Structural health monitoring for a UniFi fabric. The @sntxrr/unifi-fabric/topology model's check method compares a declared topology against live /stat/device rows and reports the failures that outcome-based monitoring cannot see: a device expected on the wire that has silently fallen back to a wireless mesh uplink, attachment to the wrong upstream device, links negotiated below their expected speed, ports carrying error counters, and — the one with no equivalent elsewhere — ports that are down but have carried real traffic before, which identifies a run that used to work. An access point that loses its wired uplink does not fail; it meshes, keeps serving clients, and every uptime check stays green while latency quietly goes from sub-millisecond to tens of milliseconds and jittery. uplink.type flipping from wire to wireless is a boolean, so it is asserted exactly rather than thresholded. Read-only: never writes to the controller. Emits a flat Prometheus-ready metric series alongside the verdict, including for healthy devices, so alerts can fire on a series dropping to zero rather than on a document changing shape. Authenticates with an API key over X-API-KEY, which sidesteps the HTTP 499 that MFA-enabled SSO accounts return for password logins.