Serve the uplink seat's verbs from both of its holders (hq ADR 0241)

What a machine resolves through had no tool: the resolver file and who
wrote it, and every link with its default route and the resolvers its
manager knows. Each holder serves the same two node-uplink verbs; the
reading is one text carried by both, held to it by a test, and only
asking the manager for a link's names is each holder's own.

modules/networkmanager/cmd/uplink-tools/manager.go

@@ -0,0 +1,52 @@
+package main
+
+// NetworkManager's word on each link's names: `nmcli device show`, read in its terse form. A link
+// NetworkManager does not manage — a tunnel a VPN client raised with `ip`, the mesh's own — is not in it,
+// and the links verb says the link without what the manager does not know.
+
+import (
+	"context"
+	"strings"
+)
+
+func managerDNS(ctx context.Context) (map[string]LinkDNS, error) {
+	out, err := execRunner(ctx, "nmcli", "-t", "-f", "GENERAL.DEVICE,GENERAL.STATE,IP4.DNS,IP6.DNS,IP4.DOMAIN,IP6.DOMAIN",
+		"device", "show")
+	if err != nil {
+		return nil, err
+	}
+	return parseNmcli(out), nil
+}
+
+// parseNmcli reads `nmcli -t device show`: blocks of KEY:value lines, one block per device.
+func parseNmcli(out string) map[string]LinkDNS {
+	links := map[string]LinkDNS{}
+	device := ""
+	var cur LinkDNS
+	flush := func() {
+		if device != "" && (len(cur.Servers) > 0 || len(cur.Domains) > 0) {
+			cur.Manager = "NetworkManager"
+			links[device] = cur
+		}
+		device, cur = "", LinkDNS{}
+	}
+	for _, line := range strings.Split(out, "\n") {
+		key, value, ok := strings.Cut(strings.TrimSpace(line), ":")
+		if !ok {
+			continue
+		}
+		switch {
+		case key == "GENERAL.DEVICE":
+			flush()
+			device = value
+		case key == "GENERAL.STATE":
+			cur.State = value
+		case strings.HasPrefix(key, "IP4.DNS"), strings.HasPrefix(key, "IP6.DNS"):
+			cur.Servers = append(cur.Servers, value)
+		case strings.HasPrefix(key, "IP4.DOMAIN"), strings.HasPrefix(key, "IP6.DOMAIN"):
+			cur.Domains = append(cur.Domains, value)
+		}
+	}
+	flush()
+	return links
+}