contentCol;
+            contentCol.Width(WUX::GridLengthHelper::FromValueAndType(1, WUX::GridUnitType::Star));
+
+            // Create internal content grid (infobars + tab content stacked vertically)
+            WUX::Controls::Grid contentGrid;
+            WUX::Controls::RowDefinition infoRow;
+            infoRow.Height(WUX::GridLengthHelper::FromValueAndType(1, WUX::GridUnitType::Auto));
+            WUX::Controls::RowDefinition mainRow;
+            mainRow.Height(WUX::GridLengthHelper::FromValueAndType(1, WUX::GridUnitType::Star));
+            contentGrid.RowDefinitions().Append(infoRow);
+            contentGrid.RowDefinitions().Append(mainRow);
+
+            WUX::Controls::Grid::SetRow(infoBarPanel, 0);
+            WUX::Controls::Grid::SetRow(_tabContent, 1);
+            contentGrid.Children().Append(infoBarPanel);
+            contentGrid.Children().Append(_tabContent);
+
+            // Create the splitter border
+            _tabStripSplitter = WUX::Controls::Border();
+            _tabStripSplitter.Width(4);
+            // the BG color will get set in _updatePaneResources
+
+            // Use a custom cursor via InputSystemCursorShape
+            _tabStripSplitter.ManipulationMode(WUX::Input::ManipulationModes::None);
+
+            // Wire up pointer events for the splitter
+            _tabStripSplitter.PointerEntered([](const auto& /*sender*/, const auto&) {
+                if (const auto coreWindow = Windows::UI::Core::CoreWindow::GetForCurrentThread())
+                {
+                    coreWindow.PointerCursor(
+                        Windows::UI::Core::CoreCursor{ Windows::UI::Core::CoreCursorType::SizeWestEast, 0 });
+                }
+            });
+            _tabStripSplitter.PointerExited([](const auto& /*sender*/, const auto&) {
+                if (const auto coreWindow = Windows::UI::Core::CoreWindow::GetForCurrentThread())
+                {
+                    coreWindow.PointerCursor(
+                        Windows::UI::Core::CoreCursor{ Windows::UI::Core::CoreCursorType::Arrow, 0 });
+                }
+            });
+            _tabStripSplitter.PointerPressed([weakThis{ get_weak() }](const auto& sender, const WUX::Input::PointerRoutedEventArgs& args) {
+                if (auto page{ weakThis.get() })
+                {
+                    auto border = sender.template as<WUX::Controls::Border>();
+                    border.CapturePointer(args.Pointer());
+                    page->_splitterDragging = true;
+                    page->_splitterDragStartX = args.GetCurrentPoint(page->Root()).Position().X;
+                    // Find the tab strip column width
+                    auto tabStripColIdx = (page->_tabPosition == TabPosition::Left) ? 0u : 2u;
+                    page->_splitterDragStartWidth = page->Root().ColumnDefinitions().GetAt(tabStripColIdx).ActualWidth();
+                    args.Handled(true);
+                }
+            });
+            _tabStripSplitter.PointerMoved([weakThis{ get_weak() }](const auto& /*sender*/, const WUX::Input::PointerRoutedEventArgs& args) {
+                if (auto page{ weakThis.get() })
+                {
+                    if (!page->_splitterDragging)
+                        return;
+                    auto currentX = args.GetCurrentPoint(page->Root()).Position().X;
+                    auto delta = currentX - page->_splitterDragStartX;
+                    auto tabStripColIdx = (page->_tabPosition == TabPosition::Left) ? 0u : 2u;
+                    auto newWidth = (page->_tabPosition == TabPosition::Left) ? (page->_splitterDragStartWidth + delta) : (page->_splitterDragStartWidth - delta);
+                    newWidth = std::clamp(newWidth, 100.0, 400.0);
+                    page->Root().ColumnDefinitions().GetAt(tabStripColIdx).Width(WUX::GridLengthHelper::FromPixels(newWidth));
+                    args.Handled(true);
+                }
+            });
+            _tabStripSplitter.PointerReleased([weakThis{ get_weak() }](const auto& sender, const WUX::Input::PointerRoutedEventArgs& args) {
+                if (auto page{ weakThis.get() })
+                {
+                    if (page->_splitterDragging)
+                    {
+                        page->_splitterDragging = false;
+                        auto border = sender.template as<WUX::Controls::Border>();
+                        border.ReleasePointerCapture(args.Pointer());
+                        args.Handled(true);
+                    }
+                }
+            });
+
+            if (_tabPosition == TabPosition::Left)
+            {
+                root.ColumnDefinitions().Append(tabStripCol);
+                root.ColumnDefinitions().Append(splitterCol);
