feat: add a --no-game-data pack narrowing

The install manifest marks each game data file "category": "game_data":
a platform entry only game data profile entries read, or a core file its
profile declares game data. Firmware carries no category. Every manifest
says "categorized": true so the installer can refuse an older list.

generate_pack.py --no-game-data cuts those files from the platform list
and the core profiles before the build, names each one with the cores that
read it as game data, and tags the pack _NoGameData through _narrowings.
verify.py and the pack check take the same cut, so --verify-packs and the
report describe the pack the builder wrote. Modes without a platform
(--emulator, --system alone, --from-md5) and --all-variants refuse it.

scripts/verify.py

@@ -1121,14 +1121,33 @@ def verify_platform(
     data_dir_registry: dict | None = None,
     regions: list[str] | None = None,
     system_filter: list[str] | None = None,
+    no_game_data: bool = False,
 ) -> dict:
     """Verify all BIOS files for a platform, including cross-reference gaps.
 
+    ``no_game_data`` reports on the pack built with --no-game-data: the
+    game data cut as the builder cuts it, and named in ``left_out``.
+
     A region priority list narrows the report to the files a pack built with the
     same list would carry, using the same selection function as the builder.
     ``system_filter`` does the same for a pack built with --system: the
     systems it keeps and the core extras those systems own.
     """
+    left_out: list[str] = []
+    if no_game_data:
+        from gamedata import without_game_data
+
+        if emu_profiles is None:
+            emu_profiles = load_emulator_profiles(emulators_dir)
+        cut = without_game_data(config, emu_profiles, data_dir_registry, target_cores)
+        config, emu_profiles = cut.config, cut.profiles
+        systems = config.get("systems", {})
+        in_scope = set(select_systems(systems, system_filter) if system_filter else systems)
+        cut.left_out = [
+            item for item in cut.left_out
+            if item.layer == "core" or item.system in in_scope
+        ]
+        left_out = cut.report_lines()
     # Normalized once: a typo in a platform YAML must not verify with one
     # mode and be scored with another.
     mode = normalize_mode(config.get("verification_mode"))
@@ -1524,6 +1543,7 @@ def verify_platform(
         "undeclared_files": undeclared,
         "exclusion_notes": exclusions,
         "region_fallbacks": sorted(region_fallbacks),
+        **({"left_out": left_out} if no_game_data else {}),
         "details": details,
         "ground_truth_coverage": {
             "with_validation": with_validation,
@@ -1833,6 +1853,8 @@ def print_platform_result(
         # them missing, as an offline build leaves them out.
         shown = ", ".join(fetched[:10]) + (f" (+{len(fetched) - 10})" if len(fetched) > 10 else "")
         print(f"  Release assets fetched when the pack is built ({len(fetched)}): {shown}")
+    for line in result.get("left_out") or []:
+        print(f"  {line}")
     fallbacks = result.get("region_fallbacks") or []
     if fallbacks:
         from packreadme import _group_label
@@ -2539,6 +2561,7 @@ def _refuse_listing_narrowings(
         ("--verbose", args.verbose),
         ("--destinations", args.destinations),
         ("--offline", args.offline),
+        ("--no-game-data", getattr(args, "no_game_data", False)),
     ):
         if on:
             parser.error(f"{flag} is incompatible with {listing}")
@@ -2562,6 +2585,9 @@ def _refuse_mode_flags(args: argparse.Namespace, parser: argparse.ArgumentParser
          "--destinations requires --platform or --all"),
         (args.offline and not (args.platform or args.all),
          "--offline requires --platform or --all"),
+        # Game data is categorized against a platform's list and its cores.
+        (getattr(args, "no_game_data", False) and not (args.platform or args.all),
+         "--no-game-data requires --platform or --all"),
         (args.destinations and getattr(args, "region", None),
          "--destinations describes the full pack and is incompatible with --region"),
     ):
@@ -2622,6 +2648,11 @@ def _main(held: contextlib.ExitStack) -> None:
         action="store_true",
         help="List available targets for the platform",
     )
+    parser.add_argument(
+        "--no-game-data", action="store_true",
+        help="Report on the pack built with --no-game-data: game data left "
+        "out and named, firmware only",
+    )
     parser.add_argument(
         "--db", default=DEFAULT_DB,
         help="database file to read (default: %(default)s)",
@@ -2783,6 +2814,7 @@ def _main(held: contextlib.ExitStack) -> None:
             data_dir_registry=data_registry,
             regions=requested_regions,
             system_filter=platform_systems,
+            no_game_data=getattr(args, "no_game_data", False),
         )
         names = [
             load_platform_config(p, args.platforms_dir).get("platform", p)