{
  "assertions": {
    "existing_connection_initially_uses_a": true,
    "existing_connection_stays_on_a": true,
    "health_check_marks_a_down": true,
    "new_connection_uses_b": true
  },
  "boundaries": [
    "loopback teaching proxy with per-connection selection",
    "not HTTP, TLS, production load balancing, draining, retry, or a performance test"
  ],
  "events": {
    "existing_after": "A:after-listener-close",
    "existing_before": "A:first",
    "health_after_a_listener_close": {"A": false, "B": true},
    "new_after": "B:new-connection"
  }
}