diff --git a/editor/AGENTS.md b/editor/AGENTS.md
index 47a4cbea..c0d4a319 100644
--- a/editor/AGENTS.md
+++ b/editor/AGENTS.md
@@ -8,7 +8,7 @@ The editor is a two-layer system.
 - The build shape of `editor/` is `XCUIEditorLib <- XCUIEditorApp`.
 - `editor/src/**` and `editor/include/XCEditor/**` belong to the framework layer.
 - `editor/app/**` belongs to the app layer and is compiled directly into `XCUIEditorApp`.
-- Platform-neutral windowing authority, planner, projection, and synchronization code now live in `editor/src/Windowing` and `editor/include/XCEditor/Windowing`.
+- App-internal windowing authority, planner, projection, and synchronization code now live in `editor/app/Windowing/System` and `editor/app/Windowing/Presentation`.
 - `app/Windowing` now owns app-side content controllers, coordinators, and frame transfer seams; `app/Platform/Win32` remains the concrete host.
 - Win32 hosting, utility windows, and editor-only rendering stay in `editor/app/**`.
 - `editor/include/XCEditor/**` exposes framework-level APIs only.
@@ -308,8 +308,8 @@ Application::Run
 - `editor/app/Windowing/Content/EditorWindowContentController.h`
 - `editor/app/Windowing/Content/EditorWorkspaceWindowContentController.*`
 - `editor/app/Windowing/Frame/EditorWindowFrameOrchestrator.*`
-- `editor/include/XCEditor/Windowing/EditorWindowSystem.h`
-- `editor/src/Windowing/EditorWindowSystem.cpp`
+- `editor/app/Windowing/System/EditorWindowSystem.h`
+- `editor/app/Windowing/System/EditorWindowSystem.cpp`
 - `editor/app/Platform/Win32/Windowing/EditorWindow.*`
 - `editor/app/Platform/Win32/Windowing/EditorWindowHostRuntime.*`
 - `editor/app/Platform/Win32/Windowing/EditorWindowWorkspaceCoordinator.*`
diff --git a/editor/CMakeLists.txt b/editor/CMakeLists.txt
index 2619374d..cbea546b 100644
--- a/editor/CMakeLists.txt
+++ b/editor/CMakeLists.txt
@@ -136,13 +136,6 @@ set(XCUI_EDITOR_WIDGET_SUPPORT_SOURCES
     src/Widgets/UIEditorFieldRowLayout.cpp
 )
 
-set(XCUI_EDITOR_WINDOWING_SOURCES
-    src/Windowing/EditorWindowPresentationPolicy.cpp
-    src/Windowing/EditorWindowSynchronizationPlanner.cpp
-    src/Windowing/EditorWindowSystem.cpp
-    src/Windowing/EditorWindowWorkspaceStore.cpp
-)
-
 set(XCUI_EDITOR_SHARED_SOURCES
     ${XCUI_EDITOR_FOUNDATION_SOURCES}
     ${XCUI_EDITOR_FIELD_SOURCES}
@@ -154,7 +147,6 @@ set(XCUI_EDITOR_SHARED_SOURCES
     ${XCUI_EDITOR_VIEWPORT_SOURCES}
     ${XCUI_EDITOR_WORKSPACE_SOURCES}
     ${XCUI_EDITOR_WIDGET_SUPPORT_SOURCES}
-    ${XCUI_EDITOR_WINDOWING_SOURCES}
 )
 
 add_library(XCUIEditorLib STATIC
@@ -177,6 +169,27 @@ target_link_libraries(XCUIEditorLib PUBLIC
 
 xcui_editor_apply_common_target_settings(XCUIEditorLib PUBLIC)
 
