refactor(dotfiles): extract registry schema

src/dotfiles/registry/schema.nix

@@ -0,0 +1,46 @@
+{ lib }:
+let
+  checkType = lib.types.submodule {
+    options = {
+      assertion = lib.mkOption {
+        type = lib.types.functionTo lib.types.bool;
+        description = ''
+          Predicate run against this registry's flattened collected entries.
+        '';
+      };
+
+      message = lib.mkOption {
+        type = lib.types.str;
+        description = ''
+          Error message shown when this registry validation check fails.
+        '';
+      };
+    };
+  };
+in
+{
+  options = {
+    type = lib.mkOption {
+      type = lib.types.raw;
+      description = ''
+        NixOS option type for one registry entry.
+      '';
+    };
+
+    replicate = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        Whether collected entries are merged and published under every host key.
+      '';
+    };
+
+    checks = lib.mkOption {
+      type = lib.types.listOf checkType;
+      default = [ ];
+      description = ''
+        Validation checks for this registry's flattened collected entries.
+      '';
+    };
+  };
+}