Extract stroke preview final composite helper

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` final
+  composite sampler/input binding and slot intent now route through one local
+  preview helper; mixer execution, per-sample stroke callbacks, framebuffer
+  copies, and final OpenGL draw ownership remain retained in the preview node.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw` pad-pass
   destination bind/copy/unbind ordering now routes through
   `legacy_canvas_stroke_execution_services.h`; shader setup, pad color

docs/modernization/roadmap.md

@@ -3097,6 +3097,10 @@ Results:
   shares the retained stroke execution helper callback surface, while shader
   setup, pad color selection, framebuffer ownership, and final OpenGL draw
   remain in the legacy Canvas path.
+- `NodeStrokePreview` final composite sampler/input binding and texture-slot
+  intent now share one local retained helper, while mixer execution,
+  per-sample stroke callbacks, framebuffer copies, and final OpenGL draw
+  ownership remain in the preview node.
 - `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