Add sandboxed-workspace module for isolated dev environments

Provides isolated development environments using either VMs (microvm.nix)
or containers (systemd-nspawn) with a unified configuration interface.

Features:
- Unified options with required type field ("vm" or "container")
- Shared base configuration for networking, SSH, users, packages
- Automatic SSH host key generation and persistence
- Shell aliases for workspace management (start/stop/status/ssh)
- Automatic /etc/hosts entries for workspace hostnames
- restartIfChanged support for both VMs and containers
- Passwordless doas in workspaces

Container backend:
- Uses hostBridge for proper bridge networking with /24 subnet
- systemd-networkd for IP configuration
- systemd-resolved for DNS

VM backend:
- TAP interface with deterministic MAC addresses
- virtiofs shares for workspace directories
- vsock CID generation

common/sandboxed-workspace/base.nix

@@ -0,0 +1,114 @@
+{ hostConfig, workspaceName, ip, networkInterface }:
+
+# Base configuration shared by all sandboxed workspaces (VMs and containers)
+# This provides common settings for networking, SSH, users, and packages
+#
+# Parameters:
+#   hostConfig      - The host's NixOS config (for inputs, ssh keys, etc.)
+#   workspaceName   - Name of the workspace (used as hostname)
+#   ip              - Static IP address for the workspace
+#   networkInterface - Match config for systemd-networkd (e.g., { Type = "ether"; } or { Name = "host0"; })
+
+{ config, lib, pkgs, ... }:
+
+{
+  imports = [
+    ../shell.nix
+    hostConfig.inputs.home-manager.nixosModules.home-manager
+    hostConfig.inputs.nix-index-database.nixosModules.default
+  ];
+
+  # Basic system configuration
+  system.stateVersion = "25.11";
+
+  # Set hostname to match the workspace name
+  networking.hostName = workspaceName;
+
+  # Networking with systemd-networkd
+  networking.useNetworkd = true;
+  systemd.network.enable = true;
+
+  # Enable resolved to populate /etc/resolv.conf from networkd's DNS settings
+  services.resolved.enable = true;
+
+  # Basic networking configuration
+  networking.useDHCP = false;
+
+  # Static IP configuration
+  # Uses the host as DNS server (host forwards to upstream DNS)
+  systemd.network.networks."20-workspace" = {
+    matchConfig = networkInterface;
+    networkConfig = {
+      Address = "${ip}/24";
+      Gateway = hostConfig.networking.sandbox.hostAddress;
+      DNS = [ hostConfig.networking.sandbox.hostAddress ];
+    };
+  };
+
+  # Disable firewall inside workspaces (we're behind NAT)
+  networking.firewall.enable = false;
+
+  # Enable SSH for access
+  services.openssh = {
+    enable = true;
+    settings = {
+      PasswordAuthentication = false;
+      PermitRootLogin = "prohibit-password";
+    };
+  };
+
+  # Use persistent SSH host keys from shared directory
+  services.openssh.hostKeys = lib.mkForce [
+    {
+      path = "/etc/ssh-host-keys/ssh_host_ed25519_key";
+      type = "ed25519";
+    }
+  ];
+
+  # Basic system packages
+  environment.systemPackages = with pkgs; [
+    kakoune
+    vim
+    git
+    htop
+    wget
+    curl
+    tmux
+    dnsutils
+  ];
+
+  # User configuration
+  users.mutableUsers = false;
+  users.users.googlebot = {
+    isNormalUser = true;
+    extraGroups = [ "wheel" ];
+    shell = pkgs.fish;
+    openssh.authorizedKeys.keys = hostConfig.machines.ssh.userKeys;
+  };
+
+  security.doas.enable = true;
+  security.sudo.enable = false;
+  security.doas.extraRules = [
+    { groups = [ "wheel" ]; noPass = true; }
+  ];
+
+  # Minimal locale settings
+  i18n.defaultLocale = "en_US.UTF-8";
+  time.timeZone = "America/Los_Angeles";
+
+  # Enable flakes
+  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+
+  # Make nixpkgs available in NIX_PATH and registry (like the NixOS ISO)
+  # This allows `nix-shell -p`, `nix repl '<nixpkgs>'`, etc. to work
+  nix.nixPath = [ "nixpkgs=${hostConfig.inputs.nixpkgs}" ];
+  nix.registry.nixpkgs.flake = hostConfig.inputs.nixpkgs;
+
+  # Enable fish shell
+  programs.fish.enable = true;
+
+  # Home Manager configuration
+  home-manager.useGlobalPkgs = true;
+  home-manager.useUserPackages = true;
+  home-manager.users.googlebot = import ./home.nix;
+}

