diff --git a/AGENTS.md b/AGENTS.md
index efdcb78..66bf32e 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -65,6 +65,7 @@ One flake builds every machine I own.
 
 - Guest modules are host-agnostic wiring, while host files own deployment-specific service configuration such as served volumes and host paths.
   For example, `guests/copyparty.nix` should expose options and translate them into guest mounts/service settings, while `hosts/pikachu/default.nix` chooses `/inbox`, `/media`, and their backing paths.
+  Guest addresses and routes are host-level configuration because a guest module can be used on multiple hosts.
 - `self.lib.registry.collect { hosts = self.nixosConfigurations; }` reads only top-level host `config.registry` declarations.
   Registry declarations inside guest interiors live under `config.containers.<guest>.config.registry`.
   The collected registry does not include those guest-interior declarations.
diff --git a/base.nix b/base.nix
deleted file mode 100644
index b5d2a51..0000000
--- a/base.nix
+++ /dev/null
@@ -1,91 +0,0 @@
-{
-  config,
-  lib,
-  inputs,
-  ...
-}:
-# The shared foundation both the host base and the guest-base build on: the
-# primary user, home-manager, and the fresher/pinned package overlays.
-let
-  inherit (lib) mkOption types;
-  user = config.user;
-
-  # Args to instantiate an extra nixpkgs source on the base platform.
-  pinArgs = prev: {
-    inherit (prev.stdenv.hostPlatform) system;
-    config.allowUnfree = true;
-  };
-in
-{
-  imports = [ inputs.home-manager.nixosModules.home-manager ];
-
-  options.user = {
-    name = mkOption {
-      type = types.str;
-      default = "alexion";
-      description = ''
-        The primary interactive user this system is built for. Drives both the
-        system account and the home-manager user in lockstep.
-      '';
-    };
-    description = mkOption {
-      type = types.str;
-      default = "Alexion";
-      description = "Human-readable description (GECOS field) for the primary user.";
-    };
-  };
-
-  config = {
-    # Reach fresher packages with `unstable.<name>` or pin with `stable.<name>`.
-    nixpkgs.overlays = [
-      (_final: prev: {
-        unstable = import inputs.nixpkgs-unstable (pinArgs prev);
-        stable = import inputs.nixpkgs-stable (pinArgs prev);
-      })
-    ];
-    nixpkgs.config.allowUnfree = true;
-
-    # Flakes, so `nixos-rebuild switch` works from the console and a direnv
-    # `use flake` resolves inside a guest.
-    nix.settings.experimental-features = [
-      "nix-command"
-      "flakes"
-    ];
-
-    # Primary user.
-    # The wheel group is the way in, since root is locked.
-    # No password is set here, since that is host-only.
-    # A guest therefore has none and is reached by SSH key or `machinectl`.
-    users.users.${user.name} = {
-      isNormalUser = true;
-      description = user.description;
-      extraGroups = [
-        "wheel"
-        "storage"
-      ];
-    };
-
-    # The shared write group.
-    # Its gid is fixed, so a host and every guest carry the same number.
-    # An identity-mapped container write then lands on the pool as this group, sparing every service the permission juggling.
-    # 10000 clears the system-group ids assigned automatically and leaves headroom above the primary user, so nothing else claims it.
-    users.groups.storage.gid = 10000;
-
-    # home-manager as a NixOS module: one build produces the system and user
-    # environment together, sharing the system's pkgs and installing user
-    # packages into the system profile.
-    home-manager = {
-      useGlobalPkgs = true;
-      useUserPackages = true;
-      extraSpecialArgs = {
-        inherit inputs;
-        my = inputs.self.lib;
-      };
-      users.${user.name} = {
-        home.username = user.name;
-        home.homeDirectory = "/home/${user.name}";
-        home.stateVersion = "26.05";
-      };
-    };
-  };
-}
diff --git a/guest.nix b/guest.nix
deleted file mode 100644
index 556a835..0000000
--- a/guest.nix
+++ /dev/null
@@ -1,32 +0,0 @@
-{
-  my,
-  inputs,
-  lib,
-  ...
-}:
-# The guest-base: the slim foundation every nested guest's interior stands on.
