The connectivity endpoint was calling routing_manager.test_connectivity()
(no args, internal health check) instead of test_routing_connectivity(target_ip).
Also ping/traceroute aren't installed in the API container; run them via
docker exec cell-wireguard instead.
Updated test_api_endpoints to mock test_routing_connectivity and cover
the new DELETE /firewall/<id> and GET /live-iptables endpoints.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>