Route NodeCanvas grid setup through 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. `NodeCanvas` now reuses
+  `legacy_canvas_draw_merge_services.h` for retained checkerboard grid shader
+  setup and the final cached-layer texture redraw setup. NodeCanvas still owns
+  panorama layer traversal, onion-frame drawing, blend destination copies,
+  sampler/texture binding, and draw ordering.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw_mix` now
   reuses `legacy_canvas_stroke_composite_services.h` for mixer-pass retained
   `kShader::CompDraw` binding and blend uniform writes, with the helper now

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.

src/node_canvas.cpp

@@ -12,6 +12,7 @@
 #include "app_core/document_animation.h"
 #include "app.h"
 #include "node_panel_grid.h"
+#include "legacy_canvas_draw_merge_services.h"
 #include "legacy_preference_storage.h"
 #include "legacy_ui_gl_dispatch.h"
 #include "legacy_ui_overlay_services.h"
@@ -374,9 +375,11 @@ void NodeCanvas::draw()
                 m_canvas->m_plane_transform[plane_index] *
                 glm::translate(glm::vec3(0, 0, -1));
 
-            ShaderManager::use(kShader::Checkerboard);
+            pp::panopainter::setup_legacy_canvas_draw_merge_checkerboard_shader(
-            ShaderManager::u_int(kShaderUniform::Colorize, false);
+                pp::panopainter::LegacyCanvasDrawMergeCheckerboardUniforms {
-            ShaderManager::u_mat4(kShaderUniform::MVP, plane_mvp);
+                    .mvp = plane_mvp,
+                    .colorize = false,
+                });
             m_face_plane.draw_fill();
 
             int z = 1;
@@ -425,9 +428,11 @@ void NodeCanvas::draw()
                     m_canvas->m_plane_transform[plane_index] *
                     glm::translate(glm::vec3(0, 0, -1));
 
-                ShaderManager::use(kShader::Checkerboard);
+                pp::panopainter::setup_legacy_canvas_draw_merge_checkerboard_shader(
-                ShaderManager::u_int(kShaderUniform::Colorize, false);
+                    pp::panopainter::LegacyCanvasDrawMergeCheckerboardUniforms {
-                ShaderManager::u_mat4(kShaderUniform::MVP, plane_mvp);
+                        .mvp = plane_mvp,
+                        .colorize = false,
+                    });
                 m_face_plane.draw_fill();
             }
         }
@@ -676,9 +681,11 @@ void NodeCanvas::draw()
                     m_canvas->m_plane_transform[plane_index] *
                     glm::translate(glm::vec3(0, 0, -1.f));
 
-                ShaderManager::use(kShader::Checkerboard);
+                pp::panopainter::setup_legacy_canvas_draw_merge_checkerboard_shader(
-                ShaderManager::u_int(kShaderUniform::Colorize, false);
+                    pp::panopainter::LegacyCanvasDrawMergeCheckerboardUniforms {
-                ShaderManager::u_mat4(kShaderUniform::MVP, plane_mvp);
+                        .mvp = plane_mvp,
+                        .colorize = false,
+                    });
                 m_face_plane.draw_fill();
             }
 
@@ -686,9 +693,11 @@ void NodeCanvas::draw()
             m_sampler.bind(0);
             set_active_texture_unit(0);
             m_cache_rtt.bindTexture();
-            ShaderManager::use(kShader::Texture);
+            pp::panopainter::setup_legacy_canvas_draw_merge_texture_shader(
-            ShaderManager::u_int(kShaderUniform::Tex, 0);
+                pp::panopainter::LegacyCanvasDrawMergeTextureUniforms {
-            ShaderManager::u_mat4(kShaderUniform::MVP, glm::ortho<float>(-1, 1, -1, 1));
+                    .mvp = glm::ortho<float>(-1, 1, -1, 1),
+                    .texture_slot = 0,
+                });
             m_face_plane.draw_fill();
             m_cache_rtt.unbindTexture();
         }