Facts carry the format as a template, so the control plane holds none (ADR 0120)

A roster fact used to be a name from a closed list, each formatted in Go
here — node-names as a hosts file, node-zones as a resolver's zones. Every
new consumer (ssh's known_hosts, an authorized_keys) meant another formatter
in the control plane, in the consumer's own configuration language.

Now a fact is a path and a Go template over the roster view (this node, the
suffix, and every served name vs the machines). The mesh owns the data; the
module owns the format. /etc/hosts is a template on the network module;
dnsmasq's zones move to dnsmasq. The controller renders and reads neither.

WireGuard stays a computed generator: the overlay is the substrate delivery
rides on, and its config is topology, not a roster projection.

Output is byte-for-byte unchanged, pinned by the hosts golden tests and the
resolver tests that compose the real dnsmasq manifest.

internal/catalogue/provided_test.go

@@ -54,7 +54,7 @@ func TestTheShippedNetworkingModulesResolveOnTheirOwn(t *testing.T) {
 	// network is what gives a machine a name, so the provider asks for the node-names fact and
 	// there is nothing else to bring in. A module that ran nothing used to be here.
 	for _, m := range got.Modules {
-		if m.Module == overlay.Name && m.Facts["node-names"] == "" {
+		if m.Module == overlay.Name && m.Facts["node-names"].Path == "" {
 			t.Fatalf("the network's provider does not ask for the names: %+v", m.Facts)
 		}
 	}