Share retained erase temporary composite helper

docs/modernization/tasks.md

@@ -509,6 +509,14 @@ Done Checks:
 
 Progress Notes:
 
+- 2026-06-13: `Canvas::draw_merge()` erase live temporary-stroke composite now
+  routes retained setup, sampler bind, texture bind, draw, and texture unbind
+  ordering through `execute_legacy_canvas_stroke_temporary_composite(...)`;
+  both live temporary composite branches now share the same retained execution
+  helper while `Canvas` keeps only concrete GL object callbacks and broader
+  final composite ownership. Next slice should target the remaining final
+  composite seam without reopening landed sample, mix, dirty, or framebuffer
+  helpers.
 - 2026-06-13: `NodeStrokePreview::stroke_draw_mix()` now routes retained
   mix-pass shader setup plus framebuffer/state/input/draw ordering through
   `execute_legacy_node_stroke_preview_mix_pass(...)`, with compositor coverage