Refine XCEditor docking and DPI rendering

new_editor/CMakeLists.txt

@@ -22,6 +22,7 @@ endfunction()
 set(XCUI_EDITOR_FOUNDATION_SOURCES
     src/Foundation/UIEditorCommandDispatcher.cpp
     src/Foundation/UIEditorCommandRegistry.cpp
+    src/Foundation/UIEditorRuntimeTrace.cpp
     src/Foundation/UIEditorShortcutManager.cpp
     src/Foundation/UIEditorTheme.cpp
 )
@@ -129,6 +130,7 @@ add_library(XCUIEditorHost STATIC
 target_include_directories(XCUIEditorHost
     PUBLIC
         ${CMAKE_CURRENT_SOURCE_DIR}
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
         ${CMAKE_SOURCE_DIR}/engine/include
 )
 

new_editor/Host/NativeRenderer.cpp

@@ -8,9 +8,8 @@ namespace XCEngine::UI::Editor::Host {
 
 namespace {
 
-D2D1_RECT_F ToD2DRect(const ::XCEngine::UI::UIRect& rect) {
-    return D2D1::RectF(rect.x, rect.y, rect.x + rect.width, rect.y + rect.height);
-}
+constexpr float kBaseDpi = 96.0f;
+constexpr float kDefaultFontSize = 16.0f;
 
 std::string HrToString(const char* operation, HRESULT hr) {
     char buffer[128] = {};
@@ -18,6 +17,27 @@ std::string HrToString(const char* operation, HRESULT hr) {
     return buffer;
 }
 
+float ClampDpiScale(float dpiScale) {
+    return dpiScale > 0.0f ? dpiScale : 1.0f;
+}
+
+float ResolveFontSize(float fontSize) {
+    return fontSize > 0.0f ? fontSize : kDefaultFontSize;
+}
+
+float SnapToPixel(float value, float dpiScale) {
+    const float scale = ClampDpiScale(dpiScale);
+    return std::round(value * scale);
+}
+
+D2D1_RECT_F ToD2DRect(const ::XCEngine::UI::UIRect& rect, float dpiScale) {
+    const float left = SnapToPixel(rect.x, dpiScale);
+    const float top = SnapToPixel(rect.y, dpiScale);
+    const float right = SnapToPixel(rect.x + rect.width, dpiScale);
+    const float bottom = SnapToPixel(rect.y + rect.height, dpiScale);
+    return D2D1::RectF(left, top, right, bottom);
+}
+
 } // namespace
 
 bool NativeRenderer::Initialize(HWND hwnd) {
@@ -64,6 +84,17 @@ void NativeRenderer::Shutdown() {
     m_hwnd = nullptr;
 }
 
+void NativeRenderer::SetDpiScale(float dpiScale) {
+    m_dpiScale = ClampDpiScale(dpiScale);
+    if (m_renderTarget) {
+        m_renderTarget->SetDpi(kBaseDpi, kBaseDpi);
+    }
+}
+
+float NativeRenderer::GetDpiScale() const {
+    return m_dpiScale;
+}
+
 void NativeRenderer::Resize(UINT width, UINT height) {
     if (!m_renderTarget || width == 0 || height == 0) {
         return;
@@ -104,6 +135,52 @@ const std::string& NativeRenderer::GetLastRenderError() const {
     return m_lastRenderError;
 }
 
+float NativeRenderer::MeasureTextWidth(
+    const ::XCEngine::UI::Editor::UIEditorTextMeasureRequest& request) const {
+    if (!m_dwriteFactory || request.text.empty()) {
+        return 0.0f;
+    }
+
+    const std::wstring text = Utf8ToWide(request.text);
+    if (text.empty()) {
+        return 0.0f;
+    }
+
+    const float dpiScale = ClampDpiScale(m_dpiScale);
+    const float scaledFontSize = ResolveFontSize(request.fontSize) * dpiScale;
+    IDWriteTextFormat* textFormat = GetTextFormat(scaledFontSize);
+    if (textFormat == nullptr) {
+        return 0.0f;
+    }
+
+    Microsoft::WRL::ComPtr<IDWriteTextLayout> textLayout;
+    HRESULT hr = m_dwriteFactory->CreateTextLayout(
+        text.c_str(),
+        static_cast<UINT32>(text.size()),
+        textFormat,
+        4096.0f,
+        scaledFontSize * 2.0f,
+        textLayout.ReleaseAndGetAddressOf());
+    if (FAILED(hr) || !textLayout) {
+        return 0.0f;
+    }
+
+    DWRITE_TEXT_METRICS textMetrics = {};
+    hr = textLayout->GetMetrics(&textMetrics);
+    if (FAILED(hr)) {
+        return 0.0f;
+    }
+
+    DWRITE_OVERHANG_METRICS overhangMetrics = {};
+    float width = textMetrics.widthIncludingTrailingWhitespace;
+    if (SUCCEEDED(textLayout->GetOverhangMetrics(&overhangMetrics))) {
+        width += (std::max)(overhangMetrics.left, 0.0f);
+        width += (std::max)(overhangMetrics.right, 0.0f);
+    }
+
+    return std::ceil(width) / dpiScale;
+}
+
 bool NativeRenderer::CaptureToPng(
     const ::XCEngine::UI::UIDrawData& drawData,
     UINT width,
@@ -146,7 +223,9 @@ bool NativeRenderer::CaptureToPng(
 
     const D2D1_RENDER_TARGET_PROPERTIES renderTargetProperties = D2D1::RenderTargetProperties(
         D2D1_RENDER_TARGET_TYPE_DEFAULT,
-        D2D1::PixelFormat(DXGI_FORMAT_B8G8R8A8_UNORM, D2D1_ALPHA_MODE_PREMULTIPLIED));
+        D2D1::PixelFormat(DXGI_FORMAT_B8G8R8A8_UNORM, D2D1_ALPHA_MODE_PREMULTIPLIED),
+        kBaseDpi,
+        kBaseDpi);
 
     Microsoft::WRL::ComPtr<ID2D1RenderTarget> offscreenRenderTarget;
     hr = m_d2dFactory->CreateWicBitmapRenderTarget(
@@ -301,7 +380,11 @@ bool NativeRenderer::CreateDeviceResources() {
     const UINT width = static_cast<UINT>((std::max)(clientRect.right - clientRect.left, 1L));
     const UINT height = static_cast<UINT>((std::max)(clientRect.bottom - clientRect.top, 1L));
 
-    const D2D1_RENDER_TARGET_PROPERTIES renderTargetProps = D2D1::RenderTargetProperties();
+    const D2D1_RENDER_TARGET_PROPERTIES renderTargetProps = D2D1::RenderTargetProperties(
+        D2D1_RENDER_TARGET_TYPE_DEFAULT,
+        D2D1::PixelFormat(DXGI_FORMAT_B8G8R8A8_UNORM, D2D1_ALPHA_MODE_PREMULTIPLIED),
+        kBaseDpi,
+        kBaseDpi);
     const D2D1_HWND_RENDER_TARGET_PROPERTIES hwndProps = D2D1::HwndRenderTargetProperties(
         m_hwnd,
         D2D1::SizeU(width, height));
@@ -324,6 +407,7 @@ bool NativeRenderer::CreateDeviceResources() {
         return false;
     }
 
+    m_renderTarget->SetDpi(kBaseDpi, kBaseDpi);
     m_renderTarget->SetTextAntialiasMode(D2D1_TEXT_ANTIALIAS_MODE_GRAYSCALE);
     m_lastRenderError.clear();
     return true;
@@ -333,6 +417,7 @@ bool NativeRenderer::RenderToTarget(
     ID2D1RenderTarget& renderTarget,
     ID2D1SolidColorBrush& solidBrush,
     const ::XCEngine::UI::UIDrawData& drawData) {
+    renderTarget.SetDpi(kBaseDpi, kBaseDpi);
     renderTarget.SetTextAntialiasMode(D2D1_TEXT_ANTIALIAS_MODE_GRAYSCALE);
     renderTarget.BeginDraw();
     renderTarget.Clear(D2D1::ColorF(0.04f, 0.05f, 0.06f, 1.0f));
@@ -358,13 +443,15 @@ void NativeRenderer::RenderCommand(
     const ::XCEngine::UI::UIDrawCommand& command,
     std::vector<D2D1_RECT_F>& clipStack) {
     solidBrush.SetColor(ToD2DColor(command.color));
+    const float dpiScale = ClampDpiScale(m_dpiScale);
 
     switch (command.type) {
     case ::XCEngine::UI::UIDrawCommandType::FilledRect: {
-        const D2D1_RECT_F rect = ToD2DRect(command.rect);
+        const D2D1_RECT_F rect = ToD2DRect(command.rect, dpiScale);
+        const float rounding = command.rounding > 0.0f ? command.rounding * dpiScale : 0.0f;
         if (command.rounding > 0.0f) {
             renderTarget.FillRoundedRectangle(
-                D2D1::RoundedRect(rect, command.rounding, command.rounding),
+                D2D1::RoundedRect(rect, rounding, rounding),
                 &solidBrush);
         } else {
             renderTarget.FillRectangle(rect, &solidBrush);
@@ -372,11 +459,12 @@ void NativeRenderer::RenderCommand(
         break;
     }
     case ::XCEngine::UI::UIDrawCommandType::RectOutline: {
-        const D2D1_RECT_F rect = ToD2DRect(command.rect);
-        const float thickness = command.thickness > 0.0f ? command.thickness : 1.0f;
+        const D2D1_RECT_F rect = ToD2DRect(command.rect, dpiScale);
+        const float thickness = (command.thickness > 0.0f ? command.thickness : 1.0f) * dpiScale;
+        const float rounding = command.rounding > 0.0f ? command.rounding * dpiScale : 0.0f;
         if (command.rounding > 0.0f) {
             renderTarget.DrawRoundedRectangle(
-                D2D1::RoundedRect(rect, command.rounding, command.rounding),
+                D2D1::RoundedRect(rect, rounding, rounding),
                 &solidBrush,
                 thickness);
         } else {
@@ -389,8 +477,9 @@ void NativeRenderer::RenderCommand(
             break;
         }
 
-        const float fontSize = command.fontSize > 0.0f ? command.fontSize : 16.0f;
-        IDWriteTextFormat* textFormat = GetTextFormat(fontSize);
+        const float fontSize = ResolveFontSize(command.fontSize);
+        const float scaledFontSize = fontSize * dpiScale;
+        IDWriteTextFormat* textFormat = GetTextFormat(scaledFontSize);
         if (textFormat == nullptr) {
             break;
         }
@@ -401,11 +490,14 @@ void NativeRenderer::RenderCommand(
         }
 
         const D2D1_SIZE_F targetSize = renderTarget.GetSize();
+        const float originX = SnapToPixel(command.position.x, dpiScale);
+        const float originY = SnapToPixel(command.position.y, dpiScale);
+        const float lineHeight = std::ceil(scaledFontSize * 1.6f);
         const D2D1_RECT_F layoutRect = D2D1::RectF(
-            command.position.x,
-            command.position.y,
+            originX,
+            originY,
             targetSize.width,
-            command.position.y + fontSize * 1.8f);
+            originY + lineHeight);
         renderTarget.DrawTextW(
             text.c_str(),
             static_cast<UINT32>(text.size()),
@@ -413,7 +505,7 @@ void NativeRenderer::RenderCommand(
             layoutRect,
             &solidBrush,
             D2D1_DRAW_TEXT_OPTIONS_CLIP,
-            DWRITE_MEASURING_MODE_NATURAL);
+            DWRITE_MEASURING_MODE_GDI_NATURAL);
         break;
     }
     case ::XCEngine::UI::UIDrawCommandType::Image: {
@@ -421,12 +513,12 @@ void NativeRenderer::RenderCommand(
             break;
         }
 
-        const D2D1_RECT_F rect = ToD2DRect(command.rect);
+        const D2D1_RECT_F rect = ToD2DRect(command.rect, dpiScale);
         renderTarget.DrawRectangle(rect, &solidBrush, 1.0f);
         break;
     }
     case ::XCEngine::UI::UIDrawCommandType::PushClipRect: {
-        const D2D1_RECT_F rect = ToD2DRect(command.rect);
+        const D2D1_RECT_F rect = ToD2DRect(command.rect, dpiScale);
         renderTarget.PushAxisAlignedClip(rect, D2D1_ANTIALIAS_MODE_PER_PRIMITIVE);
         clipStack.push_back(rect);
         break;
@@ -443,12 +535,13 @@ void NativeRenderer::RenderCommand(
     }
 }
 
-IDWriteTextFormat* NativeRenderer::GetTextFormat(float fontSize) {
+IDWriteTextFormat* NativeRenderer::GetTextFormat(float fontSize) const {
     if (!m_dwriteFactory) {
         return nullptr;
     }
 
-    const int key = static_cast<int>(std::lround(fontSize * 10.0f));
+    const float resolvedFontSize = ResolveFontSize(fontSize);
+    const int key = static_cast<int>(std::lround(resolvedFontSize * 10.0f));
     const auto found = m_textFormats.find(key);
     if (found != m_textFormats.end()) {
         return found->second.Get();
@@ -461,7 +554,7 @@ IDWriteTextFormat* NativeRenderer::GetTextFormat(float fontSize) {
         DWRITE_FONT_WEIGHT_REGULAR,
         DWRITE_FONT_STYLE_NORMAL,
         DWRITE_FONT_STRETCH_NORMAL,
-        fontSize,
+        resolvedFontSize,
         L"",
         textFormat.ReleaseAndGetAddressOf());
     if (FAILED(hr)) {

new_editor/Host/NativeRenderer.h

@@ -4,6 +4,8 @@
 #define NOMINMAX
 #endif
 
+#include <XCEditor/Foundation/UIEditorTextMeasurement.h>
+
 #include <XCEngine/UI/DrawData.h>
 
 #include <d2d1.h>
@@ -20,13 +22,17 @@
 
 namespace XCEngine::UI::Editor::Host {
 
-class NativeRenderer {
+class NativeRenderer : public ::XCEngine::UI::Editor::UIEditorTextMeasurer {
 public:
     bool Initialize(HWND hwnd);
     void Shutdown();
+    void SetDpiScale(float dpiScale);
+    float GetDpiScale() const;
     void Resize(UINT width, UINT height);
     bool Render(const ::XCEngine::UI::UIDrawData& drawData);
     const std::string& GetLastRenderError() const;
+    float MeasureTextWidth(
+        const ::XCEngine::UI::Editor::UIEditorTextMeasureRequest& request) const override;
     bool CaptureToPng(
         const ::XCEngine::UI::UIDrawData& drawData,
         UINT width,
@@ -49,7 +55,7 @@ private:
         const ::XCEngine::UI::UIDrawCommand& command,
         std::vector<D2D1_RECT_F>& clipStack);
 
-    IDWriteTextFormat* GetTextFormat(float fontSize);
+    IDWriteTextFormat* GetTextFormat(float fontSize) const;
     static D2D1_COLOR_F ToD2DColor(const ::XCEngine::UI::UIColor& color);
     static std::wstring Utf8ToWide(std::string_view text);
 
@@ -59,9 +65,10 @@ private:
     Microsoft::WRL::ComPtr<IWICImagingFactory> m_wicFactory;
     Microsoft::WRL::ComPtr<ID2D1HwndRenderTarget> m_renderTarget;
     Microsoft::WRL::ComPtr<ID2D1SolidColorBrush> m_solidBrush;
-    std::unordered_map<int, Microsoft::WRL::ComPtr<IDWriteTextFormat>> m_textFormats;
+    mutable std::unordered_map<int, Microsoft::WRL::ComPtr<IDWriteTextFormat>> m_textFormats;
     std::string m_lastRenderError = {};
     bool m_wicComInitialized = false;
+    float m_dpiScale = 1.0f;
 };
 
 } // namespace XCEngine::UI::Editor::Host

new_editor/app/Application.cpp

@@ -2,6 +2,7 @@
 
 #include "Shell/ProductShellAsset.h"
 
+#include <XCEditor/Foundation/UIEditorRuntimeTrace.h>
 #include <XCEditor/Foundation/UIEditorTheme.h>
 
 #include <XCEngine/Input/InputTypes.h>
@@ -10,8 +11,11 @@
 #include <algorithm>
 #include <cctype>
 #include <cstdlib>
+#include <sstream>
 #include <string>
 
+#include <shellscalingapi.h>
+
 #ifndef XCUIEDITOR_REPO_ROOT
 #define XCUIEDITOR_REPO_ROOT "."
 #endif
@@ -34,11 +38,112 @@ using App::BuildProductShellInteractionDefinition;
 
 constexpr const wchar_t* kWindowClassName = L"XCEditorShellHost";
 constexpr const wchar_t* kWindowTitle = L"Main Scene * - Main.xx - XCEngine Editor";
+constexpr UINT kDefaultDpi = 96u;
+constexpr float kBaseDpiScale = 96.0f;
 
 Application* GetApplicationFromWindow(HWND hwnd) {
     return reinterpret_cast<Application*>(GetWindowLongPtrW(hwnd, GWLP_USERDATA));
 }
 
+UINT QuerySystemDpi() {
+    HDC screenDc = GetDC(nullptr);
+    if (screenDc == nullptr) {
+        return kDefaultDpi;
+    }
+
+    const int dpiX = GetDeviceCaps(screenDc, LOGPIXELSX);
+    ReleaseDC(nullptr, screenDc);
+    return dpiX > 0 ? static_cast<UINT>(dpiX) : kDefaultDpi;
+}
+
+UINT QueryWindowDpi(HWND hwnd) {
+    if (hwnd != nullptr) {
+        const HMODULE user32 = GetModuleHandleW(L"user32.dll");
+        if (user32 != nullptr) {
+            using GetDpiForWindowFn = UINT(WINAPI*)(HWND);
+            const auto getDpiForWindow =
+                reinterpret_cast<GetDpiForWindowFn>(GetProcAddress(user32, "GetDpiForWindow"));
+            if (getDpiForWindow != nullptr) {
+                const UINT dpi = getDpiForWindow(hwnd);
+                if (dpi != 0u) {
+                    return dpi;
+                }
+            }
+        }
+    }
+
+    return QuerySystemDpi();
+}
+
+void EnableDpiAwareness() {
+    const HMODULE user32 = GetModuleHandleW(L"user32.dll");
+    if (user32 != nullptr) {
+        using SetProcessDpiAwarenessContextFn = BOOL(WINAPI*)(DPI_AWARENESS_CONTEXT);
+        const auto setProcessDpiAwarenessContext =
+            reinterpret_cast<SetProcessDpiAwarenessContextFn>(
+                GetProcAddress(user32, "SetProcessDpiAwarenessContext"));
+        if (setProcessDpiAwarenessContext != nullptr) {
+            if (setProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2)) {
+                return;
+            }
+            if (GetLastError() == ERROR_ACCESS_DENIED) {
+                return;
+            }
+            if (setProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE)) {
+                return;
+            }
+            if (GetLastError() == ERROR_ACCESS_DENIED) {
+                return;
+            }
+        }
+    }
+
+    const HMODULE shcore = LoadLibraryW(L"shcore.dll");
+    if (shcore != nullptr) {
+        using SetProcessDpiAwarenessFn = HRESULT(WINAPI*)(PROCESS_DPI_AWARENESS);
+        const auto setProcessDpiAwareness =
+            reinterpret_cast<SetProcessDpiAwarenessFn>(
+                GetProcAddress(shcore, "SetProcessDpiAwareness"));
+        if (setProcessDpiAwareness != nullptr) {
+            const HRESULT hr = setProcessDpiAwareness(PROCESS_PER_MONITOR_DPI_AWARE);
+            FreeLibrary(shcore);
+            if (SUCCEEDED(hr) || hr == E_ACCESSDENIED) {
+                return;
+            }
+        } else {
+            FreeLibrary(shcore);
+        }
+    }
+
+    if (user32 != nullptr) {
+        using SetProcessDPIAwareFn = BOOL(WINAPI*)();
+        const auto setProcessDPIAware =
+            reinterpret_cast<SetProcessDPIAwareFn>(GetProcAddress(user32, "SetProcessDPIAware"));
+        if (setProcessDPIAware != nullptr) {
+            setProcessDPIAware();
+        }
+    }
+}
+
+void TryEnableNonClientDpiScaling(HWND hwnd) {
+    if (hwnd == nullptr) {
+        return;
+    }
+
+    const HMODULE user32 = GetModuleHandleW(L"user32.dll");
+    if (user32 == nullptr) {
+        return;
+    }
+
+    using EnableNonClientDpiScalingFn = BOOL(WINAPI*)(HWND);
+    const auto enableNonClientDpiScaling =
+        reinterpret_cast<EnableNonClientDpiScalingFn>(
+            GetProcAddress(user32, "EnableNonClientDpiScaling"));
+    if (enableNonClientDpiScaling != nullptr) {
+        enableNonClientDpiScaling(hwnd);
+    }
+}
+
 std::string TruncateText(const std::string& text, std::size_t maxLength) {
     if (text.size() <= maxLength) {
         return text;
@@ -146,6 +251,44 @@ bool IsRepeatKeyMessage(LPARAM lParam) {
     return (static_cast<unsigned long>(lParam) & (1ul << 30)) != 0ul;
 }
 
+std::filesystem::path GetExecutableDirectory() {
+    std::vector<wchar_t> buffer(MAX_PATH);
+    while (true) {
+        const DWORD copied = ::GetModuleFileNameW(
+            nullptr,
+            buffer.data(),
+            static_cast<DWORD>(buffer.size()));
+        if (copied == 0u) {
+            return std::filesystem::current_path().lexically_normal();
+        }
+
+        if (copied < buffer.size() - 1u) {
+            return std::filesystem::path(std::wstring(buffer.data(), copied))
+                .parent_path()
+                .lexically_normal();
+        }
+
+        buffer.resize(buffer.size() * 2u);
+    }
+}
+
+std::string DescribeInputEventType(const UIInputEvent& event) {
+    switch (event.type) {
+    case UIInputEventType::PointerMove: return "PointerMove";
+    case UIInputEventType::PointerEnter: return "PointerEnter";
+    case UIInputEventType::PointerLeave: return "PointerLeave";
+    case UIInputEventType::PointerButtonDown: return "PointerDown";
+    case UIInputEventType::PointerButtonUp: return "PointerUp";
+    case UIInputEventType::PointerWheel: return "PointerWheel";
+    case UIInputEventType::KeyDown: return "KeyDown";
+    case UIInputEventType::KeyUp: return "KeyUp";
+    case UIInputEventType::Character: return "Character";
+    case UIInputEventType::FocusGained: return "FocusGained";
+    case UIInputEventType::FocusLost: return "FocusLost";
+    default: return "Unknown";
+    }
+}
+
 } // namespace
 
 int Application::Run(HINSTANCE hInstance, int nCmdShow) {
@@ -172,10 +315,17 @@ int Application::Run(HINSTANCE hInstance, int nCmdShow) {
 
 bool Application::Initialize(HINSTANCE hInstance, int nCmdShow) {
     m_hInstance = hInstance;
+    EnableDpiAwareness();
+    const std::filesystem::path logRoot =
+        GetExecutableDirectory() / "logs";
+    InitializeUIEditorRuntimeTrace(logRoot);
+    SetUnhandledExceptionFilter(&Application::HandleUnhandledException);
+    LogRuntimeTrace("app", "initialize begin");
     m_shellAsset = BuildProductShellAsset(ResolveRepoRootPath());
     m_shellValidation = ValidateEditorShellAsset(m_shellAsset);
     m_validationMessage = m_shellValidation.message;
     if (!m_shellValidation.IsValid()) {
+        LogRuntimeTrace("app", "shell asset validation failed: " + m_validationMessage);
         return false;
     }
 
@@ -188,8 +338,10 @@ bool Application::Initialize(HINSTANCE hInstance, int nCmdShow) {
     m_shellServices = {};
     m_shellServices.commandDispatcher = &m_shortcutManager.GetCommandDispatcher();
     m_shellServices.shortcutManager = &m_shortcutManager;
+    m_shellServices.textMeasurer = &m_renderer;
     m_lastStatus = "Ready";
     m_lastMessage = "Old editor shell baseline loaded.";
+    LogRuntimeTrace("app", "workspace initialized: " + DescribeWorkspaceState());
 
     WNDCLASSEXW windowClass = {};
     windowClass.cbSize = sizeof(windowClass);
@@ -200,6 +352,7 @@ bool Application::Initialize(HINSTANCE hInstance, int nCmdShow) {
     windowClass.lpszClassName = kWindowClassName;
     m_windowClassAtom = RegisterClassExW(&windowClass);
     if (m_windowClassAtom == 0) {
+        LogRuntimeTrace("app", "window class registration failed");
         return false;
     }
 
@@ -207,7 +360,7 @@ bool Application::Initialize(HINSTANCE hInstance, int nCmdShow) {
         0,
         kWindowClassName,
         kWindowTitle,
-        WS_OVERLAPPEDWINDOW | WS_VISIBLE,
+        WS_OVERLAPPEDWINDOW,
         CW_USEDEFAULT,
         CW_USEDEFAULT,
         1540,
@@ -217,26 +370,37 @@ bool Application::Initialize(HINSTANCE hInstance, int nCmdShow) {
         hInstance,
         this);
     if (m_hwnd == nullptr) {
+        LogRuntimeTrace("app", "window creation failed");
+        return false;
+    }
+    m_windowDpi = QueryWindowDpi(m_hwnd);
+    m_dpiScale = GetDpiScale();
+    m_renderer.SetDpiScale(m_dpiScale);
+
+    std::ostringstream dpiTrace = {};
+    dpiTrace << "initial dpi=" << m_windowDpi << " scale=" << m_dpiScale;
+    LogRuntimeTrace("window", dpiTrace.str());
+
+    if (!m_renderer.Initialize(m_hwnd)) {
+        LogRuntimeTrace("app", "renderer initialization failed");
         return false;
     }
 
     ShowWindow(m_hwnd, nCmdShow);
     UpdateWindow(m_hwnd);
 
-    if (!m_renderer.Initialize(m_hwnd)) {
-        return false;
-    }
-
     m_autoScreenshot.Initialize(m_shellAsset.captureRootPath);
     if (IsAutoCaptureOnStartupEnabled()) {
         m_autoScreenshot.RequestCapture("startup");
         m_lastStatus = "Capture";
         m_lastMessage = "Startup capture requested.";
     }
+    LogRuntimeTrace("app", "initialize completed");
     return true;
 }
 
 void Application::Shutdown() {
+    LogRuntimeTrace("app", "shutdown begin");
     if (GetCapture() == m_hwnd) {
         ReleaseCapture();
     }
@@ -253,6 +417,9 @@ void Application::Shutdown() {
         UnregisterClassW(kWindowClassName, m_hInstance);
         m_windowClassAtom = 0;
     }
+
+    LogRuntimeTrace("app", "shutdown end");
+    ShutdownUIEditorRuntimeTrace();
 }
 
 void Application::RenderFrame() {
@@ -262,8 +429,12 @@ void Application::RenderFrame() {
 
     RECT clientRect = {};
     GetClientRect(m_hwnd, &clientRect);
-    const float width = static_cast<float>((std::max)(clientRect.right - clientRect.left, 1L));
-    const float height = static_cast<float>((std::max)(clientRect.bottom - clientRect.top, 1L));
+    const unsigned int pixelWidth =
+        static_cast<unsigned int>((std::max)(clientRect.right - clientRect.left, 1L));
+    const unsigned int pixelHeight =
+        static_cast<unsigned int>((std::max)(clientRect.bottom - clientRect.top, 1L));
+    const float width = PixelsToDips(static_cast<float>(pixelWidth));
+    const float height = PixelsToDips(static_cast<float>(pixelHeight));
 
     UIDrawData drawData = {};
     UIDrawList& drawList = drawData.EmplaceDrawList("XCEditorShell");
@@ -277,6 +448,11 @@ void Application::RenderFrame() {
         const UIEditorShellInteractionDefinition definition = BuildShellDefinition();
         std::vector<UIInputEvent> frameEvents = std::move(m_pendingInputEvents);
         m_pendingInputEvents.clear();
+        if (!frameEvents.empty()) {
+            LogRuntimeTrace(
+                "input",
+                DescribeInputEvents(frameEvents) + " | " + DescribeWorkspaceState());
+        }
 
         m_shellFrame = UpdateUIEditorShellInteraction(
             m_shellInteractionState,
@@ -286,6 +462,24 @@ void Application::RenderFrame() {
             frameEvents,
             m_shellServices,
             metrics);
+        if (!frameEvents.empty() ||
+            m_shellFrame.result.workspaceResult.dockHostResult.layoutChanged ||
+            m_shellFrame.result.workspaceResult.dockHostResult.commandExecuted) {
+            std::ostringstream frameTrace = {};
+            frameTrace << "result consumed="
+                       << (m_shellFrame.result.consumed ? "true" : "false")
+                       << " layoutChanged="
+                       << (m_shellFrame.result.workspaceResult.dockHostResult.layoutChanged ? "true" : "false")
+                       << " commandExecuted="
+                       << (m_shellFrame.result.workspaceResult.dockHostResult.commandExecuted ? "true" : "false")
+                       << " active="
+                       << m_workspaceController.GetWorkspace().activePanelId
+                       << " message="
+                       << m_shellFrame.result.workspaceResult.dockHostResult.layoutResult.message;
+            LogRuntimeTrace(
+                "frame",
+                frameTrace.str());
+        }
         ApplyHostCaptureRequests(m_shellFrame.result);
         UpdateLastStatus(m_shellFrame.result);
         AppendUIEditorShellInteraction(
@@ -311,11 +505,78 @@ void Application::RenderFrame() {
     m_autoScreenshot.CaptureIfRequested(
         m_renderer,
         drawData,
-        static_cast<unsigned int>(width),
-        static_cast<unsigned int>(height),
+        pixelWidth,
+        pixelHeight,
         framePresented);
 }
 
+float Application::GetDpiScale() const {
+    const UINT dpi = m_windowDpi == 0u ? kDefaultDpi : m_windowDpi;
+    return static_cast<float>(dpi) / kBaseDpiScale;
+}
+
+float Application::PixelsToDips(float pixels) const {
+    const float dpiScale = GetDpiScale();
+    return dpiScale > 0.0f ? pixels / dpiScale : pixels;
+}
+
+UIPoint Application::ConvertClientPixelsToDips(LONG x, LONG y) const {
+    return UIPoint(
+        PixelsToDips(static_cast<float>(x)),
+        PixelsToDips(static_cast<float>(y)));
+}
+
+void Application::LogRuntimeTrace(
+    std::string_view channel,
+    std::string_view message) const {
+    AppendUIEditorRuntimeTrace(channel, message);
+}
+
+std::string Application::DescribeWorkspaceState() const {
+    std::ostringstream stream = {};
+    stream << "active=" << m_workspaceController.GetWorkspace().activePanelId;
+    const auto visiblePanels =
+        CollectUIEditorWorkspaceVisiblePanels(
+            m_workspaceController.GetWorkspace(),
+            m_workspaceController.GetSession());
+    stream << " visible=[";
+    for (std::size_t index = 0; index < visiblePanels.size(); ++index) {
+        if (index > 0u) {
+            stream << ',';
+        }
+        stream << visiblePanels[index].panelId;
+    }
+    stream << ']';
+
+    const auto& dockState =
+        m_shellInteractionState.workspaceInteractionState.dockHostInteractionState;
+    stream << " dragNode=" << dockState.activeTabDragNodeId;
+    stream << " dragPanel=" << dockState.activeTabDragPanelId;
+    if (dockState.dockHostState.dropPreview.visible) {
+        stream << " dropTarget=" << dockState.dockHostState.dropPreview.targetNodeId;
+    }
+    return stream.str();
+}
+
+std::string Application::DescribeInputEvents(
+    const std::vector<UIInputEvent>& events) const {
+    std::ostringstream stream = {};
+    stream << "events=[";
+    for (std::size_t index = 0; index < events.size(); ++index) {
+        if (index > 0u) {
+            stream << " | ";
+        }
+        const UIInputEvent& event = events[index];
+        stream << DescribeInputEventType(event)
+               << '@'
+               << static_cast<int>(event.position.x)
+               << ','
+               << static_cast<int>(event.position.y);
+    }
+    stream << ']';
+    return stream.str();
+}
+
 void Application::OnResize(UINT width, UINT height) {
     if (width == 0 || height == 0) {
         return;
@@ -324,6 +585,27 @@ void Application::OnResize(UINT width, UINT height) {
     m_renderer.Resize(width, height);
 }
 
+void Application::OnDpiChanged(UINT dpi, const RECT& suggestedRect) {
+    m_windowDpi = dpi == 0u ? kDefaultDpi : dpi;
+    m_dpiScale = GetDpiScale();
+    m_renderer.SetDpiScale(m_dpiScale);
+    if (m_hwnd != nullptr) {
+        SetWindowPos(
+            m_hwnd,
+            nullptr,
+            suggestedRect.left,
+            suggestedRect.top,
+            suggestedRect.right - suggestedRect.left,
+            suggestedRect.bottom - suggestedRect.top,
+            SWP_NOZORDER | SWP_NOACTIVATE);
+        InvalidateRect(m_hwnd, nullptr, FALSE);
+    }
+
+    std::ostringstream trace = {};
+    trace << "dpi changed to " << m_windowDpi << " scale=" << m_dpiScale;
+    LogRuntimeTrace("window", trace.str());
+}
+
 void Application::ApplyHostCaptureRequests(const UIEditorShellInteractionResult& result) {
     if (result.requestPointerCapture && GetCapture() != m_hwnd) {
         SetCapture(m_hwnd);
@@ -338,6 +620,10 @@ bool Application::HasInteractiveCaptureState() const {
         return true;
     }
 
+    if (!m_shellInteractionState.workspaceInteractionState.dockHostInteractionState.activeTabDragNodeId.empty()) {
+        return true;
+    }
+
     for (const auto& panelState : m_shellInteractionState.workspaceInteractionState.composeState.panelStates) {
         if (panelState.viewportShellState.inputBridgeState.captured) {
             return true;
@@ -434,9 +720,9 @@ void Application::QueuePointerEvent(
     UIInputEvent event = {};
     event.type = type;
     event.pointerButton = button;
-    event.position = UIPoint(
-        static_cast<float>(GET_X_LPARAM(lParam)),
-        static_cast<float>(GET_Y_LPARAM(lParam)));
+    event.position = ConvertClientPixelsToDips(
+        GET_X_LPARAM(lParam),
+        GET_Y_LPARAM(lParam));
     event.modifiers = m_inputModifierTracker.BuildPointerModifiers(static_cast<std::size_t>(wParam));
     m_pendingInputEvents.push_back(event);
 }
@@ -448,9 +734,7 @@ void Application::QueuePointerLeaveEvent() {
         POINT clientPoint = {};
         GetCursorPos(&clientPoint);
         ScreenToClient(m_hwnd, &clientPoint);
-        event.position = UIPoint(
-            static_cast<float>(clientPoint.x),
-            static_cast<float>(clientPoint.y));
+        event.position = ConvertClientPixelsToDips(clientPoint.x, clientPoint.y);
     }
     m_pendingInputEvents.push_back(event);
 }
@@ -468,9 +752,7 @@ void Application::QueuePointerWheelEvent(short wheelDelta, WPARAM wParam, LPARAM
 
     UIInputEvent event = {};
     event.type = UIInputEventType::PointerWheel;
-    event.position = UIPoint(
-        static_cast<float>(screenPoint.x),
-        static_cast<float>(screenPoint.y));
+    event.position = ConvertClientPixelsToDips(screenPoint.x, screenPoint.y);
     event.wheelDelta = static_cast<float>(wheelDelta);
     event.modifiers = m_inputModifierTracker.BuildPointerModifiers(static_cast<std::size_t>(wParam));
     m_pendingInputEvents.push_back(event);
@@ -507,6 +789,19 @@ std::filesystem::path Application::ResolveRepoRootPath() {
     return std::filesystem::path(root).lexically_normal();
 }
 
