Trim main task queue, recording label, and canvas draw callbacks

docs/modernization/tasks.md

@@ -159,6 +159,10 @@ Current slice:
   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` non-`draw_merged` per-frame layer draw callback setup now also
+  routes through `make_legacy_canvas_draw_merge_layer_frame_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
@@ -364,6 +368,8 @@ Current slice:
   `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
+- `main.cpp` main-thread queued task state now sits behind a narrow retained
+  helper instead of `RetainedState.main_tasklist` / `main_task_mutex` directly
 - 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
@@ -436,6 +442,9 @@ Current slice:
   retained recording bridge in `src/legacy_recording_services.cpp`, while
   `App::update()` no longer carries the dead update mutex residue; retained
   recording loop control, readback ownership, and MP4 execution are still open
+- `App::update_rec_frames()` now delegates recording label refresh through
+  `src/legacy_recording_services.cpp`, but retained recording label lookup,
+  encoder-state reads, and MP4 execution still stay on the legacy bridge
 
 Write scope:
 - `src/canvas.cpp`