Resolve node hostname to IP for DNS registration

Node addresses may be Tailscale DNS names (e.g., rift.scylla-hammerhead.ts.net:9444)
but MCNS needs an IPv4 address for A records. The master now resolves
the hostname via net.LookupHost before passing it to the DNS client.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/master/deploy.go

@@ -51,12 +51,23 @@ func (m *Master) Deploy(ctx context.Context, req *mcpv1.MasterDeployRequest) (*m
 		return resp, nil
 	}
 
-	// Parse the node's Tailnet IP from its address (host:port).
+	// Resolve the node's address to an IP for DNS registration.
+	// Node addresses may be Tailscale DNS names (e.g., rift.scylla-hammerhead.ts.net:9444)
+	// but MCNS needs an IP address for A records.
 	nodeHost, _, err := net.SplitHostPort(node.Address)
 	if err != nil {
 		resp.Error = fmt.Sprintf("invalid node address %q: %v", node.Address, err)
 		return resp, nil
 	}
+	// If nodeHost is not an IP, resolve it.
+	if net.ParseIP(nodeHost) == nil {
+		ips, lookupErr := net.LookupHost(nodeHost)
+		if lookupErr != nil || len(ips) == 0 {
+			m.Logger.Warn("cannot resolve node address", "host", nodeHost, "err", lookupErr)
+		} else {
+			nodeHost = ips[0]
+		}
+	}
 
 	// Step 2: Forward deploy to the agent.
 	client, err := m.Pool.Get(nodeName)