+LONG WINAPI Application::HandleUnhandledException(EXCEPTION_POINTERS* exceptionInfo) {
+    if (exceptionInfo != nullptr &&
+        exceptionInfo->ExceptionRecord != nullptr) {
+        AppendUIEditorCrashTrace(
+            exceptionInfo->ExceptionRecord->ExceptionCode,
+            exceptionInfo->ExceptionRecord->ExceptionAddress);
+    } else {
+        AppendUIEditorCrashTrace(0u, nullptr);
+    }
+
+    return EXCEPTION_EXECUTE_HANDLER;
+}
+
 UIEditorHostCommandEvaluationResult Application::EvaluateHostCommand(
     std::string_view commandId) const {
     UIEditorHostCommandEvaluationResult result = {};
@@ -573,6 +868,7 @@ UIEditorHostCommandDispatchResult Application::DispatchHostCommand(
 
 LRESULT CALLBACK Application::WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) {
     if (message == WM_NCCREATE) {
+        TryEnableNonClientDpiScaling(hwnd);
         const auto* createStruct = reinterpret_cast<CREATESTRUCTW*>(lParam);
         auto* application = reinterpret_cast<Application*>(createStruct->lpCreateParams);
         SetWindowLongPtrW(hwnd, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(application));
@@ -581,6 +877,14 @@ LRESULT CALLBACK Application::WndProc(HWND hwnd, UINT message, WPARAM wParam, LP
 
     Application* application = GetApplicationFromWindow(hwnd);
     switch (message) {
+    case WM_DPICHANGED:
+        if (application != nullptr && lParam != 0) {
+            application->OnDpiChanged(
+                static_cast<UINT>(LOWORD(wParam)),
+                *reinterpret_cast<RECT*>(lParam));
+            return 0;
+        }
+        break;
     case WM_SIZE:
         if (application != nullptr && wParam != SIZE_MINIMIZED) {
             application->OnResize(static_cast<UINT>(LOWORD(lParam)), static_cast<UINT>(HIWORD(lParam)));

new_editor/app/Application.h

@@ -42,10 +42,18 @@ private:
     void Shutdown();
     void RenderFrame();
     void OnResize(UINT width, UINT height);
+    void OnDpiChanged(UINT dpi, const RECT& suggestedRect);
+    float GetDpiScale() const;
+    float PixelsToDips(float pixels) const;
+    ::XCEngine::UI::UIPoint ConvertClientPixelsToDips(LONG x, LONG y) const;
+    void LogRuntimeTrace(std::string_view channel, std::string_view message) const;
     void ApplyHostCaptureRequests(const UIEditorShellInteractionResult& result);
     bool HasInteractiveCaptureState() const;
     UIEditorShellInteractionDefinition BuildShellDefinition() const;
     void UpdateLastStatus(const UIEditorShellInteractionResult& result);
+    std::string DescribeWorkspaceState() const;
+    std::string DescribeInputEvents(
+        const std::vector<::XCEngine::UI::UIInputEvent>& events) const;
     void QueuePointerEvent(
         ::XCEngine::UI::UIInputEventType type,
         ::XCEngine::UI::UIPointerButton button,
@@ -57,6 +65,7 @@ private:
     void QueueCharacterEvent(WPARAM wParam, LPARAM lParam);
     void QueueWindowFocusEvent(::XCEngine::UI::UIInputEventType type);
     static std::filesystem::path ResolveRepoRootPath();
+    static LONG WINAPI HandleUnhandledException(EXCEPTION_POINTERS* exceptionInfo);
 
     HWND m_hwnd = nullptr;
     HINSTANCE m_hInstance = nullptr;
@@ -76,6 +85,8 @@ private:
     std::string m_validationMessage = {};
     std::string m_lastStatus = {};
     std::string m_lastMessage = {};
+    UINT m_windowDpi = 96u;
+    float m_dpiScale = 1.0f;
 };
 
 int RunXCUIEditorApp(HINSTANCE hInstance, int nCmdShow);

new_editor/include/XCEditor/Collections/UIEditorTabStrip.h

@@ -22,11 +22,21 @@ struct UIEditorTabStripItem {
     float desiredHeaderLabelWidth = 0.0f;
 };
 
+struct UIEditorTabStripReorderState {
+    ::XCEngine::UI::UIPoint pressPosition = {};
+    std::size_t pressedIndex = UIEditorTabStripInvalidIndex;
+    std::size_t sourceIndex = UIEditorTabStripInvalidIndex;
+    std::size_t previewInsertionIndex = UIEditorTabStripInvalidIndex;
+    bool armed = false;
+    bool dragging = false;
+};
+
 struct UIEditorTabStripState {
     std::size_t selectedIndex = UIEditorTabStripInvalidIndex;
     std::size_t hoveredIndex = UIEditorTabStripInvalidIndex;
     std::size_t closeHoveredIndex = UIEditorTabStripInvalidIndex;
     bool focused = false;
+    UIEditorTabStripReorderState reorder = {};
 };
 
 struct UIEditorTabStripMetrics {
@@ -38,21 +48,26 @@ struct UIEditorTabStripMetrics {
     float closeInsetRight = 6.0f;
     float closeInsetY = 0.0f;
     float labelInsetX = 8.0f;
-    float labelInsetY = -2.5f;
+    float labelInsetY = -0.5f;
     float baseBorderThickness = 1.0f;
     float selectedBorderThickness = 1.0f;
     float focusedBorderThickness = 1.0f;
+    float reorderDragThreshold = 6.0f;
+    float reorderPreviewThickness = 2.0f;
+    float reorderPreviewInsetY = 3.0f;
 };
 
 struct UIEditorTabStripPalette {
     ::XCEngine::UI::UIColor stripBackgroundColor =
-        ::XCEngine::UI::UIColor(0.16f, 0.16f, 0.16f, 1.0f);
+        ::XCEngine::UI::UIColor(0.18f, 0.18f, 0.18f, 1.0f);
     ::XCEngine::UI::UIColor headerBackgroundColor =
         ::XCEngine::UI::UIColor(0.18f, 0.18f, 0.18f, 1.0f);
     ::XCEngine::UI::UIColor contentBackgroundColor =
-        ::XCEngine::UI::UIColor(0.17f, 0.17f, 0.17f, 1.0f);
+        ::XCEngine::UI::UIColor(0.18f, 0.18f, 0.18f, 1.0f);
     ::XCEngine::UI::UIColor stripBorderColor =
         ::XCEngine::UI::UIColor(0.24f, 0.24f, 0.24f, 1.0f);
+    ::XCEngine::UI::UIColor headerContentSeparatorColor =
+        ::XCEngine::UI::UIColor(0.27f, 0.27f, 0.27f, 1.0f);
     ::XCEngine::UI::UIColor focusedBorderColor =
         ::XCEngine::UI::UIColor(0.36f, 0.36f, 0.36f, 1.0f);
     ::XCEngine::UI::UIColor tabColor =
@@ -60,7 +75,7 @@ struct UIEditorTabStripPalette {
     ::XCEngine::UI::UIColor tabHoveredColor =
         ::XCEngine::UI::UIColor(0.23f, 0.23f, 0.23f, 1.0f);
     ::XCEngine::UI::UIColor tabSelectedColor =
-        ::XCEngine::UI::UIColor(0.22f, 0.22f, 0.22f, 1.0f);
+        ::XCEngine::UI::UIColor(0.18f, 0.18f, 0.18f, 1.0f);
     ::XCEngine::UI::UIColor tabBorderColor =
         ::XCEngine::UI::UIColor(0.24f, 0.24f, 0.24f, 1.0f);
     ::XCEngine::UI::UIColor tabHoveredBorderColor =
@@ -81,6 +96,14 @@ struct UIEditorTabStripPalette {
         ::XCEngine::UI::UIColor(0.30f, 0.30f, 0.30f, 1.0f);
     ::XCEngine::UI::UIColor closeGlyphColor =
         ::XCEngine::UI::UIColor(0.83f, 0.83f, 0.83f, 1.0f);
+    ::XCEngine::UI::UIColor reorderPreviewColor =
+        ::XCEngine::UI::UIColor(0.82f, 0.82f, 0.82f, 1.0f);
+};
+
+struct UIEditorTabStripInsertionPreview {
+    bool visible = false;
+    std::size_t insertionIndex = UIEditorTabStripInvalidIndex;
+    ::XCEngine::UI::UIRect indicatorRect = {};
 };
 
 struct UIEditorTabStripLayout {
@@ -91,6 +114,7 @@ struct UIEditorTabStripLayout {
     std::vector<::XCEngine::UI::UIRect> closeButtonRects = {};
     std::vector<bool> showCloseButtons = {};
     std::size_t selectedIndex = UIEditorTabStripInvalidIndex;
+    UIEditorTabStripInsertionPreview insertionPreview = {};
 };
 
 enum class UIEditorTabStripHitTargetKind : std::uint8_t {

new_editor/include/XCEditor/Collections/UIEditorTabStripInteraction.h

@@ -3,6 +3,7 @@
 #include <XCEditor/Collections/UIEditorTabStrip.h>
 
 #include <XCEngine/UI/DrawData.h>
+#include <XCEngine/UI/Widgets/UIDragDropInteraction.h>
 #include <XCEngine/UI/Widgets/UITabStripModel.h>
 
 #include <string>
@@ -13,9 +14,13 @@ namespace XCEngine::UI::Editor {
 struct UIEditorTabStripInteractionState {
     Widgets::UIEditorTabStripState tabStripState = {};
     ::XCEngine::UI::Widgets::UITabStripModel navigationModel = {};
+    ::XCEngine::UI::Widgets::UIDragDropState reorderDragState = {};
     Widgets::UIEditorTabStripHitTarget pressedTarget = {};
     ::XCEngine::UI::UIPoint pointerPosition = {};
+    std::size_t reorderSourceIndex = Widgets::UIEditorTabStripInvalidIndex;
+    std::size_t reorderPreviewIndex = Widgets::UIEditorTabStripInvalidIndex;
     bool hasPointerPosition = false;
+    bool reorderCaptureActive = false;
 };
 
 struct UIEditorTabStripInteractionResult {
@@ -23,11 +28,23 @@ struct UIEditorTabStripInteractionResult {
     bool selectionChanged = false;
     bool closeRequested = false;
     bool keyboardNavigated = false;
+    bool requestPointerCapture = false;
+    bool releasePointerCapture = false;
+    bool dragStarted = false;
+    bool dragEnded = false;
+    bool dragCanceled = false;
+    bool reorderRequested = false;
+    bool reorderPreviewActive = false;
     Widgets::UIEditorTabStripHitTarget hitTarget = {};
     std::string selectedTabId = {};
     std::size_t selectedIndex = Widgets::UIEditorTabStripInvalidIndex;
     std::string closedTabId = {};
     std::size_t closedIndex = Widgets::UIEditorTabStripInvalidIndex;
+    std::string draggedTabId = {};
+    std::size_t dragSourceIndex = Widgets::UIEditorTabStripInvalidIndex;
+    std::size_t dropInsertionIndex = Widgets::UIEditorTabStripInvalidIndex;
+    std::size_t reorderToIndex = Widgets::UIEditorTabStripInvalidIndex;
+    std::size_t reorderPreviewIndex = Widgets::UIEditorTabStripInvalidIndex;
 };
 
 struct UIEditorTabStripInteractionFrame {

new_editor/include/XCEditor/Foundation/UIEditorRuntimeTrace.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <cstdint>
+#include <filesystem>
+#include <string_view>
+
+namespace XCEngine::UI::Editor {
+
+void InitializeUIEditorRuntimeTrace(const std::filesystem::path& logRoot);
+void ShutdownUIEditorRuntimeTrace();
+
+void AppendUIEditorRuntimeTrace(
+    std::string_view channel,
+    std::string_view message);
+
+void AppendUIEditorCrashTrace(
+    std::uint32_t exceptionCode,
+    const void* exceptionAddress);
+
+std::filesystem::path GetUIEditorRuntimeTracePath();
+std::filesystem::path GetUIEditorCrashTracePath();
+
+} // namespace XCEngine::UI::Editor

new_editor/include/XCEditor/Foundation/UIEditorTextMeasurement.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include <string_view>
+
+namespace XCEngine::UI::Editor {
+
+struct UIEditorTextMeasureRequest {
+    std::string_view text = {};
+    float fontSize = 0.0f;
+};
+
+class UIEditorTextMeasurer {
+public:
+    virtual ~UIEditorTextMeasurer() = default;
+
+    virtual float MeasureTextWidth(const UIEditorTextMeasureRequest& request) const = 0;
+};
+
+} // namespace XCEngine::UI::Editor

new_editor/include/XCEditor/Shell/UIEditorDockHost.h

@@ -40,16 +40,27 @@ struct UIEditorDockHostTabStripVisualState {
     UIEditorTabStripState state = {};
 };
 
+struct UIEditorDockHostDropPreviewState {
+    bool visible = false;
+    std::string sourceNodeId = {};
+    std::string sourcePanelId = {};
+    std::string targetNodeId = {};
+    UIEditorWorkspaceDockPlacement placement =
+        UIEditorWorkspaceDockPlacement::Center;
+    std::size_t insertionIndex = UIEditorTabStripInvalidIndex;
+};
+
 struct UIEditorDockHostState {
     bool focused = false;
     UIEditorDockHostHitTarget hoveredTarget = {};
     std::string activeSplitterNodeId = {};
     std::vector<UIEditorDockHostTabStripVisualState> tabStripStates = {};
+    UIEditorDockHostDropPreviewState dropPreview = {};
 };
 
 struct UIEditorDockHostMetrics {
     ::XCEngine::UI::Layout::UISplitterMetrics splitterMetrics =
-        ::XCEngine::UI::Layout::UISplitterMetrics{ 4.0f, 12.0f };
+        ::XCEngine::UI::Layout::UISplitterMetrics{ 1.0f, 10.0f };
     UIEditorTabStripMetrics tabStripMetrics = {};
     UIEditorPanelFrameMetrics panelFrameMetrics = {};
     ::XCEngine::UI::UISize minimumStandalonePanelBodySize =
@@ -75,6 +86,10 @@ struct UIEditorDockHostPalette {
         ::XCEngine::UI::UIColor(0.70f, 0.72f, 0.74f, 1.0f);
     ::XCEngine::UI::UIColor placeholderMutedColor =
         ::XCEngine::UI::UIColor(0.58f, 0.59f, 0.62f, 1.0f);
+    ::XCEngine::UI::UIColor dropPreviewFillColor =
+        ::XCEngine::UI::UIColor(0.88f, 0.88f, 0.88f, 0.14f);
+    ::XCEngine::UI::UIColor dropPreviewBorderColor =
+        ::XCEngine::UI::UIColor(0.94f, 0.94f, 0.94f, 0.78f);
 };
 
 struct UIEditorDockHostTabItemLayout {
@@ -107,10 +122,20 @@ struct UIEditorDockHostTabStackLayout {
     UIEditorPanelFrameLayout contentFrameLayout = {};
 };
 
+struct UIEditorDockHostDropPreviewLayout {
+    bool visible = false;
+    std::string targetNodeId = {};
+    UIEditorWorkspaceDockPlacement placement =
+        UIEditorWorkspaceDockPlacement::Center;
+    std::size_t insertionIndex = UIEditorTabStripInvalidIndex;
+    ::XCEngine::UI::UIRect previewRect = {};
+};
+
 struct UIEditorDockHostLayout {
     ::XCEngine::UI::UIRect bounds = {};
     std::vector<UIEditorDockHostSplitterLayout> splitters = {};
     std::vector<UIEditorDockHostTabStackLayout> tabStacks = {};
+    UIEditorDockHostDropPreviewLayout dropPreview = {};
 };
 
 // Allows higher-level compose to own panel body presentation while DockHost

new_editor/include/XCEditor/Shell/UIEditorDockHostInteraction.h

@@ -21,6 +21,8 @@ struct UIEditorDockHostInteractionState {
     Widgets::UIEditorDockHostState dockHostState = {};
     ::XCEngine::UI::Widgets::UISplitterDragState splitterDragState = {};
     std::vector<UIEditorDockHostTabStripInteractionEntry> tabStripInteractions = {};
+    std::string activeTabDragNodeId = {};
+    std::string activeTabDragPanelId = {};
     ::XCEngine::UI::UIPoint pointerPosition = {};
     bool hasPointerPosition = false;
 };

new_editor/include/XCEditor/Shell/UIEditorMenuBar.h

@@ -29,12 +29,13 @@ struct UIEditorMenuBarMetrics {
     float barHeight = 24.0f;
     float horizontalInset = 0.0f;
     float verticalInset = 2.0f;
-    float buttonGap = 2.0f;
-    float buttonPaddingX = 10.0f;
+    float buttonGap = 1.0f;
+    float buttonPaddingX = 4.0f;
+    float labelFontSize = 13.0f;
     float estimatedGlyphWidth = 6.5f;
     float labelInsetY = -1.5f;
     float barCornerRounding = 0.0f;
-    float buttonCornerRounding = 0.0f;
+    float buttonCornerRounding = 0.75f;
     float baseBorderThickness = 1.0f;
     float focusedBorderThickness = 1.0f;
     float openBorderThickness = 1.0f;
@@ -42,23 +43,23 @@ struct UIEditorMenuBarMetrics {
 
 struct UIEditorMenuBarPalette {
     ::XCEngine::UI::UIColor barColor =
-        ::XCEngine::UI::UIColor(0.14f, 0.14f, 0.14f, 1.0f);
+        ::XCEngine::UI::UIColor(1.0f, 1.0f, 1.0f, 1.0f);
     ::XCEngine::UI::UIColor buttonColor =
-        ::XCEngine::UI::UIColor(0.18f, 0.18f, 0.18f, 1.0f);
+        ::XCEngine::UI::UIColor(0.0f, 0.0f, 0.0f, 0.0f);
     ::XCEngine::UI::UIColor buttonHoveredColor =
-        ::XCEngine::UI::UIColor(0.23f, 0.23f, 0.23f, 1.0f);
+        ::XCEngine::UI::UIColor(0.88f, 0.88f, 0.88f, 1.0f);
     ::XCEngine::UI::UIColor buttonOpenColor =
-        ::XCEngine::UI::UIColor(0.28f, 0.28f, 0.28f, 1.0f);
+        ::XCEngine::UI::UIColor(0.84f, 0.84f, 0.84f, 1.0f);
     ::XCEngine::UI::UIColor borderColor =
-        ::XCEngine::UI::UIColor(0.24f, 0.24f, 0.24f, 1.0f);
+        ::XCEngine::UI::UIColor(0.0f, 0.0f, 0.0f, 0.0f);
     ::XCEngine::UI::UIColor focusedBorderColor =
-        ::XCEngine::UI::UIColor(0.38f, 0.38f, 0.38f, 1.0f);
+        ::XCEngine::UI::UIColor(0.0f, 0.0f, 0.0f, 0.0f);
     ::XCEngine::UI::UIColor openBorderColor =
-        ::XCEngine::UI::UIColor(0.34f, 0.34f, 0.34f, 1.0f);
+        ::XCEngine::UI::UIColor(0.0f, 0.0f, 0.0f, 0.0f);
     ::XCEngine::UI::UIColor textPrimary =
-        ::XCEngine::UI::UIColor(0.85f, 0.85f, 0.85f, 1.0f);
+        ::XCEngine::UI::UIColor(0.08f, 0.08f, 0.08f, 1.0f);
     ::XCEngine::UI::UIColor textMuted =
-        ::XCEngine::UI::UIColor(0.67f, 0.67f, 0.67f, 1.0f);
+        ::XCEngine::UI::UIColor(0.28f, 0.28f, 0.28f, 1.0f);
     ::XCEngine::UI::UIColor textDisabled =
         ::XCEngine::UI::UIColor(0.50f, 0.50f, 0.50f, 1.0f);
 };

new_editor/include/XCEditor/Shell/UIEditorMenuPopup.h

@@ -34,19 +34,19 @@ struct UIEditorMenuPopupState {
 };
 
 struct UIEditorMenuPopupMetrics {
-    float contentPaddingX = 6.0f;
+    float contentPaddingX = 2.0f;
     float contentPaddingY = 6.0f;
     float itemHeight = 28.0f;
     float separatorHeight = 9.0f;
-    float checkColumnWidth = 18.0f;
-    float shortcutGap = 20.0f;
-    float submenuIndicatorWidth = 14.0f;
-    float rowCornerRounding = 5.0f;
-    float popupCornerRounding = 8.0f;
-    float labelInsetX = 14.0f;
+    float checkColumnWidth = 12.0f;
+    float shortcutGap = 14.0f;
+    float submenuIndicatorWidth = 10.0f;
+    float rowCornerRounding = 2.5f;
+    float popupCornerRounding = 4.0f;
+    float labelInsetX = 4.0f;
     float labelInsetY = -1.0f;
     float labelFontSize = 13.0f;
-    float shortcutInsetRight = 24.0f;
+    float shortcutInsetRight = 8.0f;
     float estimatedGlyphWidth = 7.0f;
     float glyphFontSize = 12.0f;
     float separatorThickness = 1.0f;

new_editor/include/XCEditor/Shell/UIEditorShellCompose.h

@@ -110,6 +110,12 @@ struct UIEditorShellComposeFrame {
     UIEditorWorkspaceComposeFrame workspaceFrame = {};
 };
 
+UIEditorShellComposeLayout BuildUIEditorShellComposeLayout(
+    const ::XCEngine::UI::UIRect& bounds,
+    const std::vector<Widgets::UIEditorMenuBarItem>& menuBarItems,
+    const std::vector<Widgets::UIEditorStatusBarSegment>& statusSegments,
+    const UIEditorShellComposeMetrics& metrics = {});
+
 UIEditorShellComposeLayout BuildUIEditorShellComposeLayout(
     const ::XCEngine::UI::UIRect& bounds,
     const std::vector<Widgets::UIEditorMenuBarItem>& menuBarItems,

new_editor/include/XCEditor/Shell/UIEditorShellInteraction.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <XCEditor/Foundation/UIEditorTextMeasurement.h>
 #include <XCEditor/Shell/UIEditorMenuModel.h>
 #include <XCEditor/Shell/UIEditorMenuSession.h>
 #include <XCEditor/Shell/UIEditorShellCompose.h>
@@ -50,6 +51,7 @@ struct UIEditorShellInteractionPalette {
 struct UIEditorShellInteractionServices {
     const UIEditorCommandDispatcher* commandDispatcher = nullptr;
     const UIEditorShortcutManager* shortcutManager = nullptr;
+    const UIEditorTextMeasurer* textMeasurer = nullptr;
 };
 
 struct UIEditorShellInteractionMenuButtonRequest {

new_editor/include/XCEditor/Shell/UIEditorWorkspaceController.h

@@ -105,6 +105,21 @@ public:
     UIEditorWorkspaceLayoutOperationResult SetSplitRatio(
         std::string_view nodeId,
         float splitRatio);
+    UIEditorWorkspaceLayoutOperationResult ReorderTab(
+        std::string_view nodeId,
+        std::string_view panelId,
+        std::size_t targetVisibleInsertionIndex);
+    UIEditorWorkspaceLayoutOperationResult MoveTabToStack(
+        std::string_view sourceNodeId,
+        std::string_view panelId,
+        std::string_view targetNodeId,
+        std::size_t targetVisibleInsertionIndex);
+    UIEditorWorkspaceLayoutOperationResult DockTabRelative(
+        std::string_view sourceNodeId,
+        std::string_view panelId,
+        std::string_view targetNodeId,
+        UIEditorWorkspaceDockPlacement placement,
+        float splitRatio = 0.5f);
     UIEditorWorkspaceCommandResult Dispatch(const UIEditorWorkspaceCommand& command);
 
 private:

new_editor/include/XCEditor/Shell/UIEditorWorkspaceModel.h

@@ -8,6 +8,8 @@
 
 namespace XCEngine::UI::Editor {
 
+struct UIEditorWorkspaceSession;
+
 enum class UIEditorWorkspaceNodeKind : std::uint8_t {
     Panel = 0,
     TabStack,
@@ -19,6 +21,14 @@ enum class UIEditorWorkspaceSplitAxis : std::uint8_t {
     Vertical
 };
 
+enum class UIEditorWorkspaceDockPlacement : std::uint8_t {
+    Center = 0,
+    Left,
+    Right,
+    Top,
+    Bottom
+};
+
 struct UIEditorWorkspacePanelState {
     std::string panelId = {};
     std::string title = {};
@@ -133,4 +143,28 @@ bool TrySetUIEditorWorkspaceSplitRatio(
     std::string_view nodeId,
     float splitRatio);
 
+bool TryReorderUIEditorWorkspaceTab(
+    UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    std::string_view nodeId,
+    std::string_view panelId,
+    std::size_t targetVisibleInsertionIndex);
+
+bool TryMoveUIEditorWorkspaceTabToStack(
+    UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    std::string_view sourceNodeId,
+    std::string_view panelId,
+    std::string_view targetNodeId,
+    std::size_t targetVisibleInsertionIndex);
+
+bool TryDockUIEditorWorkspaceTabRelative(
+    UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    std::string_view sourceNodeId,
+    std::string_view panelId,
+    std::string_view targetNodeId,
+    UIEditorWorkspaceDockPlacement placement,
+    float splitRatio = 0.5f);
+
 } // namespace XCEngine::UI::Editor

new_editor/src/Collections/UIEditorTabStrip.cpp

@@ -18,8 +18,7 @@ using ::XCEngine::UI::Layout::MeasureUITabStripHeaderWidth;
 
 constexpr float kTabRounding = 0.0f;
 constexpr float kStripRounding = 0.0f;
-constexpr float kHeaderFontSize = 11.0f;
-constexpr float kCloseFontSize = 10.0f;
+constexpr float kHeaderFontSize = 13.0f;
 
 float ClampNonNegative(float value) {
     return (std::max)(value, 0.0f);
@@ -44,10 +43,6 @@ float ResolveTabRounding(const UIEditorTabStripMetrics& metrics) {
     return kTabRounding;
 }
 
-float ResolveCloseButtonRounding(const UIEditorTabStripMetrics& metrics) {
-    return (std::min)(ClampNonNegative(metrics.closeButtonExtent) * 0.2f, 2.0f);
-}
-
 std::size_t ResolveSelectedIndex(
     std::size_t itemCount,
     std::size_t selectedIndex) {
@@ -78,20 +73,18 @@ float ResolveTabTextTop(
     return rect.y + (std::max)(0.0f, (rect.height - kHeaderFontSize) * 0.5f) + metrics.labelInsetY;
 }
 
-float ResolveCloseTextTop(const UIRect& rect) {
-    return rect.y + (std::max)(0.0f, (rect.height - kCloseFontSize) * 0.5f) - 0.5f;
-}
-
 UIColor ResolveStripBorderColor(
     const UIEditorTabStripState& state,
     const UIEditorTabStripPalette& palette) {
-    return state.focused ? palette.focusedBorderColor : palette.stripBorderColor;
+    (void)state;
+    return palette.stripBorderColor;
 }
 
 float ResolveStripBorderThickness(
     const UIEditorTabStripState& state,
     const UIEditorTabStripMetrics& metrics) {
-    return state.focused ? metrics.focusedBorderThickness : metrics.baseBorderThickness;
+    (void)state;
+    return metrics.baseBorderThickness;
 }
 
 UIColor ResolveTabFillColor(
@@ -115,7 +108,8 @@ UIColor ResolveTabBorderColor(
     bool focused,
     const UIEditorTabStripPalette& palette) {
     if (selected) {
-        return focused ? palette.focusedBorderColor : palette.tabSelectedBorderColor;
+        (void)focused;
+        return palette.tabSelectedBorderColor;
     }
 
     if (hovered) {
@@ -125,33 +119,121 @@ UIColor ResolveTabBorderColor(
     return palette.tabBorderColor;
 }
 
-float ResolveTabBorderThickness(
-    bool selected,
-    bool focused,
-    const UIEditorTabStripMetrics& metrics) {
+float ResolveTabBorderThickness(bool selected, bool focused, const UIEditorTabStripMetrics& metrics) {
     if (selected) {
-        return focused ? metrics.focusedBorderThickness : metrics.selectedBorderThickness;
+        (void)focused;
+        return metrics.selectedBorderThickness;
     }
 
     return metrics.baseBorderThickness;
 }
 
-UIRect BuildCloseButtonRect(
-    const UIRect& headerRect,
+void AppendHeaderContentSeparator(
+    UIDrawList& drawList,
+    const UIEditorTabStripLayout& layout,
+    const UIEditorTabStripPalette& palette,
     const UIEditorTabStripMetrics& metrics) {
-    const float insetY = ClampNonNegative(metrics.closeInsetY);
-    const float extent = (std::min)(
-        ClampNonNegative(metrics.closeButtonExtent),
-        (std::max)(headerRect.height - insetY * 2.0f, 0.0f));
-    if (extent <= 0.0f) {
-        return {};
+    if (layout.headerRect.width <= 0.0f ||
+        layout.headerRect.height <= 0.0f ||
+        layout.contentRect.height <= 0.0f) {
+        return;
     }
 
-    return UIRect(
-        headerRect.x + headerRect.width - ClampNonNegative(metrics.closeInsetRight) - extent,
-        headerRect.y + insetY + (std::max)(0.0f, headerRect.height - insetY * 2.0f - extent) * 0.5f,
-        extent,
-        extent);
+    const float thickness = (std::max)(ClampNonNegative(metrics.baseBorderThickness), 1.0f);
+    const float separatorY = layout.contentRect.y;
+    const float separatorLeft = layout.headerRect.x;
+    const float separatorRight = layout.headerRect.x + layout.headerRect.width;
+
+    if (layout.selectedIndex == UIEditorTabStripInvalidIndex ||
+        layout.selectedIndex >= layout.tabHeaderRects.size()) {
+        drawList.AddFilledRect(
+            UIRect(
+                separatorLeft,
+                separatorY,
+                (std::max)(separatorRight - separatorLeft, 0.0f),
+                thickness),
+            palette.headerContentSeparatorColor);
+        return;
+    }
+
+    const UIRect& selectedRect = layout.tabHeaderRects[layout.selectedIndex];
+    const float gapLeft = (std::max)(separatorLeft, selectedRect.x + 1.0f);
+    const float gapRight = (std::min)(separatorRight, selectedRect.x + selectedRect.width - 1.0f);
+
+    if (gapLeft > separatorLeft) {
+        drawList.AddFilledRect(
+            UIRect(
+                separatorLeft,
+                separatorY,
+                (std::max)(gapLeft - separatorLeft, 0.0f),
+                thickness),
+            palette.headerContentSeparatorColor);
+    }
+
+    if (gapRight < separatorRight) {
+        drawList.AddFilledRect(
+            UIRect(
+                gapRight,
+                separatorY,
+                (std::max)(separatorRight - gapRight, 0.0f),
+                thickness),
+            palette.headerContentSeparatorColor);
+    }
+}
+
+void AppendSelectedTabBottomBorderMask(
+    UIDrawList& drawList,
+    const UIRect& rect,
+    float thickness,
+    const UIEditorTabStripPalette& palette) {
+    if (rect.width <= 0.0f || rect.height <= 0.0f || thickness <= 0.0f) {
+        return;
+    }
+
+    const float maskHeight = (std::max)(1.0f, thickness + 1.0f);
+    drawList.AddFilledRect(
+        UIRect(
+            rect.x + 1.0f,
+            rect.y + rect.height - maskHeight,
+            (std::max)(rect.width - 2.0f, 0.0f),
+            maskHeight + 1.0f),
+        palette.contentBackgroundColor,
+        0.0f);
+}
+
+UIEditorTabStripInsertionPreview BuildInsertionPreview(
+    const UIEditorTabStripLayout& layout,
+    const UIEditorTabStripState& state,
+    const UIEditorTabStripMetrics& metrics) {
+    UIEditorTabStripInsertionPreview preview = {};
+    if (!state.reorder.dragging ||
+        state.reorder.previewInsertionIndex == UIEditorTabStripInvalidIndex ||
+        layout.tabHeaderRects.empty() ||
+        state.reorder.previewInsertionIndex > layout.tabHeaderRects.size() ||
+        layout.headerRect.height <= 0.0f) {
+        return preview;
+    }
+
+    float indicatorX = layout.tabHeaderRects.front().x;
+    if (state.reorder.previewInsertionIndex >= layout.tabHeaderRects.size()) {
+        const UIRect& lastRect = layout.tabHeaderRects.back();
+        indicatorX = lastRect.x + lastRect.width;
+    } else {
+        indicatorX = layout.tabHeaderRects[state.reorder.previewInsertionIndex].x;
+    }
+
+    const float thickness = (std::max)(ClampNonNegative(metrics.reorderPreviewThickness), 1.0f);
+    const float insetY = ClampNonNegative(metrics.reorderPreviewInsetY);
+    const float indicatorHeight = (std::max)(layout.headerRect.height - insetY * 2.0f, thickness);
+
+    preview.visible = true;
+    preview.insertionIndex = state.reorder.previewInsertionIndex;
+    preview.indicatorRect = UIRect(
+        indicatorX - thickness * 0.5f,
+        layout.headerRect.y + insetY,
+        thickness,
+        indicatorHeight);
+    return preview;
 }
 
 } // namespace
@@ -162,13 +244,8 @@ float ResolveUIEditorTabStripDesiredHeaderLabelWidth(
     const float labelWidth = ResolveEstimatedLabelWidth(item, metrics);
     const float horizontalPadding = ClampNonNegative(metrics.layoutMetrics.tabHorizontalPadding);
     const float extraLeftInset = (std::max)(ClampNonNegative(metrics.labelInsetX) - horizontalPadding, 0.0f);
-    const float extraRightInset = (std::max)(ClampNonNegative(metrics.closeInsetRight) - horizontalPadding, 0.0f);
-    const float closeBudget = item.closable
-        ? ClampNonNegative(metrics.closeButtonExtent) +
-            ClampNonNegative(metrics.closeButtonGap) +
-            extraRightInset
-        : 0.0f;
-    return labelWidth + extraLeftInset + closeBudget;
+    (void)item;
+    return labelWidth + extraLeftInset;
 }
 
 std::size_t ResolveUIEditorTabStripSelectedIndex(
@@ -188,34 +265,6 @@ std::size_t ResolveUIEditorTabStripSelectedIndex(
     return ResolveSelectedIndex(items.size(), fallbackIndex);
 }
 
-std::size_t ResolveUIEditorTabStripSelectedIndexAfterClose(
-    std::size_t selectedIndex,
-    std::size_t closedIndex,
-    std::size_t itemCountBeforeClose) {
-    if (itemCountBeforeClose == 0u || closedIndex >= itemCountBeforeClose) {
-        return UIEditorTabStripInvalidIndex;
-    }
-
-    const std::size_t itemCountAfterClose = itemCountBeforeClose - 1u;
-    if (itemCountAfterClose == 0u) {
-        return UIEditorTabStripInvalidIndex;
-    }
-
-    if (selectedIndex == UIEditorTabStripInvalidIndex || selectedIndex >= itemCountBeforeClose) {
-        return (std::min)(closedIndex, itemCountAfterClose - 1u);
-    }
-
-    if (closedIndex < selectedIndex) {
-        return selectedIndex - 1u;
-    }
-
-    if (closedIndex > selectedIndex) {
-        return selectedIndex;
-    }
-
-    return (std::min)(selectedIndex, itemCountAfterClose - 1u);
-}
-
 UIEditorTabStripLayout BuildUIEditorTabStripLayout(
     const UIRect& bounds,
     const std::vector<UIEditorTabStripItem>& items,
@@ -245,17 +294,7 @@ UIEditorTabStripLayout BuildUIEditorTabStripLayout(
     layout.tabHeaderRects = arranged.tabHeaderRects;
     layout.closeButtonRects.resize(items.size());
     layout.showCloseButtons.resize(items.size(), false);
-
-    for (std::size_t index = 0; index < items.size(); ++index) {
-        if (!items[index].closable) {
-            continue;
-        }
-
-        layout.closeButtonRects[index] = BuildCloseButtonRect(layout.tabHeaderRects[index], metrics);
-        layout.showCloseButtons[index] =
-            layout.closeButtonRects[index].width > 0.0f && layout.closeButtonRects[index].height > 0.0f;
-    }
-
+    layout.insertionPreview = BuildInsertionPreview(layout, state, metrics);
     return layout;
 }
 
@@ -269,15 +308,6 @@ UIEditorTabStripHitTarget HitTestUIEditorTabStrip(
         return target;
     }
 
