Let the mesh's resolver seat have several holders on record

musl takes the first reply from any listed nameserver, so a public fallback
beside the mesh's resolver answered NXDOMAIN for mesh names in every Alpine
container (hq ADR 0223). The fix is two mesh resolvers and no public one, which
needs mesh-dns-resolver held on two machines: a seat can now be replicated,
each holder recorded by 'seat <name> --add', checkClaims accepts every holder
on record and still refuses a second holder of any other mesh seat, a holder
answers its own requirement, and a roster fact gives each replicated seat's
holders, this machine first, so resolv-conf can list them. Migration 0062 keys
a holding by seat and assignment.

internal/catalogue/declaration.go

@@ -159,6 +159,11 @@ type Rendering struct {
 	// 0199): the mesh's resolver forwards each one there.
 	Zones []ZoneAt
 
+	// Holders is, for each replicated mesh seat, every machine holding it, by internal name and
+	// private address (novox/hq ADR 0223) — the same shape as Machines. What a machine's resolver
+	// file lists: every holder of the mesh's resolver, this machine first if it is one.
+	Holders map[string]map[string]string
+
 	Settings   SettingsBy
 	Generators map[string]Generator
 	// Grants are the credentials this node must create, for the provisions it offers. Passed in
@@ -979,7 +984,7 @@ func (r Resolution) compose(with Rendering, owner map[string]string,
 		// plane's; making a name resolve is the module's software. Emitted as ordinary files under
 		// this module's name, so they are applied, reported and removed exactly as anything else
 		// it declares.
-		given, err := FactsWithZonesInto(m, r, with.Names, with.Machines, with.Accounts, with.Suffix, with.Zones)
+		given, err := FactsFrom(m, r, with)
 		if err != nil {
 			return nil, err
 		}