very, very simple WP with midi CC out

include/libremidi/backends/coremidi_ump/observer.hpp

@@ -0,0 +1,13 @@
+#pragma once
+#include <libremidi/backends/coremidi/observer.hpp>
+
+namespace libremidi::coremidi_ump
+{
+
+class observer_impl final : public libremidi::observer_core
+{
+  using observer_core::observer_core;
+  libremidi::API get_current_api() const noexcept override { return libremidi::API::COREMIDI_UMP; }
+};
+
+}