[Bug]: Concurrency execution bug with callback.

[wangyb-A]

Expected Behavior

When using create_callbadk inside parallel branch. The parallel branch should exit normally when the callback succeeded.

Actual Behavior

Execution failure, I've attached the history as json file.

execution result:

{
    "DurableExecutionArn": "arn:aws:lambda:us-west-2:789814231946:function:CreateCallbackConcurrency-Python-PR-159:$LATEST/durable-execution/8439aeb6-0ecf-4839-8a44-3bd3b2f10a3d/ef779028-53fe-3640-ba1a-fb8bff8dd702",
    "DurableExecutionName": "8439aeb6-0ecf-4839-8a44-3bd3b2f10a3d",
    "FunctionArn": "arn:aws:lambda:us-west-2:789814231946:function:CreateCallbackConcurrency-Python-PR-159:$LATEST",
    "InputPayload": "null",
    "Error": {
        "ErrorMessage": "Cannot return PENDING status with no pending operations.",
        "ErrorType": "InvalidParameterValueException"
    },
    "StartTimestamp": "2025-11-27T16:27:49.245000-08:00",
    "Status": "FAILED",
    "EndTimestamp": "2025-11-27T16:27:53.956000-08:00",
    "Version": "$LATEST"
}

[result.json](https://github.com/user-attachments/files/23812168/result.json)

Steps to Reproduce

Please see PR for example: aws/aws-durable-execution-sdk-python-testing#159

SDK Version

0.0.0

Python Version

3.14

Is this a regression?

No

Last Working Version

No response

Additional Context

No response

[wangyb-A]

fixed by #234