Extract XCUI text input controller to common layer

docs/plan/XCUI_Phase_Status_2026-04-05.md

@@ -30,13 +30,14 @@ Old `editor` replacement is explicitly out of scope for this phase.
 - Shared engine-side XCUI runtime scaffolding is now present under `engine/include/XCEngine/UI/Runtime` and `engine/src/UI/Runtime`.
 - Shared engine-side `UIDocumentScreenHost` now compiles `.xcui` / `.xctheme` screen documents into a runtime-facing document host path instead of leaving all document ownership in `new_editor`.
 - Shared text-editing primitives now live under `engine/include/XCEngine/UI/Text` and `engine/src/UI/Text`, so UTF-8 caret movement, line splitting, and multiline navigation are no longer trapped inside `XCUI Demo`.
+- 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.
 - 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: reusable text-input state/view composition on top of the new text helpers, tree/list virtualization, property-grid composition, 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, tree/list virtualization, property-grid composition, and native image/source-rect level APIs.
 
 ### 2. Runtime/Game Layer
 
@@ -57,6 +58,7 @@ Current gap:
 - Native hosted preview is working as `RHI offscreen surface -> ImGui shell texture embed`.
 - `XCUI Demo` remains the long-lived effect and behavior testbed.
 - `XCUI Demo` now covers both single-line and multiline text authoring behavior, including click caret placement, delete/backspace, tab indentation, and optional text-area line numbers.
+- `XCUI Demo` now consumes the shared `UITextInputController` path for text editing instead of carrying a private key-handling state machine.
 - `LayoutLab` now includes a `ScrollView` prototype and a more editor-like three-column authored layout.
 - `LayoutLab` now also covers editor-facing widget prototypes: `TreeView`, `TreeItem`, `ListView`, `ListItem`, `PropertySection`, and `FieldRow`.
 - Panel diagnostics were expanded to clearly separate preview/runtime/input state and native vs legacy paths.
@@ -76,7 +78,7 @@ Current gap:
 - `new_editor_xcui_rhi_command_compiler_tests`: `6/6`
 - `new_editor_xcui_rhi_render_backend_tests`: `5/5`
 - `XCNewEditor` Debug target builds successfully
-- `core_ui_tests`: `21/21`
+- `core_ui_tests`: `26/26`
 - `core_ui_style_tests`: `5/5`
 - `ui_resource_tests`: `11/11`
 - `editor_tests` targeted bridge smoke: `3/3`
@@ -86,6 +88,7 @@ Current gap:
 - Demo runtime `TextField` with UTF-8 text insertion, caret state, and backspace.
 - Demo runtime multiline `TextArea` path in the sandbox and test coverage for caret movement / multiline input.
 - Common-core `UITextEditing` extraction now owns UTF-8 offset stepping, codepoint counting, line splitting, and vertical caret motion with dedicated `core_ui_tests` coverage.
+- 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.
 - Demo runtime text editing was extended with:
   - click-to-place caret
   - `Delete` support