fix: checkpoint START when retry a failed step

src/aws_durable_execution_sdk_python/operation/step.py

@@ -152,8 +152,8 @@ def check_result_status(self) -> CheckResult[T]:
         ):
             return CheckResult.create_is_ready_to_execute(checkpointed_result)
 
-        # Create START checkpoint if not exists
-        if not checkpointed_result.is_existent():
+        # Create START checkpoint if nonexistent or READY
+        if not checkpointed_result.is_existent() or checkpointed_result.is_ready():
             start_operation: OperationUpdate = OperationUpdate.create_step_start(
                 identifier=self.operation_identifier,
             )

src/aws_durable_execution_sdk_python/state.py

@@ -175,6 +175,13 @@ def is_pending(self) -> bool:
             return False
         return op.status is OperationStatus.PENDING
 
+    def is_ready(self) -> bool:
+        """Return True if the checkpointed operation is READY."""
+        op = self.operation
+        if not op:
+            return False
+        return op.status is OperationStatus.READY
+
     def is_timed_out(self) -> bool:
         """Return True if the checkpointed operation is TIMED_OUT."""
         op = self.operation

tests/operation/step_test.py

@@ -894,3 +894,58 @@ def test_step_executes_function_when_second_check_returns_started():
         mock_state.get_checkpoint_result.call_count == 1
     )  # Only one check for AT_LEAST_ONCE
     assert mock_state.create_checkpoint.call_count == 2  # START + SUCCEED checkpoints
+
+
+def test_step_creates_start_checkpoint_when_status_is_ready():
+    """Test that create_checkpoint is called with START action when the step is in READY status."""
+    mock_state = Mock(spec=ExecutionState)
+    mock_state.durable_execution_arn = "test_arn"
+
+    # Simulate a step that is in READY status (e.g., returned from a previous checkpoint)
+    ready_op = Operation(
+        operation_id="step_ready_1",
+        operation_type=OperationType.STEP,
+        status=OperationStatus.READY,
+        step_details=StepDetails(attempt=0),
+    )
+    ready_result = CheckpointedResult.create_from_operation(ready_op)
+
+    # After creating the sync START checkpoint, the refreshed result returns STARTED
+    started_op = Operation(
+        operation_id="step_ready_1",
+        operation_type=OperationType.STEP,
+        status=OperationStatus.STARTED,
+        step_details=StepDetails(attempt=0),
+    )
+    started_result = CheckpointedResult.create_from_operation(started_op)
+    mock_state.get_checkpoint_result.side_effect = [ready_result, started_result]
+
+    config = StepConfig(step_semantics=StepSemantics.AT_MOST_ONCE_PER_RETRY)
+    mock_callable = Mock(return_value="ready_step_result")
+    mock_logger = Mock(spec=Logger)
+    mock_logger.with_log_info.return_value = mock_logger
+
+    result = step_handler(
+        mock_callable,
+        mock_state,
+        OperationIdentifier("step_ready_1", None, "test_step"),
+        config,
+        mock_logger,
+    )
+
+    assert result == "ready_step_result"
+    mock_callable.assert_called_once()
+
+    # Verify START checkpoint was created
+    start_call = mock_state.create_checkpoint.call_args_list[0]
+    start_operation = start_call[1]["operation_update"]
+    assert start_operation.operation_id == "step_ready_1"
+    assert start_operation.operation_type is OperationType.STEP
+    assert start_operation.sub_type is OperationSubType.STEP
+    assert start_operation.action is OperationAction.START
+
+    # Verify SUCCEED checkpoint was also created after execution
+    assert mock_state.create_checkpoint.call_count == 2
+    success_call = mock_state.create_checkpoint.call_args_list[1]
+    success_operation = success_call[1]["operation_update"]
+    assert success_operation.action is OperationAction.SUCCEED

tests/state_test.py

@@ -332,6 +332,21 @@ def test_checkpointerd_result_is_pending():
     assert result_no_op.is_pending() is False
 
 
+def test_checkpointerd_result_is_ready():
+    """Test CheckpointedResult.is_ready method."""
+    operation = Operation(
+        operation_id="op1",
+        operation_type=OperationType.STEP,
+        status=OperationStatus.READY,
+    )
+    result = CheckpointedResult.create_from_operation(operation)
+    assert result.is_ready() is True
+
+    # Test with no operation
+    result_no_op = CheckpointedResult.create_not_found()
+    assert result_no_op.is_ready() is False
+
+
 def test_checkpointed_result_is_started():
     """Test CheckpointedResult.is_started method."""
     operation = Operation(