New partition rollback mechanism!

hosts/nixos/calypso/filesystems/default.nix

@@ -60,7 +60,7 @@
         btrfs subvolume delete /mnt/root
 
       echo "restoring blank /root subvolume..."
-      btrfs subvolume snapshot /mnt/root-blank /mnt/root
+      btrfs subvolume snapshot /mnt/blank /mnt/root
 
       # Once we're done rolling back to a blank snapshot,
       # we can unmount /mnt and continue on the boot process.

hosts/nixos/calypso/filesystems/partitions.nix

@@ -43,6 +43,16 @@
                   ];
                 };
                 # }}}
+                # {{{ /blank
+                "blank" = {
+                  mountpoint = "/blank";
+                  # should we reuse the `root` options here?
+                  mountOptions = [
+                    "compress=zstd"
+                    "noatime"
+                  ];
+                };
+                # }}}
                 # {{{ /swap
                 "swap" = {
                   mountpoint = "/.swapvol";