common/sandboxed-workspace/container.nix

@@ -0,0 +1,72 @@
+{ config, lib, ... }:
+
+# Container-specific configuration for sandboxed workspaces using systemd-nspawn
+# This module is imported by default.nix for workspaces with type = "container"
+
+with lib;
+
+let
+  cfg = config.sandboxed-workspace;
+  hostConfig = config;
+
+  # Filter for container-type workspaces only
+  containerWorkspaces = filterAttrs (n: ws: ws.type == "container") cfg.workspaces;
+in
+{
+  config = mkIf (cfg.enable && containerWorkspaces != { }) {
+    # NixOS container module only sets restartIfChanged when autoStart=true
+    # Work around this by setting it directly on the systemd service
+    systemd.services = mapAttrs'
+      (name: ws: nameValuePair "container@${name}" {
+        restartIfChanged = lib.mkForce true;
+        restartTriggers = [
+          config.containers.${name}.path
+          config.environment.etc."nixos-containers/${name}.conf".source
+        ];
+      })
+      containerWorkspaces;
+
+    # Convert container workspace configs to NixOS containers format
+    containers = mapAttrs
+      (name: ws: {
+        autoStart = ws.autoStart;
+        privateNetwork = true;
+        ephemeral = true;
+        restartIfChanged = true;
+
+        # Attach container's veth to the sandbox bridge
+        # This creates the veth pair and attaches host side to the bridge
+        hostBridge = config.networking.sandbox.bridgeName;
+
+        bindMounts = {
+          "/home/googlebot/workspace" = {
+            hostPath = "/home/googlebot/sandboxed/${name}/workspace";
+            isReadOnly = false;
+          };
+          "/etc/ssh-host-keys" = {
+            hostPath = "/home/googlebot/sandboxed/${name}/ssh-host-keys";
+            isReadOnly = false;
+          };
+          "/home/googlebot/claude-config" = {
+            hostPath = "/home/googlebot/sandboxed/${name}/claude-config";
+            isReadOnly = false;
+          };
+        };
+
+        config = { config, lib, pkgs, ... }: {
+          imports = [
+            (import ./base.nix {
+              inherit hostConfig;
+              workspaceName = name;
+              ip = ws.ip;
+              networkInterface = { Name = "eth0"; };
+            })
+            (import ws.config)
+          ];
+
+          networking.useHostResolvConf = false;
+        };
+      })
+      containerWorkspaces;
+  };
+}

