Extract brush refresh and thin unmerged NodeCanvas pass

docs/modernization/tasks.md

@@ -230,6 +230,11 @@ Current slice:
   `execute_legacy_canvas_draw_unmerged_node_canvas_shell(...)`, which trims
   another outer draw-shell block even though the broader node draw loop still
   lives in `src/node_canvas.cpp`.
+- `NodeCanvas` broader unmerged cache/viewport/background/composite pass setup
+  now also routes through
+  `execute_legacy_canvas_draw_unmerged_node_canvas_pass(...)`, which removes
+  another coherent outer-shell block even though the broader node draw loop
+  still lives in `src/node_canvas.cpp`.
 
 Write scope:
 - `src/node_stroke_preview.cpp`
@@ -308,7 +313,7 @@ targets look like helpers under one old monolith.
 Status: In Progress
 
 Why now:
-`src/app_layout.cpp` is still a 285-line mixed file that builds menus,
+`src/app_layout.cpp` is still a 229-line mixed file that builds menus,
 attaches callbacks, computes planner inputs, and mutates UI state directly.
 
 Current slice:
@@ -341,6 +346,8 @@ Current slice:
 - Draw-toolbar binding now also lives in `src/app_layout_draw_toolbar.cpp`, and
   `src/app_layout.cpp` is down to the remaining brush-refresh and
   layout/bootstrap composition.
+- Brush-refresh now also lives in `src/app_layout_brush.cpp`, and
+  `src/app_layout.cpp` is down to the remaining layout/bootstrap composition.
 
 Write scope:
 - `src/app_layout.cpp`
@@ -483,8 +490,9 @@ 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
+- `main.cpp` main-thread queued task state now lives under
+  `src/platform_windows/windows_platform_services.cpp` instead of staying in
+  the entry TU
 - Win32 pointer API loading, stylus/ink timer ownership and decay, `WT_PACKET`
   reset, and `WM_POINTERUPDATE` pen/touch handling now live in
   `src/platform_windows/windows_stylus_input.cpp` instead of `src/main.cpp`,