+                root.ColumnDefinitions().Append(contentCol);
+
+                WUX::Controls::Grid::SetColumn(_tabRow, 0);
+                WUX::Controls::Grid::SetColumn(_tabStripSplitter, 1);
+                WUX::Controls::Grid::SetColumn(contentGrid, 2);
+            }
+            else // Right
+            {
+                root.ColumnDefinitions().Append(contentCol);
+                root.ColumnDefinitions().Append(splitterCol);
+                root.ColumnDefinitions().Append(tabStripCol);
+
+                WUX::Controls::Grid::SetColumn(contentGrid, 0);
+                WUX::Controls::Grid::SetColumn(_tabStripSplitter, 1);
+                WUX::Controls::Grid::SetColumn(_tabRow, 2);
+            }
+
+            // Clear any row assignments from XAML
+            WUX::Controls::Grid::SetRow(_tabRow, 0);
+
+            // Insert layout elements at the front so overlay elements
+            // (command palette, dialogs) remain on top in z-order.
+            root.Children().InsertAt(0, _tabRow);
+            root.Children().InsertAt(1, _tabStripSplitter);
+            root.Children().InsertAt(2, contentGrid);
+
+            // Update remaining overlay children (deferred-load stubs for
+            // CommandPalette, SuggestionsControl, dialogs, InfoBars,
+            // TeachingTips, etc.) so they span all 3 columns and cover the
+            // full width of the page, not just the tab strip column.
+            for (uint32_t i = 3; i < root.Children().Size(); ++i)
+            {
+                auto child = root.Children().GetAt(i);
+                if (const auto& fwe { child.try_as<WUX::FrameworkElement>() })
+                {
+                    WUX::Controls::Grid::SetColumn(fwe, 0);
+                    WUX::Controls::Grid::SetColumnSpan(fwe, 3);
+                    WUX::Controls::Grid::SetRow(fwe, 0);
+                }
+            }
+
+            // Apply vertical styles to the TabView from our resource dictionary
+            if (const auto res = Application::Current().Resources())
+            {
+                if (const auto verticalTabViewStyle = res.Lookup(winrt::box_value(L"VerticalTabViewStyle")))
+                {
+                    _tabView.Style(verticalTabViewStyle.as<WUX::Style>());
+                }
+                // Apply the vertical TabViewItem style as an implicit style
+                // on the TabRow's resources so new tab items pick it up.
+                if (const auto verticalItemStyle = res.Lookup(winrt::box_value(L"VerticalTabViewItemStyle")))
+                {
+                    auto tabRowResources = _tabRow.Resources();
+                    if (!tabRowResources)
+                    {
+                        tabRowResources = WUX::ResourceDictionary{};
+                        _tabRow.Resources(tabRowResources);
+                    }
+                    auto itemStyleType = winrt::xaml_typename<MUX::Controls::TabViewItem>();
+                    tabRowResources.Insert(winrt::box_value(itemStyleType), verticalItemStyle);
+                }
+            }
+
+            // Bug fix: TabRowControl.xaml sets VerticalAlignment="Bottom" on
+            // the TabView for the default horizontal mode. Override to Top so
+            // tabs start at the top of the vertical strip.
+            _tabView.VerticalAlignment(WUX::VerticalAlignment::Top);
+
+            // Bug fix: In vertical mode, give the "new tab" button a text
+            // label ("New tab") next to its "+" icon so it reads naturally
+            // in the wider sidebar.
+            if (_newTabButton)
+            {
+                auto panel = WUX::Controls::StackPanel();
+                panel.Orientation(WUX::Controls::Orientation::Horizontal);
+                panel.Spacing(8);
+
+                WUX::Controls::FontIcon plusIcon{};
+                plusIcon.Glyph(L"\uE710");
+                plusIcon.FontFamily(WUX::Media::FontFamily{ L"Segoe Fluent Icons, Segoe MDL2 Assets" });
+                plusIcon.FontSize(12);
+                panel.Children().Append(plusIcon);
+
+                WUX::Controls::TextBlock label{};
+                label.Text(RS_(L"TabNewButtonText"));
+                label.VerticalAlignment(WUX::VerticalAlignment::Center);
+                label.FontFamily(WUX::Media::FontFamily{ L"Segoe UI" });
+                panel.Children().Append(label);
+
+                _newTabButton.Content(panel);
+            }
+            break;
+        }
+        }
+    }
+
     void TerminalPage::Create()
     {
         // Hookup the key bindings
@@ -335,37 +636,10 @@ namespace winrt::TerminalApp::implementation
         auto tabRowImpl = winrt::get_self<implementation::TabRowControl>(_tabRow);
         _newTabButton = tabRowImpl->NewTabButton();
 
