Route canvas mode and preview texture setup through helpers

docs/modernization/debt.md

@@ -18,6 +18,14 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `CanvasModeTransform::on_Draw`
+  and `CanvasModeFloodFill::on_Draw` retained `Texture` shader setup now route
+  through `legacy_canvas_draw_merge_services.h`; the mode paths still own
+  active texture selection, sampler/texture binding, and draw execution.
+- 2026-06-13: DEBT-0036 was narrowed again. `NodeStrokePreview::draw`
+  retained preview `Texture` shader setup now routes through
+  `legacy_canvas_draw_merge_services.h`; the node still owns preview texture
+  binding, sampler binding, and draw execution.
 - 2026-06-13: DEBT-0036 was narrowed again. `NodeViewport` retained preview
   draw and `NodePanelGrid` sun-overlay `Texture` shader setup now route
   through `legacy_canvas_draw_merge_services.h`; the node paths still own

docs/modernization/roadmap.md

@@ -3021,6 +3021,9 @@ Results:
   stroke composite shader setup helper, while render-task ordering, framebuffer
   copy bounds, sampler/texture binding, and draw execution remain in retained
   canvas-mode code.
+- `NodeStrokePreview::draw` now shares the retained draw-merge texture shader
+  setup helper for preview `Texture`, `Tex`, and `MVP` setup, while preview
+  texture binding, sampler binding, and draw execution remain in the node path.
 - `Canvas::import_layer` retained object drawing now shares the draw-merge
   texture shader setup helper for flat and spherical imports, while texture
   upload, sampler/texture binding, draw callbacks, and object geometry remain in
@@ -3048,6 +3051,10 @@ Results:
   share the retained draw-merge texture shader setup helper for `Texture`,
   `Tex`, and `MVP` setup. Texture/sampler binding, viewport/state setup, and
   draw execution remain in the node paths.
+- `CanvasModeTransform::on_Draw` and `CanvasModeFloodFill::on_Draw` now share
+  the retained draw-merge texture shader setup helper for `Texture`, `Tex`, and
+  `MVP` setup. Active texture selection, sampler/texture binding, and draw
+  execution remain in the canvas mode paths.
 - `Canvas::stroke_draw_mix` now shares the retained stroke composite shader
   helper for mixer-pass `CompDraw` setup, while preserving its caller-specific
   texture slot uniforms. Mixer framebuffer/scissor state, sampler and texture

src/canvas_modes.cpp

@@ -8,6 +8,7 @@
 #include "canvas.h"
 #include "shader.h"
 #include "node_canvas.h"
+#include "legacy_canvas_draw_merge_services.h"
 #include "legacy_canvas_stroke_composite_services.h"
 #include "legacy_ui_overlay_services.h"
 #include "legacy_ui_gl_dispatch.h"
@@ -1526,9 +1527,10 @@ void CanvasModeTransform::on_Draw(const glm::mat4& ortho, const glm::mat4& proj,
         ShaderManager::u_vec4(kShaderUniform::Col, { 0, 1, 1, .1 });
         m_shape[i].draw_fill();
 
-        ShaderManager::use(kShader::Texture);
-        ShaderManager::u_int(kShaderUniform::Tex, 0);
-        ShaderManager::u_mat4(kShaderUniform::MVP, proj * camera * m_xform * m_xform_local);
+        pp::panopainter::setup_legacy_canvas_draw_merge_texture_shader({
+            .mvp = proj * camera * m_xform * m_xform_local,
+            .texture_slot = 0,
+        });
         set_canvas_mode_active_texture_unit(0);
         m_tex[i].bind();
         Canvas::I->m_sampler_linear.bind(0);
@@ -1754,15 +1756,14 @@ void CanvasModeFloodFill::on_Draw(const glm::mat4& ortho, const glm::mat4& proj,
 {
     if (m_draw_tip)
     {
-        ShaderManager::use(kShader::Texture);
-        ShaderManager::u_mat4(kShaderUniform::MVP, 
-            glm::scale(glm::vec3(1, -1, 1))
-            * ortho
-            * glm::translate(glm::vec3(Canvas::I->m_cur_pos, 0.f))
-            * glm::scale(glm::vec3(32, 32, 1))
-            * glm::translate(glm::vec3(0.5f, -0.5f, 0))
-        );
-        ShaderManager::u_int(kShaderUniform::Tex, 0);
+        pp::panopainter::setup_legacy_canvas_draw_merge_texture_shader({
+            .mvp = glm::scale(glm::vec3(1, -1, 1))
+                * ortho
+                * glm::translate(glm::vec3(Canvas::I->m_cur_pos, 0.f))
+                * glm::scale(glm::vec3(32, 32, 1))
+                * glm::translate(glm::vec3(0.5f, -0.5f, 0)),
+            .texture_slot = 0,
+        });
     
         auto& t = TextureManager::get(m_cursor_id);
     

src/node_stroke_preview.cpp

@@ -775,9 +775,11 @@ void NodeStrokePreview::draw_stroke()
 
 void NodeStrokePreview::draw()
 {
-    ShaderManager::use(kShader::Texture);
-    ShaderManager::u_mat4(kShaderUniform::MVP, m_mvp);
-    ShaderManager::u_int(kShaderUniform::Tex, 0);
+    pp::panopainter::setup_legacy_canvas_draw_merge_texture_shader(
+        pp::panopainter::LegacyCanvasDrawMergeTextureUniforms {
+            .mvp = m_mvp,
+            .texture_slot = 0,
+        });
     m_tex_preview.bind();
     m_sampler_linear.bind(0);
     m_plane.draw_fill();