Move layout reload policy into platform api

docs/modernization/build-inventory.md

@@ -583,6 +583,11 @@ Known local toolchain state:
   while non-Windows platforms still reach retained platform bridges through
   the debt-tracked adapter isolated in
   `src/platform_legacy/legacy_platform_services.*`.
+- `pp_platform_api` also owns `plan_asset_file_load`, the SDK-free file-load
+  policy consumed by `LayoutManager` for XML layout reload decisions. The
+  helper preserves desktop mtime-based reload behavior and non-desktop
+  already-loaded skip behavior while keeping direct platform guards out of the
+  shared layout parser.
 - `pp_renderer_gl` owns the tested `OpenGlInitialState` startup depth/blend
   policy and dispatch application consumed by `App::init`, tested runtime
   version/vendor/renderer/GLSL string query dispatch, tested default clear
@@ -660,8 +665,8 @@ Known local toolchain state:
   split persistence/runtime dispatch, and malformed startup-plan rejection.
 - `pp_platform_api_tests` covers service dispatch for clipboard read/write,
   empty clipboard writes, cursor visibility, virtual-keyboard visibility,
-  external file display, file sharing, VR lifecycle, and picker callbacks
-  without platform SDK headers or a window.
+  external file display, file sharing, VR lifecycle, layout/asset file load
+  policy, and picker callbacks without platform SDK headers or a window.
 - `pp_app_core_document_cloud_tests` covers cloud upload no-canvas,
   new-document warning, clean publish prompt, and dirty save-before-upload
   decisions, plus cloud browse no-canvas/show-browser and selected-download