Tighten XCUI compositor texture registration

docs/plan/XCUI_Phase_Status_2026-04-05.md

@@ -68,6 +68,7 @@ Current gap:
 - 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`.
+- Hosted preview offscreen surfaces now keep compositor-returned `UITextureRegistration` / `UITextureHandle` data inside `Application` instead of storing `ImTextureID` directly.
 - The generic hosted-preview presenter contract no longer owns `ImGuiTransitionBackend`; the ImGui presenter now sits in a separate `ImGuiXCUIHostedPreviewPresenter` header while the native queue/surface registry remains XCUI-generic.
 - The generic hosted-preview frame contract no longer carries an ImGui draw-list pointer; the legacy ImGui presenter resolves its inline draw target from the active ImGui window context instead of pushing that type through the XCUI contract.
 - `XCNewEditor` builds successfully to `build/new_editor/bin/Debug/XCNewEditor.exe`.
@@ -139,6 +140,7 @@ Current gap:
   - `IEditorHostCompositor`
   - `ImGuiHostCompositor`
   - `Application` frame/present flow routed through the compositor instead of direct `m_imguiBackend` ownership
+- 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
   - `ImGuiTransitionBackend` moved behind `ImGuiXCUIHostedPreviewPresenter`