+set(XCUI_EDITOR_APP_WINDOWING_SOURCES
+    app/Windowing/Presentation/EditorWindowPresentationPolicy.cpp
+    app/Windowing/System/EditorWindowSynchronizationPlanner.cpp
+    app/Windowing/System/EditorWindowSystem.cpp
+    app/Windowing/System/EditorWindowWorkspaceStore.cpp
+)
+
+add_library(XCUIEditorAppWindowing STATIC
+    ${XCUI_EDITOR_APP_WINDOWING_SOURCES}
+)
+
+target_include_directories(XCUIEditorAppWindowing PUBLIC
+    ${CMAKE_CURRENT_SOURCE_DIR}/app
+)
+
+target_link_libraries(XCUIEditorAppWindowing PUBLIC
+    XCUIEditorLib
+)
+
+xcui_editor_apply_common_target_settings(XCUIEditorAppWindowing PUBLIC)
+
 set(XCUI_EDITOR_HOST_PLATFORM_SOURCES
     app/Platform/Win32/Chrome/BorderlessWindowChrome.cpp
     app/Platform/Win32/Chrome/BorderlessWindowFrame.cpp
@@ -330,6 +343,7 @@ if(XCENGINE_BUILD_XCUI_EDITOR_APP)
     target_link_libraries(XCUIEditorApp PRIVATE
         XCEngine
         XCUIEditorLib
+        XCUIEditorAppWindowing
         XCEngineRenderingEditorSupport
         d3d12.lib
         d3dcompiler.lib
diff --git a/editor/app/Bootstrap/Application.cpp b/editor/app/Bootstrap/Application.cpp
index 1754a8b6..7e9b038d 100644
--- a/editor/app/Bootstrap/Application.cpp
+++ b/editor/app/Bootstrap/Application.cpp
@@ -13,7 +13,7 @@
 #include "Support/ExecutablePath.h"
 
 #include <XCEditor/Foundation/UIEditorRuntimeTrace.h>
-#include <XCEditor/Windowing/EditorWindowSystem.h>
+#include "Windowing/System/EditorWindowSystem.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceModel.h>
 #include <XCEngine/Core/Asset/ResourceManager.h>
 
diff --git a/editor/app/Windowing/Content/EditorWindowContentController.h b/editor/app/Windowing/Content/EditorWindowContentController.h
index 4b7916a7..7b0ea12c 100644
--- a/editor/app/Windowing/Content/EditorWindowContentController.h
+++ b/editor/app/Windowing/Content/EditorWindowContentController.h
@@ -4,7 +4,7 @@
 
 #include <XCEditor/Docking/UIEditorDockHostTransfer.h>
 #include <XCEditor/Foundation/UIEditorTextMeasurement.h>
-#include <XCEditor/Windowing/EditorWorkspaceWindowProjection.h>
+#include "Windowing/Presentation/EditorWorkspaceWindowProjection.h"
 
 #include <cstdint>
 #include <filesystem>
diff --git a/editor/app/Windowing/Content/EditorWindowContentFactory.cpp b/editor/app/Windowing/Content/EditorWindowContentFactory.cpp
index fe257536..5dad43fa 100644
--- a/editor/app/Windowing/Content/EditorWindowContentFactory.cpp
+++ b/editor/app/Windowing/Content/EditorWindowContentFactory.cpp
@@ -3,7 +3,7 @@
 #include "Windowing/Content/EditorUtilityWindowContentController.h"
 #include "Windowing/Content/EditorWorkspaceWindowContentController.h"
 
-#include <XCEditor/Windowing/EditorWindowSystem.h>
+#include "Windowing/System/EditorWindowSystem.h"
 
 #include <utility>
 
diff --git a/editor/app/Windowing/Content/EditorWorkspaceWindowContentController.cpp b/editor/app/Windowing/Content/EditorWorkspaceWindowContentController.cpp
index 3386a55a..ba458c9e 100644
--- a/editor/app/Windowing/Content/EditorWorkspaceWindowContentController.cpp
+++ b/editor/app/Windowing/Content/EditorWorkspaceWindowContentController.cpp
@@ -1,8 +1,8 @@
 #include "Windowing/Content/EditorWorkspaceWindowContentController.h"
 
