Add XCUI new editor sandbox phase 1

docs/plan/XCUI_Phase_Status_2026-04-05.md

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+# XCUI Phase Status 2026-04-05
+
+## Scope
+
+Current execution stays inside the XCUI module and `new_editor`.
+Old `editor` replacement is explicitly out of scope for this phase.
+
+## Three-Layer Status
+
+### 1. Common Core
+
+- `UI::DrawData`, input event types, focus routing, style/theme resolution are in active use.
+- `UIDocumentCompiler` was restored to a stable buildable baseline after a broken parallel schema attempt corrupted the file.
+- Build-system hardening for MSVC/PDB output paths has started in root CMake, `engine/CMakeLists.txt`, `new_editor/CMakeLists.txt`, and `tests/NewEditor/CMakeLists.txt`.
+
+Current gap:
+
+- Schema/validation is not yet landed in a stable form.
+- Shared widget/runtime instantiation is still thin and mostly editor-side.
+
+### 2. Runtime/Game Layer
+
+- Runtime-side XCUI is still shallow.
+- The main concrete progress here is that the retained-mode demo runtime now supports a real `TextField` input path with UTF-8 text entry and backspace handling.
+- This proves that the runtime-facing layer is no longer limited to static cards/buttons.
+
+Current gap:
+
+- No real game-facing screen host, menu stack, HUD stack, or shared runtime widget library yet.
+
+### 3. Editor Layer
+
+- `new_editor` remains the isolated XCUI sandbox.
+- Native hosted preview is working as `RHI offscreen surface -> ImGui shell texture embed`.
+- `XCUI Demo` remains the long-lived effect and behavior testbed.
+- `LayoutLab` now includes a `ScrollView` prototype and a more editor-like three-column authored layout.
+- Panel diagnostics were expanded to clearly separate preview/runtime/input state and native vs legacy paths.
+- `XCNewEditor` builds successfully to `build/new_editor/bin/Debug/XCNewEditor.exe`.
+
+Current gap:
+
+- The shell is still ImGui-hosted.
+- Editor-specialized widgets are still incomplete: tree, list virtualization, property grid, toolbar/menu, text area, icon atlas widgets.
+
+## Validated This Phase
+
+- `new_editor_xcui_demo_runtime_tests`: `6/6`
+- `new_editor_xcui_layout_lab_runtime_tests`: `5/5`
+- `new_editor_xcui_rhi_command_compiler_tests`: `6/6`
+- `new_editor_xcui_rhi_render_backend_tests`: `5/5`
+- `XCNewEditor` Debug target builds successfully
+
+## Landed This Phase
+
+- Demo runtime `TextField` with UTF-8 text insertion, caret state, and backspace.
+- Demo authored resources updated to exercise the input field.
+- LayoutLab `ScrollView` prototype with clipping and hover rejection outside clipped content.
+- RHI image path improvements:
+  - clipped image UV adjustment
+  - mirrored image UV preservation
+  - external texture binding reuse
+  - per-batch scissor application
+- `new_editor` panel/shell diagnostics improvements for hosted preview state.
+- XCUI asset document loading changed to prefer direct source compilation before `ResourceManager` fallback for the sandbox path, fixing the LayoutLab crash.
+
+## Phase Risks Still Open
+
+- Schema/validation work must be restarted cleanly after the corrupted parallel attempt.
+- `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.
+
+## Next Phase
+
+1. Re-open common-layer schema/validation on a clean branch and land the smallest stable version.
+2. Add next editor-facing widgets: `TextArea`, list/tree, property-style sections.
+3. Move more diagnostics and shell affordances into XCUI-owned editor-layer surfaces instead of only ImGui HUDs.
+4. Continue phased validation, commit, push, and plan refresh after each stable batch.