-    for (std::size_t index = 0; index < layout.closeButtonRects.size(); ++index) {
-        if (layout.showCloseButtons[index] &&
-            IsPointInsideRect(layout.closeButtonRects[index], point)) {
-            target.kind = UIEditorTabStripHitTargetKind::CloseButton;
-            target.index = index;
-            return target;
-        }
-    }
-
     for (std::size_t index = 0; index < layout.tabHeaderRects.size(); ++index) {
         if (IsPointInsideRect(layout.tabHeaderRects[index], point)) {
             target.kind = UIEditorTabStripHitTargetKind::Tab;
@@ -322,7 +352,7 @@ void AppendUIEditorTabStripBackground(
 
     for (std::size_t index = 0; index < layout.tabHeaderRects.size(); ++index) {
         const bool selected = layout.selectedIndex == index;
-        const bool hovered = state.hoveredIndex == index || state.closeHoveredIndex == index;
+        const bool hovered = state.hoveredIndex == index;
         drawList.AddFilledRect(
             layout.tabHeaderRects[index],
             ResolveTabFillColor(selected, hovered, palette),
@@ -332,6 +362,20 @@ void AppendUIEditorTabStripBackground(
             ResolveTabBorderColor(selected, hovered, state.focused, palette),
             ResolveTabBorderThickness(selected, state.focused, metrics),
             tabRounding);
+        if (selected) {
+            AppendSelectedTabBottomBorderMask(
+                drawList,
+                layout.tabHeaderRects[index],
+                ResolveTabBorderThickness(selected, state.focused, metrics),
+                palette);
+        }
+    }
+
+    if (layout.insertionPreview.visible) {
+        drawList.AddFilledRect(
+            layout.insertionPreview.indicatorRect,
+            palette.reorderPreviewColor,
+            0.0f);
     }
 }
 
@@ -342,6 +386,8 @@ void AppendUIEditorTabStripForeground(
     const UIEditorTabStripState& state,
     const UIEditorTabStripPalette& palette,
     const UIEditorTabStripMetrics& metrics) {
+    AppendHeaderContentSeparator(drawList, layout, palette, metrics);
+
     const float leftInset = (std::max)(
         ClampNonNegative(metrics.layoutMetrics.tabHorizontalPadding),
         ClampNonNegative(metrics.labelInsetX));
@@ -349,12 +395,9 @@ void AppendUIEditorTabStripForeground(
     for (std::size_t index = 0; index < items.size() && index < layout.tabHeaderRects.size(); ++index) {
         const UIRect& tabRect = layout.tabHeaderRects[index];
         const bool selected = layout.selectedIndex == index;
-        const bool hovered = state.hoveredIndex == index || state.closeHoveredIndex == index;
+        const bool hovered = state.hoveredIndex == index;
         const float textLeft = tabRect.x + leftInset;
-        float textRight = tabRect.x + tabRect.width - ClampNonNegative(metrics.layoutMetrics.tabHorizontalPadding);
-        if (layout.showCloseButtons[index]) {
-            textRight = layout.closeButtonRects[index].x - ClampNonNegative(metrics.closeButtonGap);
-        }
+        const float textRight = tabRect.x + tabRect.width - ClampNonNegative(metrics.layoutMetrics.tabHorizontalPadding);
 
         if (textRight > textLeft) {
             const UIRect clipRect(
@@ -370,30 +413,6 @@ void AppendUIEditorTabStripForeground(
                 kHeaderFontSize);
             drawList.PopClipRect();
         }
-
-        if (!layout.showCloseButtons[index]) {
-            continue;
-        }
-
-        const bool closeHovered = state.closeHoveredIndex == index;
-        const UIRect& closeRect = layout.closeButtonRects[index];
-        const float closeRounding = ResolveCloseButtonRounding(metrics);
-        drawList.AddFilledRect(
-            closeRect,
-            closeHovered ? palette.closeButtonHoveredColor : palette.closeButtonColor,
-            closeRounding);
-        drawList.AddRectOutline(
-            closeRect,
-            palette.closeButtonBorderColor,
-            1.0f,
-            closeRounding);
-        drawList.AddText(
-            UIPoint(
-                closeRect.x + (std::max)(0.0f, (closeRect.width - 7.0f) * 0.5f),
-                ResolveCloseTextTop(closeRect)),
-            "X",
-            palette.closeGlyphColor,
-            kCloseFontSize);
     }
 }
 

new_editor/src/Collections/UIEditorTabStripInteraction.cpp

@@ -2,6 +2,7 @@
 
 #include <XCEngine/Input/InputTypes.h>
 
+#include <array>
 #include <utility>
 
 namespace XCEngine::UI::Editor {
@@ -12,6 +13,16 @@ using ::XCEngine::Input::KeyCode;
 using ::XCEngine::UI::UIInputEvent;
 using ::XCEngine::UI::UIInputEventType;
 using ::XCEngine::UI::UIPointerButton;
+using ::XCEngine::UI::Widgets::BeginUIDragDrop;
+using ::XCEngine::UI::Widgets::CancelUIDragDrop;
+using ::XCEngine::UI::Widgets::EndUIDragDrop;
+using ::XCEngine::UI::Widgets::UIDragDropOperation;
+using ::XCEngine::UI::Widgets::UIDragDropPayload;
+using ::XCEngine::UI::Widgets::UIDragDropResult;
+using ::XCEngine::UI::Widgets::UIDragDropSourceDescriptor;
+using ::XCEngine::UI::Widgets::UIDragDropTargetDescriptor;
+using ::XCEngine::UI::Widgets::UpdateUIDragDropPointer;
+using ::XCEngine::UI::Widgets::UpdateUIDragDropTarget;
 using Widgets::BuildUIEditorTabStripLayout;
 using Widgets::HitTestUIEditorTabStrip;
 using Widgets::ResolveUIEditorTabStripSelectedIndex;
@@ -19,6 +30,9 @@ using Widgets::UIEditorTabStripHitTarget;
 using Widgets::UIEditorTabStripHitTargetKind;
 using Widgets::UIEditorTabStripInvalidIndex;
 
+constexpr ::XCEngine::UI::UIElementId kTabStripDragOwnerId = 0x58435441u;
+constexpr std::string_view kTabStripDragPayloadType = "xc.editor.tab";
+
 bool ShouldUsePointerPosition(const UIInputEvent& event) {
     switch (event.type) {
     case UIInputEventType::PointerMove:
@@ -53,6 +67,14 @@ void ClearHoverState(UIEditorTabStripInteractionState& state) {
     state.tabStripState.closeHoveredIndex = UIEditorTabStripInvalidIndex;
 }
 
+void ClearReorderState(UIEditorTabStripInteractionState& state) {
+    state.tabStripState.reorder = {};
+    state.reorderDragState = {};
+    state.reorderSourceIndex = UIEditorTabStripInvalidIndex;
+    state.reorderPreviewIndex = UIEditorTabStripInvalidIndex;
+    state.reorderCaptureActive = false;
+}
+
 void SyncHoverTarget(
     UIEditorTabStripInteractionState& state,
     const Widgets::UIEditorTabStripLayout& layout) {
@@ -68,11 +90,6 @@ void SyncHoverTarget(
     }
 
     switch (hitTarget.kind) {
-    case UIEditorTabStripHitTargetKind::CloseButton:
-        state.tabStripState.hoveredIndex = hitTarget.index;
-        state.tabStripState.closeHoveredIndex = hitTarget.index;
-        break;
-
     case UIEditorTabStripHitTargetKind::Tab:
         state.tabStripState.hoveredIndex = hitTarget.index;
         break;
@@ -145,6 +162,205 @@ bool ApplyKeyboardNavigation(
     }
 }
 
+bool HasReorderInteraction(const UIEditorTabStripInteractionState& state) {
+    return state.reorderDragState.armed || state.reorderDragState.active;
+}
+
+std::size_t ResolveVisibleDropInsertionIndex(
+    const Widgets::UIEditorTabStripLayout& layout,
+    const ::XCEngine::UI::UIPoint& pointerPosition) {
+    if (!IsPointInside(layout.headerRect, pointerPosition)) {
+        return UIEditorTabStripInvalidIndex;
+    }
+
+    std::size_t insertionIndex = 0u;
+    for (const ::XCEngine::UI::UIRect& rect : layout.tabHeaderRects) {
+        const float midpoint = rect.x + rect.width * 0.5f;
+        if (pointerPosition.x > midpoint) {
+            ++insertionIndex;
+        }
+    }
+
+    return insertionIndex;
+}
+
+std::size_t ResolveReorderTargetIndex(
+    std::size_t sourceIndex,
+    std::size_t dropInsertionIndex,
+    std::size_t itemCount) {
+    if (sourceIndex >= itemCount || dropInsertionIndex > itemCount) {
+        return UIEditorTabStripInvalidIndex;
+    }
+
+    if (dropInsertionIndex <= sourceIndex) {
+        return dropInsertionIndex;
+    }
+
+    return dropInsertionIndex - 1u;
+}
+
+std::size_t ResolveDropInsertionIndexFromPreviewTargetIndex(
+    std::size_t sourceIndex,
+    std::size_t previewTargetIndex) {
+    if (sourceIndex == UIEditorTabStripInvalidIndex ||
+        previewTargetIndex == UIEditorTabStripInvalidIndex) {
+        return UIEditorTabStripInvalidIndex;
+    }
+
+    return previewTargetIndex <= sourceIndex
+        ? previewTargetIndex
+        : previewTargetIndex + 1u;
+}
+
+std::size_t ResolveCommittedReorderInsertionIndex(
+    const UIEditorTabStripInteractionState& state,
+    const Widgets::UIEditorTabStripLayout& layout) {
+    const std::size_t previewInsertionIndex =
+        ResolveDropInsertionIndexFromPreviewTargetIndex(
+            state.reorderSourceIndex,
+            state.reorderPreviewIndex);
+    if (previewInsertionIndex != UIEditorTabStripInvalidIndex) {
+        return previewInsertionIndex;
+    }
+
+    if (state.tabStripState.reorder.previewInsertionIndex != UIEditorTabStripInvalidIndex) {
+        return state.tabStripState.reorder.previewInsertionIndex;
+    }
+
+    if (!state.hasPointerPosition) {
+        return UIEditorTabStripInvalidIndex;
+    }
+
+    return ResolveVisibleDropInsertionIndex(layout, state.pointerPosition);
+}
+
+void SyncReorderPreview(
+    UIEditorTabStripInteractionState& state,
+    const Widgets::UIEditorTabStripLayout& layout,
+    const std::vector<Widgets::UIEditorTabStripItem>& items,
+    UIEditorTabStripInteractionResult& result) {
+    state.tabStripState.reorder.armed = state.reorderDragState.armed;
+    state.tabStripState.reorder.dragging = state.reorderDragState.active;
+    state.tabStripState.reorder.sourceIndex = state.reorderSourceIndex;
+    state.tabStripState.reorder.pressedIndex = state.reorderSourceIndex;
+    state.tabStripState.reorder.pressPosition = state.reorderDragState.pointerDownPosition;
+    result.dragSourceIndex = state.reorderSourceIndex;
+    if (state.reorderSourceIndex < items.size()) {
+        result.draggedTabId = items[state.reorderSourceIndex].tabId;
+    }
+
+    if (!state.reorderDragState.active || !state.hasPointerPosition || items.size() < 2u) {
+        UIDragDropResult dragDropResult = {};
+        UpdateUIDragDropTarget(state.reorderDragState, nullptr, &dragDropResult);
+        state.tabStripState.reorder.previewInsertionIndex = UIEditorTabStripInvalidIndex;
+        state.reorderPreviewIndex = UIEditorTabStripInvalidIndex;
+        result.dropInsertionIndex = UIEditorTabStripInvalidIndex;
+        result.reorderToIndex = UIEditorTabStripInvalidIndex;
+        result.reorderPreviewIndex = UIEditorTabStripInvalidIndex;
+        return;
+    }
+
+    const std::size_t dropInsertionIndex =
+        ResolveVisibleDropInsertionIndex(layout, state.pointerPosition);
+    if (dropInsertionIndex == UIEditorTabStripInvalidIndex) {
+        UIDragDropResult dragDropResult = {};
+        UpdateUIDragDropTarget(state.reorderDragState, nullptr, &dragDropResult);
+        state.tabStripState.reorder.previewInsertionIndex = UIEditorTabStripInvalidIndex;
+        state.reorderPreviewIndex = UIEditorTabStripInvalidIndex;
+        result.dropInsertionIndex = UIEditorTabStripInvalidIndex;
+        result.reorderToIndex = UIEditorTabStripInvalidIndex;
+        result.reorderPreviewIndex = UIEditorTabStripInvalidIndex;
+        return;
+    }
+
+    const std::size_t reorderToIndex =
+        ResolveReorderTargetIndex(
+            state.reorderSourceIndex,
+            dropInsertionIndex,
+            items.size());
+    if (reorderToIndex == UIEditorTabStripInvalidIndex) {
+        return;
+    }
+
+    static constexpr std::array<std::string_view, 1> kAcceptedPayloadTypes = {
+        kTabStripDragPayloadType
+    };
+    const std::string targetId = "insert:" + std::to_string(dropInsertionIndex);
+    UIDragDropTargetDescriptor target = {};
+    target.ownerId = kTabStripDragOwnerId;
+    target.targetId = targetId;
+    target.acceptedPayloadTypes = kAcceptedPayloadTypes;
+    target.acceptedOperations = UIDragDropOperation::Move;
+    target.preferredOperation = UIDragDropOperation::Move;
+
+    UIDragDropResult dragDropResult = {};
+    UpdateUIDragDropTarget(state.reorderDragState, &target, &dragDropResult);
+
+    state.tabStripState.reorder.previewInsertionIndex = dropInsertionIndex;
+    state.reorderPreviewIndex = reorderToIndex;
+    result.reorderPreviewActive = true;
+    result.dropInsertionIndex = dropInsertionIndex;
+    result.reorderToIndex = reorderToIndex;
+    result.reorderPreviewIndex = reorderToIndex;
+}
+
+void BeginTabReorder(
+    UIEditorTabStripInteractionState& state,
+    const std::vector<Widgets::UIEditorTabStripItem>& items,
+    std::size_t sourceIndex) {
+    if (sourceIndex >= items.size()) {
+        return;
+    }
+
+    UIDragDropSourceDescriptor source = {};
+    source.ownerId = kTabStripDragOwnerId;
+    source.sourceId = items[sourceIndex].tabId;
+    source.pointerDownPosition = state.pointerPosition;
+    source.payload = UIDragDropPayload{
+        std::string(kTabStripDragPayloadType),
+        items[sourceIndex].tabId,
+        items[sourceIndex].title
+    };
+    source.allowedOperations = UIDragDropOperation::Move;
+    source.activationDistance = 4.0f;
+
+    UIDragDropResult dragDropResult = {};
+    if (BeginUIDragDrop(source, state.reorderDragState, &dragDropResult)) {
+        state.tabStripState.reorder.pressPosition = state.pointerPosition;
+        state.tabStripState.reorder.pressedIndex = sourceIndex;
+        state.tabStripState.reorder.sourceIndex = sourceIndex;
+        state.tabStripState.reorder.previewInsertionIndex = UIEditorTabStripInvalidIndex;
+        state.tabStripState.reorder.armed = true;
+        state.tabStripState.reorder.dragging = false;
+        state.reorderSourceIndex = sourceIndex;
+        state.reorderPreviewIndex = UIEditorTabStripInvalidIndex;
+    }
+}
+
+void CancelTabReorder(
+    UIEditorTabStripInteractionState& state,
+    UIEditorTabStripInteractionResult& result,
+    const std::vector<Widgets::UIEditorTabStripItem>& items) {
+    if (!HasReorderInteraction(state)) {
+        return;
+    }
+
+    result.dragCanceled = true;
+    result.consumed = state.reorderCaptureActive || state.reorderDragState.active;
+    result.dragSourceIndex = state.reorderSourceIndex;
+    result.reorderPreviewIndex = state.reorderPreviewIndex;
+    if (state.reorderSourceIndex < items.size()) {
+        result.draggedTabId = items[state.reorderSourceIndex].tabId;
+    }
+    if (state.reorderCaptureActive) {
+        result.releasePointerCapture = true;
+    }
+
+    UIDragDropResult dragDropResult = {};
+    CancelUIDragDrop(state.reorderDragState, &dragDropResult);
+    ClearReorderState(state);
+}
+
 } // namespace
 
 UIEditorTabStripInteractionFrame UpdateUIEditorTabStripInteraction(
@@ -184,11 +400,33 @@ UIEditorTabStripInteractionFrame UpdateUIEditorTabStripInteraction(
             state.hasPointerPosition = false;
             state.pressedTarget = {};
             ClearHoverState(state);
+            CancelTabReorder(state, eventResult, items);
             break;
 
         case UIInputEventType::PointerMove:
         case UIInputEventType::PointerEnter:
+            if (HasReorderInteraction(state)) {
+                UIDragDropResult dragDropResult = {};
+                UpdateUIDragDropPointer(state.reorderDragState, state.pointerPosition, &dragDropResult);
+                if (dragDropResult.activated && !state.reorderCaptureActive) {
+                    state.reorderCaptureActive = true;
+                    eventResult.requestPointerCapture = true;
+                    eventResult.dragStarted = true;
+                    eventResult.consumed = true;
+                }
+
+                SyncReorderPreview(state, layout, items, eventResult);
+                if (state.reorderDragState.active) {
+                    eventResult.consumed = true;
+                }
+            }
+            break;
+
         case UIInputEventType::PointerLeave:
+            if (state.reorderDragState.active) {
+                SyncReorderPreview(state, layout, items, eventResult);
+                eventResult.consumed = true;
+            }
             break;
 
         case UIInputEventType::PointerButtonDown: {
@@ -201,6 +439,9 @@ UIEditorTabStripInteractionFrame UpdateUIEditorTabStripInteraction(
                 (state.hasPointerPosition && IsPointInside(layout.bounds, state.pointerPosition))) {
                 state.tabStripState.focused = true;
                 eventResult.consumed = true;
+                if (eventResult.hitTarget.kind == UIEditorTabStripHitTargetKind::Tab) {
+                    BeginTabReorder(state, items, eventResult.hitTarget.index);
+                }
             } else {
                 state.tabStripState.focused = false;
                 state.pressedTarget = {};
@@ -218,22 +459,49 @@ UIEditorTabStripInteractionFrame UpdateUIEditorTabStripInteraction(
             const bool matchedPressedTarget =
                 AreEquivalentTargets(state.pressedTarget, eventResult.hitTarget);
 
+            if (state.reorderDragState.active || state.reorderCaptureActive) {
+                UIDragDropResult dragDropResult = {};
+                EndUIDragDrop(state.reorderDragState, dragDropResult);
+
+                eventResult.dragEnded = state.reorderCaptureActive;
+                eventResult.releasePointerCapture = state.reorderCaptureActive;
+                eventResult.consumed = true;
+                eventResult.dragSourceIndex = state.reorderSourceIndex;
+                if (state.reorderSourceIndex < items.size()) {
+                    eventResult.draggedTabId = items[state.reorderSourceIndex].tabId;
+                }
+                eventResult.dropInsertionIndex =
+                    ResolveCommittedReorderInsertionIndex(state, layout);
+                eventResult.reorderToIndex =
+                    ResolveReorderTargetIndex(
+                        state.reorderSourceIndex,
+                        eventResult.dropInsertionIndex,
+                        items.size());
+                eventResult.reorderPreviewIndex = state.reorderPreviewIndex;
+                if (dragDropResult.completed &&
+                    eventResult.dropInsertionIndex != UIEditorTabStripInvalidIndex &&
+                    eventResult.reorderToIndex != UIEditorTabStripInvalidIndex) {
+                    eventResult.reorderRequested =
+                        eventResult.dropInsertionIndex != state.reorderSourceIndex &&
+                        eventResult.dropInsertionIndex != state.reorderSourceIndex + 1u;
+                } else {
+                    eventResult.dragCanceled = true;
+                }
+
+                ClearReorderState(state);
+                state.pressedTarget = {};
+                break;
+            }
+
+            if (state.reorderDragState.armed) {
+                UIDragDropResult dragDropResult = {};
+                CancelUIDragDrop(state.reorderDragState, &dragDropResult);
+                state.reorderSourceIndex = UIEditorTabStripInvalidIndex;
+                state.reorderPreviewIndex = UIEditorTabStripInvalidIndex;
+            }
+
             if (matchedPressedTarget) {
                 switch (eventResult.hitTarget.kind) {
-                case UIEditorTabStripHitTargetKind::CloseButton:
-                    if (eventResult.hitTarget.index < items.size() &&
-                        items[eventResult.hitTarget.index].closable) {
-                        eventResult.closeRequested = true;
-                        eventResult.closedTabId = items[eventResult.hitTarget.index].tabId;
-                        eventResult.closedIndex = eventResult.hitTarget.index;
-                        eventResult.consumed = true;
-                        state.tabStripState.focused = true;
-                    } else if (insideStrip) {
-                        state.tabStripState.focused = true;
-                        eventResult.consumed = true;
-                    }
-                    break;
-
                 case UIEditorTabStripHitTargetKind::Tab:
                     SelectTab(
                         state,
@@ -271,6 +539,12 @@ UIEditorTabStripInteractionFrame UpdateUIEditorTabStripInteraction(
         }
 
         case UIInputEventType::KeyDown:
+            if (HasReorderInteraction(state) &&
+                static_cast<KeyCode>(event.keyCode) == KeyCode::Escape) {
+                CancelTabReorder(state, eventResult, items);
+                break;
+            }
+
             if (state.tabStripState.focused &&
                 !HasNavigationModifiers(event.modifiers) &&
                 ApplyKeyboardNavigation(state, event.keyCode) &&
@@ -299,13 +573,25 @@ UIEditorTabStripInteractionFrame UpdateUIEditorTabStripInteraction(
                 HitTestUIEditorTabStrip(layout, state.tabStripState, state.pointerPosition);
         }
 
+        if (state.reorderDragState.active) {
+            SyncReorderPreview(state, layout, items, eventResult);
+        }
+
         if (eventResult.consumed ||
             eventResult.selectionChanged ||
             eventResult.closeRequested ||
             eventResult.keyboardNavigated ||
+            eventResult.requestPointerCapture ||
+            eventResult.releasePointerCapture ||
+            eventResult.dragStarted ||
+            eventResult.dragEnded ||
+            eventResult.dragCanceled ||
+            eventResult.reorderRequested ||
+            eventResult.reorderPreviewActive ||
             eventResult.hitTarget.kind != UIEditorTabStripHitTargetKind::None ||
             !eventResult.selectedTabId.empty() ||
-            !eventResult.closedTabId.empty()) {
+            !eventResult.closedTabId.empty() ||
+            !eventResult.draggedTabId.empty()) {
             interactionResult = std::move(eventResult);
         }
     }
@@ -318,6 +604,9 @@ UIEditorTabStripInteractionFrame UpdateUIEditorTabStripInteraction(
         interactionResult.hitTarget =
             HitTestUIEditorTabStrip(layout, state.tabStripState, state.pointerPosition);
     }
+    if (state.reorderDragState.active) {
+        SyncReorderPreview(state, layout, items, interactionResult);
+    }
 
     return {
         std::move(layout),

new_editor/src/Foundation/UIEditorRuntimeTrace.cpp

@@ -0,0 +1,130 @@
+#include <XCEditor/Foundation/UIEditorRuntimeTrace.h>
+
+#include <chrono>
+#include <cstdio>
+#include <filesystem>
+#include <fstream>
+#include <iomanip>
+#include <mutex>
+#include <sstream>
+#include <string>
+
+namespace XCEngine::UI::Editor {
+
+namespace {
+
+std::mutex g_traceMutex = {};
+std::filesystem::path g_logRoot = {};
+std::filesystem::path g_runtimeTracePath = {};
+std::filesystem::path g_crashTracePath = {};
+bool g_traceInitialized = false;
+
+std::string BuildTimestampString() {
+    const auto now = std::chrono::system_clock::now();
+    const std::time_t currentTime = std::chrono::system_clock::to_time_t(now);
+    std::tm localTime = {};
+    localtime_s(&localTime, &currentTime);
+
+    const auto milliseconds =
+        std::chrono::duration_cast<std::chrono::milliseconds>(
+            now.time_since_epoch()) %
+        1000;
+
+    std::ostringstream stream = {};
+    stream << std::put_time(&localTime, "%Y-%m-%d %H:%M:%S")
+           << '.'
+           << std::setw(3)
+           << std::setfill('0')
+           << milliseconds.count();
+    return stream.str();
+}
+
+void AppendTraceLine(
+    const std::filesystem::path& path,
+    std::string_view channel,
+    std::string_view message) {
+    if (path.empty()) {
+        return;
+    }
+
+    std::error_code errorCode = {};
+    std::filesystem::create_directories(path.parent_path(), errorCode);
+    std::ofstream stream(path, std::ios::out | std::ios::app);
+    if (!stream.is_open()) {
+        return;
+    }
+
+    stream << '['
+           << BuildTimestampString()
+           << "] ["
+           << channel
+           << "] "
+           << message
+           << '\n';
+}
+
+} // namespace
+
+void InitializeUIEditorRuntimeTrace(const std::filesystem::path& logRoot) {
+    std::lock_guard lock(g_traceMutex);
+    g_logRoot = logRoot.lexically_normal();
+    g_runtimeTracePath = (g_logRoot / "runtime.log").lexically_normal();
+    g_crashTracePath = (g_logRoot / "crash.log").lexically_normal();
+    g_traceInitialized = true;
+
+    std::error_code errorCode = {};
+    std::filesystem::create_directories(g_logRoot, errorCode);
+    AppendTraceLine(g_runtimeTracePath, "trace", "trace session started");
+}
+
+void ShutdownUIEditorRuntimeTrace() {
+    std::lock_guard lock(g_traceMutex);
+    if (!g_traceInitialized) {
+        return;
+    }
+
+    AppendTraceLine(g_runtimeTracePath, "trace", "trace session ended");
+    g_traceInitialized = false;
+}
+
+void AppendUIEditorRuntimeTrace(
+    std::string_view channel,
+    std::string_view message) {
+    std::lock_guard lock(g_traceMutex);
+    if (!g_traceInitialized) {
+        return;
+    }
+
+    AppendTraceLine(g_runtimeTracePath, channel, message);
+}
+
+void AppendUIEditorCrashTrace(
+    std::uint32_t exceptionCode,
+    const void* exceptionAddress) {
+    std::lock_guard lock(g_traceMutex);
+    if (!g_traceInitialized) {
+        return;
+    }
+
+    char buffer[128] = {};
+    std::snprintf(
+        buffer,
+        sizeof(buffer),
+        "Unhandled exception code=0x%08X address=%p",
+        exceptionCode,
+        exceptionAddress);
+    AppendTraceLine(g_crashTracePath, "crash", buffer);
+    AppendTraceLine(g_runtimeTracePath, "crash", buffer);
+}
+
+std::filesystem::path GetUIEditorRuntimeTracePath() {
+    std::lock_guard lock(g_traceMutex);
+    return g_runtimeTracePath;
+}
+
+std::filesystem::path GetUIEditorCrashTracePath() {
+    std::lock_guard lock(g_traceMutex);
+    return g_crashTracePath;
+}
+
+} // namespace XCEngine::UI::Editor

new_editor/src/Shell/UIEditorDockHost.cpp

@@ -501,6 +501,91 @@ UIColor ResolveSplitterColor(const UIEditorDockHostSplitterLayout& splitter, con
     return palette.splitterColor;
 }
 
+const UIEditorDockHostTabStackLayout* FindTabStackLayoutByNodeId(
+    const UIEditorDockHostLayout& layout,
+    std::string_view nodeId) {
+    for (const UIEditorDockHostTabStackLayout& tabStack : layout.tabStacks) {
+        if (tabStack.nodeId == nodeId) {
+            return &tabStack;
+        }
+    }
+
+    return nullptr;
+}
+
+UIRect InsetRect(const UIRect& rect, float inset) {
+    const float clampedInset = ClampNonNegative(inset);
+    const float insetX = (std::min)(clampedInset, rect.width * 0.5f);
+    const float insetY = (std::min)(clampedInset, rect.height * 0.5f);
+    return UIRect(
+        rect.x + insetX,
+        rect.y + insetY,
+        (std::max)(0.0f, rect.width - insetX * 2.0f),
+        (std::max)(0.0f, rect.height - insetY * 2.0f));
+}
+
+UIRect ResolveDropPreviewRect(
+    const UIEditorDockHostTabStackLayout& tabStack,
+    UIEditorWorkspaceDockPlacement placement) {
+    const UIRect bounds = tabStack.bounds;
+    switch (placement) {
+    case UIEditorWorkspaceDockPlacement::Left:
+        return UIRect(
+            bounds.x,
+            bounds.y,
+            bounds.width * 0.35f,
+            bounds.height);
+    case UIEditorWorkspaceDockPlacement::Right:
+        return UIRect(
+            bounds.x + bounds.width * 0.65f,
+            bounds.y,
+            bounds.width * 0.35f,
+            bounds.height);
+    case UIEditorWorkspaceDockPlacement::Top:
+        return UIRect(
+            bounds.x,
+            bounds.y,
+            bounds.width,
+            bounds.height * 0.35f);
+    case UIEditorWorkspaceDockPlacement::Bottom:
+        return UIRect(
+            bounds.x,
+            bounds.y + bounds.height * 0.65f,
+            bounds.width,
+            bounds.height * 0.35f);
+    case UIEditorWorkspaceDockPlacement::Center:
+    default:
+        return InsetRect(bounds, 4.0f);
+    }
+}
+
+UIEditorDockHostDropPreviewLayout ResolveDropPreviewLayout(
+    const UIEditorDockHostLayout& layout,
+    const UIEditorDockHostState& state) {
+    UIEditorDockHostDropPreviewLayout preview = {};
+    if (!state.dropPreview.visible || state.dropPreview.targetNodeId.empty()) {
+        return preview;
+    }
+
+    const UIEditorDockHostTabStackLayout* targetTabStack =
+        FindTabStackLayoutByNodeId(layout, state.dropPreview.targetNodeId);
+    if (targetTabStack == nullptr) {
+        return preview;
+    }
+
+    preview.visible = true;
+    preview.targetNodeId = state.dropPreview.targetNodeId;
+    preview.placement = state.dropPreview.placement;
+    preview.insertionIndex = state.dropPreview.insertionIndex;
+    preview.previewRect =
+        ResolveDropPreviewRect(*targetTabStack, state.dropPreview.placement);
+    if (preview.previewRect.width <= 0.0f || preview.previewRect.height <= 0.0f) {
+        preview = {};
+    }
+
+    return preview;
+}
+
 } // namespace
 
 const UIEditorDockHostSplitterLayout* FindUIEditorDockHostSplitterLayout(
@@ -539,6 +624,7 @@ UIEditorDockHostLayout BuildUIEditorDockHostLayout(
         state,
         metrics,
         layout);
+    layout.dropPreview = ResolveDropPreviewLayout(layout, state);
     return layout;
 }
 
@@ -607,8 +693,6 @@ void AppendUIEditorDockHostBackground(
     const UIEditorDockHostLayout& layout,
     const UIEditorDockHostPalette& palette,
     const UIEditorDockHostMetrics& metrics) {
-    const UIEditorPanelFrameMetrics tabContentFrameMetrics =
-        BuildTabContentFrameMetrics(metrics);
     for (const UIEditorDockHostTabStackLayout& tabStack : layout.tabStacks) {
         std::vector<UIEditorTabStripItem> tabItems = {};
         tabItems.reserve(tabStack.items.size());
@@ -626,12 +710,6 @@ void AppendUIEditorDockHostBackground(
             tabStack.tabStripState,
             palette.tabStripPalette,
             metrics.tabStripMetrics);
-        AppendUIEditorPanelFrameBackground(
-            drawList,
-            tabStack.contentFrameLayout,
-            tabStack.contentFrameState,
-            palette.panelFramePalette,
-            tabContentFrameMetrics);
     }
 
     for (const UIEditorDockHostSplitterLayout& splitter : layout.splitters) {
@@ -648,8 +726,6 @@ void AppendUIEditorDockHostForeground(
     const UIEditorDockHostForegroundOptions& options,
     const UIEditorDockHostPalette& palette,
     const UIEditorDockHostMetrics& metrics) {
-    const UIEditorPanelFrameMetrics tabContentFrameMetrics =
-        BuildTabContentFrameMetrics(metrics);
     for (const UIEditorDockHostTabStackLayout& tabStack : layout.tabStacks) {
         std::vector<UIEditorTabStripItem> tabItems = {};
         tabItems.reserve(tabStack.items.size());
@@ -668,18 +744,21 @@ void AppendUIEditorDockHostForeground(
             tabStack.tabStripState,
             palette.tabStripPalette,
             metrics.tabStripMetrics);
-        AppendUIEditorPanelFrameForeground(
-            drawList,
-            tabStack.contentFrameLayout,
-            tabStack.contentFrameState,
-            {},
-            palette.panelFramePalette,
-            tabContentFrameMetrics);
 
         if (UsesExternalBodyPresentation(options, tabStack.selectedPanelId)) {
             continue;
         }
     }
+
+    if (layout.dropPreview.visible) {
+        drawList.AddFilledRect(
+            layout.dropPreview.previewRect,
+            palette.dropPreviewFillColor);
+        drawList.AddRectOutline(
+            layout.dropPreview.previewRect,
+            palette.dropPreviewBorderColor,
+            1.0f);
+    }
 }
 
 void AppendUIEditorDockHostForeground(

new_editor/src/Shell/UIEditorDockHostInteraction.cpp

@@ -1,8 +1,10 @@
 #include <XCEditor/Shell/UIEditorDockHostInteraction.h>
+#include <XCEditor/Foundation/UIEditorRuntimeTrace.h>
 
 #include <XCEngine/UI/Widgets/UISplitterInteraction.h>
 
 #include <algorithm>
+#include <sstream>
 #include <string_view>
 #include <utility>
 #include <vector>
@@ -13,6 +15,7 @@ namespace {
 
 using ::XCEngine::UI::UIInputEvent;
 using ::XCEngine::UI::UIInputEventType;
+using ::XCEngine::UI::UIPoint;
 using ::XCEngine::UI::UIRect;
 using ::XCEngine::UI::Widgets::BeginUISplitterDrag;
 using ::XCEngine::UI::Widgets::EndUISplitterDrag;
@@ -30,8 +33,17 @@ using Widgets::UIEditorTabStripItem;
 struct DockHostTabStripEventResult {
     bool consumed = false;
     bool commandRequested = false;
+    bool reorderRequested = false;
+    bool dragStarted = false;
+    bool dragEnded = false;
+    bool dragCanceled = false;
+    bool requestPointerCapture = false;
+    bool releasePointerCapture = false;
     UIEditorWorkspaceCommandKind commandKind = UIEditorWorkspaceCommandKind::ActivatePanel;
+    std::size_t dropInsertionIndex = Widgets::UIEditorTabStripInvalidIndex;
     std::string panelId = {};
+    std::string nodeId = {};
+    std::string draggedTabId = {};
     UIEditorDockHostHitTarget hitTarget = {};
     int priority = 0;
 };
@@ -130,6 +142,13 @@ void PruneTabStripInteractionEntries(
                 return !isVisibleNodeId(entry.nodeId);
             }),
         state.dockHostState.tabStripStates.end());
+
+    if (!state.activeTabDragNodeId.empty() &&
+        !isVisibleNodeId(state.activeTabDragNodeId)) {
+        state.activeTabDragNodeId.clear();
+        state.activeTabDragPanelId.clear();
+        state.dockHostState.dropPreview = {};
+    }
 }
 
 void SyncDockHostTabStripVisualStates(UIEditorDockHostInteractionState& state) {
@@ -152,6 +171,33 @@ bool HasFocusedTabStrip(const UIEditorDockHostInteractionState& state) {
                }) != state.tabStripInteractions.end();
 }
 
