fix email notification, again, again

backup.nix

@@ -98,8 +98,16 @@ in {
     wants = [ "network-online.target" ];
     requires = [ "postgresql.service" ];
 
-    unitConfig.OnFailure = let
-      script = pkgs.writeScript "misskey-backup-failure" ''
+    unitConfig.OnFailure = "misskey-backup-failure.service";
+  };
+
+  systemd.services.misskey-backup-failure = {
+    description = "Misskey backup failure notification";
+
+    serviceConfig.User = user;
+    serviceConfig.Type = "oneshot";
+
+    script = ''
       invocationId="$(systemctl show --value -p InvocationID misskey-backup.service)"
       logs="$(journalctl _SYSTEMD_INVOCATION_ID= -u misskey-backup.service)"
 
@@ -112,7 +120,8 @@ in {
       )
       "
     '';
-    in "${script}";
+
+    requires = [ "postfix.service" ];
   };
 
   systemd.timers.misskey-backup = { timerConfig.Persistent = true; };