Move Win32 async context ownership and trim canvas draw setup

docs/modernization/tasks.md

@@ -155,6 +155,10 @@ Current slice:
   through `make_legacy_canvas_draw_merge_background_checkerboard_plane(...)`,
   but the node still owns broader live layer traversal and renderer-state
   sequencing.
+- `NodeCanvas` merged-path per-plane merged-texture draw callback setup now
+  also routes through `make_legacy_canvas_draw_merge_layer_texture_draw(...)`,
+  but the node still owns broader live layer traversal and renderer-state
+  sequencing.
 - `NodeCanvas` smoothing-mask face shader setup plus per-face draw execution
   now also route through
   `execute_legacy_canvas_draw_merge_smask_faces(...)`, but the node still owns
@@ -356,6 +360,10 @@ Current slice:
 - `main.cpp` Win32 window handles, GL task/mutex state, splash-dialog state,
   stylus timers, and VR worker state now sit behind one retained local state
   object instead of separate file-scope globals
+- Win32 async GL/context lock state now lives in
+  `src/platform_windows/windows_platform_services.cpp` instead of `main.cpp`
+  retained state, and `main.cpp` only seeds that platform-owned context handle
+  pair during initialization and context recreation
 - prepared-file background work now runs through an `AppRuntime`-owned worker
   queue instead of a retained static worker in `src/app_events.cpp`
 - canvas async import/export/save/open background work now also runs through an