Route stroke face sample ordering through helper

docs/modernization/debt.md

@@ -18,6 +18,10 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw` current and
+  dual stroke per-face framebuffer/sample callback ordering now routes through
+  the retained stroke execution helper; framebuffer ownership, shader uniform
+  timing, sampler/texture binding, and live draw execution remain retained.
 - 2026-06-13: DEBT-0036 was narrowed again. `Canvas::stroke_draw` current and
   dual stroke dirty-box mutation now routes through the retained stroke
   execution helper; framebuffer binding, shader uniform timing, sampler/texture

docs/modernization/roadmap.md

@@ -3104,6 +3104,10 @@ Results:
   the retained stroke execution helper, while framebuffer binding, shader
   uniform timing, sampler/texture binding, and live draw execution remain
   retained.
+- `Canvas::stroke_draw` current and dual stroke per-face framebuffer/sample
+  callback ordering now shares the retained stroke execution helper, while
+  framebuffer ownership, shader uniform timing, sampler/texture binding, and
+  live draw execution remain retained.
 - Remaining simple color, hue, color-quad, grid heightmap, and pen/line
   preview shader setup in UI nodes and canvas modes now shares retained helper
   surfaces, while geometry, texture/sampler binding, blend/depth state,

docs/modernization/tasks.md

@@ -509,6 +509,13 @@ Done Checks:
 
 Progress Notes:
 
+- 2026-06-13: `Canvas::stroke_draw` current and dual stroke per-face
+  framebuffer/sample callback ordering now routes through
+  `legacy_canvas_stroke_execution_services.h`; framebuffer ownership, shader
+  uniform timing, sampler/texture binding, and draw execution remain local to
+  Canvas. Next slice should target the remaining per-face retained state around
+  sample execution without reopening the new pad-pass, dirty-mutation, or
+  commit executors.
 - 2026-06-13: `Canvas::stroke_draw` current and dual stroke dirty-box mutation
   now routes through `legacy_canvas_stroke_execution_services.h`; framebuffer
   binding, shader uniform timing, sampler/texture binding, and draw execution

src/canvas.cpp

@@ -690,7 +690,7 @@ void Canvas::stroke_draw()
     std::array<glm::vec4, 6> box_face = SIXPLETTE(glm::vec4(m_size, 0, 0));
     std::array<bool, 6> box_dirty = SIXPLETTE(false);
     glm::vec4 pad_color;
-    pp::panopainter::execute_legacy_canvas_stroke_frame_faces(
+    pp::panopainter::execute_legacy_canvas_stroke_frame_samples(
         frames,
         [&](auto& f) {
             if (brush->m_tip_mix > 0.f)
@@ -698,13 +698,13 @@ void Canvas::stroke_draw()
                 stroke_draw_mix(xy(f.m_mixer_rect), zw(f.m_mixer_rect));
             }
         },
-        [&](auto& f, int i, auto& P) {
+        [&](auto&, int i, auto&) {
             m_dirty_face[i] = true;
             merge_faces[i] = true;
             box_dirty[i] = true;
-
             m_tmp[i].bindFramebuffer();
-
+        },
+        [&](auto& f, int i, auto& P) {
             pp::panopainter::use_legacy_stroke_shader();
             pp::panopainter::apply_legacy_stroke_sample_uniforms(
                 pp::panopainter::LegacyStrokeSampleUniforms {
@@ -712,11 +712,11 @@ void Canvas::stroke_draw()
                     .alpha = f.flow,
                     .opacity = f.opacity,
                 });
-            auto box_sample = stroke_draw_samples(i, P, copy_stroke_destination);
+            return stroke_draw_samples(i, P, copy_stroke_destination);
-
+        },
+        [&](auto& f, int i, glm::vec4 box_sample) {
             m_tmp[i].unbindFramebuffer();
-
+            [[maybe_unused]] const auto dirty_update = pp::panopainter::apply_legacy_canvas_stroke_face_dirty_update(
-            const auto dirty_update = pp::panopainter::apply_legacy_canvas_stroke_face_dirty_update(
                 pp::panopainter::LegacyCanvasStrokeFaceDirtyRequest {
                     .extent = stroke_extent,
                     .previous_accumulated_dirty_box = m_dirty_box[i],
@@ -726,7 +726,6 @@ void Canvas::stroke_draw()
                 },
                 m_dirty_box[i],
                 &box_face[i]);
-            // TODO: maybe average color?
             pad_color = f.col;
         });
 
@@ -804,7 +803,7 @@ void Canvas::stroke_draw()
             dual_brush->m_tip_texture->bind() :
             unbind_texture_2d();
         auto frames_dual = stroke_draw_compute(*m_dual_stroke);
-        pp::panopainter::execute_legacy_canvas_stroke_frame_faces(
+        pp::panopainter::execute_legacy_canvas_stroke_frame_samples(
             frames_dual,
             [&](auto& f) {
                 pp::panopainter::apply_legacy_stroke_sample_uniforms(
@@ -814,14 +813,15 @@ void Canvas::stroke_draw()
                         .opacity = f.opacity,
                     });
             },
-            [&](auto&, int i, auto& P) {
+            [&](auto&, int i, auto&) {
                 m_tmp_dual[i].bindFramebuffer();
-                auto box_sample = stroke_draw_samples(i, P, copy_stroke_destination);
+            },
+            [&](auto&, int i, auto& P) {
+                return stroke_draw_samples(i, P, copy_stroke_destination);
+            },
+            [&](auto&, int i, glm::vec4 box_sample) {
                 m_tmp_dual[i].unbindFramebuffer();
-
+                [[maybe_unused]] const auto dirty_update = pp::panopainter::apply_legacy_canvas_stroke_face_dirty_update(
-                // this mode overflows the main brush boundries
-                [[maybe_unused]] const auto dirty_update =
-                    pp::panopainter::apply_legacy_canvas_stroke_face_dirty_update(
                         pp::panopainter::LegacyCanvasStrokeFaceDirtyRequest {
                             .extent = stroke_extent,
                             .previous_accumulated_dirty_box = m_dirty_box[i],

src/legacy_canvas_stroke_execution_services.h

@@ -192,6 +192,32 @@ std::size_t execute_legacy_canvas_stroke_frame_faces(
     return executed_faces;
 }
 
+template <typename Frames, typename BeginFrame, typename BeginFace, typename ExecuteSample, typename FinishFace>
+std::size_t execute_legacy_canvas_stroke_frame_samples(
+    Frames&& frames,
+    BeginFrame&& begin_frame,
+    BeginFace&& begin_face,
+    ExecuteSample&& execute_sample,
+    FinishFace&& finish_face)
+{
+    std::size_t executed_faces = 0;
+    for (auto& frame : frames) {
+        begin_frame(frame);
+        for (int face_index = 0; face_index < 6; ++face_index) {
+            auto& vertices = frame.shapes[face_index];
+            if (vertices.size() < 3) {
+                continue;
+            }
+
+            begin_face(frame, face_index, vertices);
+            auto sample_dirty_box = execute_sample(frame, face_index, vertices);
+            finish_face(frame, face_index, sample_dirty_box);
+            ++executed_faces;
+        }
+    }
+    return executed_faces;
+}
+
 [[nodiscard]] inline pp::paint_renderer::CanvasStrokeBox legacy_canvas_stroke_box(glm::vec4 box) noexcept
 {
     return pp::paint_renderer::CanvasStrokeBox {