Stdio transport: the server runs as an OS process and speaks one JSON-RPC 2.0 object per line.
A server writes logs to stderr. The port does not capture stderr, so those logs go to the stderr of the Super-Pi process, never into the JSON stream. A line that is not JSON (a banner on stdout) is ignored.
Summary
Functions
Options: :command, :args, :env (map), :cwd.
Returns {:error, {:command_not_found, command}} when the executable does not exist.