diff --git a/lib/default.nix b/lib/default.nix
index f490aaa..8e3f1ba 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -10,14 +10,10 @@ let
     genAttrs
     flatten
     hasSuffix
-    escapeShellArg
     mapAttrsToList
     ;
 
   serviceIdentityRegistry = import ./service-identities.nix { inherit lib; };
-
-  # Recursively collect every `.nix` file under `dir` as a flat list, for a
-  # module's `imports`.
   collectNixFiles =
     dir:
     flatten (
@@ -35,32 +31,22 @@ let
       ) (builtins.readDir dir)
     );
 
-  # The special arguments every configuration is evaluated with, host and guest
-  # interior alike.
   specialArgs = {
     inherit inputs;
     my = self.lib;
   };
 
-  # The name of a tagged VLAN's bridge, kept here as the one definition of a
-  # convention shared across the flake.
   bridgeName = id: "br-vlan${toString id}";
 
-  # A guest with no operator-set MAC derives a stable one from its namespace path.
-  # The first octet 02 marks the address locally-administered and unicast.
-  # The rest is a slice of the path's hash.
-  # The same guest therefore always lands on the same address, which the operator can reserve at the router.
-  deriveMac =
-    name:
-    let
-      hash = builtins.hashString "sha256" name;
-      octet = i: builtins.substring (i * 2) 2 hash;
-    in
-    lib.concatStringsSep ":" ([ "02" ] ++ map octet [ 0 1 2 3 4 ]);
+  guests = import ./guests.nix {
+    inherit
+      lib
+      self
+      specialArgs
+      bridgeName
+      ;
+  };
 
-  # Build one host: every module and every guest is imported unconditionally
-  # (inert until its `enable` flag is set), alongside chaotic, the host base,
-  # and the host's own directory.
   mkHost =
     {
       hostName,
@@ -82,379 +68,6 @@ let
         ];
     };
 
-  # Build a guest: a module-shaped definition whose body realizes its interior
-  # as a nested container standing on the guest-base, keyed by its namespace path.
-  # `name` is the dotted namespace under `guests.` and `interior` is an extra
-  # module merged into the container alongside the guest-base.
-  guest =
-    {
-      name,
-      interior ? { },
-    }:
-    { config, lib, ... }:
-    let
-      optionPath = [ "guests" ] ++ lib.splitString "." name;
-      cfg = lib.getAttrFromPath optionPath config;
-      machineName = lib.replaceStrings [ "." ] [ "-" ] name;
-
-      networked = cfg.vlan != null;
-
-      # Host paths the operator maps into the guest, keyed by their in-guest path.
-      userMounts = lib.mapAttrs (_guestPath: m: {
-        inherit (m) hostPath;
-        isReadOnly = m.readOnly;
-      }) cfg.mounts;
-
-      # Each named secret bind-mounted read-only at the same `/run/secrets/<name>`
-      # path it holds on the host.
-      # No ownership is set here, since the container's one-to-one identity map
-      # carries the host file's owner through unchanged.
-      secretMounts = lib.listToAttrs (
-        map (
-          name:
-          let
-            path = config.sops.secrets.${name}.path;
-          in
-          lib.nameValuePair path {
-            hostPath = path;
-            isReadOnly = true;
-          }
-        ) cfg.secrets
-      );
-
-      # An in-guest path claimed by both a mount and a secret, which the merge
-      # below would otherwise resolve silently in the secret's favour.
-      mountCollisions = lib.attrNames (builtins.intersectAttrs userMounts secretMounts);
-
-      # The resource caps the operator places on the guest's unit, dropping any
-      # left unset so systemd keeps its uncapped default for those.
