M70k (X8-4): counts this name's three states with one ZCARD each.

Absent on a client that does not expose zcard, which is why the member is an assigned property rather than a declared method — the health indicator must be able to tell "cannot report" from "nothing there". Absent again after disconnect, for the same reason isHealthy is: the closure captures the client it was installed for, so leaving it in place would answer a depth read with that dead client's rejection instead of the absence that says the adapter cannot count right now.