Route NodeCanvas blend setup through helper

docs/modernization/roadmap.md

@@ -3000,6 +3000,11 @@ Results:
   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.
+- `NodeCanvas` non-stroke layer blending now shares the retained draw-merge
+  shader setup helper for `TextureBlend` uniforms, preserving the optional
+  destination texture uniform when copy-based blending is active. Framebuffer
+  lifetime, destination copies, texture binding, and draw execution remain
+  local to 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.