diff --git a/litellm/proxy/guardrails/guardrail_hooks/grayswan/grayswan.py b/litellm/proxy/guardrails/guardrail_hooks/grayswan/grayswan.py
index 6841098730e..65994dbd386 100644
--- a/litellm/proxy/guardrails/guardrail_hooks/grayswan/grayswan.py
+++ b/litellm/proxy/guardrails/guardrail_hooks/grayswan/grayswan.py
@@ -654,6 +654,8 @@ class GraySwanGuardrail(CustomGuardrail):
             skip_system=effective_skip_system_message_for_guardrail(self),
             skip_tool=effective_skip_tool_message_for_guardrail(self),
         )
+        if not indices:
+            return (), None
         raw_tools: Final = request_data.get("tools")
         tools: Final = (
             tuple(raw_tools) if not scan_only_tool_results and isinstance(raw_tools, list) and raw_tools else None
diff --git a/tests/integration/observability/test_grayswan_wire.py b/tests/integration/observability/test_grayswan_wire.py
index babf7170c02..1ebd07b1cea 100644
--- a/tests/integration/observability/test_grayswan_wire.py
+++ b/tests/integration/observability/test_grayswan_wire.py
@@ -119,15 +119,19 @@ def _chat_provider(message: dict[str, JsonValue]):
 
 
 def _monitor_bodies(vendor: Wire, expected: int = 1) -> tuple[dict[str, JsonValue], ...]:
-    collected: list[dict[str, JsonValue]] = []  # mutable-ok: accumulator across polling attempts
+    collected: tuple[dict[str, JsonValue], ...] = ()
 
     def drain_new() -> tuple[dict[str, JsonValue], ...]:
-        collected.extend(
-            _JSON_OBJECT.validate_json(request.body)
-            for request in vendor.drain()
-            if request.target == "/cygnal/monitor"
+        nonlocal collected
+        collected = (  # rebind-ok: eventually polls this closure, so drained bodies must persist across calls
+            *collected,
+            *(
+                _JSON_OBJECT.validate_json(request.body)
+                for request in vendor.drain()
+                if request.target == "/cygnal/monitor"
+            ),
         )
-        return tuple(collected)
+        return collected
 
     return eventually(drain_new, lambda bodies: len(bodies) >= expected, seconds=30)
 
diff --git a/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_grayswan.py b/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_grayswan.py
index bcfdab30be0..8fa0484947f 100644
--- a/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_grayswan.py
+++ b/tests/test_litellm/proxy/guardrails/guardrail_hooks/test_grayswan.py
@@ -771,6 +771,24 @@ async def test_post_call_prefers_request_route_over_logging_call_type() -> None:
     assert list(payload["tools"]) == _REQUEST_DATA["tools"]
 
 
+@pytest.mark.asyncio
+async def test_post_call_surface_without_messages_sends_response_only() -> None:
+    guardrail = _post_call_guardrail()
+    client = _CapturingClient()
+    guardrail.async_handler = client
+
+    await guardrail.apply_guardrail(
+        inputs={"texts": ["response text"]},
+        request_data={**_REQUEST_DATA, "litellm_logging_obj": _LoggingObj("aembedding")},
+        input_type="response",
+        logging_obj=_LoggingObj("aembedding"),
+    )
+
+    payload = client.calls[0]["json"]
+    assert list(payload["messages"]) == [{"role": "assistant", "content": "response text"}]
+    assert "tools" not in payload
+
+
 @pytest.mark.asyncio
 async def test_post_call_unresolvable_call_type_sends_response_only() -> None:
     guardrail = _post_call_guardrail()