Extract node events, transform mode, and preview pass shells

docs/modernization/tasks.md

@@ -91,7 +91,7 @@ Status: In Progress
 
 Why now:
 `src/canvas.cpp` is still the biggest single architectural blocker at about
-2122 lines.
+2122 lines, with `src/canvas_modes.cpp` still large at about 1014 lines.
 
 Current slice:
 - Canvas state-management helpers for picking, clear/clear-all, layer
@@ -122,6 +122,10 @@ Current slice:
   `src/legacy_canvas_mode_helpers.*` instead of staying inline in
   `src/canvas_modes.cpp`, which trims another coherent retained canvas-view
   interaction pocket from the broader canvas/render hotspot family.
+- The `CanvasModeTransform` interaction family now also lives in
+  `src/legacy_canvas_mode_transform.cpp` instead of staying inline in
+  `src/canvas_modes.cpp`, which materially thins another retained
+  transform-mode pocket from the broader canvas/render hotspot family.
 
 Write scope:
 - `src/canvas.cpp`
@@ -182,6 +186,11 @@ Current slice:
   which trims another coherent setup pocket from
   `src/node_stroke_preview.cpp` even though worker/readback ownership and
   broader preview flow still remain inline.
+- The remaining immediate preview pass shell in
+  `NodeStrokePreview::draw_stroke_immediate()` now also routes through
+  `execute_legacy_node_stroke_preview_draw_immediate_shell(...)`, which
+  materially reduces the live preview-pass body even though worker/readback
+  ownership still remains inline.
 - `NodeCanvas` merged-path per-plane merged-texture draw execution now also
   routes through `execute_legacy_canvas_draw_merge_layer_texture(...)`.
 - `NodeCanvas` merged-path and non-blend checkerboard background setup now also
@@ -706,6 +715,10 @@ Current slice:
   now also lives in `src/legacy_ui_node_execution.cpp` instead of staying
   inline in `src/node.cpp`, which materially thins the base scene-graph file
   without changing its public surface.
+- `Node::on_event(...)` plus mouse/key capture and release now also live in
+  `src/legacy_ui_node_event.*` instead of staying inline in `src/node.cpp`,
+  which materially thins the base scene-graph event shell without changing its
+  public surface.
 
 Write scope:
 - `src/node.cpp`