fix(proxy): decode nested percent-encoded file ids iteratively

An id percent-encoded a thousand or more times sent the recursive decoder past the
interpreter's recursion limit, so a proxy admin key got a 500 instead of a verdict on
the id. The decoder now walks the encodings in a loop, so any depth resolves

litellm/litellm_core_utils/cloud_storage_security.py

@@ -1,6 +1,7 @@
 import posixpath
 import re
 from collections.abc import Mapping, Sequence
+from itertools import accumulate, pairwise, repeat
 from types import MappingProxyType
 from typing import Any, Final, cast
 from urllib.parse import quote, unquote
@@ -21,8 +22,8 @@ _MAPPING_PROXY_TYPE: Final[type] = type(MappingProxyType({}))
 
 
 def _fully_unquoted(value: str) -> str:
-    decoded: Final = unquote(value)
-    return value if decoded == value else _fully_unquoted(decoded)
+    decodings: Final = accumulate(repeat(value), lambda current, _: unquote(current))
+    return next(current for current, following in pairwise(decodings) if current == following)
 
 
 def is_managed_cloud_storage_uri(file_id: str) -> bool:

tests/test_litellm/litellm_core_utils/test_cloud_storage_security.py

@@ -28,3 +28,11 @@ def test_is_managed_cloud_storage_uri_ignores_provider_and_unified_ids():
 )
 def test_is_managed_cloud_storage_uri_sees_through_percent_encoding(file_id: str):
     assert is_managed_cloud_storage_uri(file_id)
+
+
+def test_is_managed_cloud_storage_uri_survives_an_id_encoded_thousands_of_times():
+    nested_gs_id = "gs" + "%" + "25" * 5000 + "3A//bucket/x"
+    nested_plain_id = "%" + "25" * 5000
+
+    assert is_managed_cloud_storage_uri(nested_gs_id)
+    assert not is_managed_cloud_storage_uri(nested_plain_id)