I'd like to get parts of my CCE running on t184256/nix-on-droid so that I can have my Emacs Tools like SRS and org-roam running on it.

nix-on-droid.nix

This uses Arroyo Home Manager to generate a list of Arroyo modules to include in to the Nix On Droid home-manager environment and then does some basic housekeeping stuff to expose Arroyo Emacs and rixpkgs to that environment.

{ pkgs, ... }:

{
  environment.packages = with pkgs; [ vim openssh ];
  system.stateVersion = "22.11";

  nix.nixPath = [
    "nixpkgs=/data/data/com.termux.nix/files/home/.nix-defexpr/channels/nixpkgs/"
    "arroyo=/storage/emulated/0/arroyo-nix"
    "/data/data/com.termux.nix/files/home/.nix-defexpr/channels"
  ];
  nix.substituters = [
    "https://cache.nixos.org/"
    "https://nix-community.cachix.org"
  ];
  nix.trustedPublicKeys = [
    "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
    "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
  ];

  nixpkgs.overlays = [
    (let emacsOverlay = (import ./versions.nix {}).emacsOverlay null;
     in import emacsOverlay)
    (import <arroyo/overlay.nix>)
  ];

  home-manager.useGlobalPkgs = true;

  time.timeZone = "America/Los_Angeles";

  home-manager.config =
    { pkgs, ... }:
    {
      home.stateVersion = "22.05";
      imports = [
        <<home_manager_imports()>>
      ];

      programs.ssh.matchBlocks = {
        virtuous-cassette = {
          hostname = "100.96.6.32";
          user = "builder";
          identitiesOnly = true;
          identityFile = "~/.ssh/id_rsa";
        };

        window-smoke = {
          hostname = "100.79.48.59";
          user = "builder";
          identitiesOnly = true;
          identityFile = "~/.ssh/id_rsa";
        };
      };
    };
}

(->> (arroyo-home-manager-imports "droid")
     (s-join "\n"))

hm/contacts.nix
hm/deadgrep.nix
hm/direnv.nix
hm/emacs-helpers.nix
hm/emacs-pager.nix
hm/emacs.nix
hm/git.nix
hm/gnupg.nix
hm/morph.nix
hm/nix-update.nix
hm/org-fc.nix
hm/org-roam.nix
hm/profile.nix
hm/prompt.nix
hm/python.nix
hm/shell-helpers.nix
hm/spell-check.nix
hm/ssh_client.nix

Using machines running My NixOS configuration to as builders for nix-on-droid

Based on the Nix On Droid wiki examples:

Virtuous Cassette is set up with a builder user and aarch64 binfmt emulation:

{ ... }:

{
  boot.binfmt.emulatedSystems = [ "aarch64-linux" ];
  users.users.builder = {
    createHome = true;
    isNormalUser = true;
    initialPassword = "changeme!";
  };

  nix.settings.trusted-users = [ "builder" ];
}

Bootstrapping the build setup

On the droid side, it's configured to use this as the builder and SSH to the host over Tailscale:

nix.conf:

builders-use-substitutes = true
builders = ssh://virtuous-cassette;ssh://window-smoke

.ssh/config

Host virtuous-cassette
    HostName 100.96.6.32
    User builder
    IdentitiesOnly yes
    IdentityFile ~/.ssh/id_rsa

Host window-smoke
    HostName 100.79.48.59
    User builder
    IdentitiesOnly yes
    IdentityFile ~/.ssh/id_rsa

• set up ssh: nix-shell -p openssh git then ssh-keygen then ssh-copy-id builder; git is used in nix-on-droid build
• set up directories: ln -s /storage/emulated/0/org ~/org then ln -s /storage/emulated/0/arroyo-nix ~/arroyo-nix
• install home-manager channel (only used for bootstrap, subsequent builds will use Nix Version Pins)
• then finally nix-on-droid build -f ~/arroyo-nix/nix-on-droid.nix -I arroyo=$HOME/arroyo-nix

Termux app properties should be set on the Cosmo and other devices with a hardware keyboard:

# extra-keys-style = none doesn't work...
extra-keys = []
back-key = escape
ctrl-space-workaround = true