refactor: added flake parts

modules/hosts/nixos/emergent/legacy-storage.nix

@@ -0,0 +1,53 @@
+{...}: {
+  # Legacy storage configuration for emergent
+  # This file manually defines ZFS datasets matching the existing on-disk layout
+  # to allow incremental migration to the new storage module (generateBase = true).
+  #
+  # Current on-disk dataset layout:
+  #   rpool/local/                    - parent (canmount=off)
+  #   rpool/local/system/nix          - nix store
+  #   rpool/local/system/root         - root filesystem
+  #
+  # Migration plan:
+  #   Phase 1: Rename datasets on disk (boot from live USB)
+  #     zfs rename -p rpool/local/system/nix rpool/persist/local/nix
+  #     zfs rename rpool/local rpool/persist/local
+  #     # This moves: local/system/root -> persist/local/root (need to rename after)
+  #     # Actually, since local/system/root needs to become persist/local/root:
+  #     zfs rename rpool/persist/local/system/root rpool/persist/local/root
+  #     zfs destroy rpool/persist/local/system  # now empty
+  #     # Recreate blank snapshot:
+  #     zfs destroy rpool/persist/local/root@blank
+  #     zfs snapshot rpool/persist/local/root@blank
+  #
+  #   Phase 2: Delete this file, remove its import from default.nix, rebuild.
+  flake.nixosModules.emergentLegacyStorage = {...}: {
+    # Disable automatic base dataset generation so we can define them manually
+    storage.generateBase = false;
+
+    # Manually define ZFS datasets matching the existing on-disk layout
+    storage.zfs.datasets = {
+      "local" = {
+        type = "zfs_fs";
+        mount = null;
+      };
+      "local/system/nix" = {
+        type = "zfs_fs";
+        mount = "/nix";
+        atime = "off";
+        relatime = "off";
+        snapshot = {
+          autoSnapshot = false;
+        };
+      };
+      "local/system/root" = {
+        type = "zfs_fs";
+        mount = "/";
+        snapshot = {
+          blankSnapshot = true;
+          autoSnapshot = true;
+        };
+      };
+    };
+  };
+}