-# It imports the full modules tree so any module is available to enable inside a
-# guest, and stands on the same shared base a host does.
-{
-  imports = my.collectNixFiles (inputs.self + "/modules") ++ [
-    (inputs.self + "/base.nix")
-
-    # The modules tree reaches for these option namespaces, so they must be
-    # declared for the tree to evaluate even where a guest leaves them off.
-    my.registry.module
-    inputs.sops-nix.nixosModules.sops
-    inputs.stylix.nixosModules.stylix
-  ];
-
-  # A nested container has no per-host `default.nix` to pin its release.
-  system.stateVersion = "26.05";
-
-  # The baseline toolset and SSH access, so any guest shelled into is a workable
-  # environment without per-guest wiring.
-  modules.toolkit.enable = lib.mkDefault true;
-  modules.ssh.enable = lib.mkDefault true;
-
-  # A guest carries no host identity, so it presents a self-generated host key
-  # rather than restoring one from secrets.
-  modules.ssh.hostKeys.restore = lib.mkDefault false;
-}
diff --git a/hosts/neogaia/default.nix b/hosts/neogaia/default.nix
index bb25b69..b73669a 100644
--- a/hosts/neogaia/default.nix
+++ b/hosts/neogaia/default.nix
@@ -40,8 +40,6 @@
   modules.ssh.hostKeys.sopsFile = ../../secrets/neogaia.yaml;
   modules.ssh.userKey.sopsFile = ../../secrets/neogaia.yaml;
 
-  modules.toolkit.enable = true;
-
   # The walking-skeleton guest, enabled like any module: proves the guest path
   # end to end through this host's `nix flake check`.
   # Modest caps keep the skeleton guest from starving the laptop.
diff --git a/hosts/pikachu/default.nix b/hosts/pikachu/default.nix
index 77edd8e..724de55 100644
--- a/hosts/pikachu/default.nix
+++ b/hosts/pikachu/default.nix
@@ -79,8 +79,6 @@
   modules.ssh.userKey.sopsFile = ../../secrets/pikachu.yaml;
 
   modules.git.enable = true;
-  modules.toolkit.enable = true;
-
   guests.actualbudget = {
     enable = true;
     vlan = 20;
diff --git a/lib/default.nix b/lib/default.nix
index 94b1e88..7826de4 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -32,6 +32,9 @@ let
       ) (builtins.readDir dir)
     );
 
+  moduleFiles = collectNixFiles (self + "/modules");
+  guestFiles = collectNixFiles (self + "/guests");
+
   specialArgs = {
     inherit inputs self;
     my = self.lib;
@@ -42,10 +45,13 @@ let
 
   guests = import ./guests.nix {
     inherit
+      inputs
       lib
       self
       specialArgs
       bridgeName
+      moduleFiles
+      registry
       ;
   };
 
@@ -57,17 +63,19 @@ let
     inputs.nixpkgs.lib.nixosSystem {
       inherit system specialArgs;
       modules =
-        (collectNixFiles (self + "/modules"))
-        ++ (collectNixFiles (self + "/guests"))
+        moduleFiles
+        ++ guestFiles
         ++ [
           inputs.chaotic.nixosModules.default
           inputs.disko.nixosModules.disko
           inputs.sops-nix.nixosModules.sops
           inputs.stylix.nixosModules.stylix
           registry.module
-          (self + "/system.nix")
           (self + "/hosts/${hostName}")
-          { networking.hostName = hostName; }
+          {
+            networking.hostName = hostName;
+            modules.host.enable = true;
+          }
         ];
     };
 
diff --git a/lib/guests.nix b/lib/guests.nix
index 1c1a0fe..ba1a78f 100644
--- a/lib/guests.nix
+++ b/lib/guests.nix
@@ -1,8 +1,11 @@
 {
+  inputs,
   lib,
   self,
   specialArgs,
   bridgeName,
+  moduleFiles,
+  registry,
 }:
 let
   inherit (lib) escapeShellArg mapAttrsToList;
@@ -345,11 +348,18 @@ let
           inherit specialArgs;
 
           config = {
-            imports = [
-              (self + "/guest.nix")
-              guestNet
-              interior
-            ];
+            imports =
+              moduleFiles
+              ++ [
+                registry.module
+                inputs.sops-nix.nixosModules.sops
+                inputs.stylix.nixosModules.stylix
+                {
+                  modules.guest.enable = true;
+                }
+                guestNet
+                interior
+              ];
           };
         };
       };
diff --git a/modules/default.nix b/modules/default.nix
new file mode 100644
index 0000000..d5910ba
--- /dev/null
+++ b/modules/default.nix
@@ -0,0 +1,126 @@
+{
+  config,
+  lib,
+  pkgs,
+  inputs,
+  ...
