The gateway nginx serves stub_status on a loopback server of its own,
127.0.0.1:8085 (services.hyperhive.gateway.statusPort). The hive-tier
collector reads it with the contrib nginx receiver, which the pinned
otelcol-contrib 0.151.0 ships, so no exporter daemon is added. The
receiver dials http:// only (a unix: or http+unix: endpoint fails with
"unsupported protocol scheme"), so the listener is loopback TCP with
allow 127.0.0.1 / deny all rather than a unix socket.
The new gateway dashboard plots nginx.requests, nginx.connections_current
by state, and nginx.connections_accepted against handled, per hive.
Part of #5342.
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