fix(copyparty): preserve shared volume access

configs/nixos/modules/services/copyparty.nix

@@ -34,7 +34,13 @@ let
 
   renderAccess = permission: accounts: "    ${permission}: ${lib.concatStringsSep ", " accounts}";
 
-  renderFlags = flags: lib.concatMapStringsSep "\n" (flag: "    ${flag}") flags;
+  hasFlag = name: flags: lib.any (flag: lib.hasPrefix "${name}:" flag || lib.hasPrefix "${name}=" flag) flags;
+
+  defaultPermissionFlags = flags:
+    lib.optionals (!(hasFlag "chmod_d" flags)) [ "chmod_d: 2770" ]
+    ++ lib.optionals (!(hasFlag "chmod_f" flags)) [ "chmod_f: 660" ];
+
+  renderFlags = flags: lib.concatMapStringsSep "\n" (flag: "    ${flag}") (flags ++ defaultPermissionFlags flags);
 
   renderVolume = urlPath: volume: ''
     [${urlPath}]