+}:
+# The shared foundation for every host and guest.
+let
+  inherit (lib) mkOption types;
+  user = config.user;
+
+  pinArgs = prev: {
+    inherit (prev.stdenv.hostPlatform) system;
+    config.allowUnfree = true;
+  };
+in
+{
+  imports = [ inputs.home-manager.nixosModules.home-manager ];
+
+  options.user = {
+    name = mkOption {
+      type = types.str;
+      default = "alexion";
+      description = ''
+        Primary interactive user for this system.
+        This drives the system account and Home Manager user together.
+      '';
+    };
+    description = mkOption {
+      type = types.str;
+      default = "Alexion";
+      description = "Human-readable description for the primary user.";
+    };
+  };
+
+  config = {
+    nixpkgs.overlays = [
+      (_final: prev: {
+        unstable = import inputs.nixpkgs-unstable (pinArgs prev);
+        stable = import inputs.nixpkgs-stable (pinArgs prev);
+      })
+    ];
+    nixpkgs.config.allowUnfree = true;
+
+    nix.settings.experimental-features = [
+      "nix-command"
+      "flakes"
+    ];
+
+    users.users.${user.name} = {
+      isNormalUser = true;
+      description = user.description;
+      extraGroups = [
+        "wheel"
+        "storage"
+      ];
+    };
+
+    users.groups.storage.gid = 10000;
+
+    home-manager = {
+      useGlobalPkgs = true;
+      useUserPackages = true;
+      extraSpecialArgs = {
+        inherit inputs;
+        my = inputs.self.lib;
+      };
+      users.${user.name} = {
+        home.username = user.name;
+        home.homeDirectory = "/home/${user.name}";
+        home.stateVersion = "26.05";
+        home.packages = with pkgs; [
+          eza
+          wget
+        ];
+      };
+    };
+
+    registry.shell-shortcut.${config.networking.hostName} = {
+      ls = {
+        command = "eza -alg --color=always --group-directories-first --icons=always";
+        abbreviation = false;
+      };
+      la = {
+        command = "eza -a --color=always --group-directories-first --icons=always";
+        abbreviation = false;
+      };
+      ll = {
+        command = "eza -lg --color=always --group-directories-first --icons=always";
+        abbreviation = false;
+      };
+      lt = {
+        command = "eza -aT -I '.git' --color=always --group-directories-first --icons=always";
+        abbreviation = false;
+      };
+      "l." = {
+        command = "eza -a | grep -e '^\\.'";
+        abbreviation = false;
+      };
+
+      ".." = "cd ..";
+      "..." = "cd ../..";
+      "...." = "cd ../../..";
+
+      cp = "cp -v";
+      tarnow = "tar -acf ";
+      untar = "tar -zxvf ";
+      wget = "wget -c ";
+      grep = "grep --color=auto";
+      fgrep = "fgrep --color=auto";
+      egrep = "egrep --color=auto";
+      jctl = "journalctl -p 3 -xb";
+
+      update = "sudo nixos-rebuild switch --flake .#${config.networking.hostName}";
+      cleanup = "sudo nix-collect-garbage -d";
+    };
+
+    modules.fish.enable = lib.mkDefault true;
+    modules.fish.defaultShell = lib.mkDefault true;
+    modules.tmux.enable = lib.mkDefault true;
+    modules.nvim.enable = lib.mkDefault true;
+    modules.git.enable = lib.mkDefault true;
+    modules.direnv.enable = lib.mkDefault true;
+  };
+}
diff --git a/modules/guest.nix b/modules/guest.nix
new file mode 100644
index 0000000..57b1070
--- /dev/null
+++ b/modules/guest.nix
@@ -0,0 +1,14 @@
+{ config, lib, ... }:
+let
+  cfg = config.modules.guest;
+in
+{
+  options.modules.guest.enable = lib.mkEnableOption "nested-guest base configuration";
+
+  config = lib.mkIf cfg.enable {
+    system.stateVersion = "26.05";
+
+    modules.ssh.enable = lib.mkDefault true;
+    modules.ssh.hostKeys.restore = lib.mkDefault false;
+  };
+}
diff --git a/modules/host.nix b/modules/host.nix
new file mode 100644
index 0000000..993702c
--- /dev/null
+++ b/modules/host.nix
@@ -0,0 +1,42 @@
+{
+  config,
+  lib,
+  ...
