refactor(nix): dedupe home-manager wiring across hosts ♻️

Extract the per-host home-manager block (useGlobalPkgs, useUserPackages,
backupFileExtension, users.<name> with username/homeDirectory/optional
stateVersion/optional imports) into nixos/lib/home-manager-user.nix.
Each flake-module now imports it with its per-host parameters, removing
~40 lines of boilerplate across the four hosts.

nixos/flake-modules/daniel-macbook-air.nix

@@ -10,21 +10,12 @@
       ../hosts/daniel-macbook-air.nix
       ../fish.nix
 
-      # Home Manager on macOS
       inputs.home-manager.darwinModules.home-manager
-      ({ lib, ... }: {
-        home-manager.useGlobalPkgs = true;
-        home-manager.useUserPackages = true;
-        # Automatically backup files before home-manager overwrites them
-        home-manager.backupFileExtension = "backup";
-        home-manager.users.danny = { ... }: {
-          # Force an absolute path even if another module sets a bad value.
-          home.username = "danny";
-          home.homeDirectory = lib.mkForce "/Users/danny";
-          imports = [
-            ../home/danny/home.nix
-          ];
-        };
+      (import ../lib/home-manager-user.nix {
+        lib = inputs.nixpkgs.lib;
+        user = "danny";
+        homeDirectory = "/Users/danny";
+        userImports = [ ../home/danny/home.nix ];
       })
     ];
   };

nixos/flake-modules/phantom-ship.nix

@@ -5,17 +5,12 @@
       inputs.nix-openclaw.nixosModules.openclaw-gateway
       ../hosts/phantom-ship.nix
 
-      # Home Manager on NixOS
       inputs.home-manager.nixosModules.home-manager
-      ({ lib, ... }: {
-        home-manager.useGlobalPkgs = true;
-        home-manager.useUserPackages = true;
-        home-manager.backupFileExtension = "backup";
-        home-manager.users.danny = { ... }: {
-          home.username = "danny";
-          home.homeDirectory = lib.mkForce "/home/danny";
-          home.stateVersion = "25.11";
-        };
+      (import ../lib/home-manager-user.nix {
+        lib = inputs.nixpkgs.lib;
+        user = "danny";
+        homeDirectory = "/home/danny";
+        stateVersion = "25.11";
       })
     ];
   };

nixos/flake-modules/sunken-ship.nix

@@ -4,17 +4,12 @@
     modules = [
       ../hosts/sunken-ship.nix
 
-      # Home Manager on NixOS
       inputs.home-manager.nixosModules.home-manager
-      ({ lib, ... }: {
-        home-manager.useGlobalPkgs = true;
-        home-manager.useUserPackages = true;
-        home-manager.backupFileExtension = "backup";
-        home-manager.users.danny = { ... }: {
-          home.username = "danny";
-          home.homeDirectory = lib.mkForce "/home/danny";
-          home.stateVersion = "25.11";
-        };
+      (import ../lib/home-manager-user.nix {
+        lib = inputs.nixpkgs.lib;
+        user = "danny";
+        homeDirectory = "/home/danny";
+        stateVersion = "25.11";
       })
     ];
   };

nixos/flake-modules/wsl.nix

@@ -7,17 +7,12 @@
       ../hosts/wsl.nix
       ../fish.nix
 
-      # Home Manager on WSL
       inputs.home-manager.nixosModules.home-manager
-      ({ lib, ... }: {
-        home-manager.useGlobalPkgs = true;
-        home-manager.useUserPackages = true;
-        home-manager.backupFileExtension = "backup";
-        home-manager.users.dth = { ... }: {
-          home.username = "dth";
-          home.homeDirectory = lib.mkForce "/home/dth";
-          imports = [ ../home/danny/home.nix ];
-        };
+      (import ../lib/home-manager-user.nix {
+        lib = inputs.nixpkgs.lib;
+        user = "dth";
+        homeDirectory = "/home/dth";
+        userImports = [ ../home/danny/home.nix ];
       })
     ];
   };

nixos/lib/home-manager-user.nix

@@ -0,0 +1,35 @@
+# Shared home-manager wiring for NixOS and nix-darwin hosts.
+#
+# Usage (from a flake-module):
+#   modules = [
+#     inputs.home-manager.nixosModules.home-manager   # or .darwinModules
+#     (import ../lib/home-manager-user.nix {
+#       lib = inputs.nixpkgs.lib;
+#       user = "danny";
+#       homeDirectory = "/home/danny";
+#       stateVersion = "25.11";        # optional
+#       userImports = [ ../home/danny/home.nix ]; # optional
+#     })
+#   ];
+{ lib
+, user
+, homeDirectory
+, stateVersion ? null
+, userImports ? [ ]
+}:
+{
+  home-manager.useGlobalPkgs = true;
+  home-manager.useUserPackages = true;
+  # Automatically back up files before home-manager overwrites them.
+  home-manager.backupFileExtension = "backup";
+  home-manager.users.${user} = { ... }: {
+    imports = userImports;
+    home = {
+      username = user;
+      # Force an absolute path even if another module sets a bad value.
+      homeDirectory = lib.mkForce homeDirectory;
+    } // lib.optionalAttrs (stateVersion != null) {
+      stateVersion = stateVersion;
+    };
+  };
+}