Add stroke sampler dispatch helper coverage

docs/modernization/tasks.md

@@ -509,6 +509,11 @@ Done Checks:
 
 Progress Notes:
 
+- 2026-06-13: `pp_paint_renderer_stroke_execution_tests` now covers the new
+  retained sampler dispatch helper builder and its pattern bind/unbind wiring.
+  Next slice should target another narrow `stroke_draw()` seam or another
+  helper-builder regression without reopening landed texture or dual-pass
+  helpers.
 - 2026-06-13: `Canvas::stroke_draw()` live-pass sampler dispatch now reuses a
   retained helper builder for brush-tip, destination, pattern, and mixer
   sampler callbacks; the live adapter still owns the concrete sampler objects.

tests/paint_renderer/stroke_execution_tests.cpp

@@ -232,6 +232,34 @@ void retained_stroke_sampler_dispatch_routes_bind_and_unbind_per_input(pp::tests
     PP_EXPECT(h, events == expected_events);
 }
 
+void retained_stroke_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_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::pattern,
+        6,
+        dispatch);
+    pp::panopainter::unbind_legacy_canvas_stroke_sampler_input(
+        LegacyCanvasStrokeTextureInput::pattern,
+        dispatch);
+
+    const std::vector<std::string> expected_events {
+        "bind:pattern:6",
+        "unbind:pattern",
+    };
+    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();
@@ -1309,6 +1337,9 @@ int main()
     harness.run(
         "retained_stroke_sampler_dispatch_routes_bind_and_unbind_per_input",
         retained_stroke_sampler_dispatch_routes_bind_and_unbind_per_input);
+    harness.run(
+        "retained_stroke_sampler_dispatch_helper_builds_expected_callback_wiring",
+        retained_stroke_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);