Code review of a1abbff7 found two edge cases: a discovery/advertised URL with no
explicit port emitted a malformed ':-1' (opc.tcp has no Uri default port), and an
IPv6 literal host could lose/double its brackets. Omit the port when neither URL
carries one; bracket an IPv6 host only when missing. +4 tests (12 total).
An OPC UA server advertises its base address from its own config, not the route
the client took — commonly a 0.0.0.0 wildcard bind or an internal container/NAT
hostname. The OPC Foundation session dials EndpointDescription.EndpointUrl
verbatim, so a 0.0.0.0 advertisement resolved to the client's own loopback and
the connect failed. RealOpcUaClient now swaps the advertised authority for the
reachable host/port (ConnectAsync + VerifyEndpointAsync), preserving scheme+path;
no-op when already reachable. Surfaced live-gating OtOpcUa v3 (#14).
Joseph Doherty