 #include <XCEditor/Foundation/UIEditorRuntimeTrace.h>
-#include <XCEditor/Windowing/EditorWindowPresentationPolicy.h>
-#include <XCEditor/Windowing/EditorWindowSystem.h>
+#include "Windowing/Presentation/EditorWindowPresentationPolicy.h"
+#include "Windowing/System/EditorWindowSystem.h"
 #include <XCEditor/Workspace/UIEditorDetachedWindowPolicy.h>
 #include <XCEditor/Workspace/UIEditorWorkspaceLayoutPersistence.h>
 
diff --git a/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.cpp b/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.cpp
index 843e57fa..6afac72c 100644
--- a/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.cpp
+++ b/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.cpp
@@ -4,8 +4,8 @@
 #include "Windowing/Coordinator/EditorWindowLifecycleCoordinator.h"
 
 #include <XCEditor/Docking/UIEditorDockHostTransfer.h>
-#include <XCEditor/Windowing/EditorWindowPresentationPolicy.h>
-#include <XCEditor/Windowing/EditorWindowSystem.h>
+#include "Windowing/Presentation/EditorWindowPresentationPolicy.h"
+#include "Windowing/System/EditorWindowSystem.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceController.h>
 #include <XCEditor/Workspace/UIEditorWorkspaceTransfer.h>
 #include <XCEngine/UI/Types.h>
diff --git a/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.h b/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.h
index 8903e8bd..0cfaf43b 100644
--- a/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.h
+++ b/editor/app/Windowing/Coordinator/EditorWindowWorkspaceCoordinator.h
@@ -7,8 +7,8 @@
 #include "Windowing/Frame/EditorWindowTransferRequests.h"
 #include "Windowing/Host/EditorWindowHostInterfaces.h"
 
-#include <XCEditor/Windowing/EditorWindowSynchronizationPlan.h>
-#include <XCEditor/Windowing/EditorWorkspaceWindowProjection.h>
+#include "Windowing/Presentation/EditorWorkspaceWindowProjection.h"
+#include "Windowing/System/EditorWindowSynchronizationPlan.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceController.h>
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceModel.h>
 
diff --git a/editor/app/Windowing/Frame/EditorWindowTransferRequests.h b/editor/app/Windowing/Frame/EditorWindowTransferRequests.h
index 46afa5e0..f68b2742 100644
--- a/editor/app/Windowing/Frame/EditorWindowTransferRequests.h
+++ b/editor/app/Windowing/Frame/EditorWindowTransferRequests.h
@@ -7,7 +7,7 @@
 #include "Windowing/EditorWindowShared.h"
 #include "UtilityWindows/EditorUtilityWindowKind.h"
 
-#include <XCEditor/Windowing/EditorWindowSynchronizationPlan.h>
+#include "Windowing/System/EditorWindowSynchronizationPlan.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceModel.h>
 
 #include <optional>
diff --git a/editor/app/Windowing/Host/EditorWindowHostInterfaces.h b/editor/app/Windowing/Host/EditorWindowHostInterfaces.h
index 2db954ee..26037d67 100644
--- a/editor/app/Windowing/Host/EditorWindowHostInterfaces.h
+++ b/editor/app/Windowing/Host/EditorWindowHostInterfaces.h
@@ -5,7 +5,7 @@
 #include "Windowing/Host/EditorWindowPointerCapture.h"
 #include "Windowing/Host/EditorWindowTypes.h"
 
-#include <XCEditor/Windowing/EditorWorkspaceWindowProjection.h>
+#include "Windowing/Presentation/EditorWorkspaceWindowProjection.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceModel.h>
 
 #include <string>
diff --git a/editor/src/Windowing/EditorWindowPresentationPolicy.cpp b/editor/app/Windowing/Presentation/EditorWindowPresentationPolicy.cpp
similarity index 97%
rename from editor/src/Windowing/EditorWindowPresentationPolicy.cpp
rename to editor/app/Windowing/Presentation/EditorWindowPresentationPolicy.cpp
index 9e735bb6..7cd059fb 100644
--- a/editor/src/Windowing/EditorWindowPresentationPolicy.cpp
+++ b/editor/app/Windowing/Presentation/EditorWindowPresentationPolicy.cpp
@@ -1,4 +1,4 @@
-#include <XCEditor/Windowing/EditorWindowPresentationPolicy.h>
+#include "Windowing/Presentation/EditorWindowPresentationPolicy.h"
 