-      limitConfig = lib.filterAttrs (_: v: v != null) {
-        MemoryMax = cfg.limits.memory;
-        CPUQuota = cfg.limits.cpu;
-        TasksMax = cfg.limits.tasksMax;
-      };
-
-      createdMounts = lib.filterAttrs (_guestPath: m: m.create != null) cfg.mounts;
-      mountCreateScript = lib.concatStringsSep "\n" (
-        mapAttrsToList (
-          _guestPath: m:
-          let
-            create = m.create;
-          in
-          ''
-            ${config.system.path}/bin/install -d -o ${escapeShellArg (toString create.owner)} -g ${escapeShellArg create.group} -m ${escapeShellArg create.mode} ${escapeShellArg m.hostPath}
-          ''
-        ) createdMounts
-      );
-
-      # A networked guest owns its bridged interface through its own networkd, the only stable MAC pin for a nested container.
-      # The interface is eth0, the name a nested container gives its bridged veth.
-      # It takes the placement MAC, and the static address or DHCP when that is unset.
-      guestNet =
-        { lib, ... }:
-        {
-          config = lib.mkIf networked {
-            networking.useNetworkd = true;
-
-            # networkd default-enables resolved, which owns the guest's resolv.conf.
-            # The nested-container default of inheriting the host's file conflicts with that, so the guest keeps its own.
-            networking.useHostResolvConf = false;
-
-            systemd.network.networks."20-eth0" = {
-              matchConfig.Name = "eth0";
-              linkConfig.MACAddress = cfg.mac;
-              networkConfig = lib.mkIf (cfg.address == null) { DHCP = "yes"; };
-              address = lib.mkIf (cfg.address != null) [ cfg.address ];
-            };
-          };
-        };
-    in
-    {
-      options = lib.setAttrByPath optionPath {
-        enable = lib.mkEnableOption "the ${name} guest, run in its own nested container";
-        backend = lib.mkOption {
-          type = lib.types.enum [
-            "container"
-            "microvm"
-          ];
-          default = "container";
-          description = ''
-            How the guest is realized. `container` runs the guest as a
-            systemd-nspawn nested container. `microvm` is reserved for a future
-            hard-isolation backend and is not built yet.
-          '';
-        };
-        vlan = lib.mkOption {
-          type = lib.types.nullOr (lib.types.ints.between 1 4094);
-          default = null;
-          example = 10;
-          description = ''
-            The tagged VLAN this guest lives on. The guest attaches to its host's
-            `br-vlan<id>` bridge for that VLAN. Left null, the guest keeps a
-            private network with no bridge attachment. The id must be one of the
-            host's `modules.network.vlans`.
-          '';
-        };
-        mac = lib.mkOption {
-          type = lib.types.str;
-          default = deriveMac name;
-          defaultText = lib.literalMD "a stable address derived from the guest's namespace path";
-          example = "bc:24:11:00:00:01";
-          description = ''
-            The guest's MAC address on its VLAN, pinned inside the guest by its
-            own networkd. Set it to reuse an existing address so a router's DHCP
-            reservation keeps working. Left unset, a stable address is derived
-            from the guest's namespace path in the locally-administered range.
-          '';
-        };
-        address = lib.mkOption {
-          type = lib.types.nullOr lib.types.str;
-          default = null;
-          example = "10.0.10.5/24";
-          description = ''
-            The guest's static address, in CIDR form, on its VLAN. Left null, the
-            guest takes its address by DHCP, keeping IP management at the router.
-          '';
-        };
-        mounts = lib.mkOption {
-          type = lib.types.attrsOf (
-            lib.types.submodule {
-              options = {
-                hostPath = lib.mkOption {
-                  type = lib.types.str;
-                  example = "/srv/media";
-                  description = "The path on the host bind-mounted into the guest.";
-                };
-                readOnly = lib.mkOption {
-                  type = lib.types.bool;
-                  default = false;
-                  description = ''
-                    Mount the path read-only. Read-write by default, since a
-                    service must write to the pool data it owns.