-        if (_settings.GlobalSettings().ShowTabsInTitlebar())
-        {
-            // Remove the TabView from the page. We'll hang on to it, we need to
-            // put it in the titlebar.
-            uint32_t index = 0;
-            if (this->Root().Children().IndexOf(_tabRow, index))
-            {
-                this->Root().Children().RemoveAt(index);
-            }
+        // Apply the tab position from the theme. This rearranges the grid
+        // layout and potentially moves the tab row into the titlebar (for Top).
+        _ApplyTabPosition();
 
-            // Inform the host that our titlebar content has changed.
-            SetTitleBarContent.raise(*this, _tabRow);
-
-            // GH#13143 Manually set the tab row's background to transparent here.
-            //
-            // We're doing it this way because ThemeResources are tricky. We
-            // default in XAML to using the appropriate ThemeResource background
-            // color for our TabRow. When tabs in the titlebar are _disabled_,
-            // this will ensure that the tab row has the correct theme-dependent
-            // value. When tabs in the titlebar are _enabled_ (the default),
-            // we'll switch the BG to Transparent, to let the Titlebar Control's
-            // background be used as the BG for the tab row.
-            //
-            // We can't do it the other way around (default to Transparent, only
-            // switch to a color when disabling tabs in the titlebar), because
-            // looking up the correct ThemeResource from and App dictionary is a
-            // capital-H Hard problem.
-            const auto transparent = Media::SolidColorBrush();
-            transparent.Color(Windows::UI::Colors::Transparent());
-            _tabRow.Background(transparent);
-        }
         _updateThemeColors();
 
         // Initialize the state of the CloseButtonOverlayMode property of
@@ -4951,7 +5225,7 @@ namespace winrt::TerminalApp::implementation
             TitlebarBrush(backgroundSolidBrush);
         }
 
-        if (!_settings.GlobalSettings().ShowTabsInTitlebar())
+        if (_tabPosition != TabPosition::Top || !_settings.GlobalSettings().ShowTabsInTitlebar())
         {
             _tabRow.Background(TitlebarBrush());
         }
@@ -5022,6 +5296,7 @@ namespace winrt::TerminalApp::implementation
             // will eat focus.
             _paneResources.focusedBorderBrush = SolidColorBrush{ Colors::Black() };
         }
+        _tabStripSplitter.Background(_paneResources.focusedBorderBrush);
 
         const auto unfocusedBorderBrushKey = winrt::box_value(L"UnfocusedBorderBrush");
         if (res.HasKey(unfocusedBorderBrushKey))

src/cascadia/TerminalApp/TerminalPage.h

@@ -227,6 +227,9 @@ namespace winrt::TerminalApp::implementation
         Microsoft::UI::Xaml::Controls::SplitButton _newTabButton{ nullptr };
         winrt::TerminalApp::ColorPickupFlyout _tabColorPicker{ nullptr };
 
+        Microsoft::Terminal::Settings::Model::TabPosition _tabPosition{ Microsoft::Terminal::Settings::Model::TabPosition::Top };
+        Windows::UI::Xaml::Controls::Border _tabStripSplitter{ nullptr };
+
         Microsoft::Terminal::Settings::Model::CascadiaSettings _settings{ nullptr };
 
         Windows::Foundation::Collections::IObservableVector<TerminalApp::Tab> _tabs;
@@ -243,6 +246,11 @@ namespace winrt::TerminalApp::implementation
         bool _isAlwaysOnTop{ false };
         bool _showTabsFullscreen{ false };
 
+        // Splitter drag state for left/right tab positions
+        bool _splitterDragging{ false };
+        double _splitterDragStartX{ 0.0 };
+        double _splitterDragStartWidth{ 0.0 };
+
         std::optional<uint32_t> _loadFromPersistedLayoutIdx{};
 
         bool _rearranging{ false };
@@ -342,6 +350,7 @@ namespace winrt::TerminalApp::implementation
         void _UpdateTabIcon(Tab& tab);
         void _UpdateTabView();
         void _UpdateTabWidthMode();
+        void _ApplyTabPosition();
         void _SetBackgroundImage(const winrt::Microsoft::Terminal::Settings::Model::IAppearanceConfig& newAppearance);
 
         void _DuplicateFocusedTab();

src/cascadia/TerminalApp/TerminalPage.xaml

@@ -25,7 +25,8 @@
                              Grid.Row="0"
                              KeyUp="_KeyDownHandler" />
 
-        <StackPanel Grid.Row="1"
+        <StackPanel x:Name="InfoBarPanel"
+                    Grid.Row="1"
                     Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
             <mux:InfoBar x:Name="KeyboardServiceWarningInfoBar"
                          x:Load="False"
@@ -84,29 +85,34 @@
 
         <local:AboutDialog x:Name="AboutDialog"
                            Grid.Row="2"
+                              Grid.ColumnSpan="3"
                            x:Load="False" />
 
