[Bug]: parallel_first_successful example crashes. BatchResult has no successful_results attribute

[Nahuel990]

Expected Behavior

The published example examples/src/parallel/parallel_first_successful.py accesses results.successful_results on
the return value of context.parallel(...). That attribute does not exist on BatchResult anywhere in src/.
Running the example raises AttributeError: 'BatchResult' object has no attribute 'successful_results'.

The three parallel branches all complete successfully; the failure is purely in the example's post-processing
of the result object.

The example returns "First successful result: Task 1" (or whichever branch completes first) without an
exception.

Actual Behavior

The durable execution fails with:

ErrorType: AttributeError
ErrorMessage: 'BatchResult' object has no attribute 'successful_results'

The execution history shows all three parallel branches reaching StepSucceeded and ContextSucceeded for the
parallel context before the handler crashes.

Steps to Reproduce

1. git clone https://github.com/aws/aws-durable-execution-sdk-python.git
2. cd aws-durable-execution-sdk-python
3. grep -n "successful_results" examples/src/parallel/parallel_first_successful.py → matches line 23
4. grep -rn "successful_results" src/ → no matches
5. Deploy examples/src/parallel/parallel_first_successful.py as a durable Lambda (or run via the in-repo local
   test runner) and invoke it.

SDK Version

1.5.0

Python Version

3.12

Is this a regression?

No

Last Working Version

No response

Additional Context

examples/src/parallel/parallel_first_successful.py:23:

first_result = (
results.successful_results[0] if results.successful_results else "None"
)

BatchResult class: src/aws_durable_execution_sdk_python/concurrency/models.py:88. Members defined on the
class:

succeeded, failed, started, status, has_failure, throw_if_error, get_results, get_errors, success_count,
failure_count, started_count, total_count, from_dict, from_items, to_dict.

No successful_results.

BatchResult Protocol: src/aws_durable_execution_sdk_python/types.py:83. Only declares get_results(). No
successful_results.