+const UIEditorDockHostTabStackLayout* FindTabStackLayoutByNodeId(
+    const Widgets::UIEditorDockHostLayout& layout,
+    std::string_view nodeId) {
+    for (const UIEditorDockHostTabStackLayout& tabStack : layout.tabStacks) {
+        if (tabStack.nodeId == nodeId) {
+            return &tabStack;
+        }
+    }
+
+    return nullptr;
+}
+
+bool IsPointInsideRect(
+    const UIRect& rect,
+    const UIPoint& point) {
+    return point.x >= rect.x &&
+        point.x <= rect.x + rect.width &&
+        point.y >= rect.y &&
+        point.y <= rect.y + rect.height;
+}
+
+void ClearTabDockDragState(UIEditorDockHostInteractionState& state) {
+    state.activeTabDragNodeId.clear();
+    state.activeTabDragPanelId.clear();
+    state.dockHostState.dropPreview = {};
+}
+
 std::vector<UIEditorTabStripItem> BuildTabStripItems(
     const UIEditorDockHostTabStackLayout& tabStack) {
     std::vector<UIEditorTabStripItem> items = {};
@@ -198,6 +244,13 @@ UIEditorDockHostHitTarget MapTabStripHitTarget(
 }
 
 int ResolveTabStripPriority(const UIEditorTabStripInteractionResult& result) {
+    if (result.reorderRequested ||
+        result.dragStarted ||
+        result.dragEnded ||
+        result.dragCanceled) {
+        return 5;
+    }
+
     if (result.closeRequested) {
         return 4;
     }
@@ -221,6 +274,11 @@ DockHostTabStripEventResult ProcessTabStripEvent(
     DockHostTabStripEventResult resolved = {};
 
     for (const UIEditorDockHostTabStackLayout& tabStack : layout.tabStacks) {
+        if (!state.activeTabDragNodeId.empty() &&
+            tabStack.nodeId != state.activeTabDragNodeId) {
+            continue;
+        }
+
         UIEditorDockHostTabStripInteractionEntry& entry =
             FindOrCreateTabStripInteractionEntry(state, tabStack.nodeId);
         std::string selectedTabId = tabStack.selectedPanelId;
@@ -238,7 +296,15 @@ DockHostTabStripEventResult ProcessTabStripEvent(
             continue;
         }
 
+        resolved.nodeId = tabStack.nodeId;
         resolved.hitTarget = MapTabStripHitTarget(tabStack, frame.result);
+        resolved.requestPointerCapture = frame.result.requestPointerCapture;
+        resolved.releasePointerCapture = frame.result.releasePointerCapture;
+        resolved.dragStarted = frame.result.dragStarted;
+        resolved.dragEnded = frame.result.dragEnded;
+        resolved.dragCanceled = frame.result.dragCanceled;
+        resolved.dropInsertionIndex = frame.result.dropInsertionIndex;
+        resolved.draggedTabId = frame.result.draggedTabId;
         if ((frame.result.closeRequested && !frame.result.closedTabId.empty()) ||
             (event.type == UIInputEventType::PointerButtonUp &&
              frame.result.consumed &&
@@ -250,6 +316,12 @@ DockHostTabStripEventResult ProcessTabStripEvent(
                 !frame.result.closedTabId.empty()
                     ? frame.result.closedTabId
                     : resolved.hitTarget.panelId;
+        } else if (frame.result.reorderRequested &&
+            !frame.result.draggedTabId.empty() &&
+            frame.result.dropInsertionIndex != Widgets::UIEditorTabStripInvalidIndex) {
+            resolved.reorderRequested = true;
+            resolved.panelId = frame.result.draggedTabId;
+            resolved.dropInsertionIndex = frame.result.dropInsertionIndex;
         } else if ((frame.result.selectionChanged ||
                     frame.result.keyboardNavigated ||
                     (event.type == UIInputEventType::PointerButtonUp &&
@@ -266,6 +338,7 @@ DockHostTabStripEventResult ProcessTabStripEvent(
             continue;
         } else {
             resolved.commandRequested = false;
+            resolved.reorderRequested = false;
             resolved.panelId.clear();
         }
 
@@ -277,6 +350,103 @@ DockHostTabStripEventResult ProcessTabStripEvent(
     return resolved;
 }
 
+std::size_t ResolveTabHeaderDropInsertionIndex(
+    const UIEditorDockHostTabStackLayout& tabStack,
+    const UIPoint& point) {
+    if (!IsPointInsideRect(tabStack.tabStripLayout.headerRect, point)) {
+        return Widgets::UIEditorTabStripInvalidIndex;
+    }
+
+    std::size_t insertionIndex = 0u;
+    for (const UIRect& rect : tabStack.tabStripLayout.tabHeaderRects) {
+        const float midpoint = rect.x + rect.width * 0.5f;
+        if (point.x > midpoint) {
+            ++insertionIndex;
+        }
+    }
+
+    return insertionIndex;
+}
+
+UIEditorWorkspaceDockPlacement ResolveDockPlacement(
+    const UIEditorDockHostTabStackLayout& tabStack,
+    const UIPoint& point) {
+    if (IsPointInsideRect(tabStack.tabStripLayout.headerRect, point)) {
+        return UIEditorWorkspaceDockPlacement::Center;
+    }
+
+    const float leftDistance = point.x - tabStack.bounds.x;
+    const float rightDistance =
+        tabStack.bounds.x + tabStack.bounds.width - point.x;
+    const float topDistance = point.y - tabStack.bounds.y;
+    const float bottomDistance =
+        tabStack.bounds.y + tabStack.bounds.height - point.y;
+    const float minHorizontalThreshold = tabStack.bounds.width * 0.25f;
+    const float minVerticalThreshold = tabStack.bounds.height * 0.25f;
+    const float nearestEdge =
+        (std::min)((std::min)(leftDistance, rightDistance), (std::min)(topDistance, bottomDistance));
+
+    if (nearestEdge == leftDistance && leftDistance <= minHorizontalThreshold) {
+        return UIEditorWorkspaceDockPlacement::Left;
+    }
+    if (nearestEdge == rightDistance && rightDistance <= minHorizontalThreshold) {
+        return UIEditorWorkspaceDockPlacement::Right;
+    }
+    if (nearestEdge == topDistance && topDistance <= minVerticalThreshold) {
+        return UIEditorWorkspaceDockPlacement::Top;
+    }
+    if (nearestEdge == bottomDistance && bottomDistance <= minVerticalThreshold) {
+        return UIEditorWorkspaceDockPlacement::Bottom;
+    }
+
+    return UIEditorWorkspaceDockPlacement::Center;
+}
+
+void SyncDockPreview(
+    UIEditorDockHostInteractionState& state,
+    const Widgets::UIEditorDockHostLayout& layout) {
+    state.dockHostState.dropPreview = {};
+    if (state.activeTabDragNodeId.empty() ||
+        state.activeTabDragPanelId.empty() ||
+        !state.hasPointerPosition) {
+        return;
+    }
+
+    for (const UIEditorDockHostTabStackLayout& tabStack : layout.tabStacks) {
+        if (!IsPointInsideRect(tabStack.bounds, state.pointerPosition)) {
+            continue;
+        }
+
+        const UIEditorWorkspaceDockPlacement placement =
+            ResolveDockPlacement(tabStack, state.pointerPosition);
+        if (tabStack.nodeId == state.activeTabDragNodeId &&
+            placement == UIEditorWorkspaceDockPlacement::Center) {
+            return;
+        }
+
+        if (tabStack.nodeId == state.activeTabDragNodeId &&
+            tabStack.items.size() <= 1u) {
+            return;
+        }
+
+        Widgets::UIEditorDockHostDropPreviewState preview = {};
+        preview.visible = true;
+        preview.sourceNodeId = state.activeTabDragNodeId;
+        preview.sourcePanelId = state.activeTabDragPanelId;
+        preview.targetNodeId = tabStack.nodeId;
+        preview.placement = placement;
+        if (placement == UIEditorWorkspaceDockPlacement::Center) {
+            preview.insertionIndex =
+                ResolveTabHeaderDropInsertionIndex(tabStack, state.pointerPosition);
+            if (preview.insertionIndex == Widgets::UIEditorTabStripInvalidIndex) {
+                preview.insertionIndex = tabStack.items.size();
+            }
+        }
+        state.dockHostState.dropPreview = std::move(preview);
+        return;
+    }
+}
+
 void SyncHoverTarget(
     UIEditorDockHostInteractionState& state,
     const Widgets::UIEditorDockHostLayout& layout) {
@@ -290,6 +460,11 @@ void SyncHoverTarget(
         return;
     }
 
+    if (!state.activeTabDragNodeId.empty()) {
+        state.dockHostState.hoveredTarget = {};
+        return;
+    }
+
     if (!state.hasPointerPosition) {
         state.dockHostState.hoveredTarget = {};
         return;
@@ -340,6 +515,20 @@ UIEditorDockHostInteractionFrame UpdateUIEditorDockHostInteraction(
             ShouldDispatchTabStripEvent(event, state.splitterDragState.active)
                 ? ProcessTabStripEvent(state, layout, event, metrics)
                 : DockHostTabStripEventResult {};
+        eventResult.requestPointerCapture = tabStripResult.requestPointerCapture;
+        eventResult.releasePointerCapture = tabStripResult.releasePointerCapture;
+        if (!tabStripResult.draggedTabId.empty() &&
+            !state.activeTabDragNodeId.empty()) {
+            state.activeTabDragPanelId = tabStripResult.draggedTabId;
+        }
+        if (!state.activeTabDragNodeId.empty() &&
+            !state.activeTabDragPanelId.empty() &&
+            !state.splitterDragState.active) {
+            SyncDockPreview(state, layout);
+        } else if (event.type == UIInputEventType::PointerLeave ||
+            state.activeTabDragNodeId.empty()) {
+            state.dockHostState.dropPreview = {};
+        }
 
         switch (event.type) {
         case UIInputEventType::FocusGained:
@@ -355,6 +544,12 @@ UIEditorDockHostInteractionFrame UpdateUIEditorDockHostInteraction(
                 eventResult.consumed = true;
                 eventResult.releasePointerCapture = true;
             }
+            if (!state.activeTabDragNodeId.empty() || tabStripResult.dragCanceled) {
+                ClearTabDockDragState(state);
+                eventResult.consumed = true;
+                eventResult.releasePointerCapture =
+                    eventResult.releasePointerCapture || tabStripResult.releasePointerCapture;
+            }
             break;
 
         case UIInputEventType::PointerMove:
@@ -381,6 +576,21 @@ UIEditorDockHostInteractionFrame UpdateUIEditorDockHostInteraction(
                     eventResult.hitTarget.kind = UIEditorDockHostHitTargetKind::SplitterHandle;
                     eventResult.hitTarget.nodeId = state.dockHostState.activeSplitterNodeId;
                 }
+            } else if (tabStripResult.priority > 0) {
+                eventResult.consumed = tabStripResult.consumed || tabStripResult.dragStarted;
+                eventResult.hitTarget = tabStripResult.hitTarget;
+                if (tabStripResult.dragStarted) {
+                    state.activeTabDragNodeId = tabStripResult.nodeId;
+                    state.activeTabDragPanelId = tabStripResult.draggedTabId;
+                    SyncDockPreview(state, layout);
+                }
+                if (tabStripResult.dragEnded || tabStripResult.dragCanceled) {
+                    ClearTabDockDragState(state);
+                }
+                if (eventResult.consumed ||
+                    eventResult.hitTarget.kind != UIEditorDockHostHitTargetKind::None) {
+                    state.dockHostState.focused = true;
+                }
             }
             break;
 
@@ -388,6 +598,7 @@ UIEditorDockHostInteractionFrame UpdateUIEditorDockHostInteraction(
             if (!state.splitterDragState.active) {
                 state.dockHostState.hoveredTarget = {};
             }
+            state.dockHostState.dropPreview = {};
             if (!HasFocusedTabStrip(state)) {
                 state.dockHostState.focused = false;
             }
@@ -464,6 +675,96 @@ UIEditorDockHostInteractionFrame UpdateUIEditorDockHostInteraction(
                 break;
             }
 
+            if (tabStripResult.reorderRequested &&
+                !tabStripResult.nodeId.empty() &&
+                !tabStripResult.draggedTabId.empty() &&
+                tabStripResult.dropInsertionIndex != Widgets::UIEditorTabStripInvalidIndex) {
+                {
+                    std::ostringstream trace = {};
+                    trace << "same-stack reorder node=" << tabStripResult.nodeId
+                          << " panel=" << tabStripResult.draggedTabId
+                          << " insertion=" << tabStripResult.dropInsertionIndex;
+                    AppendUIEditorRuntimeTrace("dock", trace.str());
+                }
+                eventResult.layoutResult = controller.ReorderTab(
+                    tabStripResult.nodeId,
+                    tabStripResult.draggedTabId,
+                    tabStripResult.dropInsertionIndex);
+                eventResult.layoutChanged =
+                    eventResult.layoutResult.status ==
+                    UIEditorWorkspaceLayoutOperationStatus::Changed;
+                eventResult.consumed = true;
+                eventResult.hitTarget = tabStripResult.hitTarget;
+                ClearTabDockDragState(state);
+                state.dockHostState.focused = true;
+                break;
+            }
+
+            if (state.dockHostState.dropPreview.visible &&
+                !state.activeTabDragNodeId.empty() &&
+                !state.activeTabDragPanelId.empty()) {
+                const Widgets::UIEditorDockHostDropPreviewState preview =
+                    state.dockHostState.dropPreview;
+                {
+                    std::ostringstream trace = {};
+                    trace << "drop commit sourceNode=" << state.activeTabDragNodeId
+                          << " panel=" << state.activeTabDragPanelId
+                          << " targetNode=" << preview.targetNodeId
+                          << " placement=" << static_cast<int>(preview.placement)
+                          << " insertion=" << preview.insertionIndex;
+                    AppendUIEditorRuntimeTrace("dock", trace.str());
+                }
+                if (preview.placement == UIEditorWorkspaceDockPlacement::Center) {
+                    std::size_t insertionIndex = preview.insertionIndex;
+                    if (insertionIndex == Widgets::UIEditorTabStripInvalidIndex) {
+                        if (const UIEditorDockHostTabStackLayout* targetTabStack =
+                                FindTabStackLayoutByNodeId(layout, preview.targetNodeId);
+                            targetTabStack != nullptr) {
+                            insertionIndex = targetTabStack->items.size();
+                        } else {
+                            insertionIndex = 0u;
+                        }
+                    }
+
+                    eventResult.layoutResult = controller.MoveTabToStack(
+                        state.activeTabDragNodeId,
+                        state.activeTabDragPanelId,
+                        preview.targetNodeId,
+                        insertionIndex);
+                } else {
+                    eventResult.layoutResult = controller.DockTabRelative(
+                        state.activeTabDragNodeId,
+                        state.activeTabDragPanelId,
+                        preview.targetNodeId,
+                        preview.placement);
+                }
+                eventResult.layoutChanged =
+                    eventResult.layoutResult.status ==
+                    UIEditorWorkspaceLayoutOperationStatus::Changed;
+                AppendUIEditorRuntimeTrace(
+                    "dock",
+                    "drop result status=" +
+                        std::string(
+                            GetUIEditorWorkspaceLayoutOperationStatusName(
+                                eventResult.layoutResult.status)) +
+                        " message=" + eventResult.layoutResult.message);
+                eventResult.consumed = true;
+                eventResult.hitTarget.nodeId = preview.targetNodeId;
+                eventResult.releasePointerCapture =
+                    eventResult.releasePointerCapture || tabStripResult.releasePointerCapture;
+                ClearTabDockDragState(state);
+                state.dockHostState.focused = true;
+                break;
+            }
+
+            if (tabStripResult.dragEnded || tabStripResult.dragCanceled) {
+                eventResult.consumed = tabStripResult.consumed;
+                eventResult.hitTarget = tabStripResult.hitTarget;
+                ClearTabDockDragState(state);
+                state.dockHostState.focused = true;
+                break;
+            }
+
             if (tabStripResult.commandRequested && !tabStripResult.panelId.empty()) {
                 eventResult.commandResult = DispatchPanelCommand(
                     controller,
@@ -534,6 +835,14 @@ UIEditorDockHostInteractionFrame UpdateUIEditorDockHostInteraction(
             break;
 
         case UIInputEventType::KeyDown:
+            if (tabStripResult.dragCanceled) {
+                eventResult.consumed = true;
+                eventResult.hitTarget = tabStripResult.hitTarget;
+                ClearTabDockDragState(state);
+                state.dockHostState.focused = true;
+                break;
+            }
+
             if (tabStripResult.commandRequested && !tabStripResult.panelId.empty()) {
                 eventResult.commandResult = DispatchPanelCommand(
                     controller,

new_editor/src/Shell/UIEditorMenuBar.cpp

@@ -11,8 +11,6 @@ using ::XCEngine::UI::UIDrawList;
 using ::XCEngine::UI::UIPoint;
 using ::XCEngine::UI::UIRect;
 
-constexpr float kMenuBarFontSize = 13.0f;
-
 float ClampNonNegative(float value) {
     return (std::max)(value, 0.0f);
 }
@@ -24,6 +22,10 @@ bool IsPointInsideRect(const UIRect& rect, const UIPoint& point) {
         point.y <= rect.y + rect.height;
 }
 
+bool IsVisibleColor(const UIColor& color) {
+    return color.a > 0.0f;
+}
+
 float ResolveEstimatedLabelWidth(
     const UIEditorMenuBarItem& item,
     const UIEditorMenuBarMetrics& metrics) {
@@ -35,7 +37,9 @@ float ResolveEstimatedLabelWidth(
 }
 
 float ResolveLabelTop(const UIRect& rect, const UIEditorMenuBarMetrics& metrics) {
-    return rect.y + (std::max)(0.0f, (rect.height - kMenuBarFontSize) * 0.5f) + metrics.labelInsetY;
+    return rect.y +
+        (std::max)(0.0f, (rect.height - ClampNonNegative(metrics.labelFontSize)) * 0.5f) +
+        metrics.labelInsetY;
 }
 
 bool IsButtonFocused(
@@ -164,27 +168,40 @@ void AppendUIEditorMenuBarBackground(
     const UIEditorMenuBarPalette& palette,
     const UIEditorMenuBarMetrics& metrics) {
     drawList.AddFilledRect(layout.bounds, palette.barColor, metrics.barCornerRounding);
+    const UIColor barBorderColor =
+        state.focused ? palette.focusedBorderColor : palette.borderColor;
+    const float barBorderThickness =
+        state.focused ? metrics.focusedBorderThickness : metrics.baseBorderThickness;
+    if (IsVisibleColor(barBorderColor) && barBorderThickness > 0.0f) {
         drawList.AddRectOutline(
             layout.bounds,
-        state.focused ? palette.focusedBorderColor : palette.borderColor,
-        state.focused ? metrics.focusedBorderThickness : metrics.baseBorderThickness,
+            barBorderColor,
+            barBorderThickness,
             metrics.barCornerRounding);
+    }
 
     for (std::size_t index = 0; index < layout.buttonRects.size() && index < items.size(); ++index) {
         const bool open = state.openIndex == index;
         const bool hovered = state.hoveredIndex == index;
         const bool focused = IsButtonFocused(state, index);
+        const UIColor buttonFillColor = ResolveButtonFillColor(open, hovered, palette);
+        const UIColor buttonBorderColor = ResolveButtonBorderColor(open, focused, palette);
+        const float buttonBorderThickness = ResolveButtonBorderThickness(open, focused, metrics);
+        if (IsVisibleColor(buttonFillColor)) {
             drawList.AddFilledRect(
                 layout.buttonRects[index],
-            ResolveButtonFillColor(open, hovered, palette),
+                buttonFillColor,
                 metrics.buttonCornerRounding);
+        }
+        if (IsVisibleColor(buttonBorderColor) && buttonBorderThickness > 0.0f) {
             drawList.AddRectOutline(
                 layout.buttonRects[index],
-            ResolveButtonBorderColor(open, focused, palette),
-            ResolveButtonBorderThickness(open, focused, metrics),
+                buttonBorderColor,
+                buttonBorderThickness,
                 metrics.buttonCornerRounding);
         }
     }
+}
 
 void AppendUIEditorMenuBarForeground(
     UIDrawList& drawList,
@@ -206,7 +223,7 @@ void AppendUIEditorMenuBarForeground(
             UIPoint(textLeft, ResolveLabelTop(rect, metrics)),
             items[index].label,
             items[index].enabled ? palette.textPrimary : palette.textDisabled,
-            kMenuBarFontSize);
+            ClampNonNegative(metrics.labelFontSize));
         drawList.PopClipRect();
     }
 }

new_editor/src/Shell/UIEditorMenuPopup.cpp

@@ -171,8 +171,14 @@ void AppendUIEditorMenuPopupBackground(
         const UIRect& rect = layout.itemRects[index];
         if (item.kind == UIEditorMenuItemKind::Separator) {
             const float lineY = rect.y + rect.height * 0.5f;
+            const float separatorInset =
+                ClampNonNegative(metrics.contentPaddingX) + 3.0f;
             drawList.AddFilledRect(
-                UIRect(rect.x + 8.0f, lineY, (std::max)(rect.width - 16.0f, 0.0f), metrics.separatorThickness),
+                UIRect(
+                    rect.x + separatorInset,
+                    lineY,
+                    (std::max)(rect.width - separatorInset * 2.0f, 0.0f),
+                    metrics.separatorThickness),
                 palette.separatorColor);
             continue;
         }

new_editor/src/Shell/UIEditorShellCompose.cpp

@@ -191,6 +191,19 @@ void AppendUIEditorShellToolbar(
 
 } // namespace
 
+UIEditorShellComposeLayout BuildUIEditorShellComposeLayout(
+    const UIRect& bounds,
+    const std::vector<Widgets::UIEditorMenuBarItem>& menuBarItems,
+    const std::vector<Widgets::UIEditorStatusBarSegment>& statusSegments,
+    const UIEditorShellComposeMetrics& metrics) {
+    return BuildUIEditorShellComposeLayout(
+        bounds,
+        menuBarItems,
+        {},
+        statusSegments,
+        metrics);
+}
+
 UIEditorShellComposeLayout BuildUIEditorShellComposeLayout(
     const UIRect& bounds,
     const std::vector<Widgets::UIEditorMenuBarItem>& menuBarItems,

new_editor/src/Shell/UIEditorShellInteraction.cpp

@@ -148,7 +148,9 @@ const std::vector<UIEditorResolvedMenuItem>* ResolvePopupItems(
 }
 
 std::vector<Widgets::UIEditorMenuBarItem> BuildMenuBarItems(
-    const UIEditorResolvedMenuModel& model) {
+    const UIEditorResolvedMenuModel& model,
+    const UIEditorShellInteractionServices& services,
+    const Widgets::UIEditorMenuBarMetrics& metrics) {
     std::vector<Widgets::UIEditorMenuBarItem> items = {};
     items.reserve(model.menus.size());
 
@@ -157,6 +159,10 @@ std::vector<Widgets::UIEditorMenuBarItem> BuildMenuBarItems(
         item.menuId = menu.menuId;
         item.label = menu.label;
         item.enabled = !menu.items.empty();
+        if (services.textMeasurer != nullptr && !item.label.empty()) {
+            item.desiredLabelWidth = services.textMeasurer->MeasureTextWidth(
+                UIEditorTextMeasureRequest { item.label, metrics.labelFontSize });
+        }
         items.push_back(std::move(item));
     }
 
@@ -175,7 +181,9 @@ UIEditorShellComposeModel BuildShellComposeModel(
 }
 
 std::vector<Widgets::UIEditorMenuPopupItem> BuildPopupWidgetItems(
-    const std::vector<UIEditorResolvedMenuItem>& items) {
+    const std::vector<UIEditorResolvedMenuItem>& items,
+    const UIEditorShellInteractionServices& services,
+    const Widgets::UIEditorMenuPopupMetrics& metrics) {
     std::vector<Widgets::UIEditorMenuPopupItem> widgetItems = {};
     widgetItems.reserve(items.size());
 
@@ -188,6 +196,16 @@ std::vector<Widgets::UIEditorMenuPopupItem> BuildPopupWidgetItems(
         widgetItem.enabled = item.enabled;
         widgetItem.checked = item.checked;
         widgetItem.hasSubmenu = item.kind == UIEditorMenuItemKind::Submenu && !item.children.empty();
+        if (services.textMeasurer != nullptr) {
+            if (!widgetItem.label.empty()) {
+                widgetItem.desiredLabelWidth = services.textMeasurer->MeasureTextWidth(
+                    UIEditorTextMeasureRequest { widgetItem.label, metrics.labelFontSize });
+            }
+            if (!widgetItem.shortcutText.empty()) {
+                widgetItem.desiredShortcutWidth = services.textMeasurer->MeasureTextWidth(
+                    UIEditorTextMeasureRequest { widgetItem.shortcutText, metrics.labelFontSize });
+            }
+        }
         widgetItems.push_back(std::move(widgetItem));
     }
 
@@ -244,10 +262,14 @@ BuildRequestOutput BuildRequest(
     const UIEditorWorkspaceController& controller,
     const UIEditorShellInteractionModel& model,
     const UIEditorShellInteractionState& state,
-    const UIEditorShellInteractionMetrics& metrics) {
+    const UIEditorShellInteractionMetrics& metrics,
+    const UIEditorShellInteractionServices& services) {
     BuildRequestOutput output = {};
     UIEditorShellInteractionRequest& request = output.request;
-    request.menuBarItems = BuildMenuBarItems(model.resolvedMenuModel);
+    request.menuBarItems = BuildMenuBarItems(
+        model.resolvedMenuModel,
+        services,
+        metrics.shellMetrics.menuBarMetrics);
 
     const UIEditorShellComposeModel shellModel =
         BuildShellComposeModel(model, request.menuBarItems);
@@ -293,7 +315,10 @@ BuildRequestOutput BuildRequest(
         popupRequest.sourceItemId = popupState.itemId;
         popupRequest.overlayEntry = *overlayEntry;
         popupRequest.resolvedItems = *resolvedItems;
-        popupRequest.widgetItems = BuildPopupWidgetItems(popupRequest.resolvedItems);
+        popupRequest.widgetItems = BuildPopupWidgetItems(
+            popupRequest.resolvedItems,
+            services,
+            metrics.popupMetrics);
 
         const float popupWidth =
             ResolveUIEditorMenuPopupDesiredWidth(popupRequest.widgetItems, metrics.popupMetrics);
@@ -506,7 +531,8 @@ UIEditorShellInteractionRequest ResolveUIEditorShellInteractionRequest(
         controller,
         model,
         state,
-        metrics).request;
+        metrics,
+        services).request;
 }
 
 UIEditorShellInteractionFrame UpdateUIEditorShellInteraction(
@@ -525,7 +551,8 @@ UIEditorShellInteractionFrame UpdateUIEditorShellInteraction(
         controller,
         model,
         state,
-        metrics);
+        metrics,
+        services);
     UIEditorShellInteractionRequest request = std::move(requestBuild.request);
 
     if (requestBuild.hadInvalidPopupState && state.menuSession.HasOpenMenu()) {
@@ -539,7 +566,8 @@ UIEditorShellInteractionFrame UpdateUIEditorShellInteraction(
             controller,
             model,
             state,
-            metrics);
+            metrics,
+            services);
         request = std::move(requestBuild.request);
     }
 
@@ -691,7 +719,8 @@ UIEditorShellInteractionFrame UpdateUIEditorShellInteraction(
                 controller,
                 model,
                 state,
-                metrics).request;
+                metrics,
+                services).request;
         }
     }
 
@@ -714,7 +743,8 @@ UIEditorShellInteractionFrame UpdateUIEditorShellInteraction(
         controller,
         model,
         state,
-        metrics).request;
+        metrics,
+        services).request;
 
     const RequestHit finalHit =
         HitTestRequest(request, state.pointerPosition, state.hasPointerPosition);

new_editor/src/Shell/UIEditorViewportSlot.cpp

@@ -110,21 +110,13 @@ UIColor ResolveSurfaceBorderColor(
         return palette.surfaceCapturedBorderColor;
     }
 
-    if (state.surfaceActive) {
-        return palette.surfaceActiveBorderColor;
-    }
-
-    if (state.surfaceHovered) {
-        return palette.surfaceHoveredBorderColor;
-    }
-
     return palette.surfaceBorderColor;
 }
 
 float ResolveSurfaceBorderThickness(
     const UIEditorViewportSlotState& state,
     const UIEditorViewportSlotMetrics& metrics) {
-    if (state.inputCaptured || state.focused) {
+    if (state.inputCaptured) {
         return metrics.focusedSurfaceBorderThickness;
     }
 
@@ -356,8 +348,8 @@ void AppendUIEditorViewportSlotBackground(
     drawList.AddFilledRect(layout.bounds, palette.frameColor, metrics.cornerRounding);
     drawList.AddRectOutline(
         layout.bounds,
-        state.focused ? palette.focusedBorderColor : palette.borderColor,
-        state.focused ? metrics.focusedBorderThickness : metrics.outerBorderThickness,
+        palette.borderColor,
+        metrics.outerBorderThickness,
         metrics.cornerRounding);
 
     if (layout.hasTopBar) {
@@ -366,12 +358,6 @@ void AppendUIEditorViewportSlotBackground(
 
     drawList.AddFilledRect(layout.surfaceRect, palette.surfaceColor);
 
-    if (state.surfaceHovered) {
-        drawList.AddFilledRect(layout.inputRect, palette.surfaceHoverOverlayColor);
-    }
-    if (state.surfaceActive) {
-        drawList.AddFilledRect(layout.inputRect, palette.surfaceActiveOverlayColor);
-    }
     if (state.inputCaptured) {
         drawList.AddFilledRect(layout.inputRect, palette.captureOverlayColor);
     }

new_editor/src/Shell/UIEditorWorkspaceController.cpp

@@ -1,12 +1,22 @@
 #include <XCEditor/Shell/UIEditorWorkspaceController.h>
+#include <XCEditor/Foundation/UIEditorRuntimeTrace.h>
 
 #include <cmath>
+#include <sstream>
 #include <utility>
 
 namespace XCEngine::UI::Editor {
 
 namespace {
 
+bool IsPanelOpenAndVisible(
+    const UIEditorWorkspaceSession& session,
+    std::string_view panelId) {
+    const UIEditorPanelSessionState* panelState =
+        FindUIEditorPanelSessionState(session, panelId);
+    return panelState != nullptr && panelState->open && panelState->visible;
+}
+
 std::vector<std::string> CollectVisiblePanelIds(
     const UIEditorWorkspaceModel& workspace,
     const UIEditorWorkspaceSession& session) {
@@ -22,6 +32,58 @@ std::vector<std::string> CollectVisiblePanelIds(
     return ids;
 }
 
+struct VisibleTabStackInfo {
+    bool panelExists = false;
+    bool panelVisible = false;
+    std::size_t currentVisibleIndex = 0u;
+    std::size_t visibleTabCount = 0u;
+};
+
+VisibleTabStackInfo ResolveVisibleTabStackInfo(
+    const UIEditorWorkspaceNode& node,
+    const UIEditorWorkspaceSession& session,
+    std::string_view panelId) {
+    VisibleTabStackInfo info = {};
+    for (const UIEditorWorkspaceNode& child : node.children) {
+        if (child.kind != UIEditorWorkspaceNodeKind::Panel) {
+            continue;
+        }
+
+        const bool visible = IsPanelOpenAndVisible(session, child.panel.panelId);
+        if (child.panel.panelId == panelId) {
+            info.panelExists = true;
+            info.panelVisible = visible;
+            if (visible) {
+                info.currentVisibleIndex = info.visibleTabCount;
+            }
+        }
+
+        if (visible) {
+            ++info.visibleTabCount;
+        }
+    }
+
+    return info;
+}
+
+std::size_t CountVisibleTabs(
+    const UIEditorWorkspaceNode& node,
+    const UIEditorWorkspaceSession& session) {
+    if (node.kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return 0u;
+    }
+
+    std::size_t visibleCount = 0u;
+    for (const UIEditorWorkspaceNode& child : node.children) {
+        if (child.kind == UIEditorWorkspaceNodeKind::Panel &&
+            IsPanelOpenAndVisible(session, child.panel.panelId)) {
+            ++visibleCount;
+        }
+    }
+
+    return visibleCount;
+}
+
 } // namespace
 
 std::string_view GetUIEditorWorkspaceCommandKindName(UIEditorWorkspaceCommandKind kind) {
@@ -297,6 +359,290 @@ UIEditorWorkspaceLayoutOperationResult UIEditorWorkspaceController::SetSplitRati
         "Split ratio updated.");
 }
 
