Enforce download cache quotas without returning evicted paths

tests/large_file/test_download_quota.py

@@ -0,0 +1,40 @@
+import io
+import tarfile
+from pathlib import Path
+from typing import Any
+from unittest.mock import MagicMock, patch
+
+import pytest
+from great_ai.large_file import LargeFileS3
+
+
+def test_download_quota_keeps_the_requested_file_and_evicts_older_models(
+    tmp_path: Path,
+) -> None:
+    backend = MagicMock()
+    backend.list_objects_v2.side_effect = lambda **kwargs: {
+        "Contents": [{"Key": kwargs["Prefix"] + "0", "ETag": "one"}]
+    }
+
+    def download(
+        self: LargeFileS3, remote_path: Any, path: Path, hide_progress: bool
+    ) -> None:
+        data = b"x" * (2000 if self._name == "oversized" else 600)
+        with tarfile.open(path, "w:gz") as archive:
+            member = tarfile.TarInfo(self._local_name)
+            member.size = len(data)
+            archive.addfile(member, io.BytesIO(data))
+
+    with (
+        patch.object(LargeFileS3, "_client", backend),
+        patch.object(LargeFileS3, "_download", download),
+        patch.object(LargeFileS3, "cache_path", tmp_path / "cache"),
+        patch.object(LargeFileS3, "max_cache_size", "1 KB"),
+    ):
+        first = LargeFileS3("first").get()
+        second = LargeFileS3("second").get()
+        assert not first.exists()
+        assert second.read_bytes() == b"x" * 600
+        with pytest.raises(ValueError, match="exceeds max_cache_size"):
+            LargeFileS3("oversized").get()
+        assert second.exists()