fix: hold data trees while packs are verified

scripts/generate_pack.py

@@ -2993,6 +2993,9 @@ def _main(held: contextlib.ExitStack) -> None:
     # Quick-exit modes: --verify-packs alone = verify existing packs only
     # Combined with --all-variants, generation runs first then verify
     if args.verify_packs and not args.all_variants:
+        # The check resolves core files against data/ like the build did;
+        # a refresh swapping a tree mid-check would judge another tree.
+        hold_data_dirs(held, load_data_dir_registry(args.platforms_dir))
         with _pack_output_lock(args.output_dir, exclusive=False):
             _run_verify_packs(args)
         return