Right now Dach's Dai or Chai actions does not
require(relayer == msg.sender, "invalid relayer");
I could understand useful scenario such as a backend relaying meta-tx concurrently from differents EOAs while collecting fee on a specific address. However such implicit behaviour looks kind of "dangerous", given that its implicit. So right now, relayer parameter behave as a fee_recipient and if not asserted then a backend's relayer's EOA could be potentially emptied.