Can't find files in custom iso using isoImage.contents

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Heyo, I’ve been trying to make a custom installation ISO that includes a few install scripts and my dotfiles.

However, for some reason using isoImage.contents hasn’t worked for me. Before trying this I’ve used environment.etc, which did work, but wasn’t as nice.

I’m using nixos-generate --format iso --flake ./flake.nix#minimal -o result --show-trace to generate the iso.

# flake.nix
{
    description = "Basic System Flake";

    inputs = {
        nixpkgs.url = "nixpkgs/nixos-24.05";
        unstable.url = "nixpkgs/nixos-unstable";

        home-manager.url = "github:nix-community/home-manager/release-24.05";
        home-manager.inputs.nixpkgs.follows = "nixpkgs";
    };

    outputs = { self, nixpkgs, home-manager, ... }@inputs:
    let
        helpers = import ./helpers.nix { inherit nixpkgs; inherit home-manager; };

        # ...

        minimalConfig = {
            name = "minimal";
            systemSettings = helpers.newSystemSettings {
                system = "aarch64-linux";
            };
            # systemSettings = helpers.newSystemSettings {};
            userSettings = helpers.newUserSettings {};
            inherit inputs;
        };
    in {
        # ...

        nixosConfigurations.minimal = (helpers.newSystemConfiguration minimalConfig);
    };
}

# profiles/minimal/configuration.nix
{ config, pkgs, systemSettings, userSettings, modulesPath, lib, ... }:

let
    newIsoContent = source: target:
        pkgs.lib.trivial.id { inherit source; inherit target; };
in
{
    imports = [
        "${modulesPath}/installer/cd-dvd/installation-cd-minimal.nix"

        # ...
    ];

    boot.kernelPackages = pkgs.linuxPackages_latest;
    boot.supportedFilesystems = lib.mkForce [ "btrfs" "reiserfs" "vfat" "f2fs" "xfs" "ntfs" "cifs" ];

    environment.systemPackages = with pkgs; [
        parted
        neovim
        disko
        git
    ];

    nix.settings.experimental-features = [
        "nix-command"
        "flakes"
    ];

    isoImage.contents = [
        (newIsoContent ./bootstrap "/bootstrap/scripts/")
        (newIsoContent ./../../.   "/bootstrap/dotfiles/")
    ];

    system.stateVersion = "23.11";
}

This is my helper file for setting up my configurations:

# helpers.nix
{ nixpkgs, home-manager, ... }:

let
    newSystemSettings = {
        system ? "x86_64-linux",
        hostname ? "nixos",

        keymap ? "de",
        en-locale ? "en_US.UTF-8",
        de-locale ? "de_DE.UTF-8",
        timezone ? "Europe/Berlin", # America/Vancouver
    }: nixpkgs.lib.trivial.id {
        system = system;
        hostname = hostname;

        keymap = keymap;
        en-locale = en-locale;
        de-locale = de-locale;
        timezone = timezone;
    };

    newUserSettings = {
        username ? "user",
        displayname ? "user",

        terminal ? "kitty",
        browser ? "firefox",
        editor ? "nvim",
        wm ? "gnome",

        font ? "...",
    }: nixpkgs.lib.trivial.id {
        username = username;
        displayname = displayname;

        dotfilesDir = "/home/${username}/.dotfiles";

        terminal = terminal;
        browser = browser;
        editor = editor;
        wm = wm;

        font = font;
        # fontPkg = fontPkg;
    };

    newSystemConfiguration = config:
        nixpkgs.lib.trivial.id nixpkgs.lib.nixosSystem {
            system = config.systemSettings.system;
            modules = [ ./profiles/${config.name}/configuration.nix ];
            specialArgs = {
                systemSettings = config.systemSettings;
                userSettings = config.userSettings;
                inputs = config.inputs;
            };
        };
in {
    inherit newSystemSettings;
    inherit newUserSettings;

    inherit newSystemConfiguration;
    inherit newHomeManagerConfiguration;
}

When the iso is built, I upload it to my VPS provider and boot into it. But when I try to access the /bootstrap/ directory, it isn’t there…

It’s probably a stupid mistake, but I can’t for the life of me find it, so any help would be greatly appreciated.

If any more infos are required, feel free to ask.