feat(nixos): migrate system configuration

configs/nixos/registry/address.nix

@@ -0,0 +1,11 @@
+{ lib, ... }:
+{
+  type = lib.types.str;
+
+  checks = [
+    {
+      assertion = lib.registry.predicates.uniqueValue (entry: entry.value);
+      message = "Address registry values must be unique.";
+    }
+  ];
+}

configs/nixos/registry/route.nix

@@ -0,0 +1,25 @@
+{ lib, ... }:
+{
+  checks = [
+    {
+      assertion = lib.registry.predicates.uniqueValue (entry: entry.value.domain);
+      message = "Route domains must be unique.";
+    }
+  ];
+
+  type = lib.types.submodule {
+    options = {
+      domain = lib.mkOption {
+        type = lib.types.str;
+        example = "files.alexion.dev";
+        description = "Public domain served by this reverse-proxy route entry.";
+      };
+
+      port = lib.mkOption {
+        type = lib.types.ints.between 1 65535;
+        example = 3923;
+        description = "Backend TCP port served by the matching address registry entry.";
+      };
+    };
+  };
+}

configs/nixos/registry/shell-shortcut.nix

@@ -0,0 +1,21 @@
+{ lib, ... }:
+let
+  entryType = lib.types.submodule {
+    options = {
+      command = lib.mkOption {
+        type = lib.types.str;
+        example = "nvim";
+        description = "Command expanded by this shell shortcut.";
+      };
+
+      abbreviation = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        description = "Whether fish realizes this shell shortcut as an abbreviation instead of an alias.";
+      };
+    };
+  };
+in
+{
+  type = lib.types.coercedTo lib.types.str (command: { inherit command; }) entryType;
+}

configs/nixos/registry/stable-uid.nix

@@ -0,0 +1,31 @@
+{ lib, ... }:
+let
+  inherit (lib)
+    filterAttrs
+    groupBy
+    mapAttrs
+    unique
+    ;
+
+  serviceNamesByUid = entries:
+    mapAttrs (_uid: uidEntries: unique (map (entry: entry.entry) uidEntries)) (
+      groupBy (entry: toString entry.value) entries
+    );
+
+  duplicateUids = entries:
+    filterAttrs (_uid: serviceNames: builtins.length serviceNames > 1) (serviceNamesByUid entries);
+
+in
+{
+  # Next stable UID: 20003
+  replicate = true;
+
+  type = lib.types.ints.positive;
+
+  checks = [
+    {
+      assertion = entries: duplicateUids entries == { };
+      message = "Stable UID allocations must be unique.";
+    }
+  ];
+}