+UIEditorWorkspaceLayoutOperationResult UIEditorWorkspaceController::ReorderTab(
+    std::string_view nodeId,
+    std::string_view panelId,
+    std::size_t targetVisibleInsertionIndex) {
+    const UIEditorWorkspaceControllerValidationResult validation = ValidateState();
+    if (!validation.IsValid()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "Controller state invalid: " + validation.message);
+    }
+
+    if (nodeId.empty()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "ReorderTab requires a tab stack node id.");
+    }
+
+    if (panelId.empty()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "ReorderTab requires a panel id.");
+    }
+
+    const UIEditorWorkspaceNode* tabStack = FindUIEditorWorkspaceNode(m_workspace, nodeId);
+    if (tabStack == nullptr || tabStack->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "ReorderTab target tab stack is missing.");
+    }
+
+    const VisibleTabStackInfo tabInfo =
+        ResolveVisibleTabStackInfo(*tabStack, m_session, panelId);
+    if (!tabInfo.panelExists) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "ReorderTab target panel is missing from the specified tab stack.");
+    }
+
+    if (!tabInfo.panelVisible) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "ReorderTab only supports open and visible tabs.");
+    }
+
+    if (targetVisibleInsertionIndex > tabInfo.visibleTabCount) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "ReorderTab target visible insertion index is out of range.");
+    }
+
+    if (targetVisibleInsertionIndex == tabInfo.currentVisibleIndex ||
+        targetVisibleInsertionIndex == tabInfo.currentVisibleIndex + 1u) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::NoOp,
+            "Visible tab order already matches the requested insertion.");
+    }
+
+    const UIEditorWorkspaceModel previousWorkspace = m_workspace;
+    if (!TryReorderUIEditorWorkspaceTab(
+            m_workspace,
+            m_session,
+            nodeId,
+            panelId,
+            targetVisibleInsertionIndex)) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "Tab reorder rejected.");
+    }
+
+    if (AreUIEditorWorkspaceModelsEquivalent(previousWorkspace, m_workspace)) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::NoOp,
+            "Visible tab order already matches the requested insertion.");
+    }
+
+    const UIEditorWorkspaceControllerValidationResult postValidation = ValidateState();
+    if (!postValidation.IsValid()) {
+        m_workspace = previousWorkspace;
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "Tab reorder produced invalid controller state: " + postValidation.message);
+    }
+
+    return BuildLayoutOperationResult(
+        UIEditorWorkspaceLayoutOperationStatus::Changed,
+        "Tab reordered.");
+}
+
+UIEditorWorkspaceLayoutOperationResult UIEditorWorkspaceController::MoveTabToStack(
+    std::string_view sourceNodeId,
+    std::string_view panelId,
+    std::string_view targetNodeId,
+    std::size_t targetVisibleInsertionIndex) {
+    {
+        std::ostringstream trace = {};
+        trace << "MoveTabToStack begin sourceNode=" << sourceNodeId
+              << " panel=" << panelId
+              << " targetNode=" << targetNodeId
+              << " insertion=" << targetVisibleInsertionIndex;
+        AppendUIEditorRuntimeTrace("workspace", trace.str());
+    }
+    const UIEditorWorkspaceControllerValidationResult validation = ValidateState();
+    if (!validation.IsValid()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "Controller state invalid: " + validation.message);
+    }
+
+    if (sourceNodeId.empty() || targetNodeId.empty()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack requires both source and target tab stack ids.");
+    }
+
+    if (panelId.empty()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack requires a panel id.");
+    }
+
+    if (sourceNodeId == targetNodeId) {
+        return ReorderTab(sourceNodeId, panelId, targetVisibleInsertionIndex);
+    }
+
+    const UIEditorWorkspaceNode* sourceTabStack =
+        FindUIEditorWorkspaceNode(m_workspace, sourceNodeId);
+    const UIEditorWorkspaceNode* targetTabStack =
+        FindUIEditorWorkspaceNode(m_workspace, targetNodeId);
+    if (sourceTabStack == nullptr ||
+        targetTabStack == nullptr ||
+        sourceTabStack->kind != UIEditorWorkspaceNodeKind::TabStack ||
+        targetTabStack->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack source or target tab stack is missing.");
+    }
+
+    const VisibleTabStackInfo sourceInfo =
+        ResolveVisibleTabStackInfo(*sourceTabStack, m_session, panelId);
+    if (!sourceInfo.panelExists) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack target panel is missing from the source tab stack.");
+    }
+
+    if (!sourceInfo.panelVisible) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack only supports open and visible tabs.");
+    }
+
+    const std::size_t visibleTargetCount = CountVisibleTabs(*targetTabStack, m_session);
+    if (targetVisibleInsertionIndex > visibleTargetCount) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack target visible insertion index is out of range.");
+    }
+
+    const UIEditorWorkspaceModel previousWorkspace = m_workspace;
+    if (!TryMoveUIEditorWorkspaceTabToStack(
+            m_workspace,
+            m_session,
+            sourceNodeId,
+            panelId,
+            targetNodeId,
+            targetVisibleInsertionIndex)) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack rejected.");
+    }
+
+    if (AreUIEditorWorkspaceModelsEquivalent(previousWorkspace, m_workspace)) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::NoOp,
+            "Tab already matches the requested target stack insertion.");
+    }
+
+    const UIEditorWorkspaceControllerValidationResult postValidation = ValidateState();
+    if (!postValidation.IsValid()) {
+        m_workspace = previousWorkspace;
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "MoveTabToStack produced invalid controller state: " + postValidation.message);
+    }
+
+    return BuildLayoutOperationResult(
+        UIEditorWorkspaceLayoutOperationStatus::Changed,
+        "Tab moved to target stack.");
+}
+
+UIEditorWorkspaceLayoutOperationResult UIEditorWorkspaceController::DockTabRelative(
+    std::string_view sourceNodeId,
+    std::string_view panelId,
+    std::string_view targetNodeId,
+    UIEditorWorkspaceDockPlacement placement,
+    float splitRatio) {
+    {
+        std::ostringstream trace = {};
+        trace << "DockTabRelative begin sourceNode=" << sourceNodeId
+              << " panel=" << panelId
+              << " targetNode=" << targetNodeId
+              << " placement=" << static_cast<int>(placement)
+              << " splitRatio=" << splitRatio;
+        AppendUIEditorRuntimeTrace("workspace", trace.str());
+    }
+    const UIEditorWorkspaceControllerValidationResult validation = ValidateState();
+    if (!validation.IsValid()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "Controller state invalid: " + validation.message);
+    }
+
+    if (sourceNodeId.empty() || targetNodeId.empty()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "DockTabRelative requires both source and target tab stack ids.");
+    }
+
+    if (panelId.empty()) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "DockTabRelative requires a panel id.");
+    }
+
+    const UIEditorWorkspaceNode* sourceTabStack =
+        FindUIEditorWorkspaceNode(m_workspace, sourceNodeId);
+    const UIEditorWorkspaceNode* targetTabStack =
+        FindUIEditorWorkspaceNode(m_workspace, targetNodeId);
+    if (sourceTabStack == nullptr ||
+        targetTabStack == nullptr ||
+        sourceTabStack->kind != UIEditorWorkspaceNodeKind::TabStack ||
+        targetTabStack->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "DockTabRelative source or target tab stack is missing.");
+    }
+
+    const VisibleTabStackInfo sourceInfo =
+        ResolveVisibleTabStackInfo(*sourceTabStack, m_session, panelId);
+    if (!sourceInfo.panelExists) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "DockTabRelative target panel is missing from the source tab stack.");
+    }
+
+    if (!sourceInfo.panelVisible) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "DockTabRelative only supports open and visible tabs.");
+    }
+
+    const UIEditorWorkspaceModel previousWorkspace = m_workspace;
+    if (!TryDockUIEditorWorkspaceTabRelative(
+            m_workspace,
+            m_session,
+            sourceNodeId,
+            panelId,
+            targetNodeId,
+            placement,
+            splitRatio)) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "DockTabRelative rejected.");
+    }
+
+    if (AreUIEditorWorkspaceModelsEquivalent(previousWorkspace, m_workspace)) {
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::NoOp,
+            "Dock layout already matches the requested placement.");
+    }
+
+    const UIEditorWorkspaceControllerValidationResult postValidation = ValidateState();
+    if (!postValidation.IsValid()) {
+        m_workspace = previousWorkspace;
+        return BuildLayoutOperationResult(
+            UIEditorWorkspaceLayoutOperationStatus::Rejected,
+            "DockTabRelative produced invalid controller state: " + postValidation.message);
+    }
+
+    return BuildLayoutOperationResult(
+        UIEditorWorkspaceLayoutOperationStatus::Changed,
+        "Tab docked relative to target stack.");
+}
+
 UIEditorWorkspaceCommandResult UIEditorWorkspaceController::Dispatch(
     const UIEditorWorkspaceCommand& command) {
     const UIEditorWorkspaceControllerValidationResult validation = ValidateState();

new_editor/src/Shell/UIEditorWorkspaceModel.cpp

@@ -1,5 +1,6 @@
 #include <XCEditor/Shell/UIEditorPanelRegistry.h>
 #include <XCEditor/Shell/UIEditorWorkspaceModel.h>
+#include <XCEditor/Shell/UIEditorWorkspaceSession.h>
 
 #include <cmath>
 #include <unordered_set>
@@ -43,6 +44,19 @@ UIEditorWorkspaceNode WrapStandalonePanelAsTabStack(UIEditorWorkspaceNode panelN
     return tabStack;
 }
 
+void CollapseSplitNodeToOnlyChild(UIEditorWorkspaceNode& node) {
+    if (node.kind != UIEditorWorkspaceNodeKind::Split ||
+        node.children.size() != 1u) {
+        return;
+    }
+
+    // Move the remaining child through a temporary object first. Assigning
+    // directly from node.children.front() aliases a subobject of node and can
+    // trigger use-after-move when the vector storage is torn down.
+    UIEditorWorkspaceNode remainingChild = std::move(node.children.front());
+    node = std::move(remainingChild);
+}
+
 void CanonicalizeNodeRecursive(
     UIEditorWorkspaceNode& node,
     bool allowStandalonePanelLeaf) {
@@ -67,7 +81,7 @@ void CanonicalizeNodeRecursive(
 
     if (node.kind == UIEditorWorkspaceNodeKind::Split &&
         node.children.size() == 1u) {
-        node = std::move(node.children.front());
+        CollapseSplitNodeToOnlyChild(node);
     }
 }
 
@@ -131,6 +145,256 @@ UIEditorWorkspaceNode* FindMutableNodeRecursive(
     return nullptr;
 }
 
+bool FindNodePathRecursive(
+    const UIEditorWorkspaceNode& node,
+    std::string_view nodeId,
+    std::vector<std::size_t>& path) {
+    if (node.nodeId == nodeId) {
+        return true;
+    }
+
+    for (std::size_t index = 0; index < node.children.size(); ++index) {
+        path.push_back(index);
+        if (FindNodePathRecursive(node.children[index], nodeId, path)) {
+            return true;
+        }
+        path.pop_back();
+    }
+
+    return false;
+}
+
+UIEditorWorkspaceNode* ResolveMutableNodeByPath(
+    UIEditorWorkspaceNode& node,
+    const std::vector<std::size_t>& path) {
+    UIEditorWorkspaceNode* current = &node;
+    for (const std::size_t childIndex : path) {
+        if (childIndex >= current->children.size()) {
+            return nullptr;
+        }
+        current = &current->children[childIndex];
+    }
+
+    return current;
+}
+
+bool IsPanelOpenAndVisibleInSession(
+    const UIEditorWorkspaceSession& session,
+    std::string_view panelId) {
+    const UIEditorPanelSessionState* state = FindUIEditorPanelSessionState(session, panelId);
+    return state != nullptr && state->open && state->visible;
+}
+
+std::size_t CountVisibleChildren(
+    const UIEditorWorkspaceNode& node,
+    const UIEditorWorkspaceSession& session) {
+    if (node.kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return 0u;
+    }
+
+    std::size_t visibleCount = 0u;
+    for (const UIEditorWorkspaceNode& child : node.children) {
+        if (child.kind == UIEditorWorkspaceNodeKind::Panel &&
+            IsPanelOpenAndVisibleInSession(session, child.panel.panelId)) {
+            ++visibleCount;
+        }
+    }
+
+    return visibleCount;
+}
+
+std::size_t ResolveActualInsertionIndexForVisibleInsertion(
+    const UIEditorWorkspaceNode& node,
+    const UIEditorWorkspaceSession& session,
+    std::size_t targetVisibleInsertionIndex) {
+    std::vector<std::size_t> visibleIndices = {};
+    visibleIndices.reserve(node.children.size());
+    for (std::size_t index = 0; index < node.children.size(); ++index) {
+        const UIEditorWorkspaceNode& child = node.children[index];
+        if (child.kind == UIEditorWorkspaceNodeKind::Panel &&
+            IsPanelOpenAndVisibleInSession(session, child.panel.panelId)) {
+            visibleIndices.push_back(index);
+        }
+    }
+
+    if (targetVisibleInsertionIndex == 0u) {
+        return visibleIndices.empty() ? 0u : visibleIndices.front();
+    }
+
+    if (visibleIndices.empty()) {
+        return 0u;
+    }
+
+    if (targetVisibleInsertionIndex >= visibleIndices.size()) {
+        return visibleIndices.back() + 1u;
+    }
+
+    return visibleIndices[targetVisibleInsertionIndex];
+}
+
+void FixTabStackSelectedIndex(
+    UIEditorWorkspaceNode& node,
+    std::string_view preferredPanelId) {
+    if (node.kind != UIEditorWorkspaceNodeKind::TabStack || node.children.empty()) {
+        return;
+    }
+
+    for (std::size_t index = 0; index < node.children.size(); ++index) {
+        if (node.children[index].kind == UIEditorWorkspaceNodeKind::Panel &&
+            node.children[index].panel.panelId == preferredPanelId) {
+            node.selectedTabIndex = index;
+            return;
+        }
+    }
+
+    if (node.selectedTabIndex >= node.children.size()) {
+        node.selectedTabIndex = node.children.size() - 1u;
+    }
+}
+
+bool RemoveNodeByIdRecursive(
+    UIEditorWorkspaceNode& node,
+    std::string_view nodeId) {
+    if (node.kind != UIEditorWorkspaceNodeKind::Split) {
+        return false;
+    }
+
+    for (std::size_t index = 0; index < node.children.size(); ++index) {
+        if (node.children[index].nodeId == nodeId) {
+            node.children.erase(node.children.begin() + static_cast<std::ptrdiff_t>(index));
+            if (node.children.size() == 1u) {
+                CollapseSplitNodeToOnlyChild(node);
+            }
+            return true;
+        }
+    }
+
+    for (UIEditorWorkspaceNode& child : node.children) {
+        if (RemoveNodeByIdRecursive(child, nodeId)) {
+            if (node.kind == UIEditorWorkspaceNodeKind::Split &&
+                node.children.size() == 1u) {
+                CollapseSplitNodeToOnlyChild(node);
+            }
+            return true;
+        }
+    }
+
+    return false;
+}
+
+float ClampDockSplitRatio(float value) {
+    constexpr float kMinRatio = 0.1f;
+    constexpr float kMaxRatio = 0.9f;
+    return (std::min)(kMaxRatio, (std::max)(kMinRatio, value));
+}
+
+bool IsLeadingDockPlacement(UIEditorWorkspaceDockPlacement placement) {
+    return placement == UIEditorWorkspaceDockPlacement::Left ||
+        placement == UIEditorWorkspaceDockPlacement::Top;
+}
+
+UIEditorWorkspaceSplitAxis ResolveDockSplitAxis(UIEditorWorkspaceDockPlacement placement) {
+    return placement == UIEditorWorkspaceDockPlacement::Left ||
+            placement == UIEditorWorkspaceDockPlacement::Right
+        ? UIEditorWorkspaceSplitAxis::Horizontal
+        : UIEditorWorkspaceSplitAxis::Vertical;
+}
+
+std::string MakeUniqueNodeId(
+    const UIEditorWorkspaceModel& workspace,
+    std::string base) {
+    if (base.empty()) {
+        base = "workspace-node";
+    }
+
+    if (FindUIEditorWorkspaceNode(workspace, base) == nullptr) {
+        return base;
+    }
+
+    for (std::size_t suffix = 1u; suffix < 1024u; ++suffix) {
+        const std::string candidate = base + "-" + std::to_string(suffix);
+        if (FindUIEditorWorkspaceNode(workspace, candidate) == nullptr) {
+            return candidate;
+        }
+    }
+
+    return base + "-overflow";
+}
+
+bool TryExtractVisiblePanelFromTabStack(
+    UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    std::string_view sourceNodeId,
+    std::string_view panelId,
+    UIEditorWorkspaceNode& extractedPanel) {
+    std::vector<std::size_t> sourcePath = {};
+    if (!FindNodePathRecursive(workspace.root, sourceNodeId, sourcePath)) {
+        return false;
+    }
+
+    UIEditorWorkspaceNode* sourceStack =
+        ResolveMutableNodeByPath(workspace.root, sourcePath);
+    if (sourceStack == nullptr ||
+        sourceStack->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return false;
+    }
+
+    std::size_t panelIndex = sourceStack->children.size();
+    for (std::size_t index = 0; index < sourceStack->children.size(); ++index) {
+        const UIEditorWorkspaceNode& child = sourceStack->children[index];
+        if (child.kind != UIEditorWorkspaceNodeKind::Panel) {
+            return false;
+        }
+
+        if (child.panel.panelId == panelId) {
+            if (!IsPanelOpenAndVisibleInSession(session, panelId)) {
+                return false;
+            }
+            panelIndex = index;
+            break;
+        }
+    }
+
+    if (panelIndex >= sourceStack->children.size()) {
+        return false;
+    }
+
+    if (sourcePath.empty() && sourceStack->children.size() == 1u) {
+        return false;
+    }
+
+    std::string fallbackSelectedPanelId = {};
+    if (sourceStack->selectedTabIndex < sourceStack->children.size()) {
+        fallbackSelectedPanelId =
+            sourceStack->children[sourceStack->selectedTabIndex].panel.panelId;
+    }
+
+    extractedPanel = std::move(sourceStack->children[panelIndex]);
+    sourceStack->children.erase(
+        sourceStack->children.begin() + static_cast<std::ptrdiff_t>(panelIndex));
+
+    if (sourceStack->children.empty()) {
+        if (sourcePath.empty()) {
+            return false;
+        }
+
+        if (!RemoveNodeByIdRecursive(workspace.root, sourceNodeId)) {
+            return false;
+        }
+    } else {
+        if (fallbackSelectedPanelId == panelId) {
+            const std::size_t nextIndex =
+                (std::min)(panelIndex, sourceStack->children.size() - 1u);
+            fallbackSelectedPanelId =
+                sourceStack->children[nextIndex].panel.panelId;
+        }
+        FixTabStackSelectedIndex(*sourceStack, fallbackSelectedPanelId);
+    }
+
+    workspace = CanonicalizeUIEditorWorkspaceModel(std::move(workspace));
+    return true;
+}
+
 bool TryActivateRecursive(
     UIEditorWorkspaceNode& node,
     std::string_view panelId) {
@@ -484,4 +748,266 @@ bool TrySetUIEditorWorkspaceSplitRatio(
     return true;
 }
 
+bool TryReorderUIEditorWorkspaceTab(
+    UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    std::string_view nodeId,
+    std::string_view panelId,
+    std::size_t targetVisibleInsertionIndex) {
+    UIEditorWorkspaceNode* node = FindMutableNodeRecursive(workspace.root, nodeId);
+    if (node == nullptr || node->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return false;
+    }
+
+    std::vector<std::size_t> visibleChildIndices = {};
+    std::vector<UIEditorWorkspaceNode> reorderedVisibleChildren = {};
+    visibleChildIndices.reserve(node->children.size());
+    reorderedVisibleChildren.reserve(node->children.size());
+
+    std::size_t sourceVisibleIndex = node->children.size();
+    for (std::size_t index = 0; index < node->children.size(); ++index) {
+        const UIEditorWorkspaceNode& child = node->children[index];
+        if (child.kind != UIEditorWorkspaceNodeKind::Panel) {
+            return false;
+        }
+
+        if (!IsPanelOpenAndVisibleInSession(session, child.panel.panelId)) {
+            continue;
+        }
+
+        if (child.panel.panelId == panelId) {
+            sourceVisibleIndex = visibleChildIndices.size();
+        }
+
+        visibleChildIndices.push_back(index);
+        reorderedVisibleChildren.push_back(child);
+    }
+
+    if (sourceVisibleIndex >= reorderedVisibleChildren.size() ||
+        targetVisibleInsertionIndex > reorderedVisibleChildren.size()) {
+        return false;
+    }
+
+    if (targetVisibleInsertionIndex == sourceVisibleIndex ||
+        targetVisibleInsertionIndex == sourceVisibleIndex + 1u) {
+        return false;
+    }
+
+    UIEditorWorkspaceNode movedChild =
+        std::move(reorderedVisibleChildren[sourceVisibleIndex]);
+    reorderedVisibleChildren.erase(
+        reorderedVisibleChildren.begin() + static_cast<std::ptrdiff_t>(sourceVisibleIndex));
+
+    std::size_t adjustedInsertionIndex = targetVisibleInsertionIndex;
+    if (adjustedInsertionIndex > sourceVisibleIndex) {
+        --adjustedInsertionIndex;
+    }
+    if (adjustedInsertionIndex > reorderedVisibleChildren.size()) {
+        adjustedInsertionIndex = reorderedVisibleChildren.size();
+    }
+
+    reorderedVisibleChildren.insert(
+        reorderedVisibleChildren.begin() +
+            static_cast<std::ptrdiff_t>(adjustedInsertionIndex),
+        std::move(movedChild));
+
+    std::string selectedPanelId = {};
+    if (node->selectedTabIndex < node->children.size()) {
+        selectedPanelId = node->children[node->selectedTabIndex].panel.panelId;
+    }
+
+    const std::vector<UIEditorWorkspaceNode> originalChildren = node->children;
+    std::size_t nextVisibleIndex = 0u;
+    for (std::size_t index = 0; index < originalChildren.size(); ++index) {
+        const UIEditorWorkspaceNode& originalChild = originalChildren[index];
+        if (!IsPanelOpenAndVisibleInSession(session, originalChild.panel.panelId)) {
+            node->children[index] = originalChild;
+            continue;
+        }
+
+        node->children[index] = reorderedVisibleChildren[nextVisibleIndex];
+        ++nextVisibleIndex;
+    }
+
+    for (std::size_t index = 0; index < node->children.size(); ++index) {
+        if (node->children[index].panel.panelId == selectedPanelId) {
+            node->selectedTabIndex = index;
+            break;
+        }
+    }
+
+    return true;
+}
+
+bool TryMoveUIEditorWorkspaceTabToStack(
+    UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    std::string_view sourceNodeId,
+    std::string_view panelId,
+    std::string_view targetNodeId,
+    std::size_t targetVisibleInsertionIndex) {
+    if (sourceNodeId.empty() ||
+        panelId.empty() ||
+        targetNodeId.empty()) {
+        return false;
+    }
+
+    if (sourceNodeId == targetNodeId) {
+        return TryReorderUIEditorWorkspaceTab(
+            workspace,
+            session,
+            sourceNodeId,
+            panelId,
+            targetVisibleInsertionIndex);
+    }
+
+    const UIEditorWorkspaceNode* targetNode =
+        FindUIEditorWorkspaceNode(workspace, targetNodeId);
+    if (targetNode == nullptr ||
+        targetNode->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return false;
+    }
+
+    if (targetVisibleInsertionIndex > CountVisibleChildren(*targetNode, session)) {
+        return false;
+    }
+
+    UIEditorWorkspaceNode extractedPanel = {};
+    if (!TryExtractVisiblePanelFromTabStack(
+            workspace,
+            session,
+            sourceNodeId,
+            panelId,
+            extractedPanel)) {
+        return false;
+    }
+
+    UIEditorWorkspaceNode* targetStack =
+        FindMutableNodeRecursive(workspace.root, targetNodeId);
+    if (targetStack == nullptr ||
+        targetStack->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return false;
+    }
+
+    const std::size_t actualInsertionIndex =
+        ResolveActualInsertionIndexForVisibleInsertion(
+            *targetStack,
+            session,
+            targetVisibleInsertionIndex);
+    if (actualInsertionIndex > targetStack->children.size()) {
+        return false;
+    }
+
+    targetStack->children.insert(
+        targetStack->children.begin() +
+            static_cast<std::ptrdiff_t>(actualInsertionIndex),
+        std::move(extractedPanel));
+    targetStack->selectedTabIndex = actualInsertionIndex;
+    workspace.activePanelId = std::string(panelId);
+    workspace = CanonicalizeUIEditorWorkspaceModel(std::move(workspace));
+    return true;
+}
+
+bool TryDockUIEditorWorkspaceTabRelative(
+    UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    std::string_view sourceNodeId,
+    std::string_view panelId,
+    std::string_view targetNodeId,
+    UIEditorWorkspaceDockPlacement placement,
+    float splitRatio) {
+    if (placement == UIEditorWorkspaceDockPlacement::Center) {
+        const UIEditorWorkspaceNode* targetNode =
+            FindUIEditorWorkspaceNode(workspace, targetNodeId);
+        if (targetNode == nullptr ||
+            targetNode->kind != UIEditorWorkspaceNodeKind::TabStack) {
+            return false;
+        }
+
+        return TryMoveUIEditorWorkspaceTabToStack(
+            workspace,
+            session,
+            sourceNodeId,
+            panelId,
+            targetNodeId,
+            CountVisibleChildren(*targetNode, session));
+    }
+
+    if (sourceNodeId.empty() ||
+        panelId.empty() ||
+        targetNodeId.empty()) {
+        return false;
+    }
+
+    const UIEditorWorkspaceNode* sourceNode =
+        FindUIEditorWorkspaceNode(workspace, sourceNodeId);
+    const UIEditorWorkspaceNode* targetNode =
+        FindUIEditorWorkspaceNode(workspace, targetNodeId);
+    if (sourceNode == nullptr ||
+        targetNode == nullptr ||
+        sourceNode->kind != UIEditorWorkspaceNodeKind::TabStack ||
+        targetNode->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return false;
+    }
+
+    if (sourceNodeId == targetNodeId &&
+        sourceNode->children.size() <= 1u) {
+        return false;
+    }
+
+    UIEditorWorkspaceNode extractedPanel = {};
+    if (!TryExtractVisiblePanelFromTabStack(
+            workspace,
+            session,
+            sourceNodeId,
+            panelId,
+            extractedPanel)) {
+        return false;
+    }
+
+    UIEditorWorkspaceNode* targetStack =
+        FindMutableNodeRecursive(workspace.root, targetNodeId);
+    if (targetStack == nullptr ||
+        targetStack->kind != UIEditorWorkspaceNodeKind::TabStack) {
+        return false;
+    }
+
+    const std::string movedStackNodeId = MakeUniqueNodeId(
+        workspace,
+        std::string(targetNodeId) + "__dock_" + std::string(panelId) + "_stack");
+    UIEditorWorkspaceNode movedStack = {};
+    movedStack.kind = UIEditorWorkspaceNodeKind::TabStack;
+    movedStack.nodeId = movedStackNodeId;
+    movedStack.selectedTabIndex = 0u;
+    movedStack.children.push_back(std::move(extractedPanel));
+
+    UIEditorWorkspaceNode existingTarget = std::move(*targetStack);
+    UIEditorWorkspaceNode primary = {};
+    UIEditorWorkspaceNode secondary = {};
+    if (IsLeadingDockPlacement(placement)) {
+        primary = std::move(movedStack);
+        secondary = std::move(existingTarget);
+    } else {
+        primary = std::move(existingTarget);
+        secondary = std::move(movedStack);
+    }
+
+    const float requestedRatio = ClampDockSplitRatio(splitRatio);
+    const float resolvedSplitRatio =
+        IsLeadingDockPlacement(placement)
+            ? requestedRatio
+            : (1.0f - requestedRatio);
+    *targetStack = BuildUIEditorWorkspaceSplit(
+        MakeUniqueNodeId(
+            workspace,
+            std::string(targetNodeId) + "__dock_split"),
+        ResolveDockSplitAxis(placement),
+        resolvedSplitRatio,
+        std::move(primary),
+        std::move(secondary));
+    workspace.activePanelId = std::string(panelId);
+    workspace = CanonicalizeUIEditorWorkspaceModel(std::move(workspace));
+    return true;
+}
+
 } // namespace XCEngine::UI::Editor

tests/UI/Editor/integration/CMakeLists.txt

@@ -148,6 +148,11 @@ if(TARGET editor_ui_scroll_view_basic_validation)
         editor_ui_scroll_view_basic_validation)
 endif()
 
+if(TARGET editor_ui_dock_tab_reorder_same_stack_validation)
+    list(APPEND EDITOR_UI_INTEGRATION_TARGETS
+        editor_ui_dock_tab_reorder_same_stack_validation)
+endif()
+
 add_custom_target(editor_ui_integration_tests
     DEPENDS
         ${EDITOR_UI_INTEGRATION_TARGETS}

tests/UI/Editor/integration/shell/CMakeLists.txt

@@ -13,6 +13,9 @@ endif()
 if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/dock_host_basic/CMakeLists.txt")
     add_subdirectory(dock_host_basic)
 endif()
+if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/dock_tab_reorder_same_stack/CMakeLists.txt")
+    add_subdirectory(dock_tab_reorder_same_stack)
+endif()
 if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/panel_content_host_basic/CMakeLists.txt")
     add_subdirectory(panel_content_host_basic)
 endif()

tests/UI/Editor/integration/shell/dock_host_basic/main.cpp

@@ -491,7 +491,7 @@ private:
         if (action == ActionId::Reset) {
             ResetScenario();
             m_lastStatus = "Ready";
-            m_lastMessage = "场景状态已重置。请重新检查 splitter drag / tab close / panel close / active panel sync。";
+            m_lastMessage = "场景状态已重置。请重新检查 splitter drag / tab activate / panel close / active panel sync。";
             m_lastColor = kWarning;
             return;
         }
@@ -586,11 +586,11 @@ private:
 
         DrawCard(drawList, m_introRect, "这个测试验证什么功能？", "只验证 DockHost 基础交互 contract，不做 editor 业务面板。");
         drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 72.0f), "1. 验证 splitter drag 是否只通过 DockHostInteraction + WorkspaceController 完成。", kTextPrimary, 12.0f);
-        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 94.0f), "2. 验证 unified dock：tab activate / tab close / single-tab body activate。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 94.0f), "2. 验证 unified dock：tab activate / single-tab body activate / panel close。", kTextPrimary, 12.0f);
         drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 116.0f), "3. 验证 active panel、visible panels、split ratio 是否统一收口到 controller。", kTextPrimary, 12.0f);
         drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 138.0f), "4. 验证 pointer capture / release 请求是否通过 contract 明确返回。", kTextPrimary, 12.0f);
         drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 162.0f), "建议操作：先拖中间 splitter，再点 Document A。", kTextWeak, 11.0f);
-        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 180.0f), "然后关闭 Document B，最后点 Details 或 Console 的 X。", kTextWeak, 11.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 180.0f), "然后切换 Document A / B，最后点 Details 或 Console 的 X。", kTextWeak, 11.0f);
 
         DrawCard(drawList, m_controlsRect, "操作", "这里只保留当前场景必要按钮。");
         for (const ButtonState& button : m_buttons) {

tests/UI/Editor/integration/shell/dock_tab_reorder_same_stack/CMakeLists.txt

@@ -0,0 +1,30 @@
+add_executable(editor_ui_dock_tab_reorder_same_stack_validation WIN32
+    main.cpp
+)
+
+target_include_directories(editor_ui_dock_tab_reorder_same_stack_validation PRIVATE
+    ${XCENGINE_EDITOR_UI_TESTS_EDITOR_ROOT}/include
+    ${XCENGINE_EDITOR_UI_TESTS_EDITOR_ROOT}
+    ${CMAKE_SOURCE_DIR}/engine/include
+)
+
+target_compile_definitions(editor_ui_dock_tab_reorder_same_stack_validation PRIVATE
+    UNICODE
+    _UNICODE
+    XCENGINE_EDITOR_UI_TESTS_REPO_ROOT="${XCENGINE_EDITOR_UI_TESTS_REPO_ROOT_PATH}"
+)
+
+if(MSVC)
+    target_compile_options(editor_ui_dock_tab_reorder_same_stack_validation PRIVATE /utf-8 /FS)
+    set_property(TARGET editor_ui_dock_tab_reorder_same_stack_validation PROPERTY
+        MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>DLL")
+endif()
+
+target_link_libraries(editor_ui_dock_tab_reorder_same_stack_validation PRIVATE
+    XCUIEditorLib
+    XCUIEditorHost
+)
+
+set_target_properties(editor_ui_dock_tab_reorder_same_stack_validation PROPERTIES
+    OUTPUT_NAME "XCUIEditorDockTabReorderSameStackValidation"
+)

