Trim stroke mix callsite

docs/modernization/tasks.md

@@ -641,6 +641,9 @@ Progress Notes:
 - 2026-06-13: `Canvas::stroke_draw_mix()` now routes the remaining framebuffer
   setup callbacks through a local helper, leaving the method with only shell
   assembly and executor dispatch.
+- 2026-06-13: `Canvas::stroke_draw_mix()` now keeps just the retained shell
+  assembly and executor dispatch at the callsite; the framebuffer setup
+  callbacks are isolated in the helper.
 - 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.