feat: limit in-flight operations in map/parallel

max_concurrency now bounds in-flight branches via a coordinator loop, the completion decision is recorded in an SDK-owned summary envelope and obeyed on replay, and completion config bounds are validated before the operation starts. Branch threads abandoned by early completion are joined at invocation end, so no SDK-created thread outlives its invocation.

BREAKING CHANGE: max_concurrency=0 and min_successful=0 now raise ValidationError (previously unlimited / all-items). min_successful greater than the item count now raises ValidationError. BatchResult omits never-started branches. Large-result summary payloads use the SDK envelope format; custom summary_generator output is stored under the summary key instead of replacing the payload. The internal MapSummaryGenerator and ParallelSummaryGenerator classes are removed; the envelope supersedes them. CompletionConfig.all_completed() now tolerates all failures instead of failing fast.

AWS Durable Execution SDK for Python

Build reliable, long-running AWS Lambda workflows with checkpointed steps, waits, callbacks, and parallel execution.

✨ Key Features

Automatic checkpointing - Resume execution after Lambda pauses or restarts
Durable steps - Run work with retry strategies and deterministic replay
Waits and callbacks - Pause for time or external signals without blocking Lambda
Parallel and map operations - Fan out work with configurable completion criteria
Child contexts - Structure complex workflows into isolated subflows
Replay-safe logging - Use context.logger for structured, de-duplicated logs
Local and cloud testing - Validate workflows with the testing SDK

📦 Packages

Package	Description	Version
`aws-durable-execution-sdk-python`	Execution SDK for Lambda durable functions
`aws-durable-execution-sdk-python-testing`	Local/cloud test runner and pytest helpers

🚀 Quick Start

Install the execution SDK:

pip install aws-durable-execution-sdk-python

Create a durable Lambda handler:

from aws_durable_execution_sdk_python import (
    DurableContext,
    StepContext,
    durable_execution,
    durable_step,
)
from aws_durable_execution_sdk_python.config import Duration

@durable_step
def validate_order(step_ctx: StepContext, order_id: str) -> dict:
    step_ctx.logger.info("Validating order", extra={"order_id": order_id})
    return {"order_id": order_id, "valid": True}

@durable_execution
def handler(event: dict, context: DurableContext) -> dict:
    order_id = event["order_id"]
    context.logger.info("Starting workflow", extra={"order_id": order_id})

    validation = context.step(validate_order(order_id), name="validate_order")
    if not validation["valid"]:
        return {"status": "rejected", "order_id": order_id}

    # simulate approval (real world: use wait_for_callback)
    context.wait(duration=Duration.from_seconds(5), name="await_confirmation")

    return {"status": "approved", "order_id": order_id}

📚 Documentation

The complete documentation for the AWS Durable Execution SDK for Python lives on the AWS Documentation site:

AWS Durable Execution Documentation - Concepts, getting started, core operations, advanced topics, and API reference
AWS Lambda Durable Functions Guide - How durable functions work on Lambda

💬 Feedback & Support

📄 License

See the LICENSE file for our project’s licensing.