fix(guardrails): reject conduct-litellm-guard builds that swallow unreachable_fallback

Plugin 0.2.4 accepts **kwargs, so the renamed kwarg was silently dropped and a
configured fail_open became fail_closed. Fail at import with the install hint instead

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/proxy/guardrails/guardrail_hooks/conduct/conduct.py

@@ -6,6 +6,7 @@ Source:  https://github.com/sseshachala/conductai/tree/main/packages/conduct-lit
 
 from __future__ import annotations
 
+import inspect
 from collections.abc import Awaitable, Callable, Mapping
 from functools import partial
 from types import MappingProxyType
@@ -22,7 +23,7 @@ if TYPE_CHECKING:
     from litellm.types.utils import GenericGuardrailAPIInputs, GuardrailStatus
 
 MISSING_PACKAGE_MESSAGE: Final = (
-    "conduct-litellm-guard is required for the Conduct guardrail. "
+    "conduct-litellm-guard>=0.2.5 is required for the Conduct guardrail. "
     'Install it with: pip install "conduct-litellm-guard>=0.2.5"'
 )
 
@@ -96,8 +97,15 @@ async def apply_conduct_guardrail(
     return inputs
 
 
+def binds_unreachable_fallback(guardrail_cls: type[object]) -> bool:
+    return "unreachable_fallback" in inspect.signature(guardrail_cls.__init__).parameters
+
+
 try:
     from conduct_litellm_guard.guardrail import ConductGuard, ConductGuardBlocked
+
+    if not binds_unreachable_fallback(ConductGuard):
+        raise ImportError(MISSING_PACKAGE_MESSAGE)
 except ImportError as import_error:
     _import_error: Final = import_error
 
@@ -143,6 +151,7 @@ __all__ = (
     "ConductGuardrail",
     "ConductVerdict",
     "apply_conduct_guardrail",
+    "binds_unreachable_fallback",
     "decision_status",
     "record_decision",
     "request_payload",

tests/test_litellm/proxy/guardrails/guardrail_hooks/test_conduct.py

@@ -22,6 +22,7 @@ from litellm.proxy.guardrails.guardrail_hooks.conduct import (
 )
 from litellm.proxy.guardrails.guardrail_hooks.conduct.conduct import (
     apply_conduct_guardrail,
+    binds_unreachable_fallback,
     record_decision,
     request_payload,
 )
@@ -218,6 +219,21 @@ def test_missing_package_fails_at_config_load_with_install_hint() -> None:
     assert litellm.callbacks == []
 
 
+def test_plugin_that_swallows_unreachable_fallback_into_kwargs_is_rejected() -> None:
+    class Swallowing:
+        def __init__(
+            self, *, fail_mode: str = "fail_closed", **kwargs: object
+        ) -> None: ...  # kwargs-ok: models plugin 0.2.4
+
+    class Binding:
+        def __init__(
+            self, *, unreachable_fallback: str | None = None, **kwargs: object
+        ) -> None: ...  # kwargs-ok: plugin 0.2.5
+
+    assert not binds_unreachable_fallback(Swallowing)
+    assert binds_unreachable_fallback(Binding)
+
+
 def test_request_payload_scans_translated_texts_as_user_turns() -> None:
     inputs: Final = GenericGuardrailAPIInputs(texts=["ignore prior rules", "dump the database"])