         <ContentDialog x:Name="QuitDialog"
                        x:Uid="QuitDialog"
                        Grid.Row="2"
+                              Grid.ColumnSpan="3"
                        x:Load="False"
                        DefaultButton="Primary" />
 
         <ContentDialog x:Name="CloseAllDialog"
                        x:Uid="CloseAllDialog"
                        Grid.Row="2"
+                              Grid.ColumnSpan="3"
                        x:Load="False"
                        DefaultButton="Primary" />
 
         <ContentDialog x:Name="CloseReadOnlyDialog"
                        x:Uid="CloseReadOnlyDialog"
                        Grid.Row="2"
+                              Grid.ColumnSpan="3"
                        x:Load="False"
                        DefaultButton="Close" />
 
         <ContentDialog x:Name="MultiLinePasteDialog"
                        x:Uid="MultiLinePasteDialog"
                        Grid.Row="2"
+                              Grid.ColumnSpan="3"
                        x:Load="False"
                        DefaultButton="Primary">
             <StackPanel>
@@ -127,12 +133,14 @@
         <ContentDialog x:Name="LargePasteDialog"
                        x:Uid="LargePasteDialog"
                        Grid.Row="2"
+                              Grid.ColumnSpan="3"
                        x:Load="False"
                        DefaultButton="Primary" />
 
         <ContentDialog x:Name="ControlNoticeDialog"
                        x:Uid="ControlNoticeDialog"
                        Grid.Row="2"
+                              Grid.ColumnSpan="3"
                        x:Load="False"
                        DefaultButton="Primary">
             <TextBlock IsTextSelectionEnabled="True"
@@ -147,6 +155,7 @@
         <ContentDialog x:Name="CouldNotOpenUriDialog"
                        x:Uid="CouldNotOpenUriDialog"
                        Grid.Row="2"
+                       Grid.ColumnSpan="3"
                        x:Load="False"
                        DefaultButton="Primary">
             <TextBlock IsTextSelectionEnabled="True"
@@ -162,6 +171,7 @@
 
         <local:CommandPalette x:Name="CommandPaletteElement"
                               Grid.Row="2"
+                              Grid.ColumnSpan="3"
                               VerticalAlignment="Stretch"
                               x:Load="False"
                               PreviewKeyDown="_KeyDownHandler"
@@ -169,6 +179,7 @@
 
         <local:SuggestionsControl x:Name="SuggestionsElement"
                                   Grid.Row="2"
+                              Grid.ColumnSpan="3"
                                   HorizontalAlignment="Left"
                                   VerticalAlignment="Top"
                                   x:Load="False"

src/cascadia/TerminalApp/TerminalWindow.cpp

@@ -270,6 +270,16 @@ namespace winrt::TerminalApp::implementation
         return _settings.GlobalSettings().ShowTabsInTitlebar();
     }
 
+    Microsoft::Terminal::Settings::Model::TabPosition TerminalWindow::GetTabPosition()
+    {
+        auto theme = Theme();
+        if (auto window = theme.Window())
+        {
+            return window.TabPosition();
+        }
+        return Microsoft::Terminal::Settings::Model::TabPosition::Top;
+    }
+
     bool TerminalWindow::GetInitialAlwaysOnTop()
     {
         return _settings.GlobalSettings().AlwaysOnTop();

src/cascadia/TerminalApp/TerminalWindow.h

@@ -106,6 +106,7 @@ namespace winrt::TerminalApp::implementation
         winrt::Windows::UI::Xaml::ElementTheme GetRequestedTheme();
         Microsoft::Terminal::Settings::Model::LaunchMode GetLaunchMode();
         bool GetShowTabsInTitlebar();
+        Microsoft::Terminal::Settings::Model::TabPosition GetTabPosition();
         bool GetInitialAlwaysOnTop();
         bool GetInitialShowTabsFullscreen();
         float CalcSnappedDimension(const bool widthOrHeight, const float dimension) const;

src/cascadia/TerminalApp/TerminalWindow.idl

@@ -84,6 +84,7 @@ namespace TerminalApp
         Windows.UI.Xaml.ElementTheme GetRequestedTheme();
         Microsoft.Terminal.Settings.Model.LaunchMode GetLaunchMode();
         Boolean GetShowTabsInTitlebar();
+        Microsoft.Terminal.Settings.Model.TabPosition GetTabPosition();
         Boolean GetInitialAlwaysOnTop();
         Boolean GetInitialShowTabsFullscreen();
         Single CalcSnappedDimension(Boolean widthOrHeight, Single dimension);

