Extract stroke mix request wiring

docs/modernization/tasks.md

@@ -588,6 +588,9 @@ Progress Notes:
   execute, and unbind sequence through
   `execute_legacy_canvas_stroke_main_pass(...)`; the retained adapter still
   owns the concrete sampler and texture callbacks.
+- 2026-06-13: `Canvas::stroke_draw_mix()` now routes retained mix-pass request
+  wiring through `make_legacy_canvas_stroke_mix_pass_request(...)`; the legacy
+  path still owns the concrete framebuffer setup and per-plane GL callbacks.
 - 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