fix: strip only a hash suffix off variant names

slots dropped the last extension of any .variants/ name, so a
variant stored under its plain name (63 of them, aes.zip among
them) was not the family of its primary and a platform declaring
both at one path would read as a collision. The database already
stripped an eight-hex suffix only; both now read one function.

scripts/common.py

@@ -771,6 +771,18 @@ def _resolve_agnostic(
     return None
 
 
+_VARIANT_SUFFIX = re.compile(r"\.[0-9a-f]{8}$")
+
+
+def variant_base_name(name: str) -> str:
+    """The name a .variants/ copy stands in for: naomi2.zip.da79eca4 -> naomi2.zip.
+
+    Only an eight-hex-digit suffix is a variant tag. A variant stored under
+    its plain name (.variants/aes.zip) already is that name.
+    """
+    return _VARIANT_SUFFIX.sub("", name)
+
+
 def _affinity_tokens(text: str) -> set[str]:
     return {
         token

scripts/generate_db.py

@@ -28,6 +28,7 @@ from common import (
     load_provenance_snapshots,
     require_yaml,
     source_yaml_paths,
+    variant_base_name,
     write_if_changed,
     write_text_atomic,
     yaml_load,
@@ -65,17 +66,9 @@ def should_skip(path: Path) -> bool:
 
 def _canonical_name(filepath: Path) -> str:
     """Get canonical filename, stripping .variants/ hash suffix."""
-    name = filepath.name
-    if "/.variants/" in str(filepath) or "\\.variants\\" in str(filepath):
-        # naomi2.zip.da79eca4 -> naomi2.zip
-        parts = name.rsplit(".", 1)
-        if (
-            len(parts) == 2
-            and len(parts[1]) == 8
-            and all(c in "0123456789abcdef" for c in parts[1])
-        ):
-            return parts[0]
-    return name
+    if ".variants" in filepath.parts:
+        return variant_base_name(filepath.name)
+    return filepath.name
 
 
 def scan_bios_dir(bios_dir: Path, cache: dict, force: bool) -> tuple[dict, dict, dict]:

scripts/slots.py

@@ -31,6 +31,7 @@ from common import (
     resolve_local_file,
     resolve_platform_cores,
     runs_standalone,
+    variant_base_name,
 )
 from packresolve import preferred_entries
 from validation import outside_gap_scope
@@ -752,7 +753,7 @@ def _same_file_family(paths: list[str]) -> bool:
         if "/.variants/" in path:
             directory, _, name = path.rpartition("/")
             directory = directory[: -len("/.variants")]
-            name = name.rsplit(".", 1)[0]
+            name = variant_base_name(name)
             path = f"{directory}/{name}"
         canonical.add(path.casefold())
     return len(canonical) == 1

tests/test_slots.py

@@ -459,6 +459,32 @@ class TestSelfContradictingDestinations(unittest.TestCase):
             )
         )
 
+    def test_a_variant_kept_under_its_plain_name_is_one_family(self):
+        # 63 variants carry no hash suffix, aes.zip among them.
+        self.assertTrue(
+            slots._same_file_family(
+                ["bios/SNK/Neo Geo/aes.zip", "bios/SNK/Neo Geo/.variants/aes.zip"]
+            )
+        )
+
+    def test_only_a_hash_suffix_is_stripped(self):
+        self.assertFalse(
+            slots._same_file_family(
+                ["bios/M/C/rom.zip", "bios/M/C/.variants/rom.zip.zip"]
+            )
+        )
+
+    def test_the_database_and_the_arbiter_read_one_rule(self):
+        import generate_db  # noqa: PLC0415
+
+        variant = Path("bios/M/C/.variants/aes.zip")
+        self.assertEqual(generate_db._canonical_name(variant), "aes.zip")
+        for module in ("slots.py", "generate_db.py"):
+            source = (Path(__file__).resolve().parents[1] / "scripts" / module).read_text()
+            with self.subTest(module=module):
+                self.assertIn("variant_base_name(", source)
+                self.assertNotIn('rsplit(".", 1)[0]', source)
+
     def test_two_machines_are_not_one_family(self):
         self.assertFalse(
             slots._same_file_family(