Address Copilot comments

Author: steven10a

src/guardrails/agents.py

@@ -370,6 +370,9 @@ def _extract_text_from_input(input_data: Any) -> str:
                     if isinstance(content, str):
                         return content
                     elif isinstance(content, list):
+                        if not content:
+                            # Empty content list returns empty string (consistent with no text parts found)
+                            return ""
                         # Extract text from content parts
                         text_parts = []
                         for part in content:
@@ -385,6 +388,8 @@ def _extract_text_from_input(input_data: Any) -> str:
                                     text_parts.append(text)
                         if text_parts:
                             return " ".join(text_parts)
+                        # No text parts found, return empty string
+                        return ""
                     # If content is something else, try to stringify it
                     elif content is not None:
                         return str(content)
@@ -452,8 +457,12 @@ class DefaultContext:
 
     def _create_individual_guardrail(guardrail):
         """Create a function for a single specific guardrail."""
-        async def single_guardrail(ctx: RunContextWrapper[None], agent: Agent, input_data: str) -> GuardrailFunctionOutput:
-            """Guardrail function for a specific guardrail check."""
+        async def single_guardrail(ctx: RunContextWrapper[None], agent: Agent, input_data: str | list) -> GuardrailFunctionOutput:
+            """Guardrail function for a specific guardrail check.
+
+            Note: input_data is typed as str in Agents SDK, but can actually be a list
+            of message objects when conversation history is used. We handle both cases.
+            """
             try:
                 # Extract text from input_data (handle both string and conversation history formats)
                 text_data = _extract_text_from_input(input_data)

tests/unit/test_agents.py

@@ -7,7 +7,7 @@
 from collections.abc import Callable
 from dataclasses import dataclass
 from types import SimpleNamespace
-from typing import Any, TypedDict
+from typing import Any
 
 import pytest
 
@@ -130,15 +130,6 @@ async def run(self, *args: Any, **kwargs: Any) -> Any:
 import guardrails.runtime as runtime_module  # noqa: E402
 
 
-# Add mock for TResponseInputItem for testing
-class TResponseInputItem(TypedDict):
-    """Mock type for Agents SDK response input item."""
-
-    role: str
-    content: Any
-    type: str
-
-
 def _make_guardrail(name: str) -> Any:
     class _DummyCtxModel:
         model_fields: dict[str, Any] = {}
@@ -886,6 +877,20 @@ def test_extract_text_from_input_preserves_empty_strings() -> None:
     assert result == "Hello  World"  # noqa: S101
 
 
+def test_extract_text_from_input_with_empty_content_list() -> None:
+    """Empty content list should return empty string, not stringified list."""
+    input_data = [
+        {
+            "role": "user",
+            "type": "message",
+            "content": [],  # Empty content list
+        }
+    ]
+    result = agents._extract_text_from_input(input_data)
+    # Should return empty string, not "[]"
+    assert result == ""  # noqa: S101
+
+
 # =============================================================================
 # Tests for updated agent-level guardrail behavior (stage_name and metadata)
 # =============================================================================