TargetMap is an immutable map from logical target name to local TCP address.
type TargetMap structLookup returns the exact canonical address configured for name.
Resolve returns the connector-local target selected by name.
Names returns the target names in canonical sorted order.
Kind is "relay" for a connector serving the proxy target and "tunnel".
Hash returns the lowercase hexadecimal SHA-256 hash of the canonical map.
RegistrationMetadata returns the bounded description advertised to the edge.