Wrap stroke mix shell

docs/modernization/debt.md

@@ -18,6 +18,10 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Recent Reductions
 
+- 2026-06-13: `LATER-003` was narrowed again. `Canvas::stroke_draw_mix()` now
+  routes the retained mix-pass shell through
+  `execute_legacy_canvas_stroke_mix_pass_shell(...)`; the live path still owns
+  the concrete framebuffer bind and GL capability toggles.
 - 2026-06-13: `LATER-003` was narrowed again. `Canvas::stroke_draw_mix()` now
   routes the full retained mix-pass shell through
   `execute_legacy_canvas_stroke_mix_pass_with_setup(...)`; the live path

docs/modernization/tasks.md

@@ -601,6 +601,9 @@ Progress Notes:
 - 2026-06-13: `Canvas::stroke_draw_mix()` now routes the full retained mix-pass
   shell through `execute_legacy_canvas_stroke_mix_pass_with_setup(...)`; the
   live path still owns the concrete framebuffer bind and GL capability toggles.
+- 2026-06-13: `Canvas::stroke_draw_mix()` now routes the retained mix-pass
+  shell through `execute_legacy_canvas_stroke_mix_pass_shell(...)`; the live
+  path still owns the concrete framebuffer bind and GL capability toggles.
 - 2026-06-13: `Canvas::stroke_draw()` live-pass sampler wiring now reuses a
   retained helper builder, and the stroke execution tests cover it. `STR-004`
   is now done after the final pad-destination helper extraction and tracker

src/canvas.cpp

@@ -420,7 +420,7 @@ void Canvas::stroke_draw_mix(const glm::vec2& bb_min, const glm::vec2& bb_sz)
                 m_mixer.unbindFramebuffer();
             });
     [[maybe_unused]] const auto mix_result =
-        pp::panopainter::execute_legacy_canvas_stroke_mix_pass_with_setup(
+        pp::panopainter::execute_legacy_canvas_stroke_mix_pass_shell(
             mix_setup.begin,
             mix_setup.end,
             pp::panopainter::make_legacy_canvas_stroke_mix_pass_request(
@@ -477,7 +477,7 @@ void Canvas::stroke_draw_mix(const glm::vec2& bb_min, const glm::vec2& bb_sz)
             [&](int plane_index) {
                 set_active_texture_unit(0);
                 current_layer.rtt(plane_index).unbindTexture();
-            });
+            }));
     
     gl.restore();
 }

src/legacy_canvas_stroke_execution_services.h

@@ -562,6 +562,19 @@ execute_legacy_canvas_stroke_mix_pass_with_setup(
     return result;
 }
 
+template <typename BeginMixPass, typename EndMixPass>
+[[nodiscard]] inline LegacyCanvasStrokeMixPassResult
+execute_legacy_canvas_stroke_mix_pass_shell(
+    BeginMixPass&& begin_mix_pass,
+    EndMixPass&& end_mix_pass,
+    const LegacyCanvasStrokeMixPassRequest& request)
+{
+    return execute_legacy_canvas_stroke_mix_pass_with_setup(
+        std::forward<BeginMixPass>(begin_mix_pass),
+        std::forward<EndMixPass>(end_mix_pass),
+        request);
+}
+
 struct LegacyCanvasStrokeComputeRequest {
     StrokeSample previous_sample {};
     std::span<const StrokeSample> samples;