Extract canvas stroke runtime and preview draw shells

docs/modernization/roadmap.md

@@ -79,15 +79,15 @@ What is still carrying too much live ownership:
 
 Current hotspot files:
 
-- `src/canvas.cpp`: 1271 lines
+- `src/canvas.cpp`: 1010 lines
 - `src/app_layout.cpp`: 125 lines
 - `src/canvas_modes.cpp`: 720 lines
 - `src/node.cpp`: 803 lines
 - `src/main.cpp`: 271 lines
 - `src/node_panel_brush.cpp`: 435 lines
-- `src/node_stroke_preview.cpp`: 751 lines
-- `src/node_canvas.cpp`: 702 lines
-- `src/app.cpp`: 575 lines
+- `src/node_stroke_preview.cpp`: 607 lines
+- `src/node_canvas.cpp`: 219 lines
+- `src/app.cpp`: 502 lines
 - `src/app_dialogs.cpp`: 168 lines
 
 Current architecture mismatches that must be treated as real blockers:
@@ -268,6 +268,11 @@ Current architecture mismatches that must be treated as real blockers:
   `Canvas::flood_fill(...)`, and `Canvas::FloodData::apply()` now also route
   through `src/legacy_canvas_layer_services.cpp` instead of staying inline in
   `src/canvas.cpp`, which trims another coherent retained layer/fill workflow
+  pocket, while `Canvas::stroke_end(...)`, `Canvas::stroke_cancel(...)`,
+  `Canvas::stroke_draw_mix(...)`, `Canvas::stroke_draw_project(...)`,
+  `Canvas::stroke_update(...)`, and `Canvas::stroke_start(...)` now also route
+  through `src/legacy_canvas_stroke_runtime_services.*` instead of staying
+  inline in `src/canvas.cpp`, which trims another large retained stroke/runtime
   pocket, while the
   `CanvasModeTransform` interaction family now also routes through
   `src/legacy_canvas_mode_transform.cpp` instead of staying inline in
@@ -302,6 +307,14 @@ Current architecture mismatches that must be treated as real blockers:
   `src/canvas_modes.cpp`, while
   preview stroke preparation, dual-brush setup, and live pass-orchestration
   request assembly now also route through retained preview execution helpers,
+  while `NodeStrokePreview` retained lifecycle, worker-thread shell,
+  render-to-image path, on-screen handling, and preview texture ownership now
+  also route through `src/legacy_node_stroke_preview_runtime_services.cpp`
+  instead of staying inline in `src/node_stroke_preview.cpp`, while
+  `NodeCanvas::init()` plus the remaining `NodeCanvas::draw()` outer shell now
+  also route through `src/legacy_node_canvas_draw_services.*` instead of
+  staying inline in `src/node_canvas.cpp`, which materially reduces the live
+  node to a thinner controller surface around event routing and state wrappers,
   while `Node::on_event(...)` plus mouse/key capture and release ownership now
   also route through `src/legacy_ui_node_event.*` instead of staying inline in
   `src/node.cpp`, which materially thins the base scene-graph event shell