[Observability] - Auto-implement tracing/observability

[edeandrea]

When interacting with an mcp server from the client, the tool entrypoint should be auto-observed by opentelemetry (if its present), like we do with REST endpoints.

Even if I manually add tracing, like this for example, the spans do not correlate with the caller.

Also, if I add the @WithSpan annotation then things blow up.

  @Tool(name = "sendEmail", value = "Sends an email")
  public ToolResponse sendEmail(Email email) {
    var span = this.tracer.spanBuilder("sendEmail")
        .setAttribute("arg.email", email.toString())
        .setParent(Context.current().with(Span.current()))
        .setSpanKind(SpanKind.SERVER)
        .startSpan();

    try {
      var mail = Mail.withText(email.to(), email.subject(), email.body())
          .setFrom(email.from());

      this.mailer.send(mail);

      return ToolResponse.success("Email successfully sent");
    }
    finally {
      span.end();
    }
  }

[mkouba]

So it's expected, because we didn't add any observability support yet.

Also, if I add the @WithSpan annotation then things blow up.

Could you pls add the full stacktrace so that the information is complete?