Including a ServerMessageBodyWriter via an extension

[akil-rails]

I've a messagebodywriter that uses ObjectMapper as follows

public class StitchServerMessageBodyWriter
    implements ServerMessageBodyWriter<Object> {

  @Inject
  ObjectMapper objectMapper;

....

This works fine when its part of an application (and includes the annotations @produces and Provider).

When I move this to the extension, and register it as follows, there's a runtime error that objectMapper is null.

  @BuildStep
  public MessageBodyWriterBuildItem registerMessageBodyWriter() {
    List<String> mediaTypes = new ArrayList<>();
    mediaTypes.add("application/json");
    return new MessageBodyWriterBuildItem(StitchServerMessageBodyWriter.class.getName(), Object.class.getName(), mediaTypes);
  }
}

What is the correct way to register a custom writer that requires CDI (Inject) via an extension?