-                  '';
-                };
-                create = lib.mkOption {
-                  type = lib.types.nullOr (lib.types.submodule {
-                    options = {
-                      type = lib.mkOption {
-                        type = lib.types.enum [ "directory" ];
-                        default = "directory";
-                        description = "Host path type to create before the guest starts.";
-                      };
-                      owner = lib.mkOption {
-                        type = lib.types.oneOf [
-                          lib.types.str
-                          lib.types.ints.positive
-                        ];
-                        description = "Owner assigned to the created host path.";
-                      };
-                      group = lib.mkOption {
-                        type = lib.types.str;
-                        description = "Group assigned to the created host path.";
-                      };
-                      mode = lib.mkOption {
-                        type = lib.types.str;
-                        example = "0770";
-                        description = "Mode assigned to the created host path.";
-                      };
-                    };
-                  });
-                  default = null;
-                  description = ''
-                    Opt-in host path creation before the guest starts. Existing
-                    paths are left enabled unless this is set, so served storage
-                    roots can still be required to exist explicitly.
-                  '';
-                };
-              };
-            }
-          );
-          default = { };
-          example = lib.literalExpression ''
-            {
-              "/data/media" = { hostPath = "/srv/media"; };
-              "/data/config" = {
-                hostPath = "/srv/config/jellyfin";
-                readOnly = true;
-              };
-            }
-          '';
-          description = ''
-            Host paths bind-mounted into the guest, keyed by the path they appear
-            at inside the guest, so a guest sees exactly the data it should at any
-            granularity — a single folder or a whole pool. Each mount is
-            read-write unless `readOnly` is set.
-          '';
-        };
-        secrets = lib.mkOption {
-          type = lib.types.listOf lib.types.str;
-          default = [ ];
-          example = [ "jellyfin-api-key" ];
-          description = ''
-            Names of the secrets this guest needs. The host is the sole
-            decryptor: it decrypts each named secret from its own sops files and
-            bind-mounts the plaintext file into the guest read-only at
-            `/run/secrets/<name>`, the same path it would occupy on a host, so a
-            service reads its credentials at a predictable location. The guest
-            names the files it wants and receives exactly those. It holds no age
-            key and decrypts nothing itself. Ownership carries across unchanged,
-            since the container maps ids one to one, so a secret owned by a uid on
-            the host is owned by that same uid inside the guest.
-          '';
-        };
-        limits = {
-          memory = lib.mkOption {
-            type = lib.types.nullOr lib.types.str;
-            default = null;
-            example = "2G";
-            description = ''
-              Cap on the guest's memory, applied to its unit as `MemoryMax`.
-              Accepts systemd size suffixes such as `512M` or `2G`. Left null,
-              the guest's memory is uncapped.
-            '';
-          };
-          cpu = lib.mkOption {
-            type = lib.types.nullOr lib.types.str;
-            default = null;
-            example = "150%";
-            description = ''
-              Cap on the guest's CPU, applied to its unit as `CPUQuota`, where
-              `100%` is one full core. Left null, the guest's CPU is uncapped.
-            '';
-          };
-          tasksMax = lib.mkOption {
-            type = lib.types.nullOr lib.types.ints.positive;
-            default = null;
-            example = 512;
-            description = ''
-              Cap on the number of processes and threads the guest may spawn,
-              applied to its unit as `TasksMax`. Left null, the task count is
-              uncapped.
-            '';
-          };
-        };
-        nesting = lib.mkOption {
-          type = lib.types.bool;
-          default = false;
-          description = ''
-            Grant the guest's interior the prerequisites to run Podman or other
-            OCI containers of its own. Off by default, so a guest cannot nest
-            containers. On, the guest's container gains the network-administration
-            capability its container runtime uses to build bridges and firewall
-            rules, along with the tun and fuse device nodes such a runtime reaches
-            for, so the interior's `virtualisation.oci-containers` works with
-            Podman as its default runtime.
-          '';
-        };
-        autoStart = lib.mkOption {
-          type = lib.types.bool;
-          default = true;
-          description = ''
-            Start the guest at boot. On by default. Disabled, the guest stays
-            defined and can be started on demand, but does not come up at boot.
-          '';
-        };
-      };
-
-      config = lib.mkIf cfg.enable {
-        # Declared here so the host is the one that decrypts each named secret.
-        # The guest carries no age key and decrypts nothing of its own.
