Extract retained stroke preview setup planner

docs/modernization/roadmap.md

@@ -3155,6 +3155,12 @@ Results:
   dual-pass/background/main-pass/final-composite/copy-back ordering, while the
   remaining local preview ownership is concentrated around `stroke_draw_mix()`
   setup/execution.
+- `NodeStrokePreview::draw_stroke_immediate()` now routes preview stroke
+  max-size fallback, dual-preview max-size derivation, pattern-scale flips,
+  and Bezier preview-point generation through
+  `plan_legacy_node_stroke_preview_stroke_setup(...)`, while brush mutation,
+  camera wiring, retained `Stroke` population, and live GL execution remain in
+  the preview node.
 - `NodeStrokePreview::stroke_draw_mix()` now shares one local helper for mixer
   framebuffer bind/unbind, viewport/scissor/blend state, texture-slot
   binding, and final plane draw, while material planning and shader uniform