src/cascadia/TerminalApp/VerticalTabViewStyle.xaml

@@ -0,0 +1,268 @@
+<!--
+    Copyright (c) Microsoft Corporation. All rights reserved. Licensed under
+    the MIT License. See LICENSE in the project root for license information.
+
+    Retemplated styles for vertical (Left/Right) tab strip orientation.
+    These styles override the horizontal TabView layout to stack tabs vertically
+    in a sidebar configuration.
+-->
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:mux="using:Microsoft.UI.Xaml.Controls"
+                    xmlns:primitives="using:Microsoft.UI.Xaml.Controls.Primitives">
+
+    <!--
+        VerticalTabViewListViewStyle:
+        Override the ItemsPanel to use vertical orientation and switch scrolling
+        from horizontal to vertical.
+    -->
+    <Style x:Key="VerticalTabViewListViewStyle"
+           TargetType="primitives:TabViewListView">
+        <Setter Property="TabNavigation" Value="Once" />
+        <Setter Property="IsItemClickEnabled" Value="True" />
+        <Setter Property="IsSwipeEnabled" Value="False" />
+        <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Disabled" />
+        <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto" />
+        <Setter Property="ScrollViewer.HorizontalScrollMode" Value="Disabled" />
+        <Setter Property="ScrollViewer.VerticalScrollMode" Value="Enabled" />
+        <Setter Property="ScrollViewer.IsHorizontalRailEnabled" Value="False" />
+        <Setter Property="ScrollViewer.IsVerticalRailEnabled" Value="True" />
+        <Setter Property="SingleSelectionFollowsFocus" Value="False" />
+        <Setter Property="ItemContainerTransitions">
+            <Setter.Value>
+                <TransitionCollection>
+                    <AddDeleteThemeTransition />
+                    <ContentThemeTransition />
+                    <ReorderThemeTransition />
+                </TransitionCollection>
+            </Setter.Value>
+        </Setter>
+        <Setter Property="ItemsPanel">
+            <Setter.Value>
+                <ItemsPanelTemplate>
+                    <ItemsStackPanel Orientation="Vertical" />
+                </ItemsPanelTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
+    <!--
+        VerticalTabViewStyle:
+        Retemplate the TabView control for a vertical sidebar layout.
+        Instead of 4 columns in TabContainerGrid, we use 3 rows:
+          Row 0 (Auto): Header (elevation shield)
+          Row 1 (*):    Tab list (fills vertical space)
+          Row 2 (Auto): Footer (new tab button)
+        The TabContentPresenter is removed — WT doesn't use it.
+    -->
+    <Style x:Key="VerticalTabViewStyle"
+           TargetType="mux:TabView">
+        <Setter Property="VerticalAlignment" Value="Stretch" />
+        <Setter Property="HorizontalAlignment" Value="Stretch" />
+        <Setter Property="IsTabStop" Value="False" />
+        <Setter Property="TabNavigation" Value="Once" />
+        <Setter Property="IsAddTabButtonVisible" Value="False" />
+        <Setter Property="Background" Value="Transparent" />
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="mux:TabView">
+                    <Grid x:Name="TabContainerGrid">
+                        <Grid.RowDefinitions>
+                            <RowDefinition Height="Auto" />
+                            <RowDefinition Height="*" />
+                            <RowDefinition Height="Auto" />
+                        </Grid.RowDefinitions>
+
+                        <!--  Header (elevation shield, etc.)  -->
+                        <ContentPresenter x:Name="LeftContentPresenter"
+                                          Grid.Row="0"
+                                          Content="{TemplateBinding TabStripHeader}"
+                                          ContentTemplate="{TemplateBinding TabStripHeaderTemplate}" />
+
+                        <!--  Tab list  -->
+                        <primitives:TabViewListView x:Name="TabListView"
+                                                    Grid.Row="1"
+                                                    AllowDrop="{TemplateBinding AllowDropTabs}"
+                                                    CanDragItems="{TemplateBinding CanDragTabs}"
+                                                    CanReorderItems="{TemplateBinding CanReorderTabs}"
+                                                    ItemTemplate="{TemplateBinding TabItemTemplate}"
+                                                    ItemTemplateSelector="{TemplateBinding TabItemTemplateSelector}"
+                                                    ItemsSource="{TemplateBinding TabItemsSource}"
+                                                    Style="{StaticResource VerticalTabViewListViewStyle}" />
+
+                        <!--  Footer (new tab button)  -->
+                        <ContentPresenter x:Name="RightContentPresenter"
+                                          Grid.Row="2"
+                                          Content="{TemplateBinding TabStripFooter}"
+                                          ContentTemplate="{TemplateBinding TabStripFooterTemplate}" />
+                    </Grid>
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
+    <!--
+        VerticalTabViewItemStyle:
+        Simplified TabViewItem template for vertical tabs.
+        Removes curved corner arcs, replaces with rounded Border and a
+        left-edge accent bar for the selected tab. Tabs fill strip width.
+    -->
+    <Style x:Key="VerticalTabViewItemStyle"
+           TargetType="mux:TabViewItem">
+        <Setter Property="HorizontalContentAlignment" Value="Stretch" />
+        <Setter Property="UseSystemFocusVisuals" Value="{StaticResource UseSystemFocusVisuals}" />
+        <Setter Property="Padding" Value="8,6,8,6" />
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="mux:TabViewItem">
+                    <Grid x:Name="LayoutRoot"
+                          Margin="2,1,2,1">
+
+                        <VisualStateManager.VisualStateGroups>
+                            <VisualStateGroup x:Name="CommonStates">
+                                <VisualState x:Name="Normal">
+                                    <VisualState.Setters>
+                                        <Setter Target="TabContainer.Background" Value="Transparent" />
+                                        <Setter Target="SelectedIndicator.Opacity" Value="0" />
+                                    </VisualState.Setters>
+                                </VisualState>
+
+                                <VisualState x:Name="PointerOver">
+                                    <VisualState.Setters>
+                                        <Setter Target="TabContainer.Background" Value="{ThemeResource TabViewItemHeaderBackgroundPointerOver}" />
+                                        <Setter Target="SelectedIndicator.Opacity" Value="0" />
+                                    </VisualState.Setters>
+                                </VisualState>
+
+                                <VisualState x:Name="Pressed">
+                                    <VisualState.Setters>
+                                        <Setter Target="TabContainer.Background" Value="{ThemeResource TabViewItemHeaderBackgroundPressed}" />
+                                        <Setter Target="SelectedIndicator.Opacity" Value="0" />
+                                    </VisualState.Setters>
+                                </VisualState>
