message: Note JSON encoding errors when sending diagnostics console output
diff: @@ -361,8 +361,11 @@ impl Session {
  writer.write_all(b"\n").await?;
  }
  OutputFormat::Json => {
  - let buf = serde_json::to_string_pretty(response)
  - .map_err(|err| io::Error::new(io::ErrorKind::Other, err))?;
  + info!("sending json");
  + let buf = serde_json::to_string_pretty(response).map_err(|err| {
  + warn!(%err, "error outputting JSON string");
  + io::Error::new(io::ErrorKind::Other, err)
  + })?;
  writer.write_all(buf.as_bytes()).await?;
  writer.write_all(b"\n").await?;
  }
  