Extract stroke destination dispatch helper

docs/modernization/tasks.md

@@ -515,6 +515,9 @@ Progress Notes:
   closeout.
 - 2026-06-13: `STR-004` closed the last inline stroke dispatch glue. `LATER-003`
   remains at the binding-only tail.
+- 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.
 - 2026-06-13: `pp_paint_renderer_stroke_execution_tests` now also covers the
   new retained main-pass texture dispatch helper builder and its pattern/mixer
   wiring. Next slice should target another narrow `stroke_draw()` seam or stop

src/canvas.cpp

@@ -564,17 +564,17 @@ glm::vec4 Canvas::stroke_draw_samples(
             .slot = 1,
         },
     };
-    const pp::panopainter::LegacyCanvasStrokeTextureInputDispatch destination_texture_dispatch {
-        .activate_texture_unit = [&](int texture_slot) {
-            set_active_texture_unit(texture_slot);
-        },
-        .bind_stroke_destination = [&] {
-            m_tex[i].bind(); // bg, copy of framebuffer (copied before drawing)
-        },
-        .unbind_stroke_destination = [&] {
-            m_tex[i].unbind();
-        },
-    };
+    const auto destination_texture_dispatch =
+        pp::panopainter::make_legacy_canvas_stroke_destination_texture_dispatch(
+            [&](int texture_slot) {
+                set_active_texture_unit(texture_slot);
+            },
+            [&] {
+                m_tex[i].bind(); // bg, copy of framebuffer (copied before drawing)
+            },
+            [&] {
+                m_tex[i].unbind();
+            });
     const auto result = pp::panopainter::execute_legacy_canvas_stroke_face_sample_polygon(
         pp::panopainter::LegacyStrokeFaceSamplePolygonExecutionRequest {
             .context = "Canvas::stroke_draw_samples",

src/legacy_canvas_stroke_execution_services.h

@@ -116,6 +116,18 @@ struct LegacyCanvasStrokeTextureInputDispatch {
     };
 }
 
+[[nodiscard]] inline LegacyCanvasStrokeTextureInputDispatch make_legacy_canvas_stroke_destination_texture_dispatch(
+    std::function<void(int)> activate_texture_unit,
+    std::function<void()> bind_stroke_destination,
+    std::function<void()> unbind_stroke_destination)
+{
+    return LegacyCanvasStrokeTextureInputDispatch {
+        .activate_texture_unit = std::move(activate_texture_unit),
+        .bind_stroke_destination = std::move(bind_stroke_destination),
+        .unbind_stroke_destination = std::move(unbind_stroke_destination),
+    };
+}
+
 [[nodiscard]] inline LegacyCanvasStrokeTextureInputDispatch make_legacy_canvas_stroke_pad_destination_texture_dispatch(
     std::function<void(int)> activate_texture_unit,
     std::function<void()> bind_stroke_destination,

tests/paint_renderer/stroke_execution_tests.cpp

@@ -361,6 +361,28 @@ void retained_stroke_pad_destination_texture_dispatch_helper_builds_expected_cal
     PP_EXPECT(h, events == expected_events);
 }
 
+void retained_stroke_destination_texture_dispatch_helper_builds_expected_callback_wiring(pp::tests::Harness& h)
+{
+    std::vector<std::string> events;
+    const auto dispatch = pp::panopainter::make_legacy_canvas_stroke_destination_texture_dispatch(
+        [&](int slot) { events.emplace_back("activate:" + std::to_string(slot)); },
+        [&] { events.emplace_back("bind:destination"); },
+        [&] { events.emplace_back("unbind:destination"); });
+
+    pp::panopainter::bind_legacy_canvas_stroke_texture_input(
+        LegacyCanvasStrokeTextureInput::stroke_destination,
+        dispatch);
+    pp::panopainter::unbind_legacy_canvas_stroke_texture_input(
+        LegacyCanvasStrokeTextureInput::stroke_destination,
+        dispatch);
+
+    const std::vector<std::string> expected_events {
+        "bind:destination",
+        "unbind:destination",
+    };
+    PP_EXPECT(h, events == expected_events);
+}
+
 void retained_stroke_sample_executor_copies_destination_and_expands_quads(pp::tests::Harness& h)
 {
     const auto vertices = make_quad_vertices();
@@ -1450,6 +1472,9 @@ int main()
     harness.run(
         "retained_stroke_brush_tip_texture_dispatch_helper_builds_expected_callback_wiring",
         retained_stroke_brush_tip_texture_dispatch_helper_builds_expected_callback_wiring);
+    harness.run(
+        "retained_stroke_destination_texture_dispatch_helper_builds_expected_callback_wiring",
+        retained_stroke_destination_texture_dispatch_helper_builds_expected_callback_wiring);
     harness.run(
         "retained_stroke_live_pass_sampler_dispatch_helper_builds_expected_callback_wiring",
         retained_stroke_live_pass_sampler_dispatch_helper_builds_expected_callback_wiring);