 #include <XCEditor/Workspace/UIEditorDetachedWindowPolicy.h>
 #include <XCEditor/Workspace/UIEditorWorkspaceController.h>
diff --git a/editor/include/XCEditor/Windowing/EditorWindowPresentationPolicy.h b/editor/app/Windowing/Presentation/EditorWindowPresentationPolicy.h
similarity index 90%
rename from editor/include/XCEditor/Windowing/EditorWindowPresentationPolicy.h
rename to editor/app/Windowing/Presentation/EditorWindowPresentationPolicy.h
index e65a0e00..1422eb52 100644
--- a/editor/include/XCEditor/Windowing/EditorWindowPresentationPolicy.h
+++ b/editor/app/Windowing/Presentation/EditorWindowPresentationPolicy.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <XCEditor/Windowing/EditorWorkspaceWindowProjection.h>
+#include "Windowing/Presentation/EditorWorkspaceWindowProjection.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceModel.h>
 
 #include <string>
diff --git a/editor/include/XCEditor/Windowing/EditorWorkspaceWindowProjection.h b/editor/app/Windowing/Presentation/EditorWorkspaceWindowProjection.h
similarity index 100%
rename from editor/include/XCEditor/Windowing/EditorWorkspaceWindowProjection.h
rename to editor/app/Windowing/Presentation/EditorWorkspaceWindowProjection.h
diff --git a/editor/include/XCEditor/Windowing/EditorWindowSynchronizationPlan.h b/editor/app/Windowing/System/EditorWindowSynchronizationPlan.h
similarity index 100%
rename from editor/include/XCEditor/Windowing/EditorWindowSynchronizationPlan.h
rename to editor/app/Windowing/System/EditorWindowSynchronizationPlan.h
diff --git a/editor/src/Windowing/EditorWindowSynchronizationPlanner.cpp b/editor/app/Windowing/System/EditorWindowSynchronizationPlanner.cpp
similarity index 97%
rename from editor/src/Windowing/EditorWindowSynchronizationPlanner.cpp
rename to editor/app/Windowing/System/EditorWindowSynchronizationPlanner.cpp
index 48df68b1..8cc77aad 100644
--- a/editor/src/Windowing/EditorWindowSynchronizationPlanner.cpp
+++ b/editor/app/Windowing/System/EditorWindowSynchronizationPlanner.cpp
@@ -1,6 +1,6 @@
-#include "Windowing/EditorWindowSynchronizationPlanner.h"
+#include "Windowing/System/EditorWindowSynchronizationPlanner.h"
 
-#include <XCEditor/Windowing/EditorWindowPresentationPolicy.h>
+#include "Windowing/Presentation/EditorWindowPresentationPolicy.h"
 #include <XCEditor/Workspace/UIEditorWorkspaceLayoutPersistence.h>
 
 #include <algorithm>
diff --git a/editor/src/Windowing/EditorWindowSynchronizationPlanner.h b/editor/app/Windowing/System/EditorWindowSynchronizationPlanner.h
similarity index 80%
rename from editor/src/Windowing/EditorWindowSynchronizationPlanner.h
rename to editor/app/Windowing/System/EditorWindowSynchronizationPlanner.h
index 77695384..68e25591 100644
--- a/editor/src/Windowing/EditorWindowSynchronizationPlanner.h
+++ b/editor/app/Windowing/System/EditorWindowSynchronizationPlanner.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <XCEditor/Windowing/EditorWindowSynchronizationPlan.h>
+#include "Windowing/System/EditorWindowSynchronizationPlan.h"
 
 namespace XCEngine::UI::Editor {
 
diff --git a/editor/src/Windowing/EditorWindowSystem.cpp b/editor/app/Windowing/System/EditorWindowSystem.cpp
similarity index 98%
rename from editor/src/Windowing/EditorWindowSystem.cpp
rename to editor/app/Windowing/System/EditorWindowSystem.cpp
index 67514d56..a1b724fd 100644
--- a/editor/src/Windowing/EditorWindowSystem.cpp
+++ b/editor/app/Windowing/System/EditorWindowSystem.cpp
@@ -1,7 +1,7 @@
-#include <XCEditor/Windowing/EditorWindowSystem.h>
+#include "Windowing/System/EditorWindowSystem.h"
 