common/sandboxed-workspace/default.nix

@@ -0,0 +1,157 @@
+{ config, lib, pkgs, ... }:
+
+# Unified sandboxed workspace module supporting both VMs and containers
+# This module provides isolated development environments with shared configuration
+
+with lib;
+
+let
+  cfg = config.sandboxed-workspace;
+in
+{
+  imports = [
+    ./vm.nix
+    ./container.nix
+  ];
+
+  options.sandboxed-workspace = {
+    enable = mkEnableOption "sandboxed workspace management";
+
+    workspaces = mkOption {
+      type = types.attrsOf (types.submodule {
+        options = {
+          type = mkOption {
+            type = types.enum [ "vm" "container" ];
+            description = ''
+              Backend type for this workspace:
+              - "vm": microVM with cloud-hypervisor (more isolation, uses virtiofs)
+              - "container": systemd-nspawn container (less overhead, uses bind mounts)
+            '';
+          };
+
+          config = mkOption {
+            type = types.path;
+            description = "Path to the workspace configuration file";
+          };
+
+          ip = mkOption {
+            type = types.str;
+            example = "192.168.83.10";
+            description = ''
+              Static IP address for this workspace on the microvm bridge network.
+              Configures the workspace's network interface and adds an entry to /etc/hosts
+              on the host so the workspace can be accessed by name (e.g., ssh workspace-example).
+              Must be in the 192.168.83.0/24 subnet (or whatever networking.sandbox.subnet is).
+            '';
+          };
+
+          hostKey = mkOption {
+            type = types.nullOr types.str;
+            default = null;
+            example = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAA...";
+            description = ''
+              SSH host public key for this workspace. If set, adds to programs.ssh.knownHosts
+              so the host automatically trusts the workspace without prompting.
+              Get the key from: ~/sandboxed/<name>/ssh-host-keys/ssh_host_ed25519_key.pub
+            '';
+          };
+
+          autoStart = mkOption {
+            type = types.bool;
+            default = false;
+            description = "Whether to automatically start this workspace on boot";
+          };
+
+          cid = mkOption {
+            type = types.nullOr types.int;
+            default = null;
+            description = ''
+              vsock Context Identifier for this workspace (VM-only, ignored for containers).
+              If null, auto-generated from workspace name.
+              Must be unique per host. Valid range: 3 to 4294967294.
+              See: https://man7.org/linux/man-pages/man7/vsock.7.html
+            '';
+          };
+        };
+      });
+      default = { };
+      description = "Sandboxed workspace configurations";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # Automatically enable sandbox networking when workspaces are defined
+    networking.sandbox.enable = mkIf (cfg.workspaces != { }) true;
+
+    # Add workspace hostnames to /etc/hosts so they can be accessed by name
+    networking.hosts = lib.mkMerge (lib.mapAttrsToList
+      (name: ws: {
+        ${ws.ip} = [ "workspace-${name}" ];
+      })
+      cfg.workspaces);
+
+    # Add workspace SSH host keys to known_hosts so host trusts workspaces without prompting
+    programs.ssh.knownHosts = lib.mkMerge (lib.mapAttrsToList
+      (name: ws:
+        lib.optionalAttrs (ws.hostKey != null) {
+          "workspace-${name}" = {
+            publicKey = ws.hostKey;
+            extraHostNames = [ ws.ip ];
+          };
+        })
+      cfg.workspaces);
+
+    # Shell aliases for workspace management
+    # Service names differ by type: microvm@<name> for VMs, container@<name> for containers
+    environment.shellAliases = lib.mkMerge (lib.mapAttrsToList
+      (name: ws:
+        let
+          serviceName = if ws.type == "vm" then "microvm@${name}" else "container@${name}";
+        in
+        {
+          "workspace_${name}" = "ssh googlebot@workspace-${name}";
+          "workspace_${name}_start" = "doas systemctl start ${serviceName}";
+          "workspace_${name}_stop" = "doas systemctl stop ${serviceName}";
+          "workspace_${name}_restart" = "doas systemctl restart ${serviceName}";
+          "workspace_${name}_status" = "doas systemctl status ${serviceName}";
+        })
+      cfg.workspaces);
+
+    # Automatically generate SSH host keys and directories for all workspaces
+    systemd.services = lib.mapAttrs'
+      (name: ws:
+        let
+          serviceName = if ws.type == "vm" then "microvm@${name}" else "container@${name}";
+        in
+        lib.nameValuePair "workspace-${name}-setup" {
+          description = "Setup directories and SSH keys for workspace ${name}";
+          wantedBy = [ "multi-user.target" ];
+          before = [ "${serviceName}.service" ];
+
+          serviceConfig = {
+            Type = "oneshot";
+            RemainAfterExit = true;
+          };
+
+          script = ''
+            # Create directories if they don't exist
+            mkdir -p /home/googlebot/sandboxed/${name}/workspace
+            mkdir -p /home/googlebot/sandboxed/${name}/ssh-host-keys
+            mkdir -p /home/googlebot/sandboxed/${name}/claude-config
+
+            # Fix ownership
+            chown -R googlebot:users /home/googlebot/sandboxed/${name}
+
+            # Generate SSH host key if it doesn't exist
+            if [ ! -f /home/googlebot/sandboxed/${name}/ssh-host-keys/ssh_host_ed25519_key ]; then
+              ${pkgs.openssh}/bin/ssh-keygen -t ed25519 -N "" \
+                -f /home/googlebot/sandboxed/${name}/ssh-host-keys/ssh_host_ed25519_key
+              chown googlebot:users /home/googlebot/sandboxed/${name}/ssh-host-keys/ssh_host_ed25519_key*
+              echo "Generated SSH host key for workspace ${name}"
+            fi
+          '';
+        }
+      )
+      cfg.workspaces;
+  };
+}

