diff --git a/build-helpers/full-init b/build-helpers/full-init
new file mode 100755
index 0000000..46e85d4
--- /dev/null
+++ b/build-helpers/full-init
@@ -0,0 +1,39 @@
+#!/usr/bin/env doomscript
+;; -*- lexical-binding: t; -*-
+
+;; Copyright 2024 Google LLC
+;;
+;; Licensed under the Apache License, Version 2.0 (the "License");
+;; you may not use this file except in compliance with the License.
+;; You may obtain a copy of the License at
+;;
+;;     http://www.apache.org/licenses/LICENSE-2.0
+;;
+;; Unless required by applicable law or agreed to in writing, software
+;; distributed under the License is distributed on an "AS IS" BASIS,
+;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;; See the License for the specific language governing permissions and
+;; limitations under the License.
+
+(defcli! full-init
+    ((output-directory ("-o" dir) "Directory to write init.el into.")
+     (&flag full? ("--full")))
+  "Write init.el with all modules."
+  (with-temp-buffer
+    (insert ";;; init.el -*- no-byte-compile: t; -*-
+
+;;; Dynamically generated by nix-doom-emacs-unstraightened.
+
+(doom!
+")
+    (dolist (kp (doom-module-list 'all))
+      (let ((cat (car kp))
+            (name (cdr kp)))
+        (when name
+          (if full?
+              (error "unimplemented")
+            (insert (format " %s %s\n" cat name))))))
+    (insert ")\n")
+    (write-region nil nil (expand-file-name "init.el" output-directory))))
+
+(run! "full-init" (cdr (member "--" argv)))
diff --git a/checks.nix b/checks.nix
index fcc5044..61bd043 100644
--- a/checks.nix
+++ b/checks.nix
@@ -14,6 +14,7 @@
 
 {
   emacs29,
+  emptyDirectory,
   lib,
   linkFarm,
   runCommand,
@@ -36,6 +37,7 @@ let
   mkDoom = args: (makeDoomPackages (common // args)).doomEmacs;
   mkDoomDir = args: writeTextDir "init.el" (toInit args);
   minimalDoomDir = mkDoomDir { config = [ "default" ]; };
+  fullDoomDir = (makeDoomPackages (common // { doomDir = emptyDirectory; })).doomDirWithAllPackages;
   doomTest = name: init: doomArgs: testers.testEqualContents {
     assertion = "name = ${name}; modules = ${toPretty {} init}; args = ${toPretty {} doomArgs};";
     expected = writeText "doom-expected" "Doom functions";
@@ -64,10 +66,7 @@ in {
   minimalEmacs = (makeDoomPackages (common // {
     doomDir = minimalDoomDir;
   })).emacsWithDoom;
-  full = mkDoom {
-    full = true;
-    doomDir = minimalDoomDir;
-  };
+  full = mkDoom { doomDir = fullDoomDir; };
   example = mkDoom { doomDir = ./doomdirs/example; };
   example-without-loader = mkDoom {
     doomDir = ./doomdirs/example;
diff --git a/default.nix b/default.nix
index 0c8f523..f986c13 100644
--- a/default.nix
+++ b/default.nix
@@ -56,6 +56,24 @@ let
   inherit (lib) optionalAttrs optionalString;
   inherit (import ./fetch-overrides.nix) extraPins extraUrls;
 
+  # This doesn't belong here: it does not depend on doomDir (only on doomSource).
+  # But this is where all my doomscript execution lives.
+  # TODO: consider splitting off doomdir execution to a separate helper.
+  doomDirWithAllPackages = runCommandLocal "doom-full-init"
+    {
+      env = {
+        EMACS = lib.getExe emacs;
+        # Enable this to troubleshoot failures at this step.
+        #DEBUG = "1";
+      };
+      # We set DOOMLOCALDIR somewhere harmless below to stop Doom from trying to
+      # create it somewhere read-only.
+    } ''
+    mkdir $out
+    export DOOMLOCALDIR=$(mktemp -d)
+    ${runtimeShell} ${doomSource}/bin/doomscript ${./build-helpers/full-init} -o $out
+  '';
+
   # Step 1: determine which Emacs packages to pull in.
   #
   # Inputs: Doom, original DOOMDIR (only init.el and packages.el are used).
@@ -412,5 +430,5 @@ let
   '';
 in
 {
-  inherit doomEmacs emacsWithDoom;
+  inherit doomDirWithAllPackages doomEmacs emacsWithDoom;
 }