Route NodeCanvas grid setup through helper

docs/modernization/roadmap.md

@@ -2996,6 +2996,10 @@ Results:
   helper for mixer-pass `CompDraw` setup, while preserving its caller-specific
   texture slot uniforms. Mixer framebuffer/scissor state, sampler and texture
   binding, and draw execution remain retained.
+- `NodeCanvas` panorama drawing now uses the same retained draw-merge shader
+  setup helper for checkerboard grids and final cached-layer texture redraws;
+  onion-frame traversal, blend copies, texture binding, and draw order remain
+  retained in the node.
 - Canvas thumbnail layer blending now uses the same canvas destination-feedback
   plan for framebuffer-fetch versus texture-copy decisions; the thumbnail draw
   itself still executes through retained OpenGL canvas code under DEBT-0036.