+}:
+let
+  cfg = config.modules.host;
+  user = config.user;
+  passwordSecret = "${user.name}-password";
+in
+{
+  options.modules.host.enable = lib.mkEnableOption "physical-host base configuration";
+
+  config = lib.mkIf cfg.enable {
+    nix.settings.extra-substituters = [ "https://nyx-cache.chaotic.cx/" ];
+    nix.settings.extra-trusted-public-keys = [
+      "nyx-cache.chaotic.cx:dJxTrgMC3V3cFfyIiBQDQorG6k1LsqurH/srpMSq7qk="
+    ];
+
+    nix.gc.automatic = true;
+    nix.gc.dates = "Mon 03:15";
+    nix.gc.options = "--delete-older-than 30d";
+
+    nix.optimise.automatic = true;
+    nix.optimise.dates = [ "Thu 03:45" ];
+
+    boot.loader.systemd-boot.configurationLimit = 15;
+
+    services.xserver.xkb.layout = "us";
+    services.xserver.xkb.options = "caps:escape_shifted_capslock";
+    console.useXkbConfig = true;
+
+    sops.defaultSopsFile = ../secrets/shared.yaml;
+    sops.age.keyFile = "/var/lib/sops-nix/key.txt";
+    sops.age.sshKeyPaths = [ ];
+    sops.gnupg.sshKeyPaths = [ ];
+
+    users.mutableUsers = false;
+    sops.secrets.${passwordSecret}.neededForUsers = true;
+    users.users.${user.name}.hashedPasswordFile = config.sops.secrets.${passwordSecret}.path;
+  };
+}
diff --git a/modules/toolkit.nix b/modules/toolkit.nix
deleted file mode 100644
index 564d765..0000000
--- a/modules/toolkit.nix
+++ /dev/null
@@ -1,72 +0,0 @@
-{
-  config,
-  lib,
-  pkgs,
-  ...
-}:
-# The baseline interactive toolset as one deliberate bundle.
-let
-  cfg = config.modules.toolkit;
-  user = config.user.name;
-in
-{
-  options.modules.toolkit.enable =
-    lib.mkEnableOption "the baseline interactive environment — fish, tmux, nvim, git, and direnv — as one unit";
-
-  # Each piece is turned on at default priority, so a host can still override any one of them.
-  config = lib.mkIf cfg.enable {
-    home-manager.users.${user}.home.packages = with pkgs; [
-      eza
-      wget
-    ];
-
-    registry.shell-shortcut.${config.networking.hostName} = {
-      ls = {
-        command = "eza -alg --color=always --group-directories-first --icons=always";
-        abbreviation = false;
-      };
-      la = {
-        command = "eza -a --color=always --group-directories-first --icons=always";
-        abbreviation = false;
-      };
-      ll = {
-        command = "eza -lg --color=always --group-directories-first --icons=always";
-        abbreviation = false;
-      };
-      lt = {
-        command = "eza -aT -I '.git' --color=always --group-directories-first --icons=always";
-        abbreviation = false;
-      };
-      "l." = {
-        command = "eza -a | grep -e '^\\.'";
-        abbreviation = false;
-      };
-
-      # Walk up the tree.
-      ".." = "cd ..";
-      "..." = "cd ../..";
-      "...." = "cd ../../..";
-
-      cp = "cp -v";
-      tarnow = "tar -acf ";
-      untar = "tar -zxvf ";
-      wget = "wget -c ";
-      grep = "grep --color=auto";
-      fgrep = "fgrep --color=auto";
-      egrep = "egrep --color=auto";
-      jctl = "journalctl -p 3 -xb";
-
-      # Rebuild the system, and reclaim disk from old generations.
