Share retained stroke frame execution helpers

docs/modernization/debt.md

@@ -18,6 +18,10 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview::stroke_draw_compute`
+  now routes preview quad frame planning through
+  `legacy_canvas_stroke_execution_services.h`. Preview stroke sampling, mixer
+  execution, texture binding, and final OpenGL draw ordering remain retained.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw` current and
   dual stroke per-face framebuffer/sample callback ordering now routes through
   the retained stroke execution helper; framebuffer ownership, shader uniform

docs/modernization/roadmap.md

@@ -3079,6 +3079,9 @@ Results:
   compositor coverage now includes malformed retained commit plans plus
   all-input stroke-preview composite planning. Live stroke rasterization,
   callback execution, texture binding, and history mutation remain retained.
+- `NodeStrokePreview::stroke_draw_compute` now shares the retained stroke
+  execution helper for preview quad frame planning. Preview sample execution,
+  mixer passes, texture binding, and final draw ordering remain retained.
 - `Canvas::stroke_draw` pad-region planning now shares the retained stroke
   execution helper wrapping `pp_paint_renderer`, while pad color selection,
   dirty-face iteration, framebuffer copies, quad upload, and draw execution