BIND: disable IPv6

this makes it work (more reliably, at least) inside sane-vpn

hosts/common/net/dns/bind.nix

@@ -1,24 +1,51 @@
 { config, lib, ... }:
+let
+  hostCfg = config.sane.hosts.by-name."${config.networking.hostName}";
+in
 {
   config = lib.mkIf (!config.sane.services.hickory-dns.asSystemResolver) {
     services.resolved.enable = lib.mkForce false;
 
+    networking.nameservers = [
+      # be compatible with systemd-resolved
+      # "127.0.0.53"
+      # or don't be compatible with systemd-resolved, but with libc and pasta instead
+      #   see <pkgs/by-name/sane-scripts/src/sane-vpn>
+      "127.0.0.1"
+      # enable IPv6, or don't; unbound is spammy when IPv6 is enabled but unroutable
+      # "::1"
+    ];
+
+    networking.resolvconf.extraConfig = ''
+      # DNS serviced by `BIND` recursive resolver
+      name_servers='127.0.0.1'
+    '';
+
     services.bind.enable = lib.mkDefault true;
     services.bind.forwarders = [];  #< don't forward queries to upstream resolvers
     services.bind.cacheNetworks = [
       "127.0.0.0/24"
       "::1/128"
-      "10.0.0.0/16"
+      "10.0.10.0/24"  #< wireguard clients (servo)
     ];
+    services.bind.listenOn = [
+      "127.0.0.1"
+    ] ++ lib.optionals (hostCfg.wg-home.ip != null) [
+      # allow wireguard clients to use us as a recursive resolver (only needed for servo)
+      hostCfg.wg-home.ip
+    ];
+    services.bind.listenOnIpv6 = [
+      # "::1"
+    ];
+
+    services.bind.ipv4Only = true;  # unbound is spammy when it tries IPv6 without a routable address
 
     # when testing, deploy on a port other than 53
     # services.bind.extraOptions = ''
     #   listen-on port 953 { any; };
     # '';
-    # services.bind.listenOn = [];
-    # services.bind.listenOnIpv6 = [];
 
-    # networking.resolvconf.useLocalResolver = false;  #< undo bind making this default true
+    networking.resolvconf.useLocalResolver = false;  #< we manage resolvconf explicitly, above
 
     # TODO: how to exempt `pool.ntp.org` from DNSSEC checks, as i did when using unbound?
   };