Fix as_tool returning blank string on early tool termination (#2112)

Author: ihower

src/agents/agent.py

@@ -13,7 +13,6 @@
 from .agent_output import AgentOutputSchemaBase
 from .guardrail import InputGuardrail, OutputGuardrail
 from .handoffs import Handoff
-from .items import ItemHelpers
 from .logger import logger
 from .mcp import MCPUtil
 from .model_settings import ModelSettings
@@ -417,7 +416,7 @@ def as_tool(
             description_override=tool_description or "",
             is_enabled=is_enabled,
         )
-        async def run_agent(context: RunContextWrapper, input: str) -> str:
+        async def run_agent(context: RunContextWrapper, input: str) -> Any:
             from .run import DEFAULT_MAX_TURNS, Runner
 
             resolved_max_turns = max_turns if max_turns is not None else DEFAULT_MAX_TURNS
@@ -436,7 +435,7 @@ async def run_agent(context: RunContextWrapper, input: str) -> str:
             if custom_output_extractor:
                 return await custom_output_extractor(output)
 
-            return ItemHelpers.text_message_outputs(output.new_items)
+            return output.final_output
 
         return run_agent
 

tests/test_agent_as_tool.py

@@ -225,30 +225,15 @@ async def custom_extractor(result):
 
 
 @pytest.mark.asyncio
-async def test_agent_as_tool_returns_concatenated_text(monkeypatch: pytest.MonkeyPatch) -> None:
-    """Agent tool should use default text aggregation when no custom extractor is provided."""
+async def test_agent_as_tool_returns_final_output(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Agent tool should return final_output when no custom extractor is provided."""
 
     agent = Agent(name="storyteller")
 
-    message = ResponseOutputMessage(
-        id="msg_1",
-        role="assistant",
-        status="completed",
-        type="message",
-        content=[
-            ResponseOutputText(
-                annotations=[],
-                text="Hello world",
-                type="output_text",
-                logprobs=[],
-            )
-        ],
-    )
-
     result = type(
         "DummyResult",
         (),
-        {"new_items": [MessageOutputItem(agent=agent, raw_item=message)]},
+        {"final_output": "Hello world"},
     )()
 
     async def fake_run(