Give the resolver the mesh's suffix as a local domain and a module its machine's address

hal dnsmasq-app conversion, hq 08-connectivity. Converting the resolver from the module it
replaces made it forward what it cannot answer, which is what the predecessor's does, and
that found two things the controller did not say.

A resolver that forwards must not send a mesh name it does not know upstream: the
`node-zones` fact now carries `local=/<suffix>/` beside the wildcards, written here rather
than in the daemon's configuration because the suffix is the mesh's choice and this file is
the one place the mesh writes what it chose. The default lives in one helper now instead of
being spelled in two functions.

The predecessor points the container runtime's `dns` at the machine's own tunnel address —
a container cannot reach the machine's loopback. A module writing that key needs the
address, and `${machine:at}` is the machine's name; a runtime's resolver list cannot be a
name it would need that resolver to look up. So a module may say `${machine:address}`: what
`at` resolves to, read from the same names the hosts file and the wildcards are written
from, absent — and refused — off the network like `at` is.

The `mesh-resolver` and `resolver-data` constants go: nothing provided or consumed either,
the fact and `mesh-addressing` are the mechanism, and a requirement nothing provides is
refused at resolution.

Tests: the catalogue's dnsmasq, resolv-conf and resolved-split-dns manifests are parsed
and composed as a machine would receive them — fixed upstreams, no-resolv, 127.0.0.1, the
machines file, the runtime's key, the pair that decides what a machine asks refused on one
node; and on a real mesh the resolver's machines file is composed with a wildcard per
machine on the network and composed again without one that left, mirroring the hosts fact.

internal/catalogue/facts.go

@@ -122,10 +122,18 @@ func nodeNames(r Resolution, addresses map[string]string, suffix string) string
 //
 // `*.homer.internal` is homer, which is the whole rule: if homer is at an address, so is anything
 // homer serves. A module wanting this runs the resolver; the mesh only says what is true.
+//
+// **And the suffix itself, as a local domain.** A resolver that forwards what it cannot answer
+// would otherwise send a mesh name it does not know — a machine that left, a typo — to a public
+// resolver, which is a leak of the mesh's names for no answer. `local=` keeps everything under the
+// suffix here: answered from the lines below or refused. Written in this file rather than in the
+// resolver's own configuration because the suffix is the mesh's choice (the operator may have
+// picked another) and this file is the one place the mesh writes what it chose.
 func nodeZones(_ Resolution, addresses map[string]string, suffix string) string {
 	var b strings.Builder
 	b.WriteString("# Generated by the mesh. Do not edit — this file is replaced whenever a machine\n")
 	b.WriteString("# joins or leaves, and an edit would survive until then and vanish.\n\n")
+	fmt.Fprintf(&b, "local=/%s/\n", strings.TrimPrefix(suffixOr(suffix), "."))
 	for _, name := range sortedNames(addresses) {
 		internal, _ := meshName(name, suffix)
 		fmt.Fprintf(&b, "address=/%s/%s\n", internal, addresses[name])
@@ -139,16 +147,22 @@ func nodeZones(_ Resolution, addresses map[string]string, suffix string) string
 // suffix is the one the control plane composed those names with, handed down rather than written
 // here a second time — the alternative was `homer.internal.internal` on every machine.
 func meshName(name, suffix string) (internal, bare string) {
-	if suffix == "" {
-		suffix = "internal"
-	}
-	dotted := "." + strings.TrimPrefix(suffix, ".")
+	dotted := "." + strings.TrimPrefix(suffixOr(suffix), ".")
 	if strings.HasSuffix(name, dotted) {
 		return name, strings.TrimSuffix(name, dotted)
 	}
 	return name + dotted, name
 }
 
+// suffixOr is the suffix given, or the one the mesh composes names with when none was handed down.
+// The one place the default is written in this file, so a fact and a name cannot disagree about it.
+func suffixOr(suffix string) string {
+	if suffix == "" {
+		return "internal"
+	}
+	return suffix
+}
+
 func sortedNames(addresses map[string]string) []string {
 	out := make([]string, 0, len(addresses))
 	for name, at := range addresses {