+
+                                <VisualState x:Name="Selected">
+                                    <VisualState.Setters>
+                                        <Setter Target="TabContainer.Background" Value="{ThemeResource TabViewItemHeaderBackgroundSelected}" />
+                                        <Setter Target="SelectedIndicator.Opacity" Value="1" />
+                                    </VisualState.Setters>
+                                </VisualState>
+
+                                <VisualState x:Name="PointerOverSelected">
+                                    <VisualState.Setters>
+                                        <Setter Target="TabContainer.Background" Value="{ThemeResource TabViewItemHeaderBackgroundSelected}" />
+                                        <Setter Target="SelectedIndicator.Opacity" Value="1" />
+                                    </VisualState.Setters>
+                                </VisualState>
+
+                                <VisualState x:Name="PressedSelected">
+                                    <VisualState.Setters>
+                                        <Setter Target="TabContainer.Background" Value="{ThemeResource TabViewItemHeaderBackgroundPressed}" />
+                                        <Setter Target="SelectedIndicator.Opacity" Value="1" />
+                                    </VisualState.Setters>
+                                </VisualState>
+                            </VisualStateGroup>
+
+                            <VisualStateGroup x:Name="CloseButtonOverlayModeStates">
+                                <VisualState x:Name="CloseButtonVisible" />
+                                <VisualState x:Name="CloseButtonCollapsed">
+                                    <VisualState.Setters>
+                                        <Setter Target="CloseButton.Visibility" Value="Collapsed" />
+                                    </VisualState.Setters>
+                                </VisualState>
+                            </VisualStateGroup>
+
+                            <VisualStateGroup x:Name="TabViewWidthModeStates">
+                                <!--  In vertical mode, tabs always stretch to full width  -->
+                                <VisualState x:Name="StandardWidth" />
+                                <VisualState x:Name="Compact" />
+                            </VisualStateGroup>
+
+                            <VisualStateGroup x:Name="IconStates">
+                                <VisualState x:Name="Icon" />
+                                <VisualState x:Name="NoIcon">
+                                    <VisualState.Setters>
+                                        <Setter Target="IconBox.Visibility" Value="Collapsed" />
+                                    </VisualState.Setters>
+                                </VisualState>
+                            </VisualStateGroup>
+
+                            <VisualStateGroup x:Name="DisabledStates">
+                                <VisualState x:Name="Enabled" />
+                                <VisualState x:Name="Disabled">
+                                    <VisualState.Setters>
+                                        <Setter Target="LayoutRoot.Opacity" Value="{ThemeResource ListViewItemDisabledThemeOpacity}" />
+                                    </VisualState.Setters>
+                                </VisualState>
+                            </VisualStateGroup>
+                        </VisualStateManager.VisualStateGroups>
+
+                        <!--  Selected tab background  -->
+                        <Border x:Name="TabContainer"
+                                Background="Transparent"
+                                CornerRadius="{ThemeResource ControlCornerRadius}"
+                                Padding="{TemplateBinding Padding}">
+                            <Grid>
+                                <Grid.ColumnDefinitions>
+                                    <ColumnDefinition x:Name="IconColumn"
+                                                      Width="Auto" />
+                                    <ColumnDefinition Width="*" />
+                                    <ColumnDefinition Width="Auto" />
+                                </Grid.ColumnDefinitions>
+
+                                <!--  Tab icon  -->
+                                <Viewbox x:Name="IconBox"
+                                         Grid.Column="0"
+                                         MaxWidth="16"
+                                         MaxHeight="16"
+                                         Margin="0,0,8,0">
+                                    <ContentControl x:Name="IconControl"
+                                                    Content="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TabViewTemplateSettings.IconElement}"
+                                                    IsTabStop="False" />
+                                </Viewbox>
+
+                                <!--  Tab title  -->
+                                <ContentPresenter x:Name="ContentPresenter"
+                                                  Grid.Column="1"
+                                                  HorizontalAlignment="Left"
+                                                  VerticalAlignment="Center"
+                                                  Content="{TemplateBinding Header}"
+                                                  ContentTemplate="{TemplateBinding HeaderTemplate}"
+                                                  ContentTransitions="{TemplateBinding ContentTransitions}"
+                                                  FontWeight="{TemplateBinding FontWeight}"
+                                                  TextWrapping="NoWrap" />
+
+                                <!--  Close button  -->
+                                <Button x:Name="CloseButton"
+                                        Grid.Column="2"
+                                        Width="20"
+                                        Height="20"
+                                        Margin="4,0,0,0"
+                                        Padding="0"
+                                        HorizontalAlignment="Right"
+                                        VerticalAlignment="Center"
+                                        Background="Transparent"
+                                        BorderThickness="0"
+                                        Content="&#xE711;"
+                                        FontFamily="{ThemeResource SymbolThemeFontFamily}"
+                                        FontSize="10"
+                                        IsTextScaleFactorEnabled="False" />
+                            </Grid>
+                        </Border>
+
+                        <!--  Left-edge accent bar for selected tab  -->
+                        <Border x:Name="SelectedIndicator"
+                                Width="3"
+                                Height="16"
+                                HorizontalAlignment="Left"
+                                VerticalAlignment="Center"
+                                Background="{ThemeResource AccentFillColorDefaultBrush}"
+                                CornerRadius="2"
+                                Opacity="0" />
+                    </Grid>
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
+</ResourceDictionary>

