refactor(guest): assemble guest modules

flake/guest.nix

@@ -6,12 +6,9 @@
   registryAssembly,
   util,
 }:
-{
+let
   mkGuest =
-    {
-      name,
-      interior ? { },
-    }:
+    name:
     { config, lib, ... }:
     let
       cfg = config.guests.${name};
@@ -131,6 +128,11 @@
             Mounts are read-write unless `readOnly` is set.
           '';
         };
+        interior = lib.mkOption {
+          type = lib.types.deferredModule;
+          default = { };
+          description = "NixOS module imported into the guest interior.";
+        };
         limits = {
           memory = lib.mkOption {
             type = lib.types.nullOr lib.types.str;
@@ -246,7 +248,7 @@
 
               repositoryModules
               registryAssembly.module
-              interior
+              cfg.interior
 
               {
                 modules.guest.enable = true;
@@ -265,4 +267,16 @@
         };
       };
     };
+in
+{
+  mkGuests =
+    { root }:
+    let
+      files = util.collectNixFiles root;
+      guestFiles = lib.filterAttrs (file: type: type == "regular" && lib.hasSuffix ".nix" file) (builtins.readDir root);
+      names = map (file: lib.removeSuffix ".nix" file) (lib.attrNames guestFiles);
+    in
+    {
+      imports = files ++ map mkGuest names;
+    };
 }