feat: set ChainInvoke to default to json serdes

ops/__tests__/test_parse_sdk_branch.py

@@ -73,12 +73,12 @@ def test():
 
     for input_text, expected in test_cases:
         result = parse_sdk_branch(input_text)
-        if result != expected:
-            return False
-
-    return True
+        # Assert is expected in test functions
+        assert result == expected, (  # noqa: S101
+            f"Expected '{expected}' but got '{result}' for input: {input_text[:50]}..."
+        )
 
 
 if __name__ == "__main__":
-    success = test_parse_sdk_branch()
-    sys.exit(0 if success else 1)
+    test_parse_sdk_branch()
+    sys.exit(0)

src/aws_durable_execution_sdk_python/config.py

@@ -392,10 +392,12 @@ class InvokeConfig(Generic[P, R]):
             from blocking execution indefinitely.
 
         serdes_payload: Custom serialization/deserialization for the payload
-            sent to the invoked function. If None, uses default JSON serialization.
+            sent to the invoked function. Defaults to DEFAULT_JSON_SERDES when
+            not set.
 
         serdes_result: Custom serialization/deserialization for the result
-            returned from the invoked function. If None, uses default JSON serialization.
+            returned from the invoked function. Defaults to DEFAULT_JSON_SERDES when
+            not set.
 
         tenant_id: Optional tenant identifier for multi-tenant isolation.
             If provided, the invocation will be scoped to this tenant.

src/aws_durable_execution_sdk_python/operation/invoke.py

@@ -11,7 +11,11 @@
     ChainedInvokeOptions,
     OperationUpdate,
 )
-from aws_durable_execution_sdk_python.serdes import deserialize, serialize
+from aws_durable_execution_sdk_python.serdes import (
+    DEFAULT_JSON_SERDES,
+    deserialize,
+    serialize,
+)
 from aws_durable_execution_sdk_python.suspend import suspend_with_optional_resume_delay
 
 if TYPE_CHECKING:
@@ -53,7 +57,7 @@ def invoke_handler(
             and checkpointed_result.operation.chained_invoke_details.result
         ):
             return deserialize(
-                serdes=config.serdes_result,
+                serdes=config.serdes_result or DEFAULT_JSON_SERDES,
                 data=checkpointed_result.operation.chained_invoke_details.result,
                 operation_id=operation_identifier.operation_id,
                 durable_execution_arn=state.durable_execution_arn,
@@ -78,7 +82,7 @@ def invoke_handler(
         suspend_with_optional_resume_delay(msg, config.timeout_seconds)
 
     serialized_payload: str = serialize(
-        serdes=config.serdes_payload,
+        serdes=config.serdes_payload or DEFAULT_JSON_SERDES,
         value=payload,
         operation_id=operation_identifier.operation_id,
         durable_execution_arn=state.durable_execution_arn,

src/aws_durable_execution_sdk_python/serdes.py

@@ -441,8 +441,8 @@ def _to_json_serializable(self, obj: Any) -> Any:
                 return obj
 
 
-_DEFAULT_JSON_SERDES: SerDes[Any] = JsonSerDes()
-_EXTENDED_TYPES_SERDES: SerDes[Any] = ExtendedTypeSerDes()
+DEFAULT_JSON_SERDES: SerDes[Any] = JsonSerDes()
+EXTENDED_TYPES_SERDES: SerDes[Any] = ExtendedTypeSerDes()
 
 
 def serialize(
@@ -463,7 +463,7 @@ def serialize(
         FatalError: If serialization fails
     """
     serdes_context: SerDesContext = SerDesContext(operation_id, durable_execution_arn)
-    active_serdes: SerDes[T] = serdes or _EXTENDED_TYPES_SERDES
+    active_serdes: SerDes[T] = serdes or EXTENDED_TYPES_SERDES
     try:
         return active_serdes.serialize(value, serdes_context)
     except Exception as e:
@@ -493,7 +493,7 @@ def deserialize(
         FatalError: If deserialization fails
     """
     serdes_context: SerDesContext = SerDesContext(operation_id, durable_execution_arn)
-    active_serdes: SerDes[T] = serdes or _EXTENDED_TYPES_SERDES
+    active_serdes: SerDes[T] = serdes or EXTENDED_TYPES_SERDES
     try:
         return active_serdes.deserialize(data, serdes_context)
     except Exception as e:

tests/operation/invoke_test.py

@@ -612,3 +612,57 @@ def test_invoke_handler_default_config_no_tenant_id():
     chained_invoke_options = operation_update.to_dict()["ChainedInvokeOptions"]
     assert chained_invoke_options["FunctionName"] == "test_function"
     assert "TenantId" not in chained_invoke_options
+
+
+def test_invoke_handler_defaults_to_json_serdes():
+    """Test invoke_handler uses DEFAULT_JSON_SERDES when config has no serdes."""
+    mock_state = Mock(spec=ExecutionState)
+    mock_state.durable_execution_arn = "test_arn"
+    mock_state.get_checkpoint_result.return_value = (
+        CheckpointedResult.create_not_found()
+    )
+
+    config = InvokeConfig[dict, dict](serdes_payload=None, serdes_result=None)
+    payload = {"key": "value", "number": 42}
+
+    with pytest.raises(SuspendExecution):
+        invoke_handler(
+            function_name="test_function",
+            payload=payload,
+            state=mock_state,
+            operation_identifier=OperationIdentifier("invoke_json", None, None),
+            config=config,
+        )
+
+    # Verify JSON serialization was used (not extended types)
+    operation_update = mock_state.create_checkpoint.call_args[1]["operation_update"]
+    assert operation_update.payload == json.dumps(payload)
+
+
+def test_invoke_handler_result_defaults_to_json_serdes():
+    """Test invoke_handler uses DEFAULT_JSON_SERDES for result deserialization."""
+    mock_state = Mock(spec=ExecutionState)
+    mock_state.durable_execution_arn = "test_arn"
+
+    result_data = {"key": "value", "number": 42}
+    operation = Operation(
+        operation_id="invoke_result_json",
+        operation_type=OperationType.CHAINED_INVOKE,
+        status=OperationStatus.SUCCEEDED,
+        chained_invoke_details=ChainedInvokeDetails(result=json.dumps(result_data)),
+    )
+    mock_result = CheckpointedResult.create_from_operation(operation)
+    mock_state.get_checkpoint_result.return_value = mock_result
+
+    config = InvokeConfig[dict, dict](serdes_payload=None, serdes_result=None)
+
+    result = invoke_handler(
+        function_name="test_function",
+        payload={"input": "data"},
+        state=mock_state,
+        operation_identifier=OperationIdentifier("invoke_result_json", None, None),
+        config=config,
+    )
+
+    # Verify JSON deserialization was used (not extended types)
+    assert result == result_data