common/sandboxed-workspace/home.nix

@@ -0,0 +1,50 @@
+{ config, lib, pkgs, ... }:
+
+# Home Manager configuration for sandboxed workspace user environment
+# This sets up the shell and tools inside VMs and containers
+
+{
+  home.username = "googlebot";
+  home.homeDirectory = "/home/googlebot";
+  home.stateVersion = "24.11";
+
+  programs.home-manager.enable = true;
+
+  # Shell configuration
+  programs.fish.enable = true;
+  programs.starship.enable = true;
+  programs.starship.enableFishIntegration = true;
+  programs.starship.settings.container.disabled = true;
+
+  # Basic command-line tools
+  programs.btop.enable = true;
+  programs.ripgrep.enable = true;
+  programs.eza.enable = true;
+
+  # Git configuration
+  programs.git = {
+    enable = true;
+    settings = {
+      user.name = lib.mkDefault "googlebot";
+      user.email = lib.mkDefault "zuckerberg@neet.dev";
+    };
+  };
+
+  # Shell aliases
+  home.shellAliases = {
+    ls = "eza";
+    la = "eza -la";
+    ll = "eza -l";
+  };
+
+  # Environment variables for Claude Code
+  home.sessionVariables = {
+    # Isolate Claude config to a specific directory on the host
+    CLAUDE_CONFIG_DIR = "/home/googlebot/claude-config";
+  };
+
+  # Additional packages for development
+  home.packages = with pkgs; [
+    # Add packages as needed per workspace
+  ];
+}

