A transient GET failure on a healthy endpoint could park the client on an
unreachable fallback (e.g. the server host's Docker bridge gateway, which
plex.tv advertises as a local connection) for a full connect timeout, failing
every request in flight during that window (log bbr90).
The cascade now probes each candidate with an unauthenticated /identity
request under the discovery-race budget and only switches when it answers as
the expected server, mirroring the Jellyfin trust gate. Unreachable-looking
private IPv4 candidates stay in the list — a client on the server host can
legitimately reach them, so reachability is probed, not inferred.
edde746