feat: add new machine "sentinel", a Hetzner Cloud server

hosts/sentinel/fs.nix

@@ -0,0 +1,55 @@
+{
+  config,
+  lib,
+  extraLib,
+  pkgs,
+  ...
+}: {
+  disko.devices = {
+    disk = {
+      main = {
+        type = "disk";
+        device = "/dev/disk/by-id/${config.repo.secrets.local.disk.main}";
+        content = with extraLib.disko.gpt; {
+          type = "table";
+          format = "gpt";
+          partitions = [
+            (partEfi "efi" "0%" "512MiB")
+            (partLuksZfs "rpool" "512MiB" "100%")
+          ];
+        };
+      };
+    };
+    zpool = with extraLib.disko.zfs; {
+      rpool =
+        defaultZpoolOptions
+        // {
+          datasets = {
+            "local" = unmountable;
+            "local/root" =
+              filesystem "/"
+              // {
+                postCreateHook = "zfs snapshot rpool/local/root@blank";
+              };
+            "local/nix" = filesystem "/nix";
+            "safe" = unmountable;
+            "safe/persist" = filesystem "/persist";
+          };
+        };
+    };
+  };
+
+  fileSystems."/persist".neededForBoot = true;
+
+  # After importing the rpool, rollback the root system to be empty.
+  boot.initrd.systemd.services.impermanence-root = {
+    wantedBy = ["initrd.target"];
+    after = ["zfs-import-rpool.service"];
+    before = ["sysroot.mount"];
+    unitConfig.DefaultDependencies = "no";
+    serviceConfig = {
+      Type = "oneshot";
+      ExecStart = "${pkgs.zfs}/bin/zfs rollback -r rpool/local/root@blank";
+    };
+  };
+}