-        sops.secrets = lib.genAttrs cfg.secrets (_: { });
-
-        assertions = [
-          {
-            assertion = mountCollisions == [ ];
-            message = ''
-              guests.${name} maps a mount at ${lib.concatStringsSep ", " mountCollisions}, colliding with a secret bind-mounted at the same path. Rename the mount or the secret so each in-guest path is used once.
-            '';
-          }
-          {
-            assertion = cfg.backend == "container";
-            message = ''
-              guests.${name}.backend = "${cfg.backend}" is not implemented. Only the "container" backend is built; "microvm" is reserved for future work.
-            '';
-          }
-          {
-            assertion = !networked || lib.elem cfg.vlan config.modules.network.vlans;
-            message = ''
-              guests.${name}.vlan = ${toString cfg.vlan} is not among its host's modules.network.vlans (${lib.concatMapStringsSep ", " toString config.modules.network.vlans}). Declare the VLAN on the host or correct the guest's placement.
-            '';
-          }
-        ];
-
-        # The operator's resource caps land on the guest's own unit, which a
-        # networked guest also orders after the bridge its veth enslaves to at
-        # start, since the container backend orders the unit after the network
-        # is up but not after that specific bridge existing.
-        systemd.services."container@${machineName}" = lib.mkIf (cfg.backend == "container") (
-          lib.mkMerge [
-            {
-              serviceConfig = limitConfig;
-              preStart = lib.mkIf (createdMounts != { }) mountCreateScript;
-            }
-            (lib.mkIf networked (
-              let
-                bridgeDevice = "sys-subsystem-net-devices-${lib.replaceStrings [ "-" ] [ "\\x2d" ] (bridgeName cfg.vlan)}.device";
-              in
-              {
-                after = [ bridgeDevice ];
-                wants = [ bridgeDevice ];
-              }
-            ))
-          ]
-        );
-
-        containers.${machineName} = lib.mkIf (cfg.backend == "container") {
-          autoStart = cfg.autoStart;
-
-          # The guest gets its own network namespace, so its services — its own
-          # sshd included — never contend with the host's.
-          privateNetwork = lib.mkDefault true;
-
-          # A networked guest's veth is enslaved to the VLAN's bridge, making it
-          # a first-class L2 citizen on that segment.
-          hostBridge = lib.mkIf networked (bridgeName cfg.vlan);
-
-          # The container shares the host's uid and gid space one to one.
-          # A guest process writing as the shared storage group then lands on a bind-mounted pool as that same group, with no permission juggling.
-          # A private-user mapping would shift the ids and reintroduce those errors, so it stays off.
-          privateUsers = lib.mkDefault "no";
-
-          # A nesting guest runs Podman or other OCI containers in its interior.
-          # The network-administration capability lets that runtime build its
-          # bridges and firewall rules.
-          # The tun and fuse device nodes are what it reaches for to network
-          # those containers and back their overlay storage.
-          # The remaining prerequisite, a delegated cgroup subtree for the
-          # runtime to manage, the container backend already grants every guest.
-          additionalCapabilities = lib.optionals cfg.nesting [ "CAP_NET_ADMIN" ];
-          allowedDevices = lib.optionals cfg.nesting [
-            {
-              node = "/dev/net/tun";
-              modifier = "rwm";
-            }
-            {
-              node = "/dev/fuse";
-              modifier = "rwm";
-            }
-          ];
-
-          bindMounts = userMounts // secretMounts;
-
-          inherit specialArgs;
-
-          config = {
-            imports = [
-              (self + "/guest.nix")
-              guestNet
-              interior
-            ];
-          };
-        };
-      };
-    };
-
-  # Discover every host (a subdirectory of `hostsDir`) and build each one.