-      update = "sudo nixos-rebuild switch --flake .#${config.networking.hostName}";
-      cleanup = "sudo nix-collect-garbage -d";
-    };
-
-    modules.fish.enable = lib.mkDefault true;
-    # fish is also the login shell, so the bundled environment is what a shell drops into.
-    modules.fish.defaultShell = lib.mkDefault true;
-    modules.tmux.enable = lib.mkDefault true;
-    modules.nvim.enable = lib.mkDefault true;
-    modules.git.enable = lib.mkDefault true;
-    modules.direnv.enable = lib.mkDefault true;
-  };
-}
diff --git a/system.nix b/system.nix
deleted file mode 100644
index 8c23708..0000000
--- a/system.nix
+++ /dev/null
@@ -1,75 +0,0 @@
-{
-  config,
-  lib,
-  pkgs,
-  ...
-}:
-# The host base: the host-only machinery a physical machine needs on top of the
-# shared base — bootloader, secret decryption, and the maintenance timers.
-let
-  user = config.user;
-
-  passwordSecret = "${user.name}-password";
-in
-{
-  imports = [ ./base.nix ];
-
-  # chaotic's binary cache, so the CachyOS kernel is fetched rather than compiled.
-  # The `extra-` prefix keeps cache.nixos.org alongside it.
-  nix.settings.extra-substituters = [ "https://nyx-cache.chaotic.cx/" ];
-  nix.settings.extra-trusted-public-keys = [
-    "nyx-cache.chaotic.cx:dJxTrgMC3V3cFfyIiBQDQorG6k1LsqurH/srpMSq7qk="
-  ];
-
-  # A month of generations is kept, because on a rolling channel with a
-  # third-party kernel an old generation is a known-good system to boot when
-  # an update breaks something.
-  nix.gc.automatic = true;
-  nix.gc.dates = "Mon 03:15";
-  nix.gc.options = "--delete-older-than 30d";
-
-  # Deduplication runs on a timer, off the rebuild path, so it never adds
-  # latency to a `nixos-rebuild switch`.
-  # It falls on a different day from collection, so the two never contend.
-  nix.optimise.automatic = true;
-  nix.optimise.dates = [ "Thu 03:45" ];
-
-  # The EFI system partition holds a kernel and an initrd per entry at roughly
-  # 70 MiB apiece, and is fixed in size.
-  # An exhausted one fails at bootloader installation, after the build has
-  # already succeeded.
-  boot.loader.systemd-boot.configurationLimit = 15;
-
-  environment.systemPackages = [ pkgs.git ];
-
-  # Caps Lock is a second Escape.
-  # Shift+Caps Lock still toggles Caps Lock.
-  services.xserver.xkb.layout = "us";
-  services.xserver.xkb.options = "caps:escape_shifted_capslock";
-
-  # Compile the console keymap from the layout above, so the remap holds on a
-  # bare TTY and not only under a graphical session.
-  console.useXkbConfig = true;
-
-  # Decryption machinery every host depends on.
-  # The identity sits on the encrypted root, which is mounted early enough to
-  # satisfy the secret below.
-  # Clearing both `sshKeyPaths` defaults keeps the SSH host keys out of the
-  # decryption path.
-  sops.defaultSopsFile = ./secrets/shared.yaml;
-  sops.age.keyFile = "/var/lib/sops-nix/key.txt";
-  sops.age.sshKeyPaths = [ ];
-  sops.gnupg.sshKeyPaths = [ ];
-
-  # A password set by hand on a running machine otherwise takes precedence.
-  # That leaves the declared `hashedPasswordFile` below silently inert.
-  # Root has no declared password and is therefore locked.
-  # `sudo` from the wheel group is the way in.
-  users.mutableUsers = false;
-
-  # Decrypted in an earlier activation stage than ordinary secrets.
-  # That is early enough to precede the account that reads it.
-  sops.secrets.${passwordSecret}.neededForUsers = true;
-
-  users.users.${user.name}.hashedPasswordFile = config.sops.secrets.${passwordSecret}.path;
-}