Add XCUI expansion state and coverage tests

docs/plan/XCUI_Phase_Status_2026-04-05.md

@@ -33,13 +33,14 @@ Old `editor` replacement is explicitly out of scope for this phase.
 - Shared text-input controller/state now also lives under `engine/include/XCEngine/UI/Text` and `engine/src/UI/Text`, so character insertion, backspace/delete, submit, and multiline key handling no longer need to be reimplemented per host.
 - Shared editor collection primitive classification and metric helpers now also live under `engine/include/XCEngine/UI/Widgets` and `engine/src/UI/Widgets`, covering the current `ScrollView` / `TreeView` / `ListView` / `PropertySection` / `FieldRow` prototype taxonomy.
 - Shared single-selection state now also lives under `engine/include/XCEngine/UI/Widgets` and `engine/src/UI/Widgets` as `UISelectionModel`, so collection-style widget selection no longer has to stay private to `LayoutLab`.
+- Shared expansion state now also lives under `engine/include/XCEngine/UI/Widgets` and `engine/src/UI/Widgets` as `UIExpansionModel`, so collapsible tree/property-style widget state no longer has to stay private to `LayoutLab`.
 - Core regression coverage now includes `UIContext`, layout, style, runtime screen player/system, and real document-host tests through `core_ui_tests`.
 
 Current gap:
 
 - Minimal schema self-definition support is landed, including consistency checks for enum/document-only schema metadata, but schema-driven validation for `.xcui` / `.xctheme` instances is still not implemented.
 - Shared widget/runtime instantiation is still thin and mostly editor-side.
-- Common widget primitives are still incomplete: shared text-input presentation/composition on top of the new text controller, real tree/list/property widget state on top of the new editor-primitive helpers, and native image/source-rect level APIs.
+- Common widget primitives are still incomplete: shared text-input presentation/composition on top of the new text controller, multi-selection/keyboard-navigation/virtualized collection state on top of the new editor-primitive helpers, and native image/source-rect level APIs.
 
 ### 2. Runtime/Game Layer
 
@@ -68,6 +69,7 @@ Current gap:
 - `LayoutLab` now also covers editor-facing widget prototypes: `TreeView`, `TreeItem`, `ListView`, `ListItem`, `PropertySection`, and `FieldRow`.
 - `LayoutLab` now consumes the shared `UIEditorCollectionPrimitives` helper layer for collection-widget tag classification, clipping flags, and default metric resolution instead of keeping that taxonomy private to the sandbox runtime.
 - `LayoutLab` now also consumes the shared `UISelectionModel` for click-selection persistence across collection-style widgets, and the diagnostics panel now exposes both hovered and selected element ids.
+- `LayoutLab` now also consumes the shared `UIExpansionModel` for tree expansion and property-section collapse, with reserved property headers, disclosure glyphs, and persisted click-toggle behavior in the sandbox runtime.
 - Panel diagnostics were expanded to clearly separate preview/runtime/input state and native vs legacy paths.
 - The editor bridge layer now has smoke coverage for swapchain after-UI rendering hooks and SRV-backed ImGui texture descriptor registration.
 - `Application` no longer owns the ImGui backend directly; window presentation now routes through `IWindowUICompositor` with an `ImGuiWindowUICompositor` implementation, which currently delegates to `IEditorHostCompositor` / `ImGuiHostCompositor`.
@@ -80,18 +82,19 @@ Current gap:
 
 - The shell is still ImGui-hosted.
 - Legacy hosted preview still depends on an active ImGui window context for inline presentation.
-- Editor-specialized widgets are still incomplete at the shared-module level: the authored prototypes exist, but virtualization, multi-selection/tree expansion state, command routing, property editing models, toolbar/menu chrome, and icon-atlas widgets are not yet extracted into reusable XCUI modules.
+- Editor-specialized widgets are still incomplete at the shared-module level: the authored prototypes exist, but virtualization, multi-selection/keyboard-navigation state, command routing, property editing models, toolbar/menu chrome, and icon-atlas widgets are not yet extracted into reusable XCUI modules.
 