   mkHosts =
     hostsDir:
     let
@@ -467,9 +80,11 @@ in
     collectNixFiles
     mkHost
     mkHosts
-    guest
     bridgeName
     ;
+
+  inherit (guests) deriveMac guest;
+
   inherit (serviceIdentityRegistry) serviceUid;
   serviceIdentities = serviceIdentityRegistry.identities;
 }
diff --git a/lib/guests.nix b/lib/guests.nix
new file mode 100644
index 0000000..e9a0555
--- /dev/null
+++ b/lib/guests.nix
@@ -0,0 +1,349 @@
+{
+  lib,
+  self,
+  specialArgs,
+  bridgeName,
+}:
+let
+  inherit (lib) escapeShellArg mapAttrsToList;
+
+  deriveMac =
+    name:
+    let
+      hash = builtins.hashString "sha256" name;
+      octet = i: builtins.substring (i * 2) 2 hash;
+    in
+    lib.concatStringsSep ":" ([ "02" ] ++ map octet [ 0 1 2 3 4 ]);
+
+  guest =
+    {
+      name,
+      interior ? { },
+    }:
+    { config, lib, ... }:
+    let
+      optionPath = [ "guests" ] ++ lib.splitString "." name;
+      cfg = lib.getAttrFromPath optionPath config;
+      machineName = lib.replaceStrings [ "." ] [ "-" ] name;
+
+      networked = cfg.vlan != null;
+
+      userMounts = lib.mapAttrs (_guestPath: m: {
+        inherit (m) hostPath;
+        isReadOnly = m.readOnly;
+      }) cfg.mounts;
+
+      secretMounts = lib.listToAttrs (
+        map (
+          name:
+          let
+            path = config.sops.secrets.${name}.path;
+          in
+          lib.nameValuePair path {
+            hostPath = path;
+            isReadOnly = true;
+          }
+        ) cfg.secrets
+      );
+
+      mountCollisions = lib.attrNames (builtins.intersectAttrs userMounts secretMounts);
+
+      limitConfig = lib.filterAttrs (_: v: v != null) {
+        MemoryMax = cfg.limits.memory;
+        CPUQuota = cfg.limits.cpu;
+        TasksMax = cfg.limits.tasksMax;
+      };
+
+      createdMounts = lib.filterAttrs (_guestPath: m: m.create != null) cfg.mounts;
+      mountCreateScript = lib.concatStringsSep "\n" (
+        mapAttrsToList (
+          _guestPath: m:
+          let
+            create = m.create;
+          in
+          ''
+            ${config.system.path}/bin/install -d -o ${escapeShellArg (toString create.owner)} -g ${escapeShellArg create.group} -m ${escapeShellArg create.mode} ${escapeShellArg m.hostPath}
+          ''
+        ) createdMounts
+      );
+
+      guestNet =
+        { lib, ... }:
+        {
+          config = lib.mkIf networked {
+            networking.useNetworkd = true;
+            networking.useHostResolvConf = false;
+
+            systemd.network.networks."20-eth0" = {
+              matchConfig.Name = "eth0";
+              linkConfig.MACAddress = cfg.mac;
+              networkConfig = lib.mkIf (cfg.address == null) { DHCP = "yes"; };
+              address = lib.mkIf (cfg.address != null) [ cfg.address ];
+            };
+          };
+        };
+    in
+    {
+      options = lib.setAttrByPath optionPath {
+        enable = lib.mkEnableOption "the ${name} guest, run in its own nested container";
+        backend = lib.mkOption {
+          type = lib.types.enum [
+            "container"
+            "microvm"
+          ];
+          default = "container";
+          description = ''
+            How the guest is realized. `container` runs the guest as a
+            systemd-nspawn nested container. `microvm` is reserved for a future
+            hard-isolation backend and is not built yet.
+          '';
+        };
+        vlan = lib.mkOption {
+          type = lib.types.nullOr (lib.types.ints.between 1 4094);
+          default = null;
+          example = 10;
+          description = ''
+            The tagged VLAN this guest lives on. The guest attaches to its host's
+            `br-vlan<id>` bridge for that VLAN. Left null, the guest keeps a
+            private network with no bridge attachment. The id must be one of the
+            host's `modules.network.vlans`.
