fix: judge core extras by content where the builder does

The gap analysis answered from the name index, so a core extra whose
local copy contradicts its declared hash counted as held. Under a
digest mode the builder drops exactly that file, so the coverage report
described a pack that would not contain it: seven files across
Batocera, Recalbox and RetroBat.

An entry that states what its content should be is now resolved by
content; the name still answers for entries that declare nothing to
check against, and existence mode is unchanged because there the
frontend never opens the file and the pack does carry it.

tests/test_native_mode.py

@@ -116,5 +116,100 @@ class BothConsumersAgree(unittest.TestCase):
         )
 
 
+class GapAnalysisAgreesWithTheBuilder(unittest.TestCase):
+    """"Available" must mean the pack will carry it.
+
+    find_undeclared_files answered from the name index, so a core extra whose
+    local copy contradicts its declared hash counted as held. Under a digest
+    mode the builder drops exactly that file, so the coverage report described
+    a pack that would not contain it: seven such files across three platforms.
+    """
+
+    def _fixture(self):
+        import hashlib
+        import tempfile
+
+        tmp = tempfile.TemporaryDirectory()
+        root = Path(tmp.name)
+        (root / "emulators").mkdir()
+        rom = root / "collide.rom"
+        rom.write_bytes(b"THE BYTES THE COLLECTION HOLDS")
+        sha1 = hashlib.sha1(rom.read_bytes()).hexdigest()
+        db = {
+            "files": {
+                sha1: {
+                    "path": str(rom),
+                    "name": "collide.rom",
+                    "size": rom.stat().st_size,
+                    "sha1": sha1,
+                    "md5": hashlib.md5(rom.read_bytes()).hexdigest(),
+                    "sha256": hashlib.sha256(rom.read_bytes()).hexdigest(),
+                    "crc32": "00000000",
+                }
+            },
+            "indexes": {
+                "by_name": {"collide.rom": [sha1]},
+                "by_md5": {hashlib.md5(rom.read_bytes()).hexdigest(): sha1},
+                "by_sha256": {},
+                "by_crc32": {},
+                "by_path_suffix": {},
+            },
+        }
+        (root / "emulators" / "demo.yml").write_text(
+            "emulator: demo\n"
+            "type: libretro\n"
+            "display_name: Demo\n"
+            "systems: [demo-system]\n"
+            "cores: [demo]\n"
+            "files:\n"
+            "  - name: collide.rom\n"
+            "    system: demo-system\n"
+            "    required: true\n"
+            "    md5: \"" + "f" * 32 + "\"\n"
+        )
+        return tmp, root, db
+
+    def _in_repo(self, mode: str) -> bool:
+        import common
+        from verify import find_undeclared_files
+
+        tmp, root, db = self._fixture()
+        try:
+            common._emulator_profiles_cache.clear()
+            profiles = common.load_emulator_profiles(str(root / "emulators"))
+            config = {
+                "platform": "Demo",
+                "verification_mode": mode,
+                "cores": ["demo"],
+                "systems": {},
+            }
+            found = find_undeclared_files(
+                config, str(root / "emulators"), db, emu_profiles=profiles
+            )
+            entry = next(e for e in found if e["name"] == "collide.rom")
+            return bool(entry["in_repo"])
+        finally:
+            common._emulator_profiles_cache.clear()
+            tmp.cleanup()
+
+    def test_a_digest_mode_does_not_call_a_contradicted_copy_available(self):
+        self.assertFalse(
+            self._in_repo("md5"),
+            "the builder drops this file, so the report must not count it",
+        )
+
+    def test_existence_mode_still_counts_it(self):
+        """The frontend never opens the file, so the pack carries it."""
+        self.assertTrue(self._in_repo("existence"))
+
+    def test_the_two_modes_answer_the_way_the_shared_predicate_says(self):
+        for mode in nativemode.MODES:
+            with self.subTest(mode=mode):
+                self.assertEqual(
+                    self._in_repo(mode),
+                    not nativemode.hash_mismatch_excludes_file(mode),
+                )
+
+
 if __name__ == "__main__":
     unittest.main()