AsyncClientResponseProvider is not used

@Provider
public class DummyAsyncClientResponseProvider implements AsyncClientResponseProvider<String> {
    @Override
    public String fromCompletionStage(CompletionStage<?> completionStage) {
        return "injected response";
    }
}

@Path("/")
public class PingResource {

    @Context
    private UriInfo uriInfo;
    
    @GET
    @Path("async")
    public String async() {
        Client client = ClientBuilder.newClient();
        client.register(DummyAsyncClientResponseProvider.class);

        Response response = client.target(uriInfo.getBaseUriBuilder().path("async-client").build())
            .request().get();

        return response.readEntity(String.class);
    }

    @GET
    @Path("async-client")
    public CompletionStage<String> asyncClient() {
        return CompletableFuture.supplyAsync(() -> "original string");
    }
}