+          '';
+        };
+        mac = lib.mkOption {
+          type = lib.types.str;
+          default = deriveMac name;
+          defaultText = lib.literalMD "a stable address derived from the guest's namespace path";
+          example = "bc:24:11:00:00:01";
+          description = ''
+            The guest's MAC address on its VLAN, pinned inside the guest by its
+            own networkd. Set it to reuse an existing address so a router's DHCP
+            reservation keeps working. Left unset, a stable address is derived
+            from the guest's namespace path in the locally-administered range.
+          '';
+        };
+        address = lib.mkOption {
+          type = lib.types.nullOr lib.types.str;
+          default = null;
+          example = "10.0.10.5/24";
+          description = ''
+            The guest's static address, in CIDR form, on its VLAN. Left null, the
+            guest takes its address by DHCP, keeping IP management at the router.
+          '';
+        };
+        mounts = lib.mkOption {
+          type = lib.types.attrsOf (
+            lib.types.submodule {
+              options = {
+                hostPath = lib.mkOption {
+                  type = lib.types.str;
+                  example = "/srv/media";
+                  description = "The path on the host bind-mounted into the guest.";
+                };
+                readOnly = lib.mkOption {
+                  type = lib.types.bool;
+                  default = false;
+                  description = ''
+                    Mount the path read-only. Read-write by default, since a
+                    service must write to the pool data it owns.
+                  '';
+                };
+                create = lib.mkOption {
+                  type = lib.types.nullOr (lib.types.submodule {
+                    options = {
+                      type = lib.mkOption {
+                        type = lib.types.enum [ "directory" ];
+                        default = "directory";
+                        description = "Host path type to create before the guest starts.";
+                      };
+                      owner = lib.mkOption {
+                        type = lib.types.oneOf [
+                          lib.types.str
+                          lib.types.ints.positive
+                        ];
+                        description = "Owner assigned to the created host path.";
+                      };
+                      group = lib.mkOption {
+                        type = lib.types.str;
+                        description = "Group assigned to the created host path.";
+                      };
+                      mode = lib.mkOption {
+                        type = lib.types.str;
+                        example = "0770";
+                        description = "Mode assigned to the created host path.";
+                      };
+                    };
+                  });
+                  default = null;
+                  description = ''
+                    Opt-in host path creation before the guest starts. Existing
+                    paths are left enabled unless this is set, so served storage
+                    roots can still be required to exist explicitly.
+                  '';
+                };
+              };
+            }
+          );
+          default = { };
+          example = lib.literalExpression ''
+            {
+              "/data/media" = { hostPath = "/srv/media"; };
+              "/data/config" = {
+                hostPath = "/srv/config/jellyfin";
+                readOnly = true;
+              };
+            }
+          '';
+          description = ''
+            Host paths bind-mounted into the guest, keyed by the path they appear
+            at inside the guest, so a guest sees exactly the data it should at any
+            granularity — a single folder or a whole pool. Each mount is
+            read-write unless `readOnly` is set.
+          '';
+        };
+        secrets = lib.mkOption {
+          type = lib.types.listOf lib.types.str;
+          default = [ ];
+          example = [ "jellyfin-api-key" ];
+          description = ''
+            Names of the secrets this guest needs. The host is the sole
+            decryptor: it decrypts each named secret from its own sops files and
+            bind-mounts the plaintext file into the guest read-only at
+            `/run/secrets/<name>`, the same path it would occupy on a host, so a
+            service reads its credentials at a predictable location. The guest
+            names the files it wants and receives exactly those. It holds no age
+            key and decrypts nothing itself. Ownership carries across unchanged,
+            since the container maps ids one to one, so a secret owned by a uid on
+            the host is owned by that same uid inside the guest.
+          '';
+        };
+        limits = {
+          memory = lib.mkOption {
+            type = lib.types.nullOr lib.types.str;
+            default = null;
+            example = "2G";
+            description = ''
+              Cap on the guest's memory, applied to its unit as `MemoryMax`.
+              Accepts systemd size suffixes such as `512M` or `2G`. Left null,
+              the guest's memory is uncapped.
