Share retained stroke preview live pass helper

docs/modernization/debt.md

@@ -18,6 +18,11 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview` dual-pass and
+  main-pass frame-loop execution plus full-frame copy-back now route through
+  shared local helpers; checkerboard/background capture ordering, texture-unit
+  binding, mixer ownership, and final composite semantics remain retained in
+  the preview node.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw` main and
   dual live-pass per-face framebuffer begin/end execution plus pad-face array
   assembly now route through `legacy_canvas_stroke_execution_services.h`;

docs/modernization/roadmap.md

@@ -3103,6 +3103,10 @@ Results:
   assembly now shares one retained utility, while shader activation timing,
   texture/sampler binding, framebuffer ownership, pad execution, and final
   OpenGL draw ordering remain in the legacy Canvas path.
+- `NodeStrokePreview` dual-pass and main-pass frame-loop execution plus
+  full-frame copy-back now share one local retained helper surface, while
+  checkerboard/background capture ordering, texture-unit binding, mixer
+  ownership, and final composite semantics remain in the preview node.
 - `Canvas::stroke_draw` pad-pass destination bind/copy/unbind ordering now
   shares the retained stroke execution helper callback surface, while shader
   setup, pad color selection, framebuffer ownership, and final OpenGL draw

docs/modernization/tasks.md

@@ -509,6 +509,13 @@ Done Checks:
 
 Progress Notes:
 
+- 2026-06-13: `NodeStrokePreview::draw_stroke_immediate()` dual-pass and
+  main-pass frame-loop execution plus full-frame copy-back now route through
+  shared local helpers; checkerboard/background capture ordering, texture-unit
+  binding, mixer ownership, and final composite semantics remain local to the
+  preview node. Next slice should target background/final-copy helpers or
+  pass-level texture binding without reopening the new preview composite
+  helper.
 - 2026-06-13: `Canvas::stroke_draw` main and dual live-pass per-face
   framebuffer begin/end execution plus pad-face array assembly now route
   through `legacy_canvas_stroke_execution_services.h`; shader activation