fix(core): handle v1 base model validation in async path (#39576)

libs/core/langchain_core/tools/base.py

@@ -1238,7 +1238,7 @@ class ChildTool(BaseTool):
                         error_to_raise = ValueError(msg)
             else:
                 content = response
-        except ValidationError as e:
+        except (ValidationError, ValidationErrorV1) as e:
             if not self.handle_validation_error:
                 error_to_raise = e
             else:

libs/core/tests/unit_tests/test_tools.py

@@ -1148,6 +1148,30 @@ async def test_async_validation_error_handling_callable() -> None:
     assert expected == actual
 
 
+@pytest.mark.skipif(
+    sys.version_info >= (3, 14),
+    reason="pydantic.v1 namespace not supported with Python 3.14+",
+)
+async def test_async_validation_error_handling_pydantic_v1_schema() -> None:
+    """Test async validation error handling for Pydantic V1 schemas."""
+
+    class Args(BaseModelV1):
+        x: int
+
+    def foo(x: int) -> str:
+        """Return x as text."""
+        return str(x)
+
+    tool_ = StructuredTool.from_function(
+        foo,
+        args_schema=cast("ArgsSchema", Args),
+        handle_validation_error=True,
+    )
+
+    assert tool_.run({"x": "not-an-integer"}) == "Tool input validation error"
+    assert await tool_.arun({"x": "not-an-integer"}) == "Tool input validation error"
+
+
 @pytest.mark.parametrize(
     "handler",
     [