[R2] Default ZMQ serve binds `0.0.0.0` with an unauthenticated `kill` endpoint

[DsThakurRawat]

Labels: bug, security, runtime, priority:high
File: src/tether/runtime/transports/zmq/factory.py:34 (host="*", control_token=None), .../policy_server.py:96,110-112,184-186

Description. create_zmq_server defaults host="*" and no control token; kill/ping set requires_auth = control_token is not None → no auth by default. Any host reaching tcp://<robot>:5555 can send {"endpoint":"kill"} and stop the policy server mid-episode.

Tasks.

• Default-bind loopback for ZMQ; require a control_token for control endpoints.
• Warn on insecure public binds (mirror the HTTP fix in PR fix(serve): bind 127.0.0.1 by default + warn on insecure public binds #234).

Dedup. PR #234 fixes the HTTP bind default only; this is a distinct transport. Not covered.