tests/UI/Editor/integration/shell/dock_tab_reorder_same_stack/main.cpp

@@ -0,0 +1,680 @@
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+
+#include <XCEditor/Shell/UIEditorDockHost.h>
+#include <XCEditor/Shell/UIEditorDockHostInteraction.h>
+#include <XCEditor/Shell/UIEditorWorkspaceController.h>
+#include <XCEditor/Shell/UIEditorWorkspaceModel.h>
+#include "Host/AutoScreenshot.h"
+#include "Host/NativeRenderer.h"
+
+#include <XCEngine/Input/InputTypes.h>
+#include <XCEngine/UI/DrawData.h>
+
+#include <windows.h>
+#include <windowsx.h>
+
+#include <algorithm>
+#include <filesystem>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#ifndef XCENGINE_EDITOR_UI_TESTS_REPO_ROOT
+#define XCENGINE_EDITOR_UI_TESTS_REPO_ROOT "."
+#endif
+
+namespace {
+
+using XCEngine::Input::KeyCode;
+using XCEngine::UI::UIColor;
+using XCEngine::UI::UIDrawData;
+using XCEngine::UI::UIDrawList;
+using XCEngine::UI::UIInputEvent;
+using XCEngine::UI::UIInputEventType;
+using XCEngine::UI::UIPoint;
+using XCEngine::UI::UIPointerButton;
+using XCEngine::UI::UIRect;
+using XCEngine::UI::Editor::BuildDefaultUIEditorWorkspaceController;
+using XCEngine::UI::Editor::BuildUIEditorWorkspacePanel;
+using XCEngine::UI::Editor::BuildUIEditorWorkspaceSingleTabStack;
+using XCEngine::UI::Editor::BuildUIEditorWorkspaceSplit;
+using XCEngine::UI::Editor::BuildUIEditorWorkspaceTabStack;
+using XCEngine::UI::Editor::FindUIEditorWorkspaceNode;
+using XCEngine::UI::Editor::Host::AutoScreenshotController;
+using XCEngine::UI::Editor::Host::NativeRenderer;
+using XCEngine::UI::Editor::UIEditorDockHostInteractionFrame;
+using XCEngine::UI::Editor::UIEditorDockHostInteractionResult;
+using XCEngine::UI::Editor::UIEditorDockHostInteractionState;
+using XCEngine::UI::Editor::UIEditorDockHostTabStripInteractionEntry;
+using XCEngine::UI::Editor::UIEditorPanelRegistry;
+using XCEngine::UI::Editor::UIEditorWorkspaceController;
+using XCEngine::UI::Editor::UIEditorWorkspaceLayoutOperationStatus;
+using XCEngine::UI::Editor::UIEditorWorkspaceModel;
+using XCEngine::UI::Editor::UIEditorWorkspaceSplitAxis;
+using XCEngine::UI::Editor::UpdateUIEditorDockHostInteraction;
+using XCEngine::UI::Editor::Widgets::AppendUIEditorDockHostBackground;
+using XCEngine::UI::Editor::Widgets::AppendUIEditorDockHostForeground;
+using XCEngine::UI::Editor::Widgets::UIEditorDockHostHitTarget;
+using XCEngine::UI::Editor::Widgets::UIEditorDockHostHitTargetKind;
+using XCEngine::UI::Editor::Widgets::UIEditorDockHostTabStackLayout;
+
+constexpr const wchar_t* kWindowClassName = L"XCUIEditorDockTabReorderSameStackValidation";
+constexpr const wchar_t* kWindowTitle = L"XCUI Editor | Dock Tab Reorder Same Stack";
+
+constexpr UIColor kWindowBg(0.10f, 0.10f, 0.10f, 1.0f);
+constexpr UIColor kCardBg(0.16f, 0.16f, 0.16f, 1.0f);
+constexpr UIColor kCardBorder(0.28f, 0.28f, 0.28f, 1.0f);
+constexpr UIColor kPreviewBg(0.12f, 0.12f, 0.12f, 1.0f);
+constexpr UIColor kTextPrimary(0.92f, 0.92f, 0.92f, 1.0f);
+constexpr UIColor kTextMuted(0.74f, 0.74f, 0.74f, 1.0f);
+constexpr UIColor kTextWeak(0.57f, 0.57f, 0.57f, 1.0f);
+constexpr UIColor kButtonBg(0.24f, 0.24f, 0.24f, 1.0f);
+constexpr UIColor kButtonHover(0.31f, 0.31f, 0.31f, 1.0f);
+constexpr UIColor kButtonBorder(0.44f, 0.44f, 0.44f, 1.0f);
+constexpr UIColor kOk(0.47f, 0.71f, 0.50f, 1.0f);
+constexpr UIColor kWarn(0.85f, 0.68f, 0.36f, 1.0f);
+
+enum class ActionId : unsigned char {
+    Reset = 0,
+    Capture
+};
+
+struct ButtonState {
+    ActionId action = ActionId::Reset;
+    std::string label = {};
+    UIRect rect = {};
+    bool hovered = false;
+};
+
+std::filesystem::path ResolveRepoRootPath() {
+    std::string root = XCENGINE_EDITOR_UI_TESTS_REPO_ROOT;
+    if (root.size() >= 2u && root.front() == '"' && root.back() == '"') {
+        root = root.substr(1u, root.size() - 2u);
+    }
+
+    return std::filesystem::path(root).lexically_normal();
+}
+
+bool ContainsPoint(const UIRect& rect, float x, float y) {
+    return x >= rect.x &&
+        x <= rect.x + rect.width &&
+        y >= rect.y &&
+        y <= rect.y + rect.height;
+}
+
+std::string FormatBool(bool value) {
+    return value ? "是" : "否";
+}
+
+std::string FormatOptionalIndex(std::size_t index) {
+    if (index == XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex) {
+        return "无";
+    }
+
+    return std::to_string(index);
+}
+
+std::string DescribeHitTarget(const UIEditorDockHostHitTarget& target) {
+    switch (target.kind) {
+    case UIEditorDockHostHitTargetKind::Tab:
+        return "标签: " + target.panelId;
+    case UIEditorDockHostHitTargetKind::TabStripBackground:
+        return "标签栏空白";
+    case UIEditorDockHostHitTargetKind::PanelBody:
+        return "面板主体: " + target.panelId;
+    case UIEditorDockHostHitTargetKind::SplitterHandle:
+        return "分割条: " + target.nodeId;
+    case UIEditorDockHostHitTargetKind::None:
+    default:
+        return "无";
+    }
+}
+
+void DrawCard(
+    UIDrawList& drawList,
+    const UIRect& rect,
+    std::string_view title,
+    std::string_view subtitle = {}) {
+    drawList.AddFilledRect(rect, kCardBg, 10.0f);
+    drawList.AddRectOutline(rect, kCardBorder, 1.0f, 10.0f);
+    drawList.AddText(UIPoint(rect.x + 16.0f, rect.y + 14.0f), std::string(title), kTextPrimary, 17.0f);
+    if (!subtitle.empty()) {
+        drawList.AddText(UIPoint(rect.x + 16.0f, rect.y + 38.0f), std::string(subtitle), kTextMuted, 12.0f);
+    }
+}
+
+void DrawButton(UIDrawList& drawList, const ButtonState& button) {
+    drawList.AddFilledRect(button.rect, button.hovered ? kButtonHover : kButtonBg, 8.0f);
+    drawList.AddRectOutline(button.rect, kButtonBorder, 1.0f, 8.0f);
+    drawList.AddText(UIPoint(button.rect.x + 14.0f, button.rect.y + 10.0f), button.label, kTextPrimary, 12.0f);
+}
+
+UIEditorPanelRegistry BuildPanelRegistry() {
+    UIEditorPanelRegistry registry = {};
+    registry.panels = {
+        { "doc-a", "Document A", {}, true, true, true },
+        { "doc-b", "Document B", {}, true, true, true },
+        { "doc-c", "Document C", {}, true, true, true },
+        { "details", "Details", {}, true, true, true }
+    };
+    return registry;
+}
+
+UIEditorWorkspaceModel BuildWorkspace() {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.72f,
+        BuildUIEditorWorkspaceTabStack(
+            "document-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true),
+                BuildUIEditorWorkspacePanel("doc-c-node", "doc-c", "Document C", true)
+            },
+            0u),
+        BuildUIEditorWorkspaceSingleTabStack("details-node", "details", "Details", true));
+    workspace.activePanelId = "doc-a";
+    return workspace;
+}
+
+std::string CollectDocumentTabOrder(const UIEditorWorkspaceController& controller) {
+    const auto* node = FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    if (node == nullptr) {
+        return "缺失";
+    }
+
+    std::ostringstream stream = {};
+    for (std::size_t index = 0; index < node->children.size(); ++index) {
+        if (index > 0u) {
+            stream << " | ";
+        }
+        stream << node->children[index].panel.panelId;
+    }
+    return stream.str();
+}
+
+const XCEngine::UI::Editor::Widgets::UIEditorDockHostTabStackLayout* FindDocumentTabStackLayout(
+    const UIEditorDockHostInteractionFrame& frame) {
+    for (const auto& tabStack : frame.layout.tabStacks) {
+        if (tabStack.nodeId == "document-tabs") {
+            return &tabStack;
+        }
+    }
+
+    return nullptr;
+}
+
+const UIEditorDockHostTabStripInteractionEntry* FindDocumentTabStripInteractionEntry(
+    const UIEditorDockHostInteractionState& state) {
+    for (const UIEditorDockHostTabStripInteractionEntry& entry : state.tabStripInteractions) {
+        if (entry.nodeId == "document-tabs") {
+            return &entry;
+        }
+    }
+
+    return nullptr;
+}
+
+class ScenarioApp {
+public:
+    int Run(HINSTANCE hInstance, int nCmdShow) {
+        if (!Initialize(hInstance, nCmdShow)) {
+            Shutdown();
+            return 1;
+        }
+
+        MSG message = {};
+        while (message.message != WM_QUIT) {
+            if (PeekMessageW(&message, nullptr, 0U, 0U, PM_REMOVE)) {
+                TranslateMessage(&message);
+                DispatchMessageW(&message);
+                continue;
+            }
+
+            RenderFrame();
+            Sleep(8);
+        }
+
+        Shutdown();
+        return static_cast<int>(message.wParam);
+    }
+
+private:
+    static LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) {
+        if (message == WM_NCCREATE) {
+            const auto* createStruct = reinterpret_cast<CREATESTRUCTW*>(lParam);
+            auto* app = reinterpret_cast<ScenarioApp*>(createStruct->lpCreateParams);
+            SetWindowLongPtrW(hwnd, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(app));
+            return TRUE;
+        }
+
+        auto* app = reinterpret_cast<ScenarioApp*>(GetWindowLongPtrW(hwnd, GWLP_USERDATA));
+        switch (message) {
+        case WM_SIZE:
+            if (app != nullptr && wParam != SIZE_MINIMIZED) {
+                app->m_renderer.Resize(static_cast<UINT>(LOWORD(lParam)), static_cast<UINT>(HIWORD(lParam)));
+            }
+            return 0;
+        case WM_PAINT:
+            if (app != nullptr) {
+                PAINTSTRUCT paintStruct = {};
+                BeginPaint(hwnd, &paintStruct);
+                app->RenderFrame();
+                EndPaint(hwnd, &paintStruct);
+                return 0;
+            }
+            break;
+        case WM_MOUSEMOVE:
+            if (app != nullptr) {
+                if (!app->m_trackingMouseLeave) {
+                    TRACKMOUSEEVENT trackMouseEvent = {};
+                    trackMouseEvent.cbSize = sizeof(trackMouseEvent);
+                    trackMouseEvent.dwFlags = TME_LEAVE;
+                    trackMouseEvent.hwndTrack = hwnd;
+                    if (TrackMouseEvent(&trackMouseEvent)) {
+                        app->m_trackingMouseLeave = true;
+                    }
+                }
+                app->HandleMouseMove(
+                    static_cast<float>(GET_X_LPARAM(lParam)),
+                    static_cast<float>(GET_Y_LPARAM(lParam)));
+                return 0;
+            }
+            break;
+        case WM_MOUSELEAVE:
+            if (app != nullptr) {
+                app->m_trackingMouseLeave = false;
+                UIInputEvent event = {};
+                event.type = UIInputEventType::PointerLeave;
+                app->m_pendingInputEvents.push_back(event);
+                return 0;
+            }
+            break;
+        case WM_LBUTTONDOWN:
+            if (app != nullptr) {
+                SetFocus(hwnd);
+                app->HandleLeftButtonDown(
+                    static_cast<float>(GET_X_LPARAM(lParam)),
+                    static_cast<float>(GET_Y_LPARAM(lParam)));
+                return 0;
+            }
+            break;
+        case WM_LBUTTONUP:
+            if (app != nullptr) {
+                app->HandleLeftButtonUp(
+                    static_cast<float>(GET_X_LPARAM(lParam)),
+                    static_cast<float>(GET_Y_LPARAM(lParam)));
+                return 0;
+            }
+            break;
+        case WM_SETFOCUS:
+            if (app != nullptr) {
+                UIInputEvent event = {};
+                event.type = UIInputEventType::FocusGained;
+                app->m_pendingInputEvents.push_back(event);
+                return 0;
+            }
+            break;
+        case WM_KILLFOCUS:
+            if (app != nullptr) {
+                UIInputEvent event = {};
+                event.type = UIInputEventType::FocusLost;
+                app->m_pendingInputEvents.push_back(event);
+                app->m_lastInputCause = "focus_lost";
+                return 0;
+            }
+            break;
+        case WM_CAPTURECHANGED:
+            if (app != nullptr &&
+                !app->m_interactionState.activeTabDragNodeId.empty() &&
+                reinterpret_cast<HWND>(lParam) != hwnd) {
+                UIInputEvent event = {};
+                event.type = UIInputEventType::FocusLost;
+                app->m_pendingInputEvents.push_back(event);
+                app->m_lastInputCause = "focus_lost";
+                return 0;
+            }
+            break;
+        case WM_KEYDOWN:
+        case WM_SYSKEYDOWN:
+            if (app != nullptr) {
+                if (wParam == VK_F12) {
+                    app->m_autoScreenshot.RequestCapture("manual_f12");
+                    return 0;
+                }
+
+                UIInputEvent event = {};
+                event.type = UIInputEventType::KeyDown;
+                event.keyCode = static_cast<std::int32_t>(wParam == VK_ESCAPE ? KeyCode::Escape : KeyCode::None);
+                app->m_pendingInputEvents.push_back(event);
+                return 0;
+            }
+            break;
+        case WM_ERASEBKGND:
+            return 1;
+        case WM_DESTROY:
+            PostQuitMessage(0);
+            return 0;
+        default:
+            break;
+        }
+
+        return DefWindowProcW(hwnd, message, wParam, lParam);
+    }
+
+    bool Initialize(HINSTANCE hInstance, int nCmdShow) {
+        m_captureRoot =
+            ResolveRepoRootPath() / "tests/UI/Editor/integration/shell/dock_tab_reorder_same_stack/captures";
+        m_autoScreenshot.Initialize(m_captureRoot);
+
+        WNDCLASSEXW windowClass = {};
+        windowClass.cbSize = sizeof(windowClass);
+        windowClass.style = CS_HREDRAW | CS_VREDRAW;
+        windowClass.lpfnWndProc = &ScenarioApp::WndProc;
+        windowClass.hInstance = hInstance;
+        windowClass.hCursor = LoadCursorW(nullptr, IDC_ARROW);
+        windowClass.lpszClassName = kWindowClassName;
+        m_windowClassAtom = RegisterClassExW(&windowClass);
+        if (m_windowClassAtom == 0) {
+            return false;
+        }
+
+        m_hwnd = CreateWindowExW(
+            0,
+            kWindowClassName,
+            kWindowTitle,
+            WS_OVERLAPPEDWINDOW | WS_VISIBLE,
+            CW_USEDEFAULT,
+            CW_USEDEFAULT,
+            1500,
+            920,
+            nullptr,
+            nullptr,
+            hInstance,
+            this);
+        if (m_hwnd == nullptr) {
+            return false;
+        }
+
+        ShowWindow(m_hwnd, nCmdShow);
+        if (!m_renderer.Initialize(m_hwnd)) {
+            return false;
+        }
+
+        ResetScenario();
+        return true;
+    }
+
+    void Shutdown() {
+        if (GetCapture() == m_hwnd) {
+            ReleaseCapture();
+        }
+        m_autoScreenshot.Shutdown();
+        m_renderer.Shutdown();
+        if (m_hwnd != nullptr && IsWindow(m_hwnd)) {
+            DestroyWindow(m_hwnd);
+        }
+        if (m_windowClassAtom != 0) {
+            UnregisterClassW(kWindowClassName, GetModuleHandleW(nullptr));
+        }
+    }
+
+    void ResetScenario() {
+        if (GetCapture() == m_hwnd) {
+            ReleaseCapture();
+        }
+
+        m_controller = BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
+        m_interactionState = {};
+        m_cachedFrame = {};
+        m_pendingInputEvents.clear();
+        m_lastInputCause.clear();
+        m_hoverText = "无";
+        m_lastResult = "等待验证：请在同一标签栏内拖拽标签。";
+        m_lastResultColor = kWarn;
+    }
+
+    void UpdateLayout() {
+        RECT clientRect = {};
+        GetClientRect(m_hwnd, &clientRect);
+        const float width = static_cast<float>((std::max)(clientRect.right - clientRect.left, 1L));
+        const float height = static_cast<float>((std::max)(clientRect.bottom - clientRect.top, 1L));
+        constexpr float padding = 20.0f;
+        constexpr float sidebarWidth = 360.0f;
+
+        m_introRect = UIRect(padding, padding, width - padding * 2.0f, 168.0f);
+        m_previewRect = UIRect(
+            padding,
+            m_introRect.y + m_introRect.height + 16.0f,
+            width - sidebarWidth - padding * 3.0f,
+            height - m_introRect.height - padding * 3.0f);
+        m_stateRect = UIRect(
+            m_previewRect.x + m_previewRect.width + 20.0f,
+            m_previewRect.y,
+            sidebarWidth,
+            m_previewRect.height);
+        m_dockHostRect = UIRect(
+            m_previewRect.x + 16.0f,
+            m_previewRect.y + 64.0f,
+            m_previewRect.width - 32.0f,
+            m_previewRect.height - 80.0f);
+
+        const float buttonWidth = (m_stateRect.width - 44.0f) * 0.5f;
+        const float buttonY = m_stateRect.y + m_stateRect.height - 52.0f;
+        m_buttons = {
+            { ActionId::Reset, "重置", UIRect(m_stateRect.x + 16.0f, buttonY, buttonWidth, 36.0f), false },
+            { ActionId::Capture, "截图(F12)", UIRect(m_stateRect.x + 28.0f + buttonWidth, buttonY, buttonWidth, 36.0f), false }
+        };
+    }
+
+    void HandleMouseMove(float x, float y) {
+        UpdateLayout();
+        for (ButtonState& button : m_buttons) {
+            button.hovered = ContainsPoint(button.rect, x, y);
+        }
+
+        UIInputEvent event = {};
+        event.type = UIInputEventType::PointerMove;
+        event.position = UIPoint(x, y);
+        m_pendingInputEvents.push_back(event);
+    }
+
+    void HandleLeftButtonDown(float x, float y) {
+        UpdateLayout();
+        for (const ButtonState& button : m_buttons) {
+            if (ContainsPoint(button.rect, x, y)) {
+                ExecuteAction(button.action);
+                return;
+            }
+        }
+
+        UIInputEvent event = {};
+        event.type = UIInputEventType::PointerButtonDown;
+        event.position = UIPoint(x, y);
+        event.pointerButton = UIPointerButton::Left;
+        m_pendingInputEvents.push_back(event);
+    }
+
+    void HandleLeftButtonUp(float x, float y) {
+        UIInputEvent event = {};
+        event.type = UIInputEventType::PointerButtonUp;
+        event.position = UIPoint(x, y);
+        event.pointerButton = UIPointerButton::Left;
+        m_pendingInputEvents.push_back(event);
+    }
+
+    void ExecuteAction(ActionId action) {
+        if (action == ActionId::Reset) {
+            ResetScenario();
+            m_lastResult = "已重置：请重新检查提交、取消和失焦取消。";
+            m_lastResultColor = kWarn;
+            return;
+        }
+
+        m_autoScreenshot.RequestCapture("manual_button");
+        m_lastResult = "截图已排队：输出到 captures/。";
+        m_lastResultColor = kWarn;
+    }
+
+    void ApplyHostCaptureRequests(const UIEditorDockHostInteractionResult& result) {
+        if (result.requestPointerCapture && GetCapture() != m_hwnd) {
+            SetCapture(m_hwnd);
+        }
+        if (result.releasePointerCapture && GetCapture() == m_hwnd) {
+            ReleaseCapture();
+        }
+    }
+
+    void UpdateLastResult(const UIEditorDockHostInteractionResult& result) {
+        if (result.layoutResult.status == UIEditorWorkspaceLayoutOperationStatus::Changed) {
+            m_lastResult = "结果：同一标签栏内的标签重排已提交。";
+            m_lastResultColor = kOk;
+            return;
+        }
+
+        if (result.requestPointerCapture) {
+            m_lastResult = "结果：开始拖拽，宿主已拿到 pointer capture。";
+            m_lastResultColor = kOk;
+            return;
+        }
+
+        if (result.releasePointerCapture && !result.layoutChanged && !result.commandExecuted) {
+            if (m_lastInputCause == "focus_lost") {
+                m_lastResult = "结果：窗口失焦，本次重排已取消。";
+            } else {
+                m_lastResult = "结果：拖拽已取消。拖到 body 区再松开时，标签顺序应保持不变。";
+            }
+            m_lastResultColor = kWarn;
+            return;
+        }
+    }
+
+    void RenderFrame() {
+        UpdateLayout();
+        m_cachedFrame = UpdateUIEditorDockHostInteraction(
+            m_interactionState,
+            m_controller,
+            m_dockHostRect,
+            m_pendingInputEvents);
+        m_pendingInputEvents.clear();
+        ApplyHostCaptureRequests(m_cachedFrame.result);
+        UpdateLastResult(m_cachedFrame.result);
+        m_lastInputCause.clear();
+
+        RECT clientRect = {};
+        GetClientRect(m_hwnd, &clientRect);
+        const float width = static_cast<float>((std::max)(clientRect.right - clientRect.left, 1L));
+        const float height = static_cast<float>((std::max)(clientRect.bottom - clientRect.top, 1L));
+
+        UIDrawData drawData = {};
+        UIDrawList& drawList = drawData.EmplaceDrawList("DockTabReorderSameStack");
+        drawList.AddFilledRect(UIRect(0.0f, 0.0f, width, height), kWindowBg);
+
+        DrawCard(drawList, m_introRect, "这个测试验证什么功能？", "只验证同一标签栏内 tab 重排的基础 contract，不做 editor 业务。");
+        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 70.0f), "1. 拖动 Document A / B / C 的 tab header 到同一行其他位置。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 92.0f), "2. 在 header 区松开：应提交重排，并更新右侧标签顺序。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 114.0f), "3. 拖到 body 区再松开：应取消，本次标签顺序不能变化。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 16.0f, m_introRect.y + 136.0f), "4. 拖拽中切走窗口或按 Esc：应释放 capture，并取消这次重排。", kTextWeak, 11.0f);
+
+        DrawCard(drawList, m_previewRect, "预览区", "这里只保留同栏重排所需的最小工作区。");
+        drawList.AddFilledRect(m_dockHostRect, kPreviewBg, 8.0f);
+        AppendUIEditorDockHostBackground(drawList, m_cachedFrame.layout);
+        AppendUIEditorDockHostForeground(drawList, m_cachedFrame.layout);
+
+        DrawCard(drawList, m_stateRect, "状态", "拖拽时重点观察右侧状态是否和画面一致。");
+        float y = m_stateRect.y + 68.0f;
+        auto addLine = [&](std::string text, const UIColor& color = kTextPrimary, float fontSize = 12.0f) mutable {
+            drawList.AddText(UIPoint(m_stateRect.x + 16.0f, y), std::move(text), color, fontSize);
+            y += 22.0f;
+        };
+
+        const auto* documentTabStack = FindDocumentTabStackLayout(m_cachedFrame);
+        const bool previewVisible =
+            documentTabStack != nullptr &&
+            documentTabStack->tabStripLayout.insertionPreview.visible;
+        const std::size_t previewInsertionIndex =
+            documentTabStack != nullptr
+                ? documentTabStack->tabStripLayout.insertionPreview.insertionIndex
+                : XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex;
+
+        addLine("当前标签顺序: " + CollectDocumentTabOrder(m_controller), kTextPrimary, 11.0f);
+        addLine("活动面板: " + m_controller.GetWorkspace().activePanelId, kTextPrimary, 11.0f);
+        addLine("已聚焦: " + FormatBool(m_cachedFrame.focused), m_cachedFrame.focused ? kOk : kTextMuted, 11.0f);
+        addLine("宿主捕获: " + FormatBool(GetCapture() == m_hwnd), GetCapture() == m_hwnd ? kOk : kTextMuted, 11.0f);
+        addLine(
+            "拖拽标签栈: " +
+                (m_interactionState.activeTabDragNodeId.empty()
+                    ? std::string("无")
+                    : m_interactionState.activeTabDragNodeId),
+            kTextWeak,
+            11.0f);
+        addLine("预览插入位激活: " + FormatBool(previewVisible), previewVisible ? kOk : kTextWeak, 11.0f);
+        addLine("预览插入索引: " + FormatOptionalIndex(previewInsertionIndex), kTextWeak, 11.0f);
+        addLine("当前 Hover: " + m_hoverText, kTextWeak, 11.0f);
+
+        drawList.AddText(
+            UIPoint(m_stateRect.x + 16.0f, y + 8.0f),
+            "最近结果",
+            kTextPrimary,
+            13.0f);
+        drawList.AddText(
+            UIPoint(m_stateRect.x + 16.0f, y + 32.0f),
+            m_lastResult,
+            m_lastResultColor,
+            12.0f);
+
+        const std::string captureSummary =
+            m_autoScreenshot.HasPendingCapture()
+                ? "截图排队中..."
+                : (m_autoScreenshot.GetLastCaptureSummary().empty()
+                    ? "F12 或按钮 -> captures/"
+                    : m_autoScreenshot.GetLastCaptureSummary());
+        drawList.AddText(
+            UIPoint(m_stateRect.x + 16.0f, m_stateRect.y + m_stateRect.height - 86.0f),
+            captureSummary,
+            kTextWeak,
+            11.0f);
+        for (const ButtonState& button : m_buttons) {
+            DrawButton(drawList, button);
+        }
+
+        const bool framePresented = m_renderer.Render(drawData);
+        m_autoScreenshot.CaptureIfRequested(
+            m_renderer,
+            drawData,
+            static_cast<unsigned int>(width),
+            static_cast<unsigned int>(height),
+            framePresented);
+    }
+
+    HWND m_hwnd = nullptr;
+    ATOM m_windowClassAtom = 0;
+    NativeRenderer m_renderer = {};
+    AutoScreenshotController m_autoScreenshot = {};
+    std::filesystem::path m_captureRoot = {};
+    UIEditorWorkspaceController m_controller = {};
+    UIEditorDockHostInteractionState m_interactionState = {};
+    UIEditorDockHostInteractionFrame m_cachedFrame = {};
+    std::vector<UIInputEvent> m_pendingInputEvents = {};
+    std::vector<ButtonState> m_buttons = {};
+    UIRect m_introRect = {};
+    UIRect m_previewRect = {};
+    UIRect m_stateRect = {};
+    UIRect m_dockHostRect = {};
+    bool m_trackingMouseLeave = false;
+    std::string m_lastInputCause = {};
+    std::string m_hoverText = {};
+    std::string m_lastResult = {};
+    UIColor m_lastResultColor = kTextMuted;
+};
+
+} // namespace
+
+int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, LPWSTR, int nCmdShow) {
+    return ScenarioApp().Run(hInstance, nCmdShow);
+}

tests/UI/Editor/integration/shell/tab_strip_basic/main.cpp

@@ -196,11 +196,6 @@ std::string DescribeHitTarget(
             return "Tab: " + items[target.index].title;
         }
         return "Tab";
-    case UIEditorTabStripHitTargetKind::CloseButton:
-        if (target.index < items.size()) {
-            return "CloseButton: " + items[target.index].title;
-        }
-        return "CloseButton";
     case UIEditorTabStripHitTargetKind::None:
     default:
         return "None";
@@ -218,9 +213,6 @@ std::string JoinTabTitles(const std::vector<UIEditorTabStripItem>& items) {
             stream << " | ";
         }
         stream << items[index].title;
-        if (!items[index].closable) {
-            stream << " (locked)";
-        }
     }
     return stream.str();
 }
@@ -502,15 +494,6 @@ private:
     void ApplyInteractionResult(
         const UIEditorTabStripInteractionResult& result,
         std::string_view source) {
-        if (result.closeRequested && !result.closedTabId.empty()) {
-            DispatchCommand(
-                UIEditorWorkspaceCommandKind::ClosePanel,
-                result.closedTabId,
-                std::string(source) + " Close -> " + result.closedTabId);
-            PumpTabStripEvents({});
-            return;
-        }
-
         if ((result.selectionChanged || result.keyboardNavigated) &&
             !result.selectedTabId.empty()) {
             DispatchCommand(
@@ -609,7 +592,7 @@ private:
             drawList,
             introRect,
             "这个测试验证什么功能？",
-            "验证 TabStrip 的 header 命中、选中切换、关闭请求和键盘导航，不接业务面板。");
+            "验证 TabStrip 的 header 命中、选中切换和键盘导航，不接业务面板。");
         drawList.AddText(
             UIPoint(introRect.x + 16.0f, introRect.y + 68.0f),
             "1. 点击 tab，检查 selected / active panel 是否同步。",
@@ -617,7 +600,7 @@ private:
             12.0f);
         drawList.AddText(
             UIPoint(introRect.x + 16.0f, introRect.y + 92.0f),
-            "2. 点击 X，只验证关闭请求；Document C 没有关闭按钮。",
+            "2. 所有 tab 都没有关闭按钮；这里只验证命中、focus 和选中同步。",
             kTextMuted,
             12.0f);
         drawList.AddText(
@@ -719,7 +702,7 @@ private:
             12.0f);
         drawList.AddText(
             UIPoint(m_layout.contentRect.x + 20.0f, m_layout.contentRect.y + 100.0f),
-            "可点击 Document B 切换，或点击 Document C 验证不可关闭 tab。",
+            "可点击 Document B 切换，再用 Left / Right / Home / End 验证键盘导航。",
             kTextWeak,
             12.0f);
 

tests/UI/Editor/integration/shell/workspace_shell_compose/main.cpp

@@ -606,7 +606,7 @@ private:
             12.0f);
         drawList.AddText(
             UIPoint(m_introRect.x + 16.0f, m_introRect.y + 92.0f),
-            "2. tab 激活/关闭、panel 激活/关闭都必须统一回到 controller。",
+            "2. tab 激活、panel 激活/关闭都必须统一回到 controller。",
             kTextPrimary,
             12.0f);
         drawList.AddText(

tests/UI/Editor/unit/test_ui_editor_dock_host.cpp

@@ -98,8 +98,8 @@ TEST(UIEditorDockHostTest, LayoutComposesOnlyUnifiedTabStacksFromWorkspaceTree)
 
     const auto* rootSplitter = FindUIEditorDockHostSplitterLayout(layout, "root-split");
     ASSERT_NE(rootSplitter, nullptr);
-    EXPECT_FLOAT_EQ(rootSplitter->splitterLayout.handleRect.x, 395.0f);
-    EXPECT_FLOAT_EQ(rootSplitter->splitterLayout.handleRect.width, 10.0f);
+    EXPECT_FLOAT_EQ(rootSplitter->splitterLayout.handleRect.x, 399.5f);
+    EXPECT_FLOAT_EQ(rootSplitter->splitterLayout.handleRect.width, 1.0f);
 
     const auto& tabStack = layout.tabStacks.front();
     EXPECT_EQ(tabStack.nodeId, "document-tabs");
@@ -138,7 +138,7 @@ TEST(UIEditorDockHostTest, HiddenBranchCollapsesAndVisibleBranchUsesFullBounds)
     EXPECT_FLOAT_EQ(layout.tabStacks.front().bounds.height, 480.0f);
 }
 
-TEST(UIEditorDockHostTest, HitTestPrioritizesSplitterThenTabCloseThenPanelBody) {
+TEST(UIEditorDockHostTest, HitTestPrioritizesSplitterThenTabThenPanelBody) {
     const UIEditorPanelRegistry registry = BuildPanelRegistry();
     const UIEditorWorkspaceModel workspace = BuildWorkspace();
     const UIEditorWorkspaceSession session =
@@ -160,14 +160,14 @@ TEST(UIEditorDockHostTest, HitTestPrioritizesSplitterThenTabCloseThenPanelBody)
     EXPECT_EQ(splitterHit.nodeId, "root-split");
 
     ASSERT_EQ(layout.tabStacks.size(), 3u);
-    const auto& closeRect = layout.tabStacks.front().tabStripLayout.closeButtonRects[1];
-    const auto tabCloseHit = HitTestUIEditorDockHost(
+    const auto& tabRect = layout.tabStacks.front().tabStripLayout.tabHeaderRects[1];
+    const auto tabHit = HitTestUIEditorDockHost(
         layout,
-        UIPoint(closeRect.x + closeRect.width * 0.5f, closeRect.y + closeRect.height * 0.5f));
-    EXPECT_EQ(tabCloseHit.kind, UIEditorDockHostHitTargetKind::TabCloseButton);
-    EXPECT_EQ(tabCloseHit.nodeId, "document-tabs");
-    EXPECT_EQ(tabCloseHit.panelId, "doc-b");
-    EXPECT_EQ(tabCloseHit.index, 1u);
+        UIPoint(tabRect.x + tabRect.width - 6.0f, tabRect.y + tabRect.height * 0.5f));
+    EXPECT_EQ(tabHit.kind, UIEditorDockHostHitTargetKind::Tab);
+    EXPECT_EQ(tabHit.nodeId, "document-tabs");
+    EXPECT_EQ(tabHit.panelId, "doc-b");
+    EXPECT_EQ(tabHit.index, 1u);
 
     const auto panelBodyHit = HitTestUIEditorDockHost(
         layout,
@@ -186,7 +186,7 @@ TEST(UIEditorDockHostTest, BackgroundAndForegroundEmitStableCompositeCommands) {
     UIEditorDockHostState state = {};
     state.focused = true;
     state.hoveredTarget = UIEditorDockHostHitTarget{
-        UIEditorDockHostHitTargetKind::TabCloseButton,
+        UIEditorDockHostHitTargetKind::Tab,
         "document-tabs",
         "doc-b",
         1u

tests/UI/Editor/unit/test_ui_editor_dock_host_interaction.cpp

@@ -5,6 +5,9 @@
 #include <XCEditor/Shell/UIEditorWorkspaceController.h>
 #include <XCEditor/Shell/UIEditorWorkspaceModel.h>
 
+#include <algorithm>
+#include <string>
+
 namespace {
 
 using XCEngine::UI::UIInputEvent;
@@ -19,6 +22,7 @@ using XCEngine::UI::Editor::BuildUIEditorWorkspaceSingleTabStack;
 using XCEngine::UI::Editor::BuildUIEditorWorkspaceSplit;
 using XCEngine::UI::Editor::BuildUIEditorWorkspaceTabStack;
 using XCEngine::UI::Editor::FindUIEditorPanelSessionState;
+using XCEngine::UI::Editor::FindUIEditorWorkspaceNode;
 using XCEngine::UI::Editor::UIEditorDockHostInteractionState;
 using XCEngine::UI::Editor::UIEditorPanelRegistry;
 using XCEngine::UI::Editor::UIEditorWorkspaceModel;
@@ -33,6 +37,7 @@ UIEditorPanelRegistry BuildPanelRegistry() {
     registry.panels = {
         { "doc-a", "Document A", {}, true, true, true },
         { "doc-b", "Document B", {}, true, true, true },
+        { "doc-c", "Document C", {}, true, true, true },
         { "details", "Details", {}, true, true, true },
         { "console", "Console", {}, true, true, true }
     };
@@ -62,6 +67,30 @@ UIEditorWorkspaceModel BuildWorkspace() {
     return workspace;
 }
 
+UIEditorWorkspaceModel BuildThreeDocumentWorkspace() {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.5f,
+        BuildUIEditorWorkspaceTabStack(
+            "document-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true),
+                BuildUIEditorWorkspacePanel("doc-c-node", "doc-c", "Document C", true)
+            },
+            2u),
+        BuildUIEditorWorkspaceSplit(
+            "right-split",
+            UIEditorWorkspaceSplitAxis::Vertical,
+            0.6f,
+            BuildUIEditorWorkspaceSingleTabStack("details-node", "details", "Details", true),
+            BuildUIEditorWorkspaceSingleTabStack("console-node", "console", "Console", true)));
+    workspace.activePanelId = "doc-c";
+    return workspace;
+}
+
 UIInputEvent MakePointerMove(float x, float y) {
     UIInputEvent event = {};
     event.type = UIInputEventType::PointerMove;
@@ -230,60 +259,6 @@ TEST(UIEditorDockHostInteractionTest, ClickingTabActivatesTargetPanel) {
     EXPECT_EQ(documentStack->selectedPanelId, "doc-a");
 }
 
-TEST(UIEditorDockHostInteractionTest, ClickingTabCloseClosesPanelThroughController) {
-    auto controller =
-        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
-    UIEditorDockHostInteractionState state = {};
-
-    auto frame = UpdateUIEditorDockHostInteraction(
-        state,
-        controller,
-        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
-        {});
-    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
-    ASSERT_NE(documentStack, nullptr);
-    const UIRect closeRect = documentStack->tabStripLayout.closeButtonRects[1];
-    const UIPoint closeCenter = RectCenter(closeRect);
-
-    frame = UpdateUIEditorDockHostInteraction(
-        state,
-        controller,
-        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
-        { MakePointerMove(closeCenter.x, closeCenter.y) });
-    EXPECT_EQ(frame.result.hitTarget.kind, UIEditorDockHostHitTargetKind::TabCloseButton);
-    EXPECT_EQ(frame.result.hitTarget.panelId, "doc-b");
-
-    frame = UpdateUIEditorDockHostInteraction(
-        state,
-        controller,
-        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
-        { MakePointerDown(closeCenter.x, closeCenter.y) });
-    EXPECT_TRUE(frame.result.consumed);
-    EXPECT_FALSE(frame.result.commandExecuted);
-
-    frame = UpdateUIEditorDockHostInteraction(
-        state,
-        controller,
-        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
-        { MakePointerDown(closeCenter.x, closeCenter.y) });
-    EXPECT_TRUE(frame.result.consumed);
-    EXPECT_FALSE(frame.result.commandExecuted);
-
-    frame = UpdateUIEditorDockHostInteraction(
-        state,
-        controller,
-        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
-        { MakePointerUp(closeCenter.x, closeCenter.y) });
-    EXPECT_TRUE(frame.result.consumed);
-    EXPECT_TRUE(frame.result.commandExecuted);
-
-    const auto* panelState = FindUIEditorPanelSessionState(controller.GetSession(), "doc-b");
-    ASSERT_NE(panelState, nullptr);
-    EXPECT_FALSE(panelState->open);
-    EXPECT_FALSE(panelState->visible);
-    EXPECT_EQ(controller.GetWorkspace().activePanelId, "doc-a");
-}
-
 TEST(UIEditorDockHostInteractionTest, FocusedTabStripHandlesKeyboardNavigationThroughTabStripInteraction) {
     auto controller =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
@@ -399,7 +374,7 @@ TEST(UIEditorDockHostInteractionTest, ClickingSingleTabStackBodyActivatesTargetP
     EXPECT_EQ(controller.GetWorkspace().activePanelId, "details");
 }
 
-TEST(UIEditorDockHostInteractionTest, ClickingSingleTabStackTabCloseClosesPanelThroughController) {
+TEST(UIEditorDockHostInteractionTest, DraggingTabWithinSameStackRequestsCaptureAndCommitsReorder) {
     auto controller =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     UIEditorDockHostInteractionState state = {};
@@ -409,29 +384,411 @@ TEST(UIEditorDockHostInteractionTest, ClickingSingleTabStackTabCloseClosesPanelT
         controller,
         UIRect(0.0f, 0.0f, 800.0f, 600.0f),
         {});
-    const auto* consoleStack = FindTabStackByNodeId(frame.layout, "console-node");
-    ASSERT_NE(consoleStack, nullptr);
-    const UIRect closeRect = consoleStack->tabStripLayout.closeButtonRects[0];
-    const UIPoint closeCenter = RectCenter(closeRect);
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    ASSERT_NE(documentStack, nullptr);
+    const UIPoint sourceCenter = RectCenter(documentStack->tabStripLayout.tabHeaderRects[0]);
+    const UIPoint dropPoint(
+        documentStack->tabStripLayout.headerRect.x +
+            documentStack->tabStripLayout.headerRect.width - 2.0f,
+        sourceCenter.y);
 
     frame = UpdateUIEditorDockHostInteraction(
         state,
         controller,
         UIRect(0.0f, 0.0f, 800.0f, 600.0f),
-        { MakePointerMove(closeCenter.x, closeCenter.y) });
-    EXPECT_EQ(frame.result.hitTarget.kind, UIEditorDockHostHitTargetKind::TabCloseButton);
-    EXPECT_EQ(frame.result.hitTarget.panelId, "console");
-
-    frame = UpdateUIEditorDockHostInteraction(
-        state,
-        controller,
-        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
-        { MakePointerUp(closeCenter.x, closeCenter.y) });
+        { MakePointerDown(sourceCenter.x, sourceCenter.y) });
     EXPECT_TRUE(frame.result.consumed);
-    EXPECT_TRUE(frame.result.commandExecuted);
 
