Route app viewport scissor through renderer GL

docs/modernization/roadmap.md

@@ -524,6 +524,10 @@ result while the backend owns the query set and order.
 The default app clear color and color-buffer clear operation now dispatch
 through `pp_renderer_gl` as well, moving another direct OpenGL operation out
 of `App::clear` while preserving the current gray clear behavior.
+Main app UI viewport and scissor execution now dispatch through tested
+`pp_renderer_gl` viewport/scissor contracts, leaving `App::draw` and UI node
+clipping to provide rectangles while the backend owns scissor-state tokens and
+the live OpenGL call sequence.
 Windows RenderDoc frame capture hooks now also dispatch through
 `PlatformServices`, keeping capture integration in the platform service while
 leaving non-Windows adapters as no-ops.