microvms/flake.nix

{
	description = "Sandboxed MicroVMs";

	# nixConfig = {
	# 	extra-substituters = [ "https://microvm.cachix.org" ];
	# 	extra-trusted-public-keys = [ "microvm.cachix.org-1:oXnBc6hRE3eX5rSYdRyMYXnfzcCxC7yKPTbZXALsqys=" ];
	# };

	inputs = {
		nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
		microvm = {
			url = "github:microvm-nix/microvm.nix";
			inputs.nixpkgs.follows = "nixpkgs";
		};
		nullclaw.url = "github:illustris/nullclaw?ref=fix-nix";
		nix-mcp.url = "github:illustris/nix-mcp";
	};

	outputs = { self, nixpkgs, microvm, nullclaw, nix-mcp }: let
		system = "x86_64-linux";

		macFromName = name: let
			hash = builtins.hashString "sha256" name;
			b = i: builtins.substring (i * 2) 2 hash;
		in "02:${b 0}:${b 1}:${b 2}:${b 3}:${b 4}";

		mkMicrovm = name: {
			vcpu ? 2,
			mem ? 2048,
			extraModules ? []
		}: nixpkgs.lib.nixosSystem {
			inherit system;
			modules = [
				microvm.nixosModules.microvm
				({ pkgs, ... }: {
					networking.hostName = name;
					users.users.root.password = "";
					services.getty.autologinUser = "root";
					microvm = {
						hypervisor = "qemu";
						inherit vcpu mem;
						socket = "${name}.socket";
						interfaces = [{
							type = "user";
							id = "usernet";
							mac = macFromName name;
						}];
						shares = [
							{
								proto = "9p";
								tag = "ro-store";
								source = "/nix/store";
								mountPoint = "/nix/.ro-store";
							}
							{
								proto = "9p";
								tag = "${name}-data";
								source = "/home/illustris/Documents/microvms/data/${name}";
								mountPoint = "/var/lib/${name}";
							}
						];
						# qemu.extraArgs = [
						# 	"-fw_cfg" "name=opt/claude-auth,file=/home/illustris/.claude.json"
						# ];
					};
					nix = {
						nixPath = [ "nixpkgs=${pkgs.path}" ];
						settings.experimental-features = [ "nix-command" "flakes" ];
					};
					system.stateVersion = "25.11";
				})
			] ++ extraModules;
		};
	in {
		packages.${system} = nixpkgs.lib.mapAttrs (_: v: v.config.microvm.declaredRunner) self.nixosConfigurations;

		nixosModules.storeOverlay = {
			microvm.writableStoreOverlay = "/nix/.rw-store";
			fileSystems."/nix/.rw-store" = {
				fsType = "tmpfs";
				options = [ "size=4G" "mode=0755" ];
				neededForBoot = true;
			};
		};

		nixosConfigurations = nixpkgs.lib.mapAttrs mkMicrovm {
			cc-sandbox = {
				vcpu = 8;
				mem = 8192;
				extraModules = [({ pkgs, ... }: {
					nixpkgs.config.allowUnfree = true;
					nix.settings.experimental-features = [ "nix-command" "flakes" ];

					environment.systemPackages = with pkgs; [
						claude-code-bin
						git
						curl
						vim
						nix-mcp.packages.x86_64-linux.default
					];

					microvm = {
						writableStoreOverlay = "/nix/.rw-store";
						shares = [
							{
								proto = "9p";
								tag = "claude-config";
								source = "/home/illustris/.claude";
								mountPoint = "/var/lib/claude-lower";
								readOnly = true;
							}
						];
						qemu.extraArgs = [
							"-fw_cfg"
							"name=opt/claude-auth,file=/home/illustris/.claude.json"
						];
					};

					systemd.services.claude-auth = {
						description = "Copy Claude auth token from fw_cfg";
						wantedBy = [ "multi-user.target" ];
						before = [ "multi-user.target" ];
						serviceConfig = {
							Type = "oneshot";
							ExecStart = "/bin/sh -c 'cp /sys/firmware/qemu_fw_cfg/by_name/opt/claude-auth/raw /root/.claude.json && chmod 600 /root/.claude.json'";
							RemainAfterExit = true;
						};
					};

					fileSystems = {
						# tmpfs backing for the writable nix store overlay
						"/nix/.rw-store" = {
							fsType = "tmpfs";
							options = [ "size=4G" "mode=0755" ];
							neededForBoot = true;
						};

						# Claude config: ephemeral overlay on top of host's ~/.claude
						"/var/lib/claude-rw" = {
							fsType = "tmpfs";
							options = [ "size=128M" "mode=0700" ];
						};
						"/root/.claude".overlay = {
							lowerdir = [ "/var/lib/claude-lower" ];
							upperdir = "/var/lib/claude-rw/upper";
							workdir = "/var/lib/claude-rw/work";
						};
					};
				})];
			};

			nullclaw = {
				vcpu = 2;
				mem = 4096;
				extraModules = [({ pkgs, ... }: {
					imports = [ self.nixosModules.storeOverlay ];
					environment.systemPackages = with pkgs; [
						nullclaw.packages.${system}.default
						tmux
					];
				})];
			};
		};
	};
}