Share retained erase temporary composite helper

docs/modernization/roadmap.md

@@ -3141,6 +3141,10 @@ Results:
   `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.
+- `Canvas::draw_merge()` erase live temporary-stroke composite now also shares
+  `execute_legacy_canvas_stroke_temporary_composite(...)`, leaving only the
+  concrete GL object callbacks and broader final composite ownership in the
+  legacy Canvas path.
 - `NodeStrokePreview::draw_stroke_immediate()` now shares
   `execute_legacy_node_stroke_preview_pass_sequence(...)` for
   dual-pass/background/main-pass/final-composite/copy-back ordering, while the