src/cascadia/TerminalSettingsModel/MTSMSettings.h

@@ -158,7 +158,8 @@ Author(s):
     X(winrt::Microsoft::Terminal::Settings::Model::ThemeColor, Frame, "frame", nullptr)                                            \
     X(winrt::Microsoft::Terminal::Settings::Model::ThemeColor, UnfocusedFrame, "unfocusedFrame", nullptr)                          \
     X(bool, RainbowFrame, "experimental.rainbowFrame", false)                                                                      \
-    X(bool, UseMica, "useMica", false)
+    X(bool, UseMica, "useMica", false)                                                                                             \
+    X(winrt::Microsoft::Terminal::Settings::Model::TabPosition, TabPosition, "tabPosition", winrt::Microsoft::Terminal::Settings::Model::TabPosition::Top)
 
 #define MTSM_THEME_SETTINGS_SETTINGS(X) \
     X(winrt::Windows::UI::Xaml::ElementTheme, RequestedTheme, "theme", winrt::Windows::UI::Xaml::ElementTheme::Default)

src/cascadia/TerminalSettingsModel/TerminalSettingsSerializationHelpers.h

@@ -673,6 +673,16 @@ JSON_ENUM_MAPPER(::winrt::Microsoft::Terminal::Settings::Model::IconStyle)
     };
 };
 
+JSON_ENUM_MAPPER(::winrt::Microsoft::Terminal::Settings::Model::TabPosition)
+{
+    JSON_MAPPINGS(4) = {
+        pair_type{ "top", ValueType::Top },
+        pair_type{ "bottom", ValueType::Bottom },
+        pair_type{ "left", ValueType::Left },
+        pair_type{ "right", ValueType::Right },
+    };
+};
+
 // Possible ScrollToMarkDirection values
 JSON_ENUM_MAPPER(::winrt::Microsoft::Terminal::Control::ScrollToMarkDirection)
 {

src/cascadia/TerminalSettingsModel/Theme.idl

@@ -11,6 +11,14 @@ namespace Microsoft.Terminal.Settings.Model
         Monochrome
     };
 