common/sandboxed-workspace/vm.nix

@@ -0,0 +1,138 @@
+{ config, lib, ... }:
+
+# VM-specific configuration for sandboxed workspaces using microvm.nix
+# This module is imported by default.nix for workspaces with type = "vm"
+
+with lib;
+
+let
+  cfg = config.sandboxed-workspace;
+  hostConfig = config;
+
+  # Generate a deterministic vsock CID from workspace name.
+  #
+  # vsock (virtual sockets) enables host-VM communication without networking.
+  # cloud-hypervisor uses vsock for systemd-notify integration: when a VM finishes
+  # booting, systemd sends READY=1 to the host via vsock, allowing the host's
+  # microvm@ service to accurately track VM boot status instead of guessing.
+  #
+  # Each VM needs a unique CID (Context Identifier). Reserved CIDs per vsock(7):
+  #   - VMADDR_CID_HYPERVISOR (0): reserved for hypervisor
+  #   - VMADDR_CID_LOCAL (1): loopback address
+  #   - VMADDR_CID_HOST (2): host address
+  # See: https://man7.org/linux/man-pages/man7/vsock.7.html
+  #      https://docs.kernel.org/virt/kvm/vsock.html
+  #
+  # We auto-generate from SHA256 hash to ensure uniqueness without manual assignment.
+  # Range: 100 - 16777315 (offset avoids reserved CIDs and leaves 3-99 for manual use)
+  nameToCid = name:
+    let
+      hash = builtins.hashString "sha256" name;
+      hexPart = builtins.substring 0 6 hash;
+    in
+    100 + (builtins.foldl'
+      (acc: c: acc * 16 + (
+        if c == "a" then 10
+        else if c == "b" then 11
+        else if c == "c" then 12
+        else if c == "d" then 13
+        else if c == "e" then 14
+        else if c == "f" then 15
+        else lib.strings.toInt c
+      )) 0
+      (lib.stringToCharacters hexPart));
+
+  # Filter for VM-type workspaces only
+  vmWorkspaces = filterAttrs (n: ws: ws.type == "vm") cfg.workspaces;
+
+  # Generate VM configuration for a workspace
+  mkVmConfig = name: ws: {
+    config = import ws.config;
+    specialArgs = { inputs = hostConfig.inputs; };
+    extraModules = [
+      (import ./base.nix {
+        inherit hostConfig;
+        workspaceName = name;
+        ip = ws.ip;
+        networkInterface = { Type = "ether"; };
+      })
+      {
+        # MicroVM specific configuration
+        microvm = {
+          # Use cloud-hypervisor for better performance
+          hypervisor = lib.mkDefault "cloud-hypervisor";
+
+          # Resource allocation
+          vcpu = 8;
+          mem = 4096; # 4GB RAM
+
+          # Disk for writable overlay
+          volumes = [{
+            image = "overlay.img";
+            mountPoint = "/nix/.rw-store";
+            size = 8192; # 8GB
+          }];
+
+          # Shared directories with host using virtiofs
+          shares = [
+            {
+              # Share the host's /nix/store for accessing packages
+              proto = "virtiofs";
+              tag = "ro-store";
+              source = "/nix/store";
+              mountPoint = "/nix/.ro-store";
+            }
+            {
+              proto = "virtiofs";
+              tag = "workspace";
+              source = "/home/googlebot/sandboxed/${name}/workspace";
+              mountPoint = "/home/googlebot/workspace";
+            }
+            {
+              proto = "virtiofs";
+              tag = "ssh-host-keys";
+              source = "/home/googlebot/sandboxed/${name}/ssh-host-keys";
+              mountPoint = "/etc/ssh-host-keys";
+            }
+            {
+              proto = "virtiofs";
+              tag = "claude-config";
+              source = "/home/googlebot/sandboxed/${name}/claude-config";
+              mountPoint = "/home/googlebot/claude-config";
+            }
+          ];
+
+          # Writeable overlay for /nix/store
+          writableStoreOverlay = "/nix/.rw-store";
+
+          # TAP interface for bridged networking
+          # The interface name "vm-*" matches the pattern in common/network/microvm.nix
+          # which automatically attaches it to the microbr bridge
+          interfaces = [{
+            type = "tap";
+            id = "vm-${name}";
+            # Generate a deterministic MAC from workspace name (02: prefix = locally administered)
+            mac =
+              let
+                hash = builtins.hashString "sha256" name;
+              in
+              "02:${builtins.substring 0 2 hash}:${builtins.substring 2 2 hash}:${builtins.substring 4 2 hash}:${builtins.substring 6 2 hash}:${builtins.substring 8 2 hash}";
+          }];
+
+          # Enable vsock for systemd-notify integration
+          vsock.cid =
+            if ws.cid != null
+            then ws.cid
+            else nameToCid name;
+        };
+      }
+    ];
+    autostart = ws.autoStart;
+  };
+in
+{
+  config = mkIf (cfg.enable && vmWorkspaces != { }) {
+    # Convert VM workspace configs to microvm.nix format
+    microvm.vms = mapAttrs mkVmConfig vmWorkspaces;
+  };
+}