Extract stroke mix setup shell

docs/modernization/tasks.md

@@ -595,6 +595,9 @@ Progress Notes:
   execution shell through `execute_legacy_canvas_stroke_mix_pass_with_setup(...)`
   with a concrete request builder; the live path still owns the OpenGL setup
   and per-plane texture wiring.
+- 2026-06-13: `Canvas::stroke_draw_mix()` now routes the setup/end shell through
+  `make_legacy_canvas_stroke_mix_pass_setup(...)`; the live path still owns the
+  concrete framebuffer bind and GL capability toggles.
 - 2026-06-13: `Canvas::stroke_draw()` live-pass sampler wiring now reuses a
   retained helper builder, and the stroke execution tests cover it. `STR-004`
   is now done after the final pad-destination helper extraction and tracker