-#include "Windowing/EditorWindowSynchronizationPlanner.h"
-#include "Windowing/EditorWindowWorkspaceStore.h"
+#include "Windowing/System/EditorWindowSynchronizationPlanner.h"
+#include "Windowing/System/EditorWindowWorkspaceStore.h"
 
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceModel.h>
 
diff --git a/editor/include/XCEditor/Windowing/EditorWindowSystem.h b/editor/app/Windowing/System/EditorWindowSystem.h
similarity index 97%
rename from editor/include/XCEditor/Windowing/EditorWindowSystem.h
rename to editor/app/Windowing/System/EditorWindowSystem.h
index 1af794bb..141bd7a1 100644
--- a/editor/include/XCEditor/Windowing/EditorWindowSystem.h
+++ b/editor/app/Windowing/System/EditorWindowSystem.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <XCEditor/Windowing/EditorWindowSynchronizationPlan.h>
+#include "Windowing/System/EditorWindowSynchronizationPlan.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceController.h>
 
 #include <memory>
diff --git a/editor/src/Windowing/EditorWindowWorkspaceStore.cpp b/editor/app/Windowing/System/EditorWindowWorkspaceStore.cpp
similarity index 95%
rename from editor/src/Windowing/EditorWindowWorkspaceStore.cpp
rename to editor/app/Windowing/System/EditorWindowWorkspaceStore.cpp
index bad32ec2..eee44147 100644
--- a/editor/src/Windowing/EditorWindowWorkspaceStore.cpp
+++ b/editor/app/Windowing/System/EditorWindowWorkspaceStore.cpp
@@ -1,4 +1,4 @@
-#include "Windowing/EditorWindowWorkspaceStore.h"
+#include "Windowing/System/EditorWindowWorkspaceStore.h"
 
 #include <algorithm>
 #include <utility>
diff --git a/editor/src/Windowing/EditorWindowWorkspaceStore.h b/editor/app/Windowing/System/EditorWindowWorkspaceStore.h
similarity index 100%
rename from editor/src/Windowing/EditorWindowWorkspaceStore.h
rename to editor/app/Windowing/System/EditorWindowWorkspaceStore.h
diff --git a/tests/UI/Editor/unit/CMakeLists.txt b/tests/UI/Editor/unit/CMakeLists.txt
index 284bc0ac..bdb258b2 100644
--- a/tests/UI/Editor/unit/CMakeLists.txt
+++ b/tests/UI/Editor/unit/CMakeLists.txt
@@ -104,6 +104,7 @@ add_executable(editor_windowing_phase1_tests
 
 target_link_libraries(editor_windowing_phase1_tests
     PRIVATE
+        XCUIEditorAppWindowing
         XCUIEditorLib
         GTest::gtest_main
 )
diff --git a/tests/UI/Editor/unit/test_editor_window_synchronization_planner.cpp b/tests/UI/Editor/unit/test_editor_window_synchronization_planner.cpp
index b8ac4613..e5509f0b 100644
--- a/tests/UI/Editor/unit/test_editor_window_synchronization_planner.cpp
+++ b/tests/UI/Editor/unit/test_editor_window_synchronization_planner.cpp
@@ -1,8 +1,8 @@
 #include <gtest/gtest.h>
 
