feat(machines): add tart-agent-sandbox VM config

NixOS configuration for running LLM agents in isolated Tart VMs on
Apple Silicon. Includes:
- Headless server setup with SSH access
- Agent user with passwordless sudo
- Docker support
- Dev tools for cloning large repos
- Git config optimized for large repositories

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

machines/tart-agent-sandbox/configuration.nix

@@ -0,0 +1,98 @@
+# Agent sandbox VM configuration for Tart
+# Designed for LLM agents with full sudo access in an isolated environment
+{ config, pkgs, lib, ... }:
+
+{
+  imports = [
+    ./hardware-configuration.nix
+  ];
+
+  # Bootloader
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+
+  networking.hostName = "tart-agent-sandbox";
+
+  # SSH access from host
+  services.openssh = {
+    enable = true;
+    settings = {
+      PermitRootLogin = "yes";
+      PasswordAuthentication = true;
+    };
+  };
+
+  # Agent user - full sudo, no password required
+  users.users.agent = {
+    isNormalUser = true;
+    description = "Agent sandbox user";
+    extraGroups = [ "wheel" "docker" ];
+    initialPassword = "agent";
+    openssh.authorizedKeys.keys = [
+      # Add your SSH public key here for passwordless access
+      # "ssh-ed25519 AAAA... your-key"
+    ];
+  };
+
+  # Passwordless sudo for wheel group
+  security.sudo.wheelNeedsPassword = false;
+
+  # Dev tools for agents
+  environment.systemPackages = with pkgs; [
+    # Core
+    git
+    curl
+    wget
+    vim
+    htop
+    tmux
+
+    # Build tools
+    gnumake
+    gcc
+    binutils
+
+    # Languages (add what your agents need)
+    python3
+    nodejs
+
+    # Utilities
+    jq
+    ripgrep
+    fd
+    tree
+    unzip
+    zip
+
+    # Networking
+    openssh
+    rsync
+  ];
+
+  # Docker for containerized workloads
+  virtualisation.docker.enable = true;
+
+  # Increase file descriptor limits for large operations
+  security.pam.loginLimits = [
+    { domain = "*"; type = "soft"; item = "nofile"; value = "65536"; }
+    { domain = "*"; type = "hard"; item = "nofile"; value = "65536"; }
+  ];
+
+  # Git config for large repos
+  programs.git = {
+    enable = true;
+    config = {
+      core.compression = 0;
+      http.postBuffer = 524288000;  # 500MB
+      pack.windowMemory = "100m";
+    };
+  };
+
+  # Nix settings
+  nix.settings = {
+    experimental-features = [ "nix-command" "flakes" ];
+    auto-optimise-store = true;
+  };
+
+  system.stateVersion = "25.11";
+}

machines/tart-agent-sandbox/hardware-configuration.nix

@@ -0,0 +1,30 @@
+# Hardware configuration for Tart VM (Apple Virtualization.framework)
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports = [
+    (modulesPath + "/profiles/qemu-guest.nix")
+  ];
+
+  boot.initrd.availableKernelModules = [ "xhci_pci" "virtio_pci" "virtio_blk" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  # Root filesystem (will be /dev/vda1 after partitioning)
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/nixos";
+    fsType = "ext4";
+  };
+
+  # EFI boot partition
+  fileSystems."/boot" = {
+    device = "/dev/disk/by-label/boot";
+    fsType = "vfat";
+    options = [ "fmask=0077" "dmask=0077" ];
+  };
+
+  swapDevices = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "aarch64-linux";
+}