Promote preview mix pass execution task

docs/modernization/tasks.md

@@ -1868,6 +1868,35 @@ ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_stroke_ex
 & 'C:\Program Files\Microsoft Visual Studio\18\Community\MSBuild\Current\Bin\MSBuild.exe' out\build\windows-msvc-default\tests\pp_paint_renderer_stroke_execution_tests.vcxproj /p:Configuration=Debug /p:Platform=x64
 ```
 
+### STR-041 - Extract Preview Mix Pass Execution Ownership
+
+Status: Ready
+Score: no score movement
+Debt: `DEBT-0036`
+Scope: `src/node_stroke_preview.cpp`, `tests/paint_renderer/compositor_tests.cpp`
+
+Goal:
+
+Move the remaining `NodeStrokePreview::stroke_draw_mix()` execution ownership
+into a retained helper so the callsite keeps only the structural mix-pass
+orchestration.
+
+Done Checks:
+
+- `NodeStrokePreview::stroke_draw_mix()` no longer owns the mix-pass execution
+  block inline.
+- Regression coverage proves the helper preserves mixer framebuffer, viewport,
+  and draw ordering.
+- `docs/modernization/debt.md` records the reduced preview mix-pass execution
+  surface.
+
+Validation:
+
+```powershell
+ctest --preset desktop-fast --build-config Debug -R "pp_paint_renderer_compositor|pp_paint_renderer_stroke_execution" --output-onfailure
+cmake --build --preset windows-msvc-default --config Debug --target PanoPainter
+```
+
 ### STR-010 - Extract Remaining Draw Merge Composite Orchestration
 
 ### STR-016 - Extract Draw Merge Layer Composite Execution