Share retained stroke temporary composite helper

docs/modernization/roadmap.md

@@ -3137,6 +3137,10 @@ Results:
   `execute_legacy_canvas_stroke_face_sample_polygon(...)` for face-indexed
   destination bind/copy/unbind and brush upload/draw dispatch, while concrete
   GL object callbacks remain in the legacy Canvas path.
+- `Canvas::draw_merge()` non-erase live temporary-stroke composite now shares
+  `execute_legacy_canvas_stroke_temporary_composite(...)` for setup, sampler
+  bind, texture bind, draw, and texture unbind ordering, while erase-path and
+  broader final composite ownership remain in the legacy Canvas path.
 - `NodeStrokePreview::stroke_draw_mix()` now shares one local helper for mixer
   framebuffer bind/unbind, viewport/scissor/blend state, texture-slot
   binding, and final plane draw, while material planning and shader uniform