+            '';
+          };
+          cpu = lib.mkOption {
+            type = lib.types.nullOr lib.types.str;
+            default = null;
+            example = "150%";
+            description = ''
+              Cap on the guest's CPU, applied to its unit as `CPUQuota`, where
+              `100%` is one full core. Left null, the guest's CPU is uncapped.
+            '';
+          };
+          tasksMax = lib.mkOption {
+            type = lib.types.nullOr lib.types.ints.positive;
+            default = null;
+            example = 512;
+            description = ''
+              Cap on the number of processes and threads the guest may spawn,
+              applied to its unit as `TasksMax`. Left null, the task count is
+              uncapped.
+            '';
+          };
+        };
+        nesting = lib.mkOption {
+          type = lib.types.bool;
+          default = false;
+          description = ''
+            Grant the guest's interior the prerequisites to run Podman or other
+            OCI containers of its own. Off by default, so a guest cannot nest
+            containers. On, the guest's container gains the network-administration
+            capability its container runtime uses to build bridges and firewall
+            rules, along with the tun and fuse device nodes such a runtime reaches
+            for, so the interior's `virtualisation.oci-containers` works with
+            Podman as its default runtime.
+          '';
+        };
+        autoStart = lib.mkOption {
+          type = lib.types.bool;
+          default = true;
+          description = ''
+            Start the guest at boot. On by default. Disabled, the guest stays
+            defined and can be started on demand, but does not come up at boot.
+          '';
+        };
+      };
+
+      config = lib.mkIf cfg.enable {
+        sops.secrets = lib.genAttrs cfg.secrets (_: { });
+
+        assertions = [
+          {
+            assertion = mountCollisions == [ ];
+            message = ''
+              guests.${name} maps a mount at ${lib.concatStringsSep ", " mountCollisions}, colliding with a secret bind-mounted at the same path. Rename the mount or the secret so each in-guest path is used once.
+            '';
+          }
+          {
+            assertion = cfg.backend == "container";
+            message = ''
+              guests.${name}.backend = "${cfg.backend}" is not implemented. Only the "container" backend is built; "microvm" is reserved for future work.
+            '';
+          }
+          {
+            assertion = !networked || lib.elem cfg.vlan config.modules.network.vlans;
+            message = ''
+              guests.${name}.vlan = ${toString cfg.vlan} is not among its host's modules.network.vlans (${lib.concatMapStringsSep ", " toString config.modules.network.vlans}). Declare the VLAN on the host or correct the guest's placement.
+            '';
+          }
+        ];
+
+        systemd.services."container@${machineName}" = lib.mkIf (cfg.backend == "container") (
+          lib.mkMerge [
+            {
+              serviceConfig = limitConfig;
+              preStart = lib.mkIf (createdMounts != { }) mountCreateScript;
+            }
+            (lib.mkIf networked (
+              let
+                bridgeDevice = "sys-subsystem-net-devices-${lib.replaceStrings [ "-" ] [ "\\x2d" ] (bridgeName cfg.vlan)}.device";
+              in
+              {
+                after = [ bridgeDevice ];
+                wants = [ bridgeDevice ];
+              }
+            ))
+          ]
+        );
+
+        containers.${machineName} = lib.mkIf (cfg.backend == "container") {
+          autoStart = cfg.autoStart;
+          privateNetwork = lib.mkDefault true;
+          hostBridge = lib.mkIf networked (bridgeName cfg.vlan);
+          privateUsers = lib.mkDefault "no";
+          additionalCapabilities = lib.optionals cfg.nesting [ "CAP_NET_ADMIN" ];
+          allowedDevices = lib.optionals cfg.nesting [
+            {
+              node = "/dev/net/tun";
+              modifier = "rwm";
+            }
+            {
+              node = "/dev/fuse";
+              modifier = "rwm";
+            }
+          ];
+
+          bindMounts = userMounts // secretMounts;
+
+          inherit specialArgs;
+
+          config = {
+            imports = [
+              (self + "/guest.nix")
+              guestNet
+              interior
+            ];
+          };
+        };
+      };
+    };
+in
+{
+  inherit deriveMac guest;
+}