Promote stroke draw pad copy task

docs/modernization/tasks.md

@@ -838,6 +838,32 @@ Validation:
 ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_compositor|pp_paint_renderer_stroke_execution" --output-onfailure
 ```
 
+### STR-029 - Extract Stroke Draw Pad Copy Callback Body
+
+Status: Ready
+Score: +1 renderer boundary and OpenGL parity
+Debt: `DEBT-0036`
+Scope: `src/canvas.cpp`, `src/legacy_canvas_stroke_execution_services.h`, `tests/paint_renderer/compositor_tests.cpp`
+
+Goal:
+
+Move the inline pad-stroke copy callback body in `Canvas::stroke_draw()` into
+a retained helper so the pad branch owns only concrete copy-region wiring.
+
+Done Checks:
+
+- `Canvas::stroke_draw()` no longer contains the inline pad-stroke copy
+  callback body.
+- Regression coverage proves the extracted helper preserves pad copy-region
+  behavior.
+- `docs/modernization/debt.md` records the reduced pad copy-callback surface.
+
+Validation:
+
+```powershell
+ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_compositor|pp_paint_renderer_stroke_execution" --output-onfailure
+```
+
 Progress Notes:
 
 - 2026-06-13: `NodeStrokePreview::draw_stroke_immediate()` now routes final