-    const auto* panelState = FindUIEditorPanelSessionState(controller.GetSession(), "console");
-    ASSERT_NE(panelState, nullptr);
-    EXPECT_FALSE(panelState->open);
-    EXPECT_FALSE(panelState->visible);
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerMove(dropPoint.x, dropPoint.y) });
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerUp(dropPoint.x, dropPoint.y) });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.layoutChanged)
+        << " status=" << static_cast<int>(frame.result.layoutResult.status)
+        << " message=" << frame.result.layoutResult.message
+        << " commandExecuted=" << frame.result.commandExecuted;
+
+    const auto* documentTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    ASSERT_NE(documentTabs, nullptr);
+    ASSERT_EQ(documentTabs->children.size(), 2u);
+    EXPECT_EQ(documentTabs->children[0].panel.panelId, "doc-b");
+    EXPECT_EQ(documentTabs->children[1].panel.panelId, "doc-a");
+}
+
+TEST(UIEditorDockHostInteractionTest, DraggingRightmostTabIntoMiddleCommitsSameStackReorder) {
+    auto controller =
+        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildThreeDocumentWorkspace());
+    UIEditorDockHostInteractionState state = {};
+
+    auto frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {});
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    ASSERT_NE(documentStack, nullptr);
+    const UIPoint sourceCenter = RectCenter(documentStack->tabStripLayout.tabHeaderRects[2]);
+    const UIPoint dropPoint(
+        documentStack->tabStripLayout.tabHeaderRects[1].x + 4.0f,
+        sourceCenter.y);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerDown(sourceCenter.x, sourceCenter.y) });
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerMove(dropPoint.x, dropPoint.y) });
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerUp(dropPoint.x, dropPoint.y) });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.layoutChanged)
+        << " status=" << static_cast<int>(frame.result.layoutResult.status)
+        << " message=" << frame.result.layoutResult.message
+        << " commandExecuted=" << frame.result.commandExecuted;
+
+    const auto* documentTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    ASSERT_NE(documentTabs, nullptr);
+    ASSERT_EQ(documentTabs->children.size(), 3u);
+    EXPECT_EQ(documentTabs->children[0].panel.panelId, "doc-a");
+    EXPECT_EQ(documentTabs->children[1].panel.panelId, "doc-c");
+    EXPECT_EQ(documentTabs->children[2].panel.panelId, "doc-b");
+}
+
+TEST(UIEditorDockHostInteractionTest, DraggingRightmostTabToFrontCommitsSameStackReorder) {
+    auto controller =
+        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildThreeDocumentWorkspace());
+    UIEditorDockHostInteractionState state = {};
+
+    auto frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {});
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    ASSERT_NE(documentStack, nullptr);
+    const UIPoint sourceCenter = RectCenter(documentStack->tabStripLayout.tabHeaderRects[2]);
+    const UIPoint dropPoint(
+        documentStack->tabStripLayout.tabHeaderRects[0].x + 4.0f,
+        sourceCenter.y);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerDown(sourceCenter.x, sourceCenter.y) });
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerMove(dropPoint.x, dropPoint.y) });
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerUp(dropPoint.x, dropPoint.y) });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.layoutChanged);
+
+    const auto* documentTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    ASSERT_NE(documentTabs, nullptr);
+    ASSERT_EQ(documentTabs->children.size(), 3u);
+    EXPECT_EQ(documentTabs->children[0].panel.panelId, "doc-c");
+    EXPECT_EQ(documentTabs->children[1].panel.panelId, "doc-a");
+    EXPECT_EQ(documentTabs->children[2].panel.panelId, "doc-b");
+}
+
+TEST(UIEditorDockHostInteractionTest, SameStackReorderCommitsFromLastVisiblePreviewEvenIfReleaseDropsBelowHeader) {
+    auto controller =
+        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
+    UIEditorDockHostInteractionState state = {};
+
+    auto frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {});
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    ASSERT_NE(documentStack, nullptr);
+    const UIPoint sourceCenter = RectCenter(documentStack->tabStripLayout.tabHeaderRects[0]);
+    const UIPoint previewPoint(
+        documentStack->tabStripLayout.headerRect.x +
+            documentStack->tabStripLayout.headerRect.width - 2.0f,
+        sourceCenter.y);
+    const UIPoint releasePoint(
+        previewPoint.x,
+        documentStack->tabStripLayout.headerRect.y +
+            documentStack->tabStripLayout.headerRect.height + 8.0f);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerDown(sourceCenter.x, sourceCenter.y) });
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerMove(previewPoint.x, previewPoint.y) });
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(frame.result.consumed);
+    const auto tabStripStateIt = std::find_if(
+        state.dockHostState.tabStripStates.begin(),
+        state.dockHostState.tabStripStates.end(),
+        [](const auto& tabStripState) {
+            return tabStripState.nodeId == "document-tabs";
+        });
+    ASSERT_NE(tabStripStateIt, state.dockHostState.tabStripStates.end());
+    ASSERT_NE(
+        tabStripStateIt->state.reorder.previewInsertionIndex,
+        XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerUp(releasePoint.x, releasePoint.y) });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.layoutChanged);
+
+    const auto* documentTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    ASSERT_NE(documentTabs, nullptr);
+    ASSERT_EQ(documentTabs->children.size(), 2u);
+    EXPECT_EQ(documentTabs->children[0].panel.panelId, "doc-b");
+    EXPECT_EQ(documentTabs->children[1].panel.panelId, "doc-a");
+}
+
+TEST(UIEditorDockHostInteractionTest, ReleasingDraggedTabOutsideHeaderCancelsWithoutChangingOrder) {
+    auto controller =
+        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
+    UIEditorDockHostInteractionState state = {};
+
+    auto frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {});
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    ASSERT_NE(documentStack, nullptr);
+    const UIPoint sourceCenter = RectCenter(documentStack->tabStripLayout.tabHeaderRects[0]);
+    const UIPoint activatePoint(
+        documentStack->tabStripLayout.headerRect.x +
+            documentStack->tabStripLayout.headerRect.width - 2.0f,
+        sourceCenter.y);
+    const UIPoint cancelPoint = RectCenter(documentStack->contentFrameLayout.bodyRect);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(activatePoint.x, activatePoint.y),
+            MakePointerMove(cancelPoint.x, cancelPoint.y),
+            MakePointerUp(cancelPoint.x, cancelPoint.y)
+        });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_FALSE(frame.result.layoutChanged);
+
+    const auto* documentTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    ASSERT_NE(documentTabs, nullptr);
+    ASSERT_EQ(documentTabs->children.size(), 2u);
+    EXPECT_EQ(documentTabs->children[0].panel.panelId, "doc-a");
+    EXPECT_EQ(documentTabs->children[1].panel.panelId, "doc-b");
+}
+
+TEST(UIEditorDockHostInteractionTest, DraggingTabOntoAnotherStackHeaderMergesIntoTargetStack) {
+    auto controller =
+        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
+    UIEditorDockHostInteractionState state = {};
+
+    auto frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {});
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    const auto* detailsStack = FindTabStackByNodeId(frame.layout, "details-node");
+    ASSERT_NE(documentStack, nullptr);
+    ASSERT_NE(detailsStack, nullptr);
+    const UIPoint sourceCenter =
+        RectCenter(documentStack->tabStripLayout.tabHeaderRects[0]);
+    const UIPoint targetHeaderCenter =
+        RectCenter(detailsStack->tabStripLayout.headerRect);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerDown(sourceCenter.x, sourceCenter.y) });
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerMove(targetHeaderCenter.x, targetHeaderCenter.y) });
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(state.dockHostState.dropPreview.visible);
+    EXPECT_EQ(state.dockHostState.dropPreview.targetNodeId, "details-node");
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerUp(targetHeaderCenter.x, targetHeaderCenter.y) });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.layoutChanged);
+
+    const auto* documentTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    const auto* detailsTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "details-node");
+    ASSERT_NE(documentTabs, nullptr);
+    ASSERT_NE(detailsTabs, nullptr);
+    ASSERT_EQ(documentTabs->children.size(), 1u);
+    ASSERT_EQ(detailsTabs->children.size(), 2u);
+    EXPECT_EQ(documentTabs->children[0].panel.panelId, "doc-b");
+    EXPECT_EQ(detailsTabs->children[1].panel.panelId, "doc-a");
+    EXPECT_EQ(controller.GetWorkspace().activePanelId, "doc-a");
+}
+
+TEST(UIEditorDockHostInteractionTest, DraggingTabOntoPanelBodyEdgeCreatesDockSplit) {
+    auto controller =
+        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
+    UIEditorDockHostInteractionState state = {};
+
+    auto frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {});
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    const auto* detailsStack = FindTabStackByNodeId(frame.layout, "details-node");
+    ASSERT_NE(documentStack, nullptr);
+    ASSERT_NE(detailsStack, nullptr);
+    const UIPoint sourceCenter =
+        RectCenter(documentStack->tabStripLayout.tabHeaderRects[0]);
+    const UIPoint targetBottomCenter(
+        detailsStack->contentFrameLayout.bodyRect.x +
+            detailsStack->contentFrameLayout.bodyRect.width * 0.5f,
+        detailsStack->contentFrameLayout.bodyRect.y +
+            detailsStack->contentFrameLayout.bodyRect.height - 4.0f);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerDown(sourceCenter.x, sourceCenter.y) });
+    EXPECT_TRUE(frame.result.consumed);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerMove(targetBottomCenter.x, targetBottomCenter.y) });
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(state.dockHostState.dropPreview.visible);
+    EXPECT_EQ(
+        state.dockHostState.dropPreview.placement,
+        XCEngine::UI::Editor::UIEditorWorkspaceDockPlacement::Bottom);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakePointerUp(targetBottomCenter.x, targetBottomCenter.y) });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.layoutChanged);
+    EXPECT_EQ(controller.GetWorkspace().activePanelId, "doc-a");
+
+    bool foundDockedTab = false;
+    for (const std::string candidate : { "details-node__dock_doc-a_stack", "details-node__dock_doc-a_stack-1" }) {
+        const auto* docked =
+            FindUIEditorWorkspaceNode(controller.GetWorkspace(), candidate);
+        if (docked != nullptr &&
+            docked->children.size() == 1u &&
+            docked->children[0].panel.panelId == "doc-a") {
+            foundDockedTab = true;
+            break;
+        }
+    }
+    EXPECT_TRUE(foundDockedTab);
+}
+
+TEST(UIEditorDockHostInteractionTest, FocusLostWhileDraggingTabCancelsAndReleasesCapture) {
+    auto controller =
+        BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
+    UIEditorDockHostInteractionState state = {};
+
+    auto frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {});
+    const auto* documentStack = FindTabStackByNodeId(frame.layout, "document-tabs");
+    ASSERT_NE(documentStack, nullptr);
+    const UIPoint sourceCenter = RectCenter(documentStack->tabStripLayout.tabHeaderRects[0]);
+    const UIPoint activatePoint(
+        documentStack->tabStripLayout.headerRect.x +
+            documentStack->tabStripLayout.headerRect.width - 2.0f,
+        sourceCenter.y);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(activatePoint.x, activatePoint.y)
+        });
+    ASSERT_TRUE(frame.result.requestPointerCapture);
+
+    frame = UpdateUIEditorDockHostInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 800.0f, 600.0f),
+        { MakeFocusLost() });
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_FALSE(frame.result.layoutChanged);
+
+    const auto* documentTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    ASSERT_NE(documentTabs, nullptr);
+    ASSERT_EQ(documentTabs->children.size(), 2u);
+    EXPECT_EQ(documentTabs->children[0].panel.panelId, "doc-a");
+    EXPECT_EQ(documentTabs->children[1].panel.panelId, "doc-b");
 }

tests/UI/Editor/unit/test_ui_editor_menu_bar.cpp

@@ -96,12 +96,11 @@ TEST(UIEditorMenuBarTest, BackgroundAndForegroundEmitStableCommands) {
 
     UIDrawList background("MenuBarBackground");
     AppendUIEditorMenuBarBackground(background, layout, items, state);
-    ASSERT_EQ(background.GetCommandCount(), 6u);
+    ASSERT_EQ(background.GetCommandCount(), 3u);
     const auto& backgroundCommands = background.GetCommands();
     EXPECT_EQ(backgroundCommands[0].type, UIDrawCommandType::FilledRect);
-    EXPECT_EQ(backgroundCommands[1].type, UIDrawCommandType::RectOutline);
+    EXPECT_EQ(backgroundCommands[1].type, UIDrawCommandType::FilledRect);
     EXPECT_EQ(backgroundCommands[2].type, UIDrawCommandType::FilledRect);
-    EXPECT_EQ(backgroundCommands[5].type, UIDrawCommandType::RectOutline);
 
     UIDrawList foreground("MenuBarForeground");
     AppendUIEditorMenuBarForeground(foreground, layout, items, state);

tests/UI/Editor/unit/test_ui_editor_shell_interaction.cpp

@@ -41,6 +41,8 @@ using XCEngine::UI::Editor::UIEditorShellInteractionModel;
 using XCEngine::UI::Editor::UIEditorShellInteractionPopupItemRequest;
 using XCEngine::UI::Editor::UIEditorShellInteractionServices;
 using XCEngine::UI::Editor::UIEditorShellInteractionState;
+using XCEngine::UI::Editor::UIEditorTextMeasureRequest;
+using XCEngine::UI::Editor::UIEditorTextMeasurer;
 using XCEngine::UI::Editor::UIEditorWorkspaceController;
 using XCEngine::UI::Editor::UIEditorWorkspaceCommandKind;
 using XCEngine::UI::Editor::UIEditorWorkspaceCommandStatus;
@@ -52,6 +54,13 @@ using XCEngine::UI::Editor::Widgets::UIEditorMenuPopupInvalidIndex;
 using XCEngine::UI::Editor::Widgets::UIEditorStatusBarSlot;
 using XCEngine::UI::Widgets::UIPopupDismissReason;
 
+class StubTextMeasurer final : public UIEditorTextMeasurer {
+public:
+    float MeasureTextWidth(const UIEditorTextMeasureRequest& request) const override {
+        return static_cast<float>(request.text.size()) * (request.fontSize * 0.6f);
+    }
+};
+
 UIEditorPanelRegistry BuildPanelRegistry() {
     UIEditorPanelRegistry registry = {};
     registry.panels = {
@@ -219,6 +228,76 @@ UIEditorWorkspaceController BuildController() {
     return BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
 }
 
+UIPoint RectCenter(const UIRect& rect);
+UIInputEvent MakeLeftPointerDown(const UIPoint& position);
+
+TEST(UIEditorShellInteractionTest, RequestUsesTextMeasurerForMenuBarWidths) {
+    UIEditorWorkspaceController controller = BuildController();
+    const UIEditorShellInteractionModel model = BuildInteractionModel();
+    StubTextMeasurer textMeasurer = {};
+    UIEditorShellInteractionServices services = {};
+    services.textMeasurer = &textMeasurer;
+
+    const auto request = ResolveUIEditorShellInteractionRequest(
+        UIRect(0.0f, 0.0f, 480.0f, 320.0f),
+        controller,
+        model,
+        {},
+        {},
+        services);
+
+    ASSERT_EQ(request.menuBarItems.size(), 2u);
+    EXPECT_FLOAT_EQ(
+        request.menuBarItems[0].desiredLabelWidth,
+        textMeasurer.MeasureTextWidth(UIEditorTextMeasureRequest { "File", 13.0f }));
+    EXPECT_FLOAT_EQ(
+        request.menuBarItems[1].desiredLabelWidth,
+        textMeasurer.MeasureTextWidth(UIEditorTextMeasureRequest { "Window", 13.0f }));
+    EXPECT_GT(request.menuButtons[1].rect.width, request.menuButtons[0].rect.width);
+}
+
+TEST(UIEditorShellInteractionTest, PopupWidgetWidthsUseTextMeasurerForLabelAndShortcut) {
+    UIEditorWorkspaceController controller = BuildController();
+    const UIEditorShellInteractionModel model = BuildInteractionModel();
+    StubTextMeasurer textMeasurer = {};
+    UIEditorShellInteractionServices services = {};
+    services.textMeasurer = &textMeasurer;
+
+    UIEditorShellInteractionState state = {};
+    const auto request = ResolveUIEditorShellInteractionRequest(
+        UIRect(0.0f, 0.0f, 480.0f, 320.0f),
+        controller,
+        model,
+        state,
+        {},
+        services);
+    ASSERT_FALSE(request.menuButtons.empty());
+
+    UIInputEvent openMenuEvent = {};
+    openMenuEvent.type = UIInputEventType::PointerButtonDown;
+    openMenuEvent.pointerButton = UIPointerButton::Left;
+    openMenuEvent.position = UIPoint(
+        request.menuButtons.front().rect.x + request.menuButtons.front().rect.width * 0.5f,
+        request.menuButtons.front().rect.y + request.menuButtons.front().rect.height * 0.5f);
+
+    const auto frame = UpdateUIEditorShellInteraction(
+        state,
+        controller,
+        UIRect(0.0f, 0.0f, 480.0f, 320.0f),
+        model,
+        std::vector<UIInputEvent> { openMenuEvent },
+        services);
+
+    ASSERT_EQ(frame.request.popupRequests.size(), 1u);
+    ASSERT_GE(frame.request.popupRequests.front().widgetItems.size(), 2u);
+    EXPECT_FLOAT_EQ(
+        frame.request.popupRequests.front().widgetItems[0].desiredLabelWidth,
+        textMeasurer.MeasureTextWidth(UIEditorTextMeasureRequest { "Workspace Tools", 13.0f }));
+    EXPECT_FLOAT_EQ(
+        frame.request.popupRequests.front().widgetItems[1].desiredShortcutWidth,
+        textMeasurer.MeasureTextWidth(UIEditorTextMeasureRequest { "Ctrl+W", 13.0f }));
+}
+
 const UIEditorShellInteractionMenuButtonRequest* FindMenuButton(
     const UIEditorShellInteractionFrame& frame,
     std::string_view menuId) {

tests/UI/Editor/unit/test_ui_editor_tab_strip.cpp

@@ -15,7 +15,6 @@ using XCEngine::UI::Editor::Widgets::BuildUIEditorTabStripLayout;
 using XCEngine::UI::Editor::Widgets::HitTestUIEditorTabStrip;
 using XCEngine::UI::Editor::Widgets::ResolveUIEditorTabStripDesiredHeaderLabelWidth;
 using XCEngine::UI::Editor::Widgets::ResolveUIEditorTabStripSelectedIndex;
-using XCEngine::UI::Editor::Widgets::ResolveUIEditorTabStripSelectedIndexAfterClose;
 using XCEngine::UI::Editor::Widgets::UIEditorTabStripHitTargetKind;
 using XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex;
 using XCEngine::UI::Editor::Widgets::UIEditorTabStripItem;
@@ -23,7 +22,7 @@ using XCEngine::UI::Editor::Widgets::UIEditorTabStripLayout;
 using XCEngine::UI::Editor::Widgets::UIEditorTabStripMetrics;
 using XCEngine::UI::Editor::Widgets::UIEditorTabStripState;
 
-TEST(UIEditorTabStripTest, DesiredHeaderWidthReservesCloseButtonBudget) {
+TEST(UIEditorTabStripTest, DesiredHeaderWidthUsesLabelWidthAndLeftInsetOnly) {
     UIEditorTabStripMetrics metrics = {};
     metrics.layoutMetrics.tabHorizontalPadding = 10.0f;
     metrics.estimatedGlyphWidth = 8.0f;
@@ -32,14 +31,14 @@ TEST(UIEditorTabStripTest, DesiredHeaderWidthReservesCloseButtonBudget) {
     metrics.closeInsetRight = 14.0f;
     metrics.labelInsetX = 12.0f;
 
-    const float closableWidth = ResolveUIEditorTabStripDesiredHeaderLabelWidth(
+    const float measuredWidth = ResolveUIEditorTabStripDesiredHeaderLabelWidth(
         UIEditorTabStripItem{ "doc-a", "ABCD", true, 0.0f },
         metrics);
     const float fixedWidth = ResolveUIEditorTabStripDesiredHeaderLabelWidth(
         UIEditorTabStripItem{ "doc-b", "Ignored", false, 42.0f },
         metrics);
 
-    EXPECT_FLOAT_EQ(closableWidth, 58.0f);
+    EXPECT_FLOAT_EQ(measuredWidth, 34.0f);
     EXPECT_FLOAT_EQ(fixedWidth, 44.0f);
 }
 
@@ -58,16 +57,7 @@ TEST(UIEditorTabStripTest, SelectedIndexResolvesByTabIdAndFallsBackToValidRange)
         UIEditorTabStripInvalidIndex);
 }
 
-TEST(UIEditorTabStripTest, ClosingTabsResolvesSelectionFallbackFromClosedIndex) {
-    EXPECT_EQ(ResolveUIEditorTabStripSelectedIndexAfterClose(1u, 1u, 3u), 1u);
-    EXPECT_EQ(ResolveUIEditorTabStripSelectedIndexAfterClose(2u, 2u, 3u), 1u);
-    EXPECT_EQ(ResolveUIEditorTabStripSelectedIndexAfterClose(2u, 0u, 3u), 1u);
-    EXPECT_EQ(
-        ResolveUIEditorTabStripSelectedIndexAfterClose(0u, 0u, 1u),
-        UIEditorTabStripInvalidIndex);
-}
-
-TEST(UIEditorTabStripTest, LayoutUsesCoreTabArrangementAndBuildsCloseRects) {
+TEST(UIEditorTabStripTest, LayoutUsesCoreTabArrangementWithoutCloseButtons) {
     UIEditorTabStripMetrics metrics = {};
     metrics.layoutMetrics.headerHeight = 30.0f;
     metrics.layoutMetrics.tabMinWidth = 80.0f;
@@ -101,20 +91,16 @@ TEST(UIEditorTabStripTest, LayoutUsesCoreTabArrangementAndBuildsCloseRects) {
 
     ASSERT_EQ(layout.tabHeaderRects.size(), 2u);
     EXPECT_FLOAT_EQ(layout.tabHeaderRects[0].x, 10.0f);
-    EXPECT_FLOAT_EQ(layout.tabHeaderRects[0].width, 90.0f);
-    EXPECT_FLOAT_EQ(layout.tabHeaderRects[1].x, 104.0f);
+    EXPECT_FLOAT_EQ(layout.tabHeaderRects[0].width, 80.0f);
+    EXPECT_FLOAT_EQ(layout.tabHeaderRects[1].x, 94.0f);
     EXPECT_FLOAT_EQ(layout.tabHeaderRects[1].width, 80.0f);
 
     ASSERT_EQ(layout.closeButtonRects.size(), 2u);
-    EXPECT_TRUE(layout.showCloseButtons[0]);
+    EXPECT_FALSE(layout.showCloseButtons[0]);
     EXPECT_FALSE(layout.showCloseButtons[1]);
-    EXPECT_FLOAT_EQ(layout.closeButtonRects[0].x, 76.0f);
-    EXPECT_FLOAT_EQ(layout.closeButtonRects[0].y, 29.0f);
-    EXPECT_FLOAT_EQ(layout.closeButtonRects[0].width, 12.0f);
-    EXPECT_FLOAT_EQ(layout.closeButtonRects[0].height, 12.0f);
 }
 
-TEST(UIEditorTabStripTest, HitTestPrioritizesCloseButtonThenTabThenContent) {
+TEST(UIEditorTabStripTest, HitTestPrioritizesTabThenHeaderThenContent) {
     const std::vector<UIEditorTabStripItem> items = {
         { "doc-a", "Document A", true, 48.0f },
         { "doc-b", "Document B", false, 40.0f }
@@ -125,14 +111,23 @@ TEST(UIEditorTabStripTest, HitTestPrioritizesCloseButtonThenTabThenContent) {
     const UIEditorTabStripLayout layout =
         BuildUIEditorTabStripLayout(UIRect(10.0f, 20.0f, 260.0f, 180.0f), items, state);
 
-    const auto closeHit = HitTestUIEditorTabStrip(layout, state, UIPoint(85.0f, 34.0f));
-    EXPECT_EQ(closeHit.kind, UIEditorTabStripHitTargetKind::CloseButton);
-    EXPECT_EQ(closeHit.index, 0u);
+    const auto rightSideTabHit = HitTestUIEditorTabStrip(
+        layout,
+        state,
+        UIPoint(
+            layout.tabHeaderRects[0].x + layout.tabHeaderRects[0].width - 2.0f,
+            layout.tabHeaderRects[0].y + layout.tabHeaderRects[0].height * 0.5f));
+    EXPECT_EQ(rightSideTabHit.kind, UIEditorTabStripHitTargetKind::Tab);
+    EXPECT_EQ(rightSideTabHit.index, 0u);
 
     const auto tabHit = HitTestUIEditorTabStrip(layout, state, UIPoint(40.0f, 34.0f));
     EXPECT_EQ(tabHit.kind, UIEditorTabStripHitTargetKind::Tab);
     EXPECT_EQ(tabHit.index, 0u);
 
+    const auto headerHit = HitTestUIEditorTabStrip(layout, state, UIPoint(200.0f, 34.0f));
+    EXPECT_EQ(headerHit.kind, UIEditorTabStripHitTargetKind::HeaderBackground);
+    EXPECT_EQ(headerHit.index, UIEditorTabStripInvalidIndex);
+
     const auto contentHit = HitTestUIEditorTabStrip(layout, state, UIPoint(40.0f, 70.0f));
     EXPECT_EQ(contentHit.kind, UIEditorTabStripHitTargetKind::Content);
     EXPECT_EQ(contentHit.index, UIEditorTabStripInvalidIndex);
@@ -147,7 +142,6 @@ TEST(UIEditorTabStripTest, BackgroundAndForegroundEmitStableChromeCommands) {
     UIEditorTabStripState state = {};
     state.selectedIndex = 0u;
     state.hoveredIndex = 1u;
-    state.closeHoveredIndex = 0u;
     state.focused = true;
 
     const UIEditorTabStripLayout layout =
@@ -155,24 +149,28 @@ TEST(UIEditorTabStripTest, BackgroundAndForegroundEmitStableChromeCommands) {
 
     UIDrawList background("TabStripBackground");
     AppendUIEditorTabStripBackground(background, layout, state);
-    ASSERT_EQ(background.GetCommandCount(), 8u);
+    ASSERT_EQ(background.GetCommandCount(), 9u);
     const auto& backgroundCommands = background.GetCommands();
     EXPECT_EQ(backgroundCommands[0].type, UIDrawCommandType::FilledRect);
     EXPECT_EQ(backgroundCommands[3].type, UIDrawCommandType::RectOutline);
     EXPECT_EQ(backgroundCommands[4].type, UIDrawCommandType::FilledRect);
-    EXPECT_EQ(backgroundCommands[7].type, UIDrawCommandType::RectOutline);
+    EXPECT_EQ(backgroundCommands[5].type, UIDrawCommandType::RectOutline);
+    EXPECT_EQ(backgroundCommands[6].type, UIDrawCommandType::FilledRect);
+    EXPECT_EQ(backgroundCommands[7].type, UIDrawCommandType::FilledRect);
+    EXPECT_EQ(backgroundCommands[8].type, UIDrawCommandType::RectOutline);
 
     UIDrawList foreground("TabStripForeground");
     AppendUIEditorTabStripForeground(foreground, layout, items, state);
-    ASSERT_EQ(foreground.GetCommandCount(), 9u);
+    ASSERT_EQ(foreground.GetCommandCount(), 8u);
     const auto& foregroundCommands = foreground.GetCommands();
-    EXPECT_EQ(foregroundCommands[0].type, UIDrawCommandType::PushClipRect);
-    EXPECT_EQ(foregroundCommands[1].type, UIDrawCommandType::Text);
-    EXPECT_EQ(foregroundCommands[1].text, "Document A");
-    EXPECT_EQ(foregroundCommands[5].type, UIDrawCommandType::Text);
-    EXPECT_EQ(foregroundCommands[5].text, "X");
-    EXPECT_EQ(foregroundCommands[7].type, UIDrawCommandType::Text);
-    EXPECT_EQ(foregroundCommands[7].text, "Document B");
+    EXPECT_EQ(foregroundCommands[0].type, UIDrawCommandType::FilledRect);
+    EXPECT_EQ(foregroundCommands[1].type, UIDrawCommandType::FilledRect);
+    EXPECT_EQ(foregroundCommands[2].type, UIDrawCommandType::PushClipRect);
+    EXPECT_EQ(foregroundCommands[3].type, UIDrawCommandType::Text);
+    EXPECT_EQ(foregroundCommands[3].text, "Document A");
+    EXPECT_EQ(foregroundCommands[5].type, UIDrawCommandType::PushClipRect);
+    EXPECT_EQ(foregroundCommands[6].type, UIDrawCommandType::Text);
+    EXPECT_EQ(foregroundCommands[6].text, "Document B");
 }
 
 } // namespace

tests/UI/Editor/unit/test_ui_editor_tab_strip_interaction.cpp

@@ -15,6 +15,7 @@ using XCEngine::UI::UIRect;
 using XCEngine::UI::Editor::UIEditorTabStripInteractionState;
 using XCEngine::UI::Editor::UpdateUIEditorTabStripInteraction;
 using XCEngine::UI::Editor::Widgets::UIEditorTabStripHitTargetKind;
+using XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex;
 using XCEngine::UI::Editor::Widgets::UIEditorTabStripItem;
 
 std::vector<UIEditorTabStripItem> BuildTabItems() {
@@ -73,7 +74,7 @@ UIPoint RectCenter(const XCEngine::UI::UIRect& rect) {
 
 } // namespace
 
-TEST(UIEditorTabStripInteractionTest, PointerMoveUpdatesHoveredTabAndCloseState) {
+TEST(UIEditorTabStripInteractionTest, PointerMoveUpdatesHoveredTabOnly) {
     const auto items = BuildTabItems();
     std::string selectedTabId = "doc-a";
     UIEditorTabStripInteractionState state = {};
@@ -85,7 +86,7 @@ TEST(UIEditorTabStripInteractionTest, PointerMoveUpdatesHoveredTabAndCloseState)
         items,
         {});
 
-    auto frame = UpdateUIEditorTabStripInteraction(
+    const auto frame = UpdateUIEditorTabStripInteraction(
         state,
         selectedTabId,
         UIRect(0.0f, 0.0f, 320.0f, 180.0f),
@@ -93,21 +94,11 @@ TEST(UIEditorTabStripInteractionTest, PointerMoveUpdatesHoveredTabAndCloseState)
         { MakePointerMove(
             initialFrame.layout.tabHeaderRects[1].x + 12.0f,
             initialFrame.layout.tabHeaderRects[1].y + 12.0f) });
+
     EXPECT_EQ(frame.result.hitTarget.kind, UIEditorTabStripHitTargetKind::Tab);
     EXPECT_EQ(state.tabStripState.hoveredIndex, 1u);
-    EXPECT_EQ(state.tabStripState.closeHoveredIndex, XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex);
-
-    frame = UpdateUIEditorTabStripInteraction(
-        state,
-        selectedTabId,
-        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
-        items,
-        { MakePointerMove(
-            initialFrame.layout.closeButtonRects[0].x + 4.0f,
-            initialFrame.layout.closeButtonRects[0].y + 4.0f) });
-    EXPECT_EQ(frame.result.hitTarget.kind, UIEditorTabStripHitTargetKind::CloseButton);
-    EXPECT_EQ(state.tabStripState.hoveredIndex, 0u);
-    EXPECT_EQ(state.tabStripState.closeHoveredIndex, 0u);
+    EXPECT_EQ(state.tabStripState.closeHoveredIndex, UIEditorTabStripInvalidIndex);
+    EXPECT_FALSE(frame.result.closeRequested);
 }
 
 TEST(UIEditorTabStripInteractionTest, LeftClickTabSelectsAndFocusesStrip) {
@@ -141,38 +132,6 @@ TEST(UIEditorTabStripInteractionTest, LeftClickTabSelectsAndFocusesStrip) {
     EXPECT_TRUE(state.tabStripState.focused);
 }
 
