Trim stroke mix shell wrapper

docs/modernization/debt.md

@@ -78,6 +78,10 @@ agent or engineer to remove them without reconstructing context from chat.
   route through `src/platform_apple/apple_platform_services.*` instead of the
   catch-all legacy adapter; the Apple path still owns the OS-specific clipboard
   calls.
+- 2026-06-13: `LATER-003` was narrowed again. `Canvas::stroke_draw_mix()`
+  now calls the retained mix-pass executor directly instead of a local wrapper
+  shell helper; the live path still owns the concrete mixer framebuffer setup
+  and GL capability toggles.
 - 2026-06-13: `DEBT-0036` was narrowed again. `NodeStrokePreview::draw_stroke_immediate()`
   now routes final composite execution and preview copy-back through a retained
   local wrapper, leaving the call site with only sequence wiring.

docs/modernization/tasks.md

@@ -623,6 +623,9 @@ Progress Notes:
   execution through a local wrapper around
   `execute_legacy_canvas_stroke_mix_pass_shell(...)`; the live path still owns
   the concrete mixer framebuffer setup and GL capability toggles.
+- 2026-06-13: `Canvas::stroke_draw_mix()` now calls the retained mix-pass
+  executor directly instead of a local wrapper shell helper; the live path
+  still owns the concrete mixer framebuffer setup and GL capability toggles.
 - 2026-06-13: `Canvas::stroke_draw_samples()` now reuses a retained destination
   texture dispatch helper for the live sample path; `Canvas` still owns the
   concrete face textures and callback execution.

src/canvas.cpp

@@ -419,7 +419,10 @@ void Canvas::stroke_draw_mix(const glm::vec2& bb_min, const glm::vec2& bb_sz)
         [&] {
             m_mixer.unbindFramebuffer();
         });
-    [[maybe_unused]] const auto mix_result = execute_canvas_stroke_mix_pass_shell(mix_shell);
+    [[maybe_unused]] const auto mix_result = pp::panopainter::execute_legacy_canvas_stroke_mix_pass_shell(
+        mix_shell.setup.begin,
+        mix_shell.setup.end,
+        mix_shell.request);
 
     gl.restore();
 }
@@ -533,15 +536,6 @@ static void execute_canvas_draw_merge_final_plane_composite(
     pp::panopainter::execute_legacy_canvas_draw_merge_final_plane_composite(uniforms, execution);
 }
 
-static void execute_canvas_stroke_mix_pass_shell(
-    const pp::panopainter::LegacyCanvasStrokeMixPassShell& shell)
-{
-    pp::panopainter::execute_legacy_canvas_stroke_mix_pass_shell(
-        shell.setup.begin,
-        shell.setup.end,
-        shell.request);
-}
-
 glm::vec4 Canvas::stroke_draw_samples(
     int i,
     std::vector<vertex_t>& P,