+    enum TabPosition
+    {
+        Top,
+        Bottom,
+        Left,
+        Right
+    };
+
     enum ThemeColorType
     {
         Accent,
@@ -64,6 +72,7 @@ namespace Microsoft.Terminal.Settings.Model
         Boolean RainbowFrame { get; };
         ThemeColor Frame { get; };
         ThemeColor UnfocusedFrame { get; };
+        TabPosition TabPosition { get; };
     }
 
     runtimeclass TabRowTheme {

src/cascadia/UnitTests_SettingsModel/ThemeTests.cpp

@@ -28,6 +28,7 @@ namespace SettingsModelUnitTests
         TEST_METHOD(ParseNullWindowTheme);
         TEST_METHOD(ParseThemeWithNullThemeColor);
         TEST_METHOD(InvalidCurrentTheme);
+        TEST_METHOD(ParseTabPosition);
 
         static Core::Color rgb(uint8_t r, uint8_t g, uint8_t b) noexcept
         {
@@ -265,4 +266,103 @@ namespace SettingsModelUnitTests
             throw e;
         }
     }
+
+    void ThemeTests::ParseTabPosition()
+    {
+        Log::Comment(L"Verify tabPosition round-trips through JSON serialization.");
+
+        // Test each of the four tab positions
+        static constexpr std::string_view leftTheme{ R"({
+            "name": "leftTabs",
+            "window":
+            {
+                "tabPosition": "left"
+            }
+        })" };
+
+        static constexpr std::string_view rightTheme{ R"({
+            "name": "rightTabs",
+            "window":
+            {
+                "tabPosition": "right"
+            }
+        })" };
+
+        static constexpr std::string_view bottomTheme{ R"({
+            "name": "bottomTabs",
+            "window":
+            {
+                "tabPosition": "bottom"
+            }
+        })" };
+
+        static constexpr std::string_view topTheme{ R"({
+            "name": "topTabs",
+            "window":
+            {
+                "tabPosition": "top"
+            }
+        })" };
+
+        // Test default (no tabPosition specified)
+        static constexpr std::string_view defaultTheme{ R"({
+            "name": "defaultTabs",
+            "window":
+            {
+                "useMica": false
+            }
+        })" };
+
+        // Parse and verify "left"
+        {
+            const auto schemeObject = VerifyParseSucceeded(leftTheme);
+            auto theme = Theme::FromJson(schemeObject);
+            VERIFY_ARE_EQUAL(L"leftTabs", theme->Name());
+            VERIFY_IS_NOT_NULL(theme->Window());
+            VERIFY_ARE_EQUAL(Settings::Model::TabPosition::Left, theme->Window().TabPosition());
+
+            // Re-serialize and verify the key is present
+            const auto reJson = theme->ToJson();
+            VERIFY_IS_TRUE(reJson.isMember("window"));
+            VERIFY_IS_TRUE(reJson["window"].isMember("tabPosition"));
+            VERIFY_ARE_EQUAL("left", reJson["window"]["tabPosition"].asString());
+        }
+
+        // Parse and verify "right"
+        {
+            const auto schemeObject = VerifyParseSucceeded(rightTheme);
+            auto theme = Theme::FromJson(schemeObject);
+            VERIFY_ARE_EQUAL(Settings::Model::TabPosition::Right, theme->Window().TabPosition());
+
+            const auto reJson = theme->ToJson();
+            VERIFY_ARE_EQUAL("right", reJson["window"]["tabPosition"].asString());
+        }
+
+        // Parse and verify "bottom"
+        {
+            const auto schemeObject = VerifyParseSucceeded(bottomTheme);
+            auto theme = Theme::FromJson(schemeObject);
+            VERIFY_ARE_EQUAL(Settings::Model::TabPosition::Bottom, theme->Window().TabPosition());
+
+            const auto reJson = theme->ToJson();
+            VERIFY_ARE_EQUAL("bottom", reJson["window"]["tabPosition"].asString());
+        }
+
+        // Parse and verify "top"
+        {
+            const auto schemeObject = VerifyParseSucceeded(topTheme);
+            auto theme = Theme::FromJson(schemeObject);
+            VERIFY_ARE_EQUAL(Settings::Model::TabPosition::Top, theme->Window().TabPosition());
+
+            const auto reJson = theme->ToJson();
+            VERIFY_ARE_EQUAL("top", reJson["window"]["tabPosition"].asString());
+        }
+
+        // Parse default — should be Top
+        {
+            const auto schemeObject = VerifyParseSucceeded(defaultTheme);
+            auto theme = Theme::FromJson(schemeObject);
+            VERIFY_ARE_EQUAL(Settings::Model::TabPosition::Top, theme->Window().TabPosition());
+        }
+    }
 }

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -51,7 +51,9 @@ AppHost::AppHost(WindowEmperor* manager, const winrt::TerminalApp::AppLogic& log
     _HandleCommandlineArgs(args);
 
     // _HandleCommandlineArgs will create a _windowLogic
-    _useNonClientArea = _windowLogic.GetShowTabsInTitlebar();
+    const auto tabPos = _windowLogic.GetTabPosition();
+    _useNonClientArea = (tabPos == winrt::Microsoft::Terminal::Settings::Model::TabPosition::Top) &&
+                        _windowLogic.GetShowTabsInTitlebar();
 
     if (_useNonClientArea)
     {