refactor(registry): add per-host uniqueness predicate

configs/nixos/registry/keybind.nix

@@ -2,10 +2,7 @@
 {
   checks = [
     {
-      assertion = util.registry.predicates.uniqueValue (entry: {
-        inherit (entry) host;
-        inherit (entry.value) keys;
-      });
+      assertion = util.registry.predicates.uniquePerHost (entry: entry.value.keys);
       message = "Desktop keybinds must use unique key chords per host.";
     }
   ];

src/dotfiles/util.nix

@@ -16,14 +16,23 @@ let
           [ ]
       ) (builtins.readDir dir)
     );
+
+  uniqueValue =
+    value: entries: builtins.length (lib.unique (map value entries)) == builtins.length entries;
 in
 {
   inherit collectNixFiles;
 
   removeNixSuffix = path: lib.removeSuffix ".nix" (builtins.baseNameOf path);
 
-  registry.predicates.uniqueValue =
-    value: entries: builtins.length (lib.unique (map value entries)) == builtins.length entries;
+  registry.predicates.uniqueValue = uniqueValue;
+
+  registry.predicates.uniquePerHost =
+    value:
+    uniqueValue (entry: {
+      inherit (entry) host;
+      value = value entry;
+    });
 
   bridgeName = id: "br-vlan${toString id}";