old_contents: class CommandError(Exception):
      def __init__(self, args, ret, out, err):
          self.args = args
          self.ret = ret
          self.out = out
          self.err = err
  
  class ServerError(Exception):
      pass
  
  class ResponseError(ServerError, ValueError):
      pass
  
  class CapabilityError(ServerError):
      pass
  
new_contents: class CommandError(Exception):
      def __init__(self, args, ret, out, err):
          self.args = args
          self.ret = ret
          self.out = out
          self.err = err
  
      def __str__(self):
          return self.err
  
  class ServerError(Exception):
      pass
  
  class ResponseError(ServerError, ValueError):
      pass
  
  class CapabilityError(ServerError):
      pass
  
subject: return stderr as __str__ for CommandError