Extract stroke destination dispatch helper

docs/modernization/tasks.md

@@ -515,6 +515,9 @@ Progress Notes:
   closeout.
 - 2026-06-13: `STR-004` closed the last inline stroke dispatch glue. `LATER-003`
   remains at the binding-only tail.
+- 2026-06-13: `Canvas::stroke_draw_samples()` now reuses a retained destination
+  texture dispatch helper for the live sample path; `Canvas` still owns the
+  concrete face textures and callback execution.
 - 2026-06-13: `pp_paint_renderer_stroke_execution_tests` now also covers the
   new retained main-pass texture dispatch helper builder and its pattern/mixer
   wiring. Next slice should target another narrow `stroke_draw()` seam or stop