Extract preview mix pass execution

docs/modernization/debt.md

@@ -201,6 +201,10 @@ agent or engineer to remove them without reconstructing context from chat.
   `execute_legacy_canvas_draw_merge_layer_texture(...)`; per-plane iteration,
   temporary-stroke branch selection, and concrete layer RTT ownership remain in
   the legacy Canvas path.
+- 2026-06-14: DEBT-0036 was narrowed again. `NodeStrokePreview::stroke_draw_mix()`
+  now routes the mix-pass execution request through
+  `make_stroke_draw_mix_execution_request(...)`; the retained path still owns
+  the concrete framebuffer, viewport, and draw ordering.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::draw_merge()` temporary
   composite setup now routes through `execute_canvas_draw_merge_temporary_composite(...)`;
   setup, sampler, texture, draw, and unbind callbacks still remain retained in

docs/modernization/tasks.md

@@ -1870,7 +1870,7 @@ ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_stroke_ex
 
 ### STR-041 - Extract Preview Mix Pass Execution Ownership
 
-Status: Ready
+Status: Done
 Score: no score movement
 Debt: `DEBT-0036`
 Scope: `src/node_stroke_preview.cpp`, `tests/paint_renderer/compositor_tests.cpp`
@@ -1881,6 +1881,8 @@ Move the remaining `NodeStrokePreview::stroke_draw_mix()` execution ownership
 into a retained helper so the callsite keeps only the structural mix-pass
 orchestration.
 
+Closeout: `cf859cd4`
+
 Done Checks:
 
 - `NodeStrokePreview::stroke_draw_mix()` no longer owns the mix-pass execution