 ## Validated This Phase
 
 - `new_editor_xcui_demo_runtime_tests`: `7/7`
-- `new_editor_xcui_layout_lab_runtime_tests`: `7/7`
+- `new_editor_xcui_layout_lab_runtime_tests`: `9/9`
 - `new_editor_xcui_rhi_command_compiler_tests`: `6/6`
 - `new_editor_xcui_rhi_render_backend_tests`: `5/5`
 - `new_editor_xcui_hosted_preview_presenter_tests`: `12/12`
+- `new_editor_imgui_window_ui_compositor_tests`: `5/5`
 - `XCNewEditor` Debug target builds successfully
-- `core_ui_tests`: `30/30`
-- `scene_tests`: `65/65`
+- `core_ui_tests`: `38 total` (`36` passed, `2` skipped because `KeyCode::Delete` currently aliases `Backspace`)
+- `scene_tests`: `68/68`
 - `core_ui_style_tests`: `5/5`
 - `ui_resource_tests`: `11/11`
 - `editor_tests` targeted bridge smoke: `3/3`
@@ -104,6 +107,7 @@ Current gap:
 - Common-core `UITextInputController` extraction now owns per-field text state, character insertion, enter-submit, and multiline keyboard editing behavior with dedicated `core_ui_tests` coverage.
 - Common-core `UIEditorCollectionPrimitives` extraction now owns the editor collection tag taxonomy and default metric resolution used by current `LayoutLab` widget prototypes, with dedicated `core_ui_tests` coverage.
 - Common-core `UISelectionModel` extraction now owns reusable single-selection state for collection-style widgets, with dedicated `core_ui_tests` coverage.
+- Common-core `UIExpansionModel` extraction now owns reusable expansion/collapse state for tree/property-style widgets, with dedicated `core_ui_tests` coverage.
 - Demo runtime text editing was extended with:
   - click-to-place caret
   - `Delete` support
@@ -113,6 +117,7 @@ Current gap:
 - LayoutLab `ScrollView` prototype with clipping and hover rejection outside clipped content.
 - LayoutLab editor-widget prototypes for tree/list/property-style sections with dedicated runtime coverage.
 - LayoutLab click-selection now persists through the shared `UISelectionModel`, including selected-state diagnostics and reusable visual selection feedback on cards, collection rows, and field rows.
+- LayoutLab tree expansion and property-section collapse now persist through the shared `UIExpansionModel`, including reserved property headers, disclosure glyphs, and runtime coverage for collapsed/expanded visibility.
 - Schema document support extended with:
   - retained `UISchemaDefinition` data on `UIDocumentModel`
   - artifact schema version bump for UI documents
@@ -156,6 +161,12 @@ Current gap:
   - `IEditorHostCompositor`
   - `ImGuiHostCompositor`
   - `Application` frame/present flow routed through the compositor instead of direct `m_imguiBackend` ownership
+- The window-level XCUI compositor seam now also has a dedicated regression target around `ImGuiWindowUICompositor`, covering initialization, render-frame ordering, Win32 message forwarding, texture registration forwarding, and shutdown safety.
+- `SceneRuntime` layered XCUI routing now has dedicated regression coverage for:
+  - top-interactive layer input ownership
+  - blocking/modal layer suppression of lower layers
+  - hidden top-layer pass-through back to visible underlying layers
+- Shared `UITextInputController` coverage now includes more caret-boundary / modifier branches; the remaining `Delete` distinction stays blocked on `KeyCode::Delete` and `KeyCode::Backspace` still sharing the same enum value.
 - Window compositor texture registration now also flows back into `Application` as XCUI-owned `UITextureRegistration` / `UITextureHandle` data instead of exposing raw `ImTextureID` there.
 - Hosted preview contracts were tightened again:
   - generic preview surface metadata stays on XCUI-owned value types
@@ -174,7 +185,7 @@ Current gap:
 - `ScrollView` is still authored/static; no wheel-driven scrolling or virtualization yet.
 - `Image` widgets still do not have source-rect/atlas-subregion level API in the high-level draw command model.
 - Editor shell still depends on ImGui as host chrome.
-- Editor widget coverage is still prototype-driven inside `LayoutLab`; it has not yet been promoted into a reusable shared widget/runtime layer.
+- Editor widget coverage is still prototype-driven inside `LayoutLab`; it has not yet been promoted into a full reusable shared widget/runtime layer with command routing, virtualization, and property-edit transactions.
 
 ## Next Phase