Add live pass sampler dispatch helper coverage

docs/modernization/tasks.md

@@ -509,6 +509,10 @@ Done Checks:
 
 Progress Notes:
 
+- 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`
+  should now focus only on the last tiny binding leftovers or be marked done
+  once the debt note is updated.
 - 2026-06-13: `STR-004` is now the next ready slice for the last inline stroke
   dispatch glue; `LATER-003` is effectively at the binding-only tail. Keep
   this task focused on removing or consolidating helper-builder wiring rather

src/canvas.cpp

@@ -732,7 +732,7 @@ void Canvas::stroke_draw()
         },
     };
     const pp::panopainter::LegacyCanvasStrokeSamplerDispatch live_pass_sampler_dispatch =
-        pp::panopainter::make_legacy_canvas_stroke_sampler_dispatch(
+        pp::panopainter::make_legacy_canvas_stroke_live_pass_sampler_dispatch(
             [&](int slot) {
                 m_sampler_brush.bind(slot);
             },

src/legacy_canvas_stroke_execution_services.h

@@ -127,6 +127,28 @@ struct LegacyCanvasStrokeSamplerDispatch {
     std::function<void()> unbind_mixer_sampler;
 };
 
+[[nodiscard]] inline LegacyCanvasStrokeSamplerDispatch make_legacy_canvas_stroke_live_pass_sampler_dispatch(
+    std::function<void(int)> bind_brush_tip_sampler,
+    std::function<void()> unbind_brush_tip_sampler,
+    std::function<void(int)> bind_stroke_destination_sampler,
+    std::function<void()> unbind_stroke_destination_sampler,
+    std::function<void(int)> bind_pattern_sampler,
+    std::function<void()> unbind_pattern_sampler,
+    std::function<void(int)> bind_mixer_sampler,
+    std::function<void()> unbind_mixer_sampler)
+{
+    return LegacyCanvasStrokeSamplerDispatch {
+        .bind_brush_tip_sampler = std::move(bind_brush_tip_sampler),
+        .unbind_brush_tip_sampler = std::move(unbind_brush_tip_sampler),
+        .bind_stroke_destination_sampler = std::move(bind_stroke_destination_sampler),
+        .unbind_stroke_destination_sampler = std::move(unbind_stroke_destination_sampler),
+        .bind_pattern_sampler = std::move(bind_pattern_sampler),
+        .unbind_pattern_sampler = std::move(unbind_pattern_sampler),
+        .bind_mixer_sampler = std::move(bind_mixer_sampler),
+        .unbind_mixer_sampler = std::move(unbind_mixer_sampler),
+    };
+}
+
 [[nodiscard]] inline LegacyCanvasStrokeSamplerDispatch make_legacy_canvas_stroke_sampler_dispatch(
     std::function<void(int)> bind_brush_tip_sampler,
     std::function<void()> unbind_brush_tip_sampler,

tests/paint_renderer/stroke_execution_tests.cpp

@@ -287,6 +287,34 @@ void retained_stroke_main_pass_texture_dispatch_helper_builds_expected_callback_
     PP_EXPECT(h, events == expected_events);
 }
 
+void retained_stroke_live_pass_sampler_dispatch_helper_builds_expected_callback_wiring(pp::tests::Harness& h)
+{
+    std::vector<std::string> events;
+    const auto dispatch = pp::panopainter::make_legacy_canvas_stroke_live_pass_sampler_dispatch(
+        [&](int slot) { events.emplace_back("bind:brush_tip:" + std::to_string(slot)); },
+        [&] { events.emplace_back("unbind:brush_tip"); },
+        [&](int slot) { events.emplace_back("bind:destination:" + std::to_string(slot)); },
+        [&] { events.emplace_back("unbind:destination"); },
+        [&](int slot) { events.emplace_back("bind:pattern:" + std::to_string(slot)); },
+        [&] { events.emplace_back("unbind:pattern"); },
+        [&](int slot) { events.emplace_back("bind:mixer:" + std::to_string(slot)); },
+        [&] { events.emplace_back("unbind:mixer"); });
+
+    pp::panopainter::bind_legacy_canvas_stroke_sampler_input(
+        LegacyCanvasStrokeTextureInput::brush_tip,
+        4,
+        dispatch);
+    pp::panopainter::unbind_legacy_canvas_stroke_sampler_input(
+        LegacyCanvasStrokeTextureInput::brush_tip,
+        dispatch);
+
+    const std::vector<std::string> expected_events {
+        "bind:brush_tip:4",
+        "unbind:brush_tip",
+    };
+    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();
@@ -1370,6 +1398,9 @@ int main()
     harness.run(
         "retained_stroke_main_pass_texture_dispatch_helper_builds_expected_callback_wiring",
         retained_stroke_main_pass_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);
     harness.run(
         "retained_stroke_sample_executor_unbinds_and_skips_draw_when_bounds_are_empty",
         retained_stroke_sample_executor_unbinds_and_skips_draw_when_bounds_are_empty);