The signal you want already exists in that protocol. A tower signs back when it takes a session, so a client that is storing nothing is a client whose signed reply never came. The failure was not a missing signal. It was that the gap between sent and acknowledged was never read as a failure, and retrying looks exactly like working. What fixed it for me was not another dashboard. I wiped the client database, re-added the tower, and then judged from the tower's own log, where a session either arrives or it does not. My side can be green and hopeful. The other side cannot be green and wrong. 257,000 sessions is a good number to be scared of, because every one of them was written by something that had no reason to doubt itself.