-#include <XCEditor/Windowing/EditorWindowPresentationPolicy.h>
-#include <XCEditor/Windowing/EditorWindowSynchronizationPlan.h>
-#include <XCEditor/Windowing/EditorWindowSystem.h>
+#include "Windowing/Presentation/EditorWindowPresentationPolicy.h"
+#include "Windowing/System/EditorWindowSynchronizationPlan.h"
+#include "Windowing/System/EditorWindowSystem.h"
 #include <XCEditor/Workspace/UIEditorWindowWorkspaceController.h>
 #include <XCEditor/Workspace/UIEditorWorkspaceController.h>
 #include <XCEditor/Workspace/UIEditorWorkspaceModel.h>
@@ -82,6 +82,16 @@ EditorWindowHostSnapshot BuildWorkspaceSnapshot(
     return snapshot;
 }
 
+XCEngine::UI::Editor::UIEditorWindowWorkspaceState BuildWindowState(
+    std::string windowId,
+    const XCEngine::UI::Editor::UIEditorWorkspaceController& workspaceController) {
+    XCEngine::UI::Editor::UIEditorWindowWorkspaceState windowState = {};
+    windowState.windowId = std::move(windowId);
+    windowState.workspace = workspaceController.GetWorkspace();
+    windowState.session = workspaceController.GetSession();
+    return windowState;
+}
+
 EditorWindowSystem BuildSystem() {
     return EditorWindowSystem(BuildPanelRegistry());
 }
@@ -93,7 +103,10 @@ TEST(EditorWindowSynchronizationPlannerTest, ProducesNoActionsWhenHostAlreadyMat
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     auto plan = system.BuildSynchronizationPlan(
         EditorWindowSynchronizationPlannerInput{
@@ -118,7 +131,10 @@ TEST(EditorWindowSynchronizationPlannerTest, ProducesCreateActionForDetachedWind
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     UIEditorWindowWorkspaceController mutationController =
         system.BuildWorkspaceMutationController();
@@ -156,7 +172,10 @@ TEST(EditorWindowSynchronizationPlannerTest, ProducesCloseActionForRemovedDetach
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     UIEditorWindowWorkspaceController mutationController =
         system.BuildWorkspaceMutationController();
@@ -206,7 +225,10 @@ TEST(EditorWindowSynchronizationPlannerTest, ProducesUpdateActionWhenPrimaryWind
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     UIEditorWindowWorkspaceController mutationController =
         system.BuildWorkspaceMutationController();
@@ -346,7 +368,10 @@ TEST(EditorWindowSynchronizationPlannerTest, LiveWindowMutationBuildsCommitPlanW
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     auto liveController = workspaceController;
     const auto commandResult = liveController.Dispatch(
@@ -356,9 +381,11 @@ TEST(EditorWindowSynchronizationPlannerTest, LiveWindowMutationBuildsCommitPlanW
         });
     ASSERT_EQ(commandResult.status, UIEditorWorkspaceCommandStatus::Changed);
 
-    auto plan = system.BuildPlanForLiveWindowMutation(
-        "main",
-        liveController,
+    EditorWindowWorkspaceMutationRequest request = {};
+    request.windowState = BuildWindowState("main", liveController);
+
+    auto plan = system.BuildPlanForWorkspaceMutationRequest(
+        request,
         {
             BuildWorkspaceSnapshot(
                 "main",
@@ -384,7 +411,10 @@ TEST(EditorWindowSynchronizationPlannerTest, WorkspaceMutationRequestBuildsCommi
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     auto liveController = workspaceController;
     const auto commandResult = liveController.Dispatch(
@@ -428,7 +458,10 @@ TEST(EditorWindowSynchronizationPlannerTest, WorkspaceMutationRequestRejectsUnkn
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     EditorWindowWorkspaceMutationRequest request = {};
     request.windowState.windowId = "missing-window";
@@ -456,7 +489,10 @@ TEST(EditorWindowSynchronizationPlannerTest, DestroyedPrimaryWindowProducesClose
     const auto workspaceController =
         BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
     std::string error = {};
-    ASSERT_TRUE(system.BootstrapPrimaryWindow("main", workspaceController, error)) << error;
+    ASSERT_TRUE(system.BootstrapPrimaryWindow(
+        "main",
+        BuildWindowState("main", workspaceController),
+        error)) << error;
 
     UIEditorWindowWorkspaceController mutationController =
         system.BuildWorkspaceMutationController();