Share retained stroke preview mix executor

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::stroke_draw_mix()`
+  now routes retained mix-pass shader setup plus framebuffer/state/input/draw
+  ordering through `execute_legacy_node_stroke_preview_mix_pass(...)`; the
+  preview node keeps only the concrete GL save/restore, texture-object bind,
+  and plane-draw callbacks.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw` live-pass
   sampler bind/unbind plus semantic texture-input dispatch now route through
   retained stroke execution helpers; concrete GL object mapping, framebuffer

docs/modernization/roadmap.md

@@ -3150,6 +3150,11 @@ Results:
   framebuffer bind/unbind, viewport/scissor/blend state, texture-slot
   binding, and final plane draw, while material planning and shader uniform
   setup remain in the preview node.
+- `NodeStrokePreview::stroke_draw_mix()` now routes retained mix-pass shader
+  setup plus framebuffer/state/input/draw ordering through
+  `execute_legacy_node_stroke_preview_mix_pass(...)`, while the preview node
+  keeps only the concrete GL save/restore, texture-object bind, and plane-draw
+  callbacks.
 - `pp_paint_renderer_stroke_execution_tests` now covers retained stroke texture
   input binding order, sample execution destination-copy behavior, live-pass
   face-framebuffer dirty tracking, and pad-face destination-copy behavior

docs/modernization/tasks.md

@@ -509,6 +509,14 @@ Done Checks:
 
 Progress Notes:
 
+- 2026-06-13: `NodeStrokePreview::stroke_draw_mix()` now routes retained
+  mix-pass shader setup plus framebuffer/state/input/draw ordering through
+  `execute_legacy_node_stroke_preview_mix_pass(...)`, with compositor coverage
+  locking the retained callback order and shader-plan handoff. The preview node
+  keeps only the concrete GL save/restore, texture-object bind, and plane-draw
+  callbacks. Next slice should target another retained preview or canvas stroke
+  seam without reopening the landed preview sample, material-planning,
+  pass-sequence, or final-composite helpers.
 - 2026-06-13: `NodeStrokePreview::draw_stroke_immediate()` now routes
   dual-pass/background/main-pass/final-composite/copy-back ordering through
   `execute_legacy_node_stroke_preview_pass_sequence(...)`; the remaining local