Add systemd repart to grow root partition on boot

systems/base/configuration.nix

@@ -21,7 +21,6 @@
     services.qemuGuest.enable = lib.mkDefault true;
 
     boot.loader.systemd-boot.enable = true;
-    boot.growPartition = lib.mkDefault true;
 
     # Allow remote updates with flakes and non-root users
     nix.settings.trusted-users = [
@@ -98,6 +97,45 @@
       };
     };
 
+    # Resize partition on boot
+    systemd.repart.partitions = {
+      "00-esp" = {
+        Type = "esp";
+        SizeMinBytes = "550M";
+        SizeMaxBytes = "550M";
+        Format = "vfat";
+      };
+      "10-root" = {
+        Type = "linux-generic";
+        Format = "btrfs";
+      };
+    };
+    boot.initrd = {
+      # Ensure `sgdisk` is included in the initrd
+      packages = [ pkgs.gptfdisk ];
+
+      # Custom systemd units in the initrd
+      systemd = {
+        enable = true;
+        units = {
+          "resize-gpt.service" = {
+            description = "Resize GPT to use full disk size";
+            wants = [ "systemd-repart.service" ];
+            before = [ "systemd-repart.service" ];
+            serviceConfig = {
+              Type = "oneshot";
+              ExecStart = "/run/current-system/sw/bin/sgdisk --move-second-header /dev/sdX";
+            };
+          };
+          "systemd-repart.service".wants = [ "resize-gpt.service" ];
+        };
+        repart = {
+          enable = true;
+          device = "/dev/sda";
+        };
+      };
+    };
+
     system.stateVersion = lib.mkDefault "24.05";
   };
 }