Driving the protocol with no effect system at all.
verdict4s-core carries only cats-core, circe and Iron: no effect type, no HTTP client, no fs2. That is what this object is for. Render a request to JSON, send it with whatever HTTP client you already have, and parse the reply back into typed answers:
val body = SystemOne.render(request)
val text = myHttpClient.post(SystemOne.evaluateUrl, body) // your code
val evaluation = SystemOne.parse(text)
This is the path for Twitter Future, for Akka or Pekko HTTP, for sttp, and for a plain blocking client — anything without a lawful cats-effect instance. If you do have one, verdict4s-client is less work.