Isolate legacy stroke edge shader setup

docs/modernization/debt.md

@@ -18,6 +18,12 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-12: DEBT-0036 was narrowed again. Canvas stroke padding and commit
+  dilate shader setup now route retained `kShader::StrokePad` and
+  `kShader::StrokeDilate` binding/uniform writes through
+  `legacy_canvas_stroke_edge_services.h`. Quad expansion, dirty-box policy,
+  texture/framebuffer binding and copies, and draw ordering remain retained
+  legacy execution.
 - 2026-06-12: DEBT-0036 was narrowed again. Canvas live draw-merge and
   `NodeStrokePreview` final stroke composite `kShader::CompDraw` setup now
   share `legacy_canvas_stroke_composite_services.h` for retained shader binding

docs/modernization/roadmap.md

@@ -1350,9 +1350,11 @@ OpenGL stroke execution service seam. Live stroke `kShader::Stroke` binding,
 setup, blend, pattern, and per-sample uniform writes now pass through
 `legacy_canvas_stroke_shader_services.h`. Live draw-merge and preview final
 stroke composite `kShader::CompDraw` setup now pass through
-`legacy_canvas_stroke_composite_services.h`, leaving RTT/texture ownership,
-dirty-box policy, pad/checkerboard/commit composite shaders, and retained
-callback execution under `DEBT-0036`.
+`legacy_canvas_stroke_composite_services.h`. Stroke padding and commit dilate
+`kShader::StrokePad`/`kShader::StrokeDilate` setup now pass through
+`legacy_canvas_stroke_edge_services.h`, leaving RTT/texture ownership,
+dirty-box policy, checkerboard/commit composite shaders, quad expansion, and
+retained callback execution under `DEBT-0036`.
 It also owns renderer API texture-format to
 OpenGL internal/pixel/component token mapping, including depth-stencil formats,
 for future backend texture objects. `Texture2D` 2D texture binding, upload,

src/canvas.cpp

@@ -4,6 +4,7 @@
 #include "app.h"
 #include "legacy_gl_renderbuffer_dispatch.h"
 #include "legacy_canvas_stroke_composite_services.h"
+#include "legacy_canvas_stroke_edge_services.h"
 #include "legacy_canvas_stroke_execution_services.h"
 #include "legacy_canvas_stroke_shader_services.h"
 #include "legacy_canvas_stroke_services.h"
@@ -765,12 +766,14 @@ void Canvas::stroke_draw()
     // NOTE: at the moment this works on the whole canvas, but it can be optimized 
     // to only affect the current dirty box. In this case it may be necessary to do this
     // work on documents that doesn't have the padding, so on document loading.
-    ShaderManager::use(kShader::StrokePad);
-    ShaderManager::u_vec4(kShaderUniform::Col, pad_color);
+    pp::panopainter::setup_legacy_stroke_pad_shader(
+        pp::panopainter::LegacyStrokePadUniforms {
+            .color = pad_color,
+            .uses_destination_feedback = copy_stroke_destination,
+        });
     if (copy_stroke_destination)
     {
         set_active_texture_unit(1);
-        ShaderManager::u_int(kShaderUniform::TexBG, 1);
     }
     for (int i = 0; i < 6; i++)
     {
@@ -1122,9 +1125,10 @@ void Canvas::stroke_commit()
 //        }
 
         // Dilate borders to avoid interpolation bleeding
-        ShaderManager::use(kShader::StrokeDilate);
-        ShaderManager::u_mat4(kShaderUniform::MVP, glm::ortho(-.5f, .5f, -.5f, .5f, -1.f, 1.f));
-        ShaderManager::u_int(kShaderUniform::TexBG, 0);
+        pp::panopainter::setup_legacy_stroke_dilate_shader(
+            pp::panopainter::LegacyStrokeDilateUniforms {
+                .mvp = glm::ortho(-.5f, .5f, -.5f, .5f, -1.f, 1.f),
+            });
         set_active_texture_unit(0);
         m_tex2[i].bind();
         copy_framebuffer_to_texture_2d(0, 0, 0, 0, m_width, m_height);

src/legacy_canvas_stroke_edge_services.h

@@ -0,0 +1,66 @@
+#pragma once
+
+#include "shader.h"
+#include "util.h"
+
+#include <functional>
+
+namespace pp::panopainter {
+
+struct LegacyStrokePadUniforms {
+    glm::vec4 color {};
+    bool uses_destination_feedback = false;
+};
+
+struct LegacyStrokeDilateUniforms {
+    glm::mat4 mvp { 1.0f };
+};
+
+struct LegacyStrokeEdgeShaderExecution {
+    std::function<void(kShader)> use_shader;
+    std::function<void(kShaderUniform, int)> set_int;
+    std::function<void(kShaderUniform, const glm::vec4&)> set_vec4;
+    std::function<void(kShaderUniform, const glm::mat4&)> set_mat4;
+};
+
+[[nodiscard]] inline LegacyStrokeEdgeShaderExecution legacy_shader_manager_stroke_edge_execution() noexcept
+{
+    return {
+        .use_shader = [](kShader shader) { ShaderManager::use(shader); },
+        .set_int = [](kShaderUniform uniform, int value) { ShaderManager::u_int(uniform, value); },
+        .set_vec4 = [](kShaderUniform uniform, const glm::vec4& value) { ShaderManager::u_vec4(uniform, value); },
+        .set_mat4 = [](kShaderUniform uniform, const glm::mat4& value) { ShaderManager::u_mat4(uniform, value); },
+    };
+}
+
+inline void setup_legacy_stroke_pad_shader(
+    const LegacyStrokePadUniforms& uniforms,
+    const LegacyStrokeEdgeShaderExecution& execution) noexcept
+{
+    execution.use_shader(kShader::StrokePad);
+    execution.set_vec4(kShaderUniform::Col, uniforms.color);
+    if (uniforms.uses_destination_feedback) {
+        execution.set_int(kShaderUniform::TexBG, 1);
+    }
+}
+
+inline void setup_legacy_stroke_pad_shader(const LegacyStrokePadUniforms& uniforms)
+{
+    setup_legacy_stroke_pad_shader(uniforms, legacy_shader_manager_stroke_edge_execution());
+}
+
+inline void setup_legacy_stroke_dilate_shader(
+    const LegacyStrokeDilateUniforms& uniforms,
+    const LegacyStrokeEdgeShaderExecution& execution) noexcept
+{
+    execution.use_shader(kShader::StrokeDilate);
+    execution.set_mat4(kShaderUniform::MVP, uniforms.mvp);
+    execution.set_int(kShaderUniform::TexBG, 0);
+}
+
+inline void setup_legacy_stroke_dilate_shader(const LegacyStrokeDilateUniforms& uniforms)
+{
+    setup_legacy_stroke_dilate_shader(uniforms, legacy_shader_manager_stroke_edge_execution());
+}
+
+} // namespace pp::panopainter