refactor: share the core file lookup with verify

verify replayed the builder's placement of core files with a bare name lookup, without the archive index, the data directories or the core's own choice of copy. It compared other bytes than the pack's (blueMSX's MSX2P.rom from bios/ against the data tree's copy) and let an unresolved file take a path the builder leaves free. ExtraResolver now holds the builder's lookup and both call it.

tests/test_audit_regressions.py

@@ -2711,6 +2711,9 @@ class ARegionDroppedExtraBlocksNothing(unittest.TestCase):
         with tempfile.TemporaryDirectory(dir=TMP_ROOT) as directory:
             other = Path(directory) / "FOO.ROM"
             other.write_bytes(b"other bytes")
+            first = Path(directory) / "foo.rom"
+            first.write_bytes(b"first bytes")
+            copies = {"foo.rom": str(first), "FOO.ROM": str(other)}
             extras = [
                 {"name": "foo.rom", "destination": "foo.rom", "source_emulator": "a"},
                 {"name": "FOO.ROM", "destination": "FOO.ROM", "source_emulator": "b"},
@@ -2721,7 +2724,8 @@ class ARegionDroppedExtraBlocksNothing(unittest.TestCase):
                 with mock.patch.object(packextras, "_collect_emulator_extras",
                                        return_value=extras), \
                         mock.patch.object(packextras, "resolve_local_file",
-                                          return_value=(str(other), "name_exact")):
+                                          side_effect=lambda fe, *a, **k: (
+                                              copies[fe["name"]], "name_exact")):
                     return packextras.hidden_extras(
                         config, "emulators", {"files": {}}, {}, {}, None, region_drops
                     )

tests/test_hidden_extras.py

@@ -154,5 +154,38 @@ class TheGapReportIsComputedOnce(unittest.TestCase):
         self.assertEqual(counted.call_count, 1)
 
 
+class TheReplayResolvesAsTheBuilder(unittest.TestCase):
+    """verify replayed the builder's placement with a bare name lookup: it
+    compared other bytes than the pack's, and an extra it could not resolve
+    still took its path and blocked the next one the builder places."""
+
+    def test_an_unresolved_extra_blocks_nothing(self):
+        from unittest import mock
+
+        import packextras
+
+        extras = [
+            {"destination": "box.bin/inner.rom", "name": "inner.rom",
+             "source_emulator": "a", "source_name": "inner.rom", "source_path": ""},
+            {"destination": "box.bin", "name": "box.bin",
+             "source_emulator": "b", "source_name": "box.bin", "source_path": ""},
+        ]
+
+        class Resolver:
+            def resolve(self, fe, dest):
+                return (None, "not_found", "") if fe["name"] == "inner.rom" else (
+                    "bios/box.bin", "sha1_exact", ""
+                )
+
+        placed: set[str] = set()
+        with mock.patch.object(packextras, "_collect_emulator_extras", return_value=extras):
+            hidden = packextras.hidden_extras(
+                {"systems": {}}, "emulators", {"files": {}}, {}, {},
+                placed=placed, resolver=Resolver(),
+            )
+        self.assertEqual(hidden, {})
+        self.assertEqual(placed, {"box.bin"})
+
+
 if __name__ == "__main__":
     unittest.main()