-TEST(UIEditorTabStripInteractionTest, LeftClickCloseButtonRequestsCloseWithoutChangingSelection) {
-    const auto items = BuildTabItems();
-    std::string selectedTabId = "doc-a";
-    UIEditorTabStripInteractionState state = {};
-
-    const auto initialFrame = UpdateUIEditorTabStripInteraction(
-        state,
-        selectedTabId,
-        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
-        items,
-        {});
-    const UIPoint closeCenter = RectCenter(initialFrame.layout.closeButtonRects[1]);
-
-    const auto frame = UpdateUIEditorTabStripInteraction(
-        state,
-        selectedTabId,
-        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
-        items,
-        {
-            MakePointerDown(closeCenter.x, closeCenter.y),
-            MakePointerUp(closeCenter.x, closeCenter.y)
-        });
-
-    EXPECT_TRUE(frame.result.consumed);
-    EXPECT_TRUE(frame.result.closeRequested);
-    EXPECT_FALSE(frame.result.selectionChanged);
-    EXPECT_EQ(frame.result.closedTabId, "doc-b");
-    EXPECT_EQ(frame.result.closedIndex, 1u);
-    EXPECT_EQ(selectedTabId, "doc-a");
-    EXPECT_TRUE(state.tabStripState.focused);
-}
-
 TEST(UIEditorTabStripInteractionTest, KeyboardNavigationMovesSelectionWhenFocused) {
     const auto items = BuildTabItems();
     std::string selectedTabId = "doc-b";
@@ -238,7 +197,377 @@ TEST(UIEditorTabStripInteractionTest, OutsideClickAndFocusLostClearFocusAndHover
         items,
         { MakePointerLeave(), MakeFocusLost() });
     EXPECT_FALSE(state.tabStripState.focused);
-    EXPECT_EQ(state.tabStripState.hoveredIndex, XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex);
-    EXPECT_EQ(state.tabStripState.closeHoveredIndex, XCEngine::UI::Editor::Widgets::UIEditorTabStripInvalidIndex);
+    EXPECT_EQ(state.tabStripState.hoveredIndex, UIEditorTabStripInvalidIndex);
+    EXPECT_EQ(state.tabStripState.closeHoveredIndex, UIEditorTabStripInvalidIndex);
     EXPECT_FALSE(state.hasPointerPosition);
 }
+
+TEST(UIEditorTabStripInteractionTest, DraggingTabRequestsPointerCaptureAndShowsInsertionPreview) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-a";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[0]);
+    const auto& lastRect = initialFrame.layout.tabHeaderRects.back();
+    const UIPoint dragPoint(lastRect.x + lastRect.width - 2.0f, sourceCenter.y);
+
+    const auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dragPoint.x, dragPoint.y)
+        });
+
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(frame.result.dragStarted);
+    EXPECT_TRUE(frame.result.consumed);
+    EXPECT_EQ(frame.result.draggedTabId, "doc-a");
+    EXPECT_EQ(frame.result.dragSourceIndex, 0u);
+    EXPECT_EQ(frame.result.dropInsertionIndex, items.size());
+    EXPECT_EQ(frame.result.reorderToIndex, 2u);
+    EXPECT_TRUE(frame.result.reorderPreviewActive);
+    EXPECT_EQ(frame.result.reorderPreviewIndex, 2u);
+    EXPECT_TRUE(state.reorderCaptureActive);
+    EXPECT_EQ(state.reorderSourceIndex, 0u);
+    EXPECT_EQ(state.reorderPreviewIndex, 2u);
+    EXPECT_TRUE(frame.layout.insertionPreview.visible);
+    EXPECT_EQ(frame.layout.insertionPreview.insertionIndex, items.size());
+}
+
+TEST(UIEditorTabStripInteractionTest, DroppingDraggedTabEmitsSameStackReorderRequest) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-a";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[0]);
+    const auto& lastRect = initialFrame.layout.tabHeaderRects.back();
+    const UIPoint dragPoint(lastRect.x + lastRect.width - 2.0f, sourceCenter.y);
+
+    const auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dragPoint.x, dragPoint.y),
+            MakePointerUp(dragPoint.x, dragPoint.y)
+        });
+
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.dragEnded);
+    EXPECT_TRUE(frame.result.reorderRequested);
+    EXPECT_FALSE(frame.result.dragCanceled);
+    EXPECT_EQ(frame.result.draggedTabId, "doc-a");
+    EXPECT_EQ(frame.result.dragSourceIndex, 0u);
+    EXPECT_EQ(frame.result.dropInsertionIndex, items.size());
+    EXPECT_EQ(frame.result.reorderToIndex, 2u);
+    EXPECT_FALSE(state.reorderCaptureActive);
+    EXPECT_EQ(state.reorderSourceIndex, UIEditorTabStripInvalidIndex);
+    EXPECT_EQ(state.reorderPreviewIndex, UIEditorTabStripInvalidIndex);
+    EXPECT_FALSE(frame.layout.insertionPreview.visible);
+}
+
+TEST(UIEditorTabStripInteractionTest, DroppingRightmostTabToFrontCommitsReorderRequest) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-c";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[2]);
+    const UIPoint dropPoint(
+        initialFrame.layout.tabHeaderRects[0].x + 4.0f,
+        sourceCenter.y);
+
+    const auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dropPoint.x, dropPoint.y),
+            MakePointerUp(dropPoint.x, dropPoint.y)
+        });
+
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.dragEnded);
+    EXPECT_TRUE(frame.result.reorderRequested);
+    EXPECT_FALSE(frame.result.dragCanceled);
+    EXPECT_EQ(frame.result.draggedTabId, "doc-c");
+    EXPECT_EQ(frame.result.dragSourceIndex, 2u);
+    EXPECT_EQ(frame.result.dropInsertionIndex, 0u);
+    EXPECT_EQ(frame.result.reorderToIndex, 0u);
+}
+
+TEST(UIEditorTabStripInteractionTest, DroppingRightmostTabIntoMiddleCommitsReorderRequest) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-c";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[2]);
+    const UIPoint dropPoint(
+        initialFrame.layout.tabHeaderRects[1].x + 4.0f,
+        sourceCenter.y);
+
+    const auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dropPoint.x, dropPoint.y),
+            MakePointerUp(dropPoint.x, dropPoint.y)
+        });
+
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.dragEnded);
+    EXPECT_TRUE(frame.result.reorderRequested);
+    EXPECT_FALSE(frame.result.dragCanceled);
+    EXPECT_EQ(frame.result.draggedTabId, "doc-c");
+    EXPECT_EQ(frame.result.dragSourceIndex, 2u);
+    EXPECT_EQ(frame.result.dropInsertionIndex, 1u);
+    EXPECT_EQ(frame.result.reorderToIndex, 1u);
+}
+
+TEST(UIEditorTabStripInteractionTest, SeparateFrameDropOfRightmostTabIntoMiddleStillCommitsReorderRequest) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-c";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[2]);
+    const UIPoint dropPoint(
+        initialFrame.layout.tabHeaderRects[1].x + 4.0f,
+        sourceCenter.y);
+
+    auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dropPoint.x, dropPoint.y)
+        });
+    ASSERT_TRUE(frame.result.requestPointerCapture);
+    ASSERT_TRUE(frame.result.reorderPreviewActive);
+    ASSERT_TRUE(state.reorderDragState.active);
+    ASSERT_FALSE(state.reorderDragState.targetId.empty());
+
+    frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        { MakePointerUp(dropPoint.x, dropPoint.y) });
+
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.dragEnded);
+    EXPECT_TRUE(frame.result.reorderRequested);
+    EXPECT_FALSE(frame.result.dragCanceled);
+    EXPECT_EQ(frame.result.draggedTabId, "doc-c");
+    EXPECT_EQ(frame.result.dragSourceIndex, 2u);
+    EXPECT_EQ(frame.result.dropInsertionIndex, 1u);
+    EXPECT_EQ(frame.result.reorderToIndex, 1u);
+}
+
+TEST(UIEditorTabStripInteractionTest, ReleasingOutsideHeaderStillCommitsLastVisibleReorderPreview) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-a";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[0]);
+    const auto& lastRect = initialFrame.layout.tabHeaderRects.back();
+    const UIPoint dragPoint(lastRect.x + lastRect.width - 2.0f, sourceCenter.y);
+    const UIPoint releasePoint(
+        dragPoint.x,
+        initialFrame.layout.headerRect.y + initialFrame.layout.headerRect.height + 8.0f);
+
+    auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dragPoint.x, dragPoint.y)
+        });
+    ASSERT_TRUE(frame.result.reorderPreviewActive);
+    ASSERT_EQ(state.tabStripState.reorder.previewInsertionIndex, items.size());
+
+    frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        { MakePointerUp(releasePoint.x, releasePoint.y) });
+
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_TRUE(frame.result.dragEnded);
+    EXPECT_TRUE(frame.result.reorderRequested);
+    EXPECT_FALSE(frame.result.dragCanceled);
+    EXPECT_EQ(frame.result.draggedTabId, "doc-a");
+    EXPECT_EQ(frame.result.dragSourceIndex, 0u);
+    EXPECT_EQ(frame.result.dropInsertionIndex, items.size());
+    EXPECT_EQ(frame.result.reorderToIndex, 2u);
+}
+
+TEST(UIEditorTabStripInteractionTest, EscapeCancelsActiveTabDragAndReleasesCapture) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-a";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[1]);
+    const UIPoint dragPoint(
+        initialFrame.layout.tabHeaderRects[2].x + 8.0f,
+        sourceCenter.y);
+
+    auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dragPoint.x, dragPoint.y)
+        });
+    ASSERT_TRUE(frame.result.dragStarted);
+    ASSERT_TRUE(state.reorderCaptureActive);
+
+    frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        { MakeKeyDown(KeyCode::Escape) });
+
+    EXPECT_TRUE(frame.result.dragCanceled);
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_FALSE(frame.result.reorderRequested);
+    EXPECT_EQ(frame.result.draggedTabId, "doc-b");
+    EXPECT_FALSE(state.reorderCaptureActive);
+    EXPECT_EQ(state.reorderSourceIndex, UIEditorTabStripInvalidIndex);
+}
+
+TEST(UIEditorTabStripInteractionTest, FocusLostCancelsActiveTabDragAndClearsPreview) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-a";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[0]);
+    const UIPoint dragPoint(
+        initialFrame.layout.tabHeaderRects[2].x + 8.0f,
+        sourceCenter.y);
+
+    auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(dragPoint.x, dragPoint.y)
+        });
+    ASSERT_TRUE(frame.result.dragStarted);
+    ASSERT_TRUE(frame.result.reorderPreviewActive);
+
+    frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        { MakeFocusLost() });
+
+    EXPECT_TRUE(frame.result.dragCanceled);
+    EXPECT_TRUE(frame.result.releasePointerCapture);
+    EXPECT_FALSE(frame.result.reorderRequested);
+    EXPECT_FALSE(state.tabStripState.focused);
+    EXPECT_FALSE(state.reorderCaptureActive);
+    EXPECT_EQ(state.reorderPreviewIndex, UIEditorTabStripInvalidIndex);
+    EXPECT_FALSE(frame.layout.insertionPreview.visible);
+}
+
+TEST(UIEditorTabStripInteractionTest, VisibleInsertionIndexTracksHeaderGapsInsteadOfFinalTabIndices) {
+    const auto items = BuildTabItems();
+    std::string selectedTabId = "doc-b";
+    UIEditorTabStripInteractionState state = {};
+
+    const auto initialFrame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {});
+    const UIPoint sourceCenter = RectCenter(initialFrame.layout.tabHeaderRects[1]);
+    const float betweenFirstAndSecond =
+        (initialFrame.layout.tabHeaderRects[0].x + initialFrame.layout.tabHeaderRects[0].width +
+            initialFrame.layout.tabHeaderRects[1].x) * 0.5f;
+
+    const auto frame = UpdateUIEditorTabStripInteraction(
+        state,
+        selectedTabId,
+        UIRect(0.0f, 0.0f, 320.0f, 180.0f),
+        items,
+        {
+            MakePointerDown(sourceCenter.x, sourceCenter.y),
+            MakePointerMove(betweenFirstAndSecond, sourceCenter.y)
+        });
+
+    EXPECT_TRUE(frame.result.requestPointerCapture);
+    EXPECT_TRUE(frame.result.reorderPreviewActive);
+    EXPECT_EQ(frame.result.dragSourceIndex, 1u);
+    EXPECT_EQ(frame.result.dropInsertionIndex, 1u);
+    EXPECT_EQ(frame.result.reorderToIndex, 1u);
+    EXPECT_EQ(frame.result.reorderPreviewIndex, 1u);
+}

tests/UI/Editor/unit/test_ui_editor_viewport_shell.cpp

@@ -37,9 +37,9 @@ TEST(UIEditorViewportShellTest, ResolveRequestUsesViewportInputRectSize) {
         spec);
 
     EXPECT_FLOAT_EQ(request.slotLayout.inputRect.width, 800.0f);
-    EXPECT_FLOAT_EQ(request.slotLayout.inputRect.height, 532.0f);
+    EXPECT_FLOAT_EQ(request.slotLayout.inputRect.height, 554.0f);
     EXPECT_FLOAT_EQ(request.requestedViewportSize.width, 800.0f);
-    EXPECT_FLOAT_EQ(request.requestedViewportSize.height, 532.0f);
+    EXPECT_FLOAT_EQ(request.requestedViewportSize.height, 554.0f);
 }
 
 TEST(UIEditorViewportShellTest, ResolveRequestTracksChromeBarVisibility) {

tests/UI/Editor/unit/test_ui_editor_viewport_slot.cpp

@@ -92,7 +92,7 @@ TEST(UIEditorViewportSlotTest, DesiredToolWidthUsesExplicitValueBeforeEstimatedL
     inferredWidth.label = "Scene";
 
     EXPECT_FLOAT_EQ(ResolveUIEditorViewportSlotDesiredToolWidth(explicitWidth), 88.0f);
-    EXPECT_FLOAT_EQ(ResolveUIEditorViewportSlotDesiredToolWidth(inferredWidth), 55.0f);
+    EXPECT_FLOAT_EQ(ResolveUIEditorViewportSlotDesiredToolWidth(inferredWidth), 48.5f);
 }
 
 TEST(UIEditorViewportSlotTest, LayoutBuildsTopBarSurfaceBottomBarAndAspectFittedTexture) {
@@ -142,12 +142,12 @@ TEST(UIEditorViewportSlotTest, ToolItemsAlignToEdgesAndTitleRectClampsBetweenToo
             BuildToolItems(),
             {});
 
-    EXPECT_FLOAT_EQ(layout.toolItemRects[0].x, 12.0f);
+    EXPECT_FLOAT_EQ(layout.toolItemRects[0].x, 8.0f);
     EXPECT_FLOAT_EQ(layout.toolItemRects[0].width, 96.0f);
-    EXPECT_FLOAT_EQ(layout.toolItemRects[1].x, 762.0f);
-    EXPECT_FLOAT_EQ(layout.toolItemRects[2].x, 816.0f);
-    EXPECT_FLOAT_EQ(layout.titleRect.x, 118.0f);
-    EXPECT_FLOAT_EQ(layout.titleRect.width, 634.0f);
+    EXPECT_FLOAT_EQ(layout.toolItemRects[1].x, 768.0f);
+    EXPECT_FLOAT_EQ(layout.toolItemRects[2].x, 820.0f);
+    EXPECT_FLOAT_EQ(layout.titleRect.x, 110.0f);
+    EXPECT_FLOAT_EQ(layout.titleRect.width, 652.0f);
 }
 
 TEST(UIEditorViewportSlotTest, HitTestPrioritizesToolThenStatusThenSurface) {

tests/UI/Editor/unit/test_ui_editor_workspace_controller.cpp

@@ -2,6 +2,8 @@
 
 #include <XCEditor/Shell/UIEditorWorkspaceController.h>
 
+#include <string>
+
 namespace {
 
 using XCEngine::UI::Editor::BuildDefaultUIEditorWorkspaceController;
@@ -9,6 +11,9 @@ using XCEngine::UI::Editor::BuildDefaultUIEditorWorkspaceSession;
 using XCEngine::UI::Editor::BuildUIEditorWorkspacePanel;
 using XCEngine::UI::Editor::BuildUIEditorWorkspaceSplit;
 using XCEngine::UI::Editor::BuildUIEditorWorkspaceTabStack;
+using XCEngine::UI::Editor::AreUIEditorWorkspaceModelsEquivalent;
+using XCEngine::UI::Editor::FindUIEditorPanelSessionState;
+using XCEngine::UI::Editor::FindUIEditorWorkspaceNode;
 using XCEngine::UI::Editor::GetUIEditorWorkspaceCommandKindName;
 using XCEngine::UI::Editor::GetUIEditorWorkspaceCommandStatusName;
 using XCEngine::UI::Editor::UIEditorPanelRegistry;
@@ -17,7 +22,11 @@ using XCEngine::UI::Editor::UIEditorWorkspaceCommandKind;
 using XCEngine::UI::Editor::UIEditorWorkspaceCommandStatus;
 using XCEngine::UI::Editor::UIEditorWorkspaceControllerValidationCode;
 using XCEngine::UI::Editor::UIEditorWorkspaceController;
+using XCEngine::UI::Editor::UIEditorWorkspaceDockPlacement;
+using XCEngine::UI::Editor::UIEditorWorkspaceLayoutOperationStatus;
 using XCEngine::UI::Editor::UIEditorWorkspaceModel;
+using XCEngine::UI::Editor::UIEditorWorkspaceNode;
+using XCEngine::UI::Editor::UIEditorWorkspaceSession;
 using XCEngine::UI::Editor::UIEditorWorkspaceSplitAxis;
 
 UIEditorPanelRegistry BuildPanelRegistry() {
@@ -25,6 +34,9 @@ UIEditorPanelRegistry BuildPanelRegistry() {
     registry.panels = {
         { "doc-a", "Document A", {}, true, true, true },
         { "doc-b", "Document B", {}, true, true, true },
+        { "doc-c", "Document C", {}, true, true, true },
+        { "hidden-a", "Hidden A", {}, true, true, true },
+        { "hidden-b", "Hidden B", {}, true, true, true },
         { "details", "Details", {}, true, true, true },
         { "root", "Root", {}, true, false, false }
     };
@@ -49,6 +61,34 @@ UIEditorWorkspaceModel BuildWorkspace() {
     return workspace;
 }
 
+UIEditorWorkspaceModel BuildReorderWorkspace() {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceTabStack(
+        "document-tabs",
+        {
+            BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+            BuildUIEditorWorkspacePanel("hidden-a-node", "hidden-a", "Hidden A", true),
+            BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true),
+            BuildUIEditorWorkspacePanel("hidden-b-node", "hidden-b", "Hidden B", true),
+            BuildUIEditorWorkspacePanel("doc-c-node", "doc-c", "Document C", true)
+        },
+        2u);
+    workspace.activePanelId = "doc-b";
+    return workspace;
+}
+
+UIEditorWorkspaceSession BuildReorderSession() {
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "hidden-a", true, false },
+        { "doc-b", true, true },
+        { "hidden-b", true, false },
+        { "doc-c", true, true }
+    };
+    return session;
+}
+
 } // namespace
 
 TEST(UIEditorWorkspaceControllerTest, CommandNameHelpersExposeStableDebugNames) {
@@ -146,3 +186,201 @@ TEST(UIEditorWorkspaceControllerTest, RejectsUnknownPanelAndNonCloseablePanelCom
     EXPECT_EQ(nonCloseable.status, UIEditorWorkspaceCommandStatus::Rejected);
     EXPECT_EQ(rootController.GetWorkspace().activePanelId, "root");
 }
+
+TEST(UIEditorWorkspaceControllerTest, ReorderTabUsesModelSurgeryAndPreservesSelectionActiveAndSession) {
+    UIEditorWorkspaceController controller(
+        BuildPanelRegistry(),
+        BuildReorderWorkspace(),
+        BuildReorderSession());
+
+    const auto result = controller.ReorderTab("document-tabs", "doc-c", 0u);
+    EXPECT_EQ(result.status, UIEditorWorkspaceLayoutOperationStatus::Changed);
+    EXPECT_EQ(result.activePanelId, "doc-b");
+    ASSERT_EQ(result.visiblePanelIds.size(), 1u);
+    EXPECT_EQ(result.visiblePanelIds[0], "doc-b");
+
+    const UIEditorWorkspaceNode* tabStack =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "document-tabs");
+    ASSERT_NE(tabStack, nullptr);
+    ASSERT_EQ(tabStack->children.size(), 5u);
+    EXPECT_EQ(tabStack->children[0].panel.panelId, "doc-c");
+    EXPECT_EQ(tabStack->children[1].panel.panelId, "hidden-a");
+    EXPECT_EQ(tabStack->children[2].panel.panelId, "doc-a");
+    EXPECT_EQ(tabStack->children[3].panel.panelId, "hidden-b");
+    EXPECT_EQ(tabStack->children[4].panel.panelId, "doc-b");
+    EXPECT_EQ(tabStack->selectedTabIndex, 4u);
+
+    const auto* hiddenState =
+        FindUIEditorPanelSessionState(controller.GetSession(), "hidden-a");
+    ASSERT_NE(hiddenState, nullptr);
+    EXPECT_TRUE(hiddenState->open);
+    EXPECT_FALSE(hiddenState->visible);
+}
+
+TEST(UIEditorWorkspaceControllerTest, ReorderTabRejectsHiddenPanelsAndOutOfRangeTargetsAndReportsNoOp) {
+    UIEditorWorkspaceController controller(
+        BuildPanelRegistry(),
+        BuildReorderWorkspace(),
+        BuildReorderSession());
+
+    const auto hidden = controller.ReorderTab("document-tabs", "hidden-a", 0u);
+    EXPECT_EQ(hidden.status, UIEditorWorkspaceLayoutOperationStatus::Rejected);
+
+    const auto outOfRange = controller.ReorderTab("document-tabs", "doc-a", 4u);
+    EXPECT_EQ(outOfRange.status, UIEditorWorkspaceLayoutOperationStatus::Rejected);
+
+    const auto noOp = controller.ReorderTab("document-tabs", "doc-a", 0u);
+    EXPECT_EQ(noOp.status, UIEditorWorkspaceLayoutOperationStatus::NoOp);
+}
+
+TEST(UIEditorWorkspaceControllerTest, MoveTabToStackMovesVisibleTabAcrossStacks) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.55f,
+        BuildUIEditorWorkspaceTabStack(
+            "left-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspacePanel("details-node", "details", "Details", true));
+    workspace.activePanelId = "doc-a";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "doc-b", true, true },
+        { "details", true, true }
+    };
+
+    UIEditorWorkspaceController controller(BuildPanelRegistry(), workspace, session);
+
+    const auto result = controller.MoveTabToStack("left-tabs", "doc-b", "details-node", 1u);
+    EXPECT_EQ(result.status, UIEditorWorkspaceLayoutOperationStatus::Changed);
+    EXPECT_EQ(result.activePanelId, "doc-b");
+
+    const UIEditorWorkspaceNode* leftTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "left-tabs");
+    const UIEditorWorkspaceNode* detailsTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "details-node");
+    ASSERT_NE(leftTabs, nullptr);
+    ASSERT_NE(detailsTabs, nullptr);
+    ASSERT_EQ(leftTabs->children.size(), 1u);
+    ASSERT_EQ(detailsTabs->children.size(), 2u);
+    EXPECT_EQ(detailsTabs->children[1].panel.panelId, "doc-b");
+}
+
+TEST(UIEditorWorkspaceControllerTest, DockTabRelativeCreatesSplitAroundTargetStack) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.55f,
+        BuildUIEditorWorkspaceTabStack(
+            "left-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspacePanel("details-node", "details", "Details", true));
+    workspace.activePanelId = "doc-a";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "doc-b", true, true },
+        { "details", true, true }
+    };
+
+    UIEditorWorkspaceController controller(BuildPanelRegistry(), workspace, session);
+
+    const auto result = controller.DockTabRelative(
+        "left-tabs",
+        "doc-b",
+        "details-node",
+        UIEditorWorkspaceDockPlacement::Bottom,
+        0.4f);
+    EXPECT_EQ(result.status, UIEditorWorkspaceLayoutOperationStatus::Changed);
+    EXPECT_EQ(result.activePanelId, "doc-b");
+
+    const UIEditorWorkspaceNode* detailsTabs =
+        FindUIEditorWorkspaceNode(controller.GetWorkspace(), "details-node");
+    ASSERT_NE(detailsTabs, nullptr);
+    EXPECT_EQ(detailsTabs->kind, XCEngine::UI::Editor::UIEditorWorkspaceNodeKind::TabStack);
+
+    bool foundDockedTab = false;
+    for (const std::string candidate : { "details-node__dock_doc-b_stack", "details-node__dock_doc-b_stack-1" }) {
+        const UIEditorWorkspaceNode* docked =
+            FindUIEditorWorkspaceNode(controller.GetWorkspace(), candidate);
+        if (docked != nullptr) {
+            foundDockedTab = docked->children.size() == 1u &&
+                docked->children[0].panel.panelId == "doc-b";
+            if (foundDockedTab) {
+                break;
+            }
+        }
+    }
+    EXPECT_TRUE(foundDockedTab);
+}
+
+TEST(UIEditorWorkspaceControllerTest, DockTabRelativeReturnsNoOpWhenRedockingAlreadyDockedSingleTabStack) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.55f,
+        BuildUIEditorWorkspaceTabStack(
+            "left-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspacePanel("details-node", "details", "Details", true));
+    workspace.activePanelId = "doc-a";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "doc-b", true, true },
+        { "details", true, true }
+    };
+
+    UIEditorWorkspaceController controller(BuildPanelRegistry(), workspace, session);
+
+    const auto first = controller.DockTabRelative(
+        "left-tabs",
+        "doc-b",
+        "details-node",
+        UIEditorWorkspaceDockPlacement::Bottom,
+        0.4f);
+    ASSERT_EQ(first.status, UIEditorWorkspaceLayoutOperationStatus::Changed);
+
+    std::string movedStackId = {};
+    for (const std::string candidate : { "details-node__dock_doc-b_stack", "details-node__dock_doc-b_stack-1" }) {
+        if (FindUIEditorWorkspaceNode(controller.GetWorkspace(), candidate) != nullptr) {
+            movedStackId = candidate;
+            break;
+        }
+    }
+    ASSERT_FALSE(movedStackId.empty());
+
+    const UIEditorWorkspaceModel afterFirstDock = controller.GetWorkspace();
+
+    const auto second = controller.DockTabRelative(
+        movedStackId,
+        "doc-b",
+        "details-node",
+        UIEditorWorkspaceDockPlacement::Bottom,
+        0.4f);
+    EXPECT_EQ(second.status, UIEditorWorkspaceLayoutOperationStatus::NoOp);
+    EXPECT_EQ(second.activePanelId, "doc-b");
+    EXPECT_TRUE(
+        AreUIEditorWorkspaceModelsEquivalent(
+            controller.GetWorkspace(),
+            afterFirstDock));
+}

tests/UI/Editor/unit/test_ui_editor_workspace_model.cpp

@@ -1,6 +1,7 @@
 #include <gtest/gtest.h>
 
 #include <XCEditor/Shell/UIEditorWorkspaceModel.h>
+#include <XCEditor/Shell/UIEditorWorkspaceSession.h>
 
 #include <algorithm>
 #include <string>
@@ -12,17 +13,25 @@ using XCEngine::UI::Editor::BuildUIEditorWorkspacePanel;
 using XCEngine::UI::Editor::BuildUIEditorWorkspaceSingleTabStack;
 using XCEngine::UI::Editor::BuildUIEditorWorkspaceSplit;
 using XCEngine::UI::Editor::BuildUIEditorWorkspaceTabStack;
+using XCEngine::UI::Editor::AreUIEditorWorkspaceModelsEquivalent;
 using XCEngine::UI::Editor::CanonicalizeUIEditorWorkspaceModel;
 using XCEngine::UI::Editor::CollectUIEditorWorkspaceVisiblePanels;
 using XCEngine::UI::Editor::ContainsUIEditorWorkspacePanel;
 using XCEngine::UI::Editor::FindUIEditorWorkspaceActivePanel;
 using XCEngine::UI::Editor::FindUIEditorWorkspaceNode;
 using XCEngine::UI::Editor::TryActivateUIEditorWorkspacePanel;
+using XCEngine::UI::Editor::TryDockUIEditorWorkspaceTabRelative;
+using XCEngine::UI::Editor::TryMoveUIEditorWorkspaceTabToStack;
+using XCEngine::UI::Editor::TryReorderUIEditorWorkspaceTab;
 using XCEngine::UI::Editor::TrySetUIEditorWorkspaceSplitRatio;
+using XCEngine::UI::Editor::UIEditorWorkspaceDockPlacement;
 using XCEngine::UI::Editor::UIEditorWorkspaceModel;
+using XCEngine::UI::Editor::UIEditorWorkspaceNode;
+using XCEngine::UI::Editor::UIEditorWorkspaceSession;
 using XCEngine::UI::Editor::UIEditorWorkspaceNodeKind;
 using XCEngine::UI::Editor::UIEditorWorkspaceSplitAxis;
 using XCEngine::UI::Editor::UIEditorWorkspaceValidationCode;
+using XCEngine::UI::Editor::UIEditorWorkspaceVisiblePanel;
 using XCEngine::UI::Editor::ValidateUIEditorWorkspace;
 
 std::vector<std::string> CollectVisiblePanelIds(const UIEditorWorkspaceModel& workspace) {
@@ -170,6 +179,78 @@ TEST(UIEditorWorkspaceModelTest, SplitRatioMutationTargetsSplitNodeAndRejectsInv
     EXPECT_FALSE(TrySetUIEditorWorkspaceSplitRatio(workspace, "root-split", 1.0f));
 }
 
+TEST(UIEditorWorkspaceModelTest, ReorderTabMovesVisibleTabsAndPreservesHiddenOrderSelectionAndActivePanel) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceTabStack(
+        "document-tabs",
+        {
+            BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+            BuildUIEditorWorkspacePanel("hidden-a-node", "hidden-a", "Hidden A", true),
+            BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true),
+            BuildUIEditorWorkspacePanel("hidden-b-node", "hidden-b", "Hidden B", true),
+            BuildUIEditorWorkspacePanel("doc-c-node", "doc-c", "Document C", true)
+        },
+        2u);
+    workspace.activePanelId = "doc-b";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "hidden-a", true, false },
+        { "doc-b", true, true },
+        { "hidden-b", true, false },
+        { "doc-c", true, true }
+    };
+
+    ASSERT_TRUE(TryReorderUIEditorWorkspaceTab(
+        workspace,
+        session,
+        "document-tabs",
+        "doc-c",
+        0u));
+
+    const UIEditorWorkspaceNode* tabStack =
+        FindUIEditorWorkspaceNode(workspace, "document-tabs");
+    ASSERT_NE(tabStack, nullptr);
+    ASSERT_EQ(tabStack->children.size(), 5u);
+    EXPECT_EQ(tabStack->children[0].panel.panelId, "doc-c");
+    EXPECT_EQ(tabStack->children[1].panel.panelId, "hidden-a");
+    EXPECT_EQ(tabStack->children[2].panel.panelId, "doc-a");
+    EXPECT_EQ(tabStack->children[3].panel.panelId, "hidden-b");
+    EXPECT_EQ(tabStack->children[4].panel.panelId, "doc-b");
+    EXPECT_EQ(tabStack->selectedTabIndex, 4u);
+    EXPECT_EQ(workspace.activePanelId, "doc-b");
+
+    EXPECT_FALSE(TryReorderUIEditorWorkspaceTab(
+        workspace,
+        session,
+        "document-tabs",
+        "hidden-a",
+        0u));
+
+    ASSERT_TRUE(TryReorderUIEditorWorkspaceTab(
+        workspace,
+        session,
+        "document-tabs",
+        "doc-a",
+        3u));
+    tabStack = FindUIEditorWorkspaceNode(workspace, "document-tabs");
+    ASSERT_NE(tabStack, nullptr);
+    EXPECT_EQ(tabStack->children[0].panel.panelId, "doc-c");
+    EXPECT_EQ(tabStack->children[1].panel.panelId, "hidden-a");
+    EXPECT_EQ(tabStack->children[2].panel.panelId, "doc-b");
+    EXPECT_EQ(tabStack->children[3].panel.panelId, "hidden-b");
+    EXPECT_EQ(tabStack->children[4].panel.panelId, "doc-a");
+    EXPECT_EQ(tabStack->selectedTabIndex, 2u);
+
+    EXPECT_FALSE(TryReorderUIEditorWorkspaceTab(
+        workspace,
+        session,
+        "document-tabs",
+        "doc-a",
+        4u));
+}
+
 TEST(UIEditorWorkspaceModelTest, CanonicalizeWrapsStandalonePanelsIntoSingleTabStacks) {
     UIEditorWorkspaceModel workspace = {};
     workspace.root = BuildUIEditorWorkspaceSplit(
@@ -195,3 +276,254 @@ TEST(UIEditorWorkspaceModelTest, CanonicalizeWrapsStandalonePanelsIntoSingleTabS
         "left");
     EXPECT_EQ(canonicalWorkspace.root.children[1].kind, UIEditorWorkspaceNodeKind::TabStack);
 }
+
+TEST(UIEditorWorkspaceModelTest, MoveTabToStackMergesIntoTargetStackAndActivatesMovedPanel) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.58f,
+        BuildUIEditorWorkspaceTabStack(
+            "left-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspaceSingleTabStack(
+            "right-tabs",
+            "details",
+            "Details",
+            true));
+    workspace.activePanelId = "doc-a";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "doc-b", true, true },
+        { "details", true, true }
+    };
+
+    ASSERT_TRUE(TryMoveUIEditorWorkspaceTabToStack(
+        workspace,
+        session,
+        "left-tabs",
+        "doc-b",
+        "right-tabs",
+        1u));
+
+    const UIEditorWorkspaceNode* leftTabs =
+        FindUIEditorWorkspaceNode(workspace, "left-tabs");
+    const UIEditorWorkspaceNode* rightTabs =
+        FindUIEditorWorkspaceNode(workspace, "right-tabs");
+    ASSERT_NE(leftTabs, nullptr);
+    ASSERT_NE(rightTabs, nullptr);
+    ASSERT_EQ(leftTabs->children.size(), 1u);
+    ASSERT_EQ(rightTabs->children.size(), 2u);
+    EXPECT_EQ(leftTabs->children[0].panel.panelId, "doc-a");
+    EXPECT_EQ(rightTabs->children[0].panel.panelId, "details");
+    EXPECT_EQ(rightTabs->children[1].panel.panelId, "doc-b");
+    EXPECT_EQ(rightTabs->selectedTabIndex, 1u);
+    EXPECT_EQ(workspace.activePanelId, "doc-b");
+}
+
+TEST(UIEditorWorkspaceModelTest, DockTabRelativeSplitsTargetStackAndCreatesNewLeaf) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.58f,
+        BuildUIEditorWorkspaceTabStack(
+            "left-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspaceSingleTabStack(
+            "right-tabs",
+            "details",
+            "Details",
+            true));
+    workspace.activePanelId = "doc-a";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "doc-b", true, true },
+        { "details", true, true }
+    };
+
+    ASSERT_TRUE(TryDockUIEditorWorkspaceTabRelative(
+        workspace,
+        session,
+        "left-tabs",
+        "doc-b",
+        "right-tabs",
+        UIEditorWorkspaceDockPlacement::Bottom,
+        0.4f));
+
+    const UIEditorWorkspaceNode* rightTabs =
+        FindUIEditorWorkspaceNode(workspace, "right-tabs");
+    ASSERT_NE(rightTabs, nullptr);
+    ASSERT_EQ(rightTabs->kind, UIEditorWorkspaceNodeKind::TabStack);
+    ASSERT_EQ(rightTabs->children.size(), 1u);
+    EXPECT_EQ(rightTabs->children[0].panel.panelId, "details");
+
+    const UIEditorWorkspaceNode* movedTabStack = nullptr;
+    if (const UIEditorWorkspaceNode* rootSplit =
+            FindUIEditorWorkspaceNode(workspace, "root-split");
+        rootSplit != nullptr) {
+        const auto visibleIds = CollectVisiblePanelIds(workspace);
+        ASSERT_EQ(visibleIds.size(), 3u);
+        EXPECT_EQ(visibleIds[0], "doc-a");
+        EXPECT_EQ(visibleIds[1], "details");
+        EXPECT_EQ(visibleIds[2], "doc-b");
+    }
+
+    const std::vector<UIEditorWorkspaceVisiblePanel> visiblePanels =
+        CollectUIEditorWorkspaceVisiblePanels(workspace);
+    ASSERT_EQ(visiblePanels.size(), 3u);
+    EXPECT_EQ(visiblePanels[2].panelId, "doc-b");
+
+    for (const std::string candidate : { "right-tabs__dock_doc-b_stack", "right-tabs__dock_doc-b_stack-1" }) {
+        movedTabStack = FindUIEditorWorkspaceNode(workspace, candidate);
+        if (movedTabStack != nullptr) {
+            break;
+        }
+    }
+    ASSERT_NE(movedTabStack, nullptr);
+    ASSERT_EQ(movedTabStack->kind, UIEditorWorkspaceNodeKind::TabStack);
+    ASSERT_EQ(movedTabStack->children.size(), 1u);
+    EXPECT_EQ(movedTabStack->children[0].panel.panelId, "doc-b");
+    EXPECT_EQ(workspace.activePanelId, "doc-b");
+}
+
+TEST(UIEditorWorkspaceModelTest, DockTabRelativeCanRedockSingleTabBranchBackOntoSiblingStack) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceTabStack(
+        "center-tabs",
+        {
+            BuildUIEditorWorkspacePanel("scene-node", "scene", "Scene", true),
+            BuildUIEditorWorkspacePanel("game-node", "game", "Game", true)
+        },
+        0u);
+    workspace.activePanelId = "scene";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "scene", true, true },
+        { "game", true, true }
+    };
+
+    ASSERT_TRUE(TryDockUIEditorWorkspaceTabRelative(
+        workspace,
+        session,
+        "center-tabs",
+        "scene",
+        "center-tabs",
+        UIEditorWorkspaceDockPlacement::Top,
+        0.5f));
+
+    const UIEditorWorkspaceNode* firstDockStack =
+        FindUIEditorWorkspaceNode(workspace, "center-tabs__dock_scene_stack");
+    ASSERT_NE(firstDockStack, nullptr);
+    ASSERT_EQ(firstDockStack->kind, UIEditorWorkspaceNodeKind::TabStack);
+    ASSERT_EQ(firstDockStack->children.size(), 1u);
+    EXPECT_EQ(firstDockStack->children[0].panel.panelId, "scene");
+
+    ASSERT_TRUE(TryDockUIEditorWorkspaceTabRelative(
+        workspace,
+        session,
+        "center-tabs__dock_scene_stack",
+        "scene",
+        "center-tabs",
+        UIEditorWorkspaceDockPlacement::Top,
+        0.5f));
+
+    const auto validation = ValidateUIEditorWorkspace(workspace);
+    ASSERT_TRUE(validation.IsValid()) << validation.message;
+
+    const std::vector<UIEditorWorkspaceVisiblePanel> visiblePanels =
+        CollectUIEditorWorkspaceVisiblePanels(workspace);
+    ASSERT_EQ(visiblePanels.size(), 2u);
+    EXPECT_EQ(visiblePanels[0].panelId, "scene");
+    EXPECT_EQ(visiblePanels[1].panelId, "game");
+    EXPECT_EQ(workspace.activePanelId, "scene");
+}
+
+TEST(UIEditorWorkspaceModelTest, DockTabRelativeCanRedockGeneratedSingleTabStackWithoutChangingLayout) {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.58f,
+        BuildUIEditorWorkspaceTabStack(
+            "left-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspaceSingleTabStack(
+            "right-tabs",
+            "details",
+            "Details",
+            true));
+    workspace.activePanelId = "doc-a";
+
+    UIEditorWorkspaceSession session = {};
+    session.panelStates = {
+        { "doc-a", true, true },
+        { "doc-b", true, true },
+        { "details", true, true }
+    };
+
+    ASSERT_TRUE(TryDockUIEditorWorkspaceTabRelative(
+        workspace,
+        session,
+        "left-tabs",
+        "doc-b",
+        "right-tabs",
+        UIEditorWorkspaceDockPlacement::Bottom,
+        0.4f));
+
+    std::string movedStackId = {};
+    for (const std::string candidate : { "right-tabs__dock_doc-b_stack", "right-tabs__dock_doc-b_stack-1" }) {
+        if (FindUIEditorWorkspaceNode(workspace, candidate) != nullptr) {
+            movedStackId = candidate;
+            break;
+        }
+    }
+    ASSERT_FALSE(movedStackId.empty());
+
+    const UIEditorWorkspaceModel afterFirstDock = workspace;
+
+    ASSERT_TRUE(TryDockUIEditorWorkspaceTabRelative(
+        workspace,
+        session,
+        movedStackId,
+        "doc-b",
+        "right-tabs",
+        UIEditorWorkspaceDockPlacement::Bottom,
+        0.4f));
+
+    const auto validation = ValidateUIEditorWorkspace(workspace);
+    ASSERT_TRUE(validation.IsValid()) << validation.message;
+    EXPECT_TRUE(AreUIEditorWorkspaceModelsEquivalent(workspace, afterFirstDock));
+    EXPECT_EQ(workspace.activePanelId, "doc-b");
+
+    const UIEditorWorkspaceNode* rightTabs =
+        FindUIEditorWorkspaceNode(workspace, "right-tabs");
+    ASSERT_NE(rightTabs, nullptr);
+    EXPECT_EQ(rightTabs->kind, UIEditorWorkspaceNodeKind::TabStack);
+    ASSERT_EQ(rightTabs->children.size(), 1u);
+    EXPECT_EQ(rightTabs->children[0].panel.panelId, "details");
+
+    const UIEditorWorkspaceNode* movedTabStack =
+        FindUIEditorWorkspaceNode(workspace, movedStackId);
+    ASSERT_NE(movedTabStack, nullptr);
+    ASSERT_EQ(movedTabStack->kind, UIEditorWorkspaceNodeKind::TabStack);
+    ASSERT_EQ(movedTabStack->children.size(), 1u);
+    EXPECT_EQ(movedTabStack->children[0].panel.panelId, "doc-b");
+}