treewide: implement auto importing for modules

Reduce maintenance burden and increase efficiency by automatically
importing modules following a specific convention.

Co-authored-by: awwpotato <awwpotato@voidq.com>
Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

modules/programs/codex/default.nix

@@ -0,0 +1,67 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  inherit (lib) mkIf;
+
+  cfg = config.programs.codex;
+
+  settingsFormat = pkgs.formats.yaml { };
+in
+{
+  meta.maintainers = [
+    lib.hm.maintainers.delafthi
+  ];
+
+  options.programs.codex = {
+    enable = lib.mkEnableOption "Lightweight coding agent that runs in your terminal";
+
+    package = lib.mkPackageOption pkgs "codex" { nullable = true; };
+
+    settings = lib.mkOption {
+      inherit (settingsFormat) type;
+      description = ''
+        Configuration written to {file}`~/.codex/config.yaml`.
+        See <https://github.com/openai/codex#configuration-guide> for supported values.
+      '';
+      default = { };
+      defaultText = lib.literalExpression "{ }";
+      example = lib.literalExpression ''
+        {
+          model = "gemma3:latest";
+          provider = "ollama";
+          providers = {
+            ollama = {
+              name = "Ollama";
+              baseURL = "http://localhost:11434/v1";
+              envKey = "OLLAMA_API_KEY";
+            };
+          };
+        }
+      '';
+    };
+    custom-instructions = lib.mkOption {
+      type = lib.types.lines;
+      description = "Define custom guidance for the agents; this value is written to {file}~/.codex/AGENTS.md";
+      default = "";
+      example = lib.literalExpression ''
+        '''
+          - Always respond with emojis
+          - Only use git commands when explicitly requested
+        '''
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = mkIf (cfg.package != null) [ cfg.package ];
+    home.file = {
+      ".codex/config.yaml".source = settingsFormat.generate "codex-config" cfg.settings;
+      ".codex/AGENTS.md".text = cfg.custom-instructions;
+    };
+  };
+
+}