fix: refuse profile narrowings without cores

MiSTer and BizHawk declare cores: []. --region, --one-per-slot and
--no-game-data read the profiles of the cores a platform runs, so their
packs and manifests withdrew nothing under a name and README that said
they had. generate_pack and verify now refuse the flags for a named
platform and leave it out under --all.

scripts/generate_pack.py

@@ -75,6 +75,7 @@ from common import (
     load_database,
     load_emulator_profiles,
     load_platform_config,
+    profile_blind_platforms,
     MANUFACTURER_PREFIXES,
     require_yaml,
     ProfileSelectionError,
@@ -3074,6 +3075,42 @@ def _pack_label(source: str, required_only: bool) -> str:
     return f"[source={source}, required]" if required_only else f"[source={source}]"
 
 
+def _without_profile_blind(
+    args: argparse.Namespace,
+    platforms: list[str],
+    emu_profiles: dict,
+    target_cores_cache: dict[str, set[str] | None],
+) -> list[str]:
+    """Refuse a narrowing read from profiles on a platform that runs none.
+
+    Named, the platform is refused. Under --all it is left out with a
+    notice, as an empty truth pack is under --all-variants.
+    """
+    flags = [
+        flag for flag, given in (
+            ("--region", getattr(args, "regions", None)),
+            ("--one-per-slot", getattr(args, "one_per_slot", False)),
+            ("--no-game-data", getattr(args, "no_game_data", False)),
+        ) if given
+    ]
+    if not flags:
+        return platforms
+    blind = profile_blind_platforms(
+        platforms, args.platforms_dir, emu_profiles,
+        target_cores_cache if args.target else None,
+    )
+    for name in blind:
+        message = (
+            f"{name} runs no core a profile describes, and {', '.join(flags)} "
+            "reads the profiles"
+        )
+        if not args.all:
+            print(f"ERROR: {message}: drop {', '.join(flags)}", file=sys.stderr)
+            sys.exit(1)
+        print(f"  {message}: left out")
+    return [name for name in platforms if name not in blind]
+
+
 def _truth_layer_is_empty(
     platform: str, platforms_dir: str, emu_profiles: dict, target_cores: set[str] | None
 ) -> bool:
@@ -3785,6 +3822,9 @@ def _main(held: contextlib.ExitStack) -> None:
         platforms = _platforms_with_systems(
             args, platforms, system_filter, emu_profiles, target_cores_cache
         )
+    platforms = _without_profile_blind(
+        args, platforms, emu_profiles, target_cores_cache
+    )
 
     data_registry = load_data_dir_registry(args.platforms_dir)
     # The output directory is claimed before the data directory refresh: a