feat(emacs): Add prebuilt Doom option using nix-doom-emacs-unstraightened

Implement pre-built Doom Emacs packages for the live USB image, eliminating
the need to run `doom sync` after first boot.

Changes:
- Add nix-doom-emacs-unstraightened flake input
- Add homeModule to all three module sets (nixos, unstable, darwin)
- Add `prebuiltDoom` option to emacs role (default: false)
- Enable prebuiltDoom for live-usb configuration
- Pin custom packages in packages.el for deterministic builds:
  - claude-code-ide, gptel-tool-library, beads

When prebuiltDoom=true, all Doom packages are compiled at nix build time
using emacs-overlay. The doom configuration is stored in the nix store
(read-only), and no `doom sync` is required at runtime.

This is ideal for:
- Live USB images
- Immutable/reproducible systems
- Offline deployments

Closes: nixos-configs-1wd

home/roles/emacs/default.nix

@@ -23,55 +23,90 @@ let
     if pkgs.stdenv.isDarwin
     then pkgs.emacs-macport.pkgs.withPackages emacsPackages
     else pkgs.emacs.pkgs.withPackages emacsPackages;
+
+  # Path to doom config directory (relative to this file)
+  doomConfigDir = ./doom;
 in
 {
   options.home.roles.emacs = {
     enable = mkEnableOption "Doom Emacs with vterm and tree-sitter support";
+
+    prebuiltDoom = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Use nix-doom-emacs-unstraightened to pre-build all Doom packages at
+        nix build time. This eliminates the need to run `doom sync` after
+        first boot, making it ideal for live USB images or immutable systems.
+
+        When enabled, the doom configuration is read-only (stored in nix store).
+      '';
+    };
   };
 
-  config = mkIf cfg.enable {
-    home.packages = [
-      pkgs.emacs-all-the-icons-fonts
-      pkgs.fira-code
-      pkgs.fontconfig
-      pkgs.graphviz
-      pkgs.isort
-      pkgs.nerd-fonts.fira-code
-      pkgs.nerd-fonts.droid-sans-mono
-      pkgs.nil # nix lsp language server
-      pkgs.nixfmt-rfc-style
-      (pkgs.ripgrep.override {withPCRE2 = true;})
-      pkgs.pipenv
-      pkgs.poetry
-      pkgs.python3
-    ];
+  config = mkIf cfg.enable (mkMerge [
+    # Common configuration for both modes
+    {
+      home.packages = [
+        pkgs.emacs-all-the-icons-fonts
+        pkgs.fira-code
+        pkgs.fontconfig
+        pkgs.graphviz
+        pkgs.isort
+        pkgs.nerd-fonts.fira-code
+        pkgs.nerd-fonts.droid-sans-mono
+        pkgs.nil # nix lsp language server
+        pkgs.nixfmt-rfc-style
+        (pkgs.ripgrep.override {withPCRE2 = true;})
+        pkgs.pipenv
+        pkgs.poetry
+        pkgs.python3
+      ];
 
-    programs.emacs = {
-      enable = true;
-      package = defaultEmacsPackage;
-    };
+      fonts.fontconfig.enable = true;
+    }
 
-    fonts.fontconfig.enable = true;
+    # Standard Doom Emacs mode (requires doom sync at runtime)
+    (mkIf (!cfg.prebuiltDoom) {
+      programs.emacs = {
+        enable = true;
+        package = defaultEmacsPackage;
+      };
 
-    # Mount emacs and tree-sitter grammars from nix store
-    home.file = {
-      "${config.xdg.configHome}/emacs".source = doomEmacs;
-    };
+      # Mount emacs and tree-sitter grammars from nix store
+      home.file = {
+        "${config.xdg.configHome}/emacs".source = doomEmacs;
+      };
 
-    home.sessionPath = [
-      "${config.xdg.configHome}/emacs/bin"
-    ];
+      home.sessionPath = [
+        "${config.xdg.configHome}/emacs/bin"
+      ];
 
-    home.sessionVariables = {
-      DOOMDIR = "${config.xdg.configHome}/doom";
-      DOOMLOCALDIR = "${config.xdg.dataHome}/doom";
-    };
+      home.sessionVariables = {
+        DOOMDIR = "${config.xdg.configHome}/doom";
+        DOOMLOCALDIR = "${config.xdg.dataHome}/doom";
+      };
 
-    # TODO: Use mkOutOfStoreSymlink instead?
-    home.activation.doomConfig = lib.hm.dag.entryAfter ["writeBoundary"] ''
-      # Always remove and recreate the symlink to ensure it points to the source directory
-      rm -rf "${config.xdg.configHome}/doom"
-      ln -sf "${config.home.homeDirectory}/nixos-configs/home/roles/emacs/doom" "${config.xdg.configHome}/doom"
-    '';
-  };
+      # TODO: Use mkOutOfStoreSymlink instead?
+      home.activation.doomConfig = lib.hm.dag.entryAfter ["writeBoundary"] ''
+        # Always remove and recreate the symlink to ensure it points to the source directory
+        rm -rf "${config.xdg.configHome}/doom"
+        ln -sf "${config.home.homeDirectory}/nixos-configs/home/roles/emacs/doom" "${config.xdg.configHome}/doom"
+      '';
+    })
+
+    # Pre-built Doom Emacs mode (no doom sync needed - ideal for live USB)
+    (mkIf cfg.prebuiltDoom {
+      programs.doom-emacs = {
+        enable = true;
+        doomDir = doomConfigDir;
+        doomLocalDir = "${config.xdg.dataHome}/doom";
+        # Add extra packages that aren't part of Doom but needed for our config
+        extraPackages = epkgs: [
+          epkgs.vterm
+          epkgs.treesit-grammars.with-all-grammars
+        ];
+      };
+    })
+  ]);
 }