Add a generic installer that asks for the basics and builds offline

The installer ISO no longer needs a prebuilt system: `router-setup` asks
for the disk, the WAN and LAN interfaces, DHCP or PPPoE (optionally on a
VLAN), host name, LAN address and a password, writes settings.json and
the secrets, builds that router offline (the ISO carries a reference
router system whose closure has everything the build needs) and installs
it with `router-install --system`.

The password is used for the web UI and, hashed, as root's console
password (routerSettings sets root's hashedPasswordFile; it applies when
the account is created at installation).

checks.setup answers router-setup on the console and checks the installed
box: its settings, the web UI and console login with that password, and
a rebuild that reproduces the installed system.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AeFqV9dZrK6nipHkPfyM4F

tests/setup.nix

@@ -0,0 +1,122 @@
+# The generic installer: router-setup is answered on its console (DHCP uplink,
+# LAN address, web UI password), builds the router offline and installs it.
+# The installed box must come up with those settings, serve the web UI with
+# that password, and rebuild to exactly itself.
+{ self, pkgs }:
+let
+  common = import ./common.nix;
+
+  # Only so the test driver can talk to the installed system.
+  local = pkgs.writeText "local.nix" ''
+    { lib, modulesPath, ... }:
+    {
+      imports = [ (modulesPath + "/testing/test-instrumentation.nix") ];
+      # The instrumentation empties root's password; keep router-setup's.
+      users.users.root.hashedPasswordFile = lib.mkForce "/var/lib/router/root-password";
+    }
+  '';
+
+  sharedDisk = {
+    virtualisation.diskImage = "./target.qcow2";
+    virtualisation.diskSize = 8192;
+    # Evaluating and building a NixOS system takes memory.
+    virtualisation.memorySize = 3072;
+  };
+
+  answers = pkgs.writeText "answers" ''
+    /dev/vda
+    eth1
+    eth2
+    dhcp
+    gw
+    192.168.10.1
+    hunter2hunter2
+    hunter2hunter2
+
+    /dev/vda
+  '';
+in
+pkgs.testers.runNixOSTest {
+  name = "router-setup";
+
+  nodes = {
+    installer =
+      { lib, ... }:
+      {
+        imports = [
+          sharedDisk
+          (self.lib.setupModule { inherit local; })
+          common.tools
+        ];
+        environment.etc."router-test-local.nix".source = local;
+        # The interfaces router-setup offers.
+        virtualisation.vlans = [
+          1
+          2
+        ];
+        virtualisation.fileSystems."/".autoFormat = true;
+        virtualisation.emptyDiskImages = [ 1024 ];
+        virtualisation.rootDevice = "/dev/vdb";
+        nix.settings.substituters = lib.mkForce [ ];
+      };
+
+    target = {
+      imports = [ sharedDisk ];
+      virtualisation.vlans = [
+        1
+        2
+      ];
+      virtualisation.useBootLoader = true;
+      virtualisation.useEFIBoot = true;
+      virtualisation.useDefaultFilesystems = false;
+      virtualisation.efi.keepVariables = false;
+      virtualisation.fileSystems."/" = {
+        device = "/dev/disk/by-label/this-is-not-real-and-will-never-be-used";
+        fsType = "ext4";
+      };
+    };
+  };
+
+  testScript = ''
+    installer.start()
+    installer.wait_for_unit("multi-user.target")
+
+    with subtest("router-setup refuses to install without the disk name"):
+        installer.fail("printf '/dev/vda\\neth1\\neth2\\ndhcp\\n\\n\\nhunter2hunter2\\nhunter2hunter2\\n\\nno\\n' | router-setup")
+        installer.fail("blkid /dev/vda1")
+
+    with subtest("router-setup builds the answered configuration offline and installs it"):
+        installer.succeed("router-setup --local /etc/router-test-local.nix < ${answers} >&2")
+        installer.shutdown()
+
+    target.state_dir = installer.state_dir
+    target.start()
+    target.wait_for_unit("multi-user.target")
+
+    with subtest("the installed router has the answered settings"):
+        assert target.succeed("hostname").strip() == "gw"
+        target.wait_until_succeeds("ip -4 addr show dev eth2 | grep -q 192.168.10.1/24")
+        target.succeed("grep -q '192.168.10.100 - 192.168.10.200' /etc/kea/dhcp4-server.conf")
+        settings = target.succeed("cat /var/lib/router/config/settings.json")
+        assert '"eth1"' in settings and '"dhcp"' in settings, settings
+        assert target.succeed("stat -c %a /var/lib/router/webui-password").strip() == "600"
+
+    with subtest("the web UI accepts the password given to router-setup"):
+        target.wait_for_unit("router-webui.service")
+        target.wait_until_succeeds("curl -sk -o /dev/null https://127.0.0.1/login")
+        code = target.succeed("curl -sk -o /dev/null -w '%{http_code}' -d password=hunter2hunter2 https://127.0.0.1/login")
+        assert code == "303", code
+
+    with subtest("root logs in on the console with the same password"):
+        target.wait_until_tty_matches("1", "login: ")
+        target.send_chars("root\n")
+        target.wait_until_tty_matches("1", "Password: ")
+        target.send_chars("hunter2hunter2\n")
+        target.wait_until_succeeds("pgrep -u root -t tty1 bash")
+        assert target.succeed("stat -c %a /var/lib/router/root-password").strip() == "600"
+
+    with subtest("the box rebuilds to exactly the installed system"):
+        out = target.succeed("router-apply 2>&1")
+        assert "no changes" in out, out
+  '';
+}