Extract pad stroke copy region helper

docs/modernization/debt.md

@@ -541,6 +541,9 @@ agent or engineer to remove them without reconstructing context from chat.
   brush-tip dispatch now uses a retained helper object, with regression
   coverage proving the helper order; the live path still owns the concrete
   brush-tip texture object and dual-pass branch wiring.
+- 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw()` pad copy
+  behavior now uses a retained helper for copy-region wiring; the pad branch
+  still owns the concrete framebuffer and texture-object callbacks.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::draw_merge` checkerboard
   background shader setup and final merged-texture redraw setup now route
   through `legacy_canvas_draw_merge_services.h`. The retained Canvas path still