feat(xcui): advance core and editor validation flow

new_editor/src/Host/Application.cpp

@@ -82,6 +82,17 @@ std::string FormatPoint(const UIPoint& point) {
     return "(" + FormatFloat(point.x) + ", " + FormatFloat(point.y) + ")";
 }
 
+void AppendErrorMessage(std::string& target, const std::string& message) {
+    if (message.empty()) {
+        return;
+    }
+
+    if (!target.empty()) {
+        target += " | ";
+    }
+    target += message;
+}
+
 std::int32_t MapVirtualKeyToUIKeyCode(WPARAM wParam) {
     switch (wParam) {
     case 'A': return static_cast<std::int32_t>(KeyCode::A);
@@ -392,9 +403,19 @@ bool Application::LoadStructuredScreen(const char* triggerReason) {
     m_screenAsset.themePath = m_shellAssetDefinition.themePath.string();
 
     const bool loaded = m_screenPlayer.Load(m_screenAsset);
+    const EditorShellAssetValidationResult shellAssetValidation =
+        ValidateEditorShellAsset(m_shellAssetDefinition);
     m_useStructuredScreen = loaded;
     m_runtimeStatus = loaded ? "XCUI Editor Shell" : "Editor Shell | Load Error";
-    m_runtimeError = loaded ? std::string() : m_screenPlayer.GetLastError();
+    m_runtimeError.clear();
+    if (!loaded) {
+        AppendErrorMessage(m_runtimeError, m_screenPlayer.GetLastError());
+    }
+    if (!shellAssetValidation.IsValid()) {
+        AppendErrorMessage(
+            m_runtimeError,
+            "Editor shell asset invalid: " + shellAssetValidation.message);
+    }
     RebuildTrackedFileStates();
     return loaded;
 }