feat: Add automatic trace propagation for Lambda Durable Functions

[jchrostek-dd]

Summary

Adds automatic tracing support for AWS Lambda Durable Functions (preview feature announced at re:Invent 2025).

Key features:

• Auto-patches @aws/durable-execution-sdk-js when datadog-lambda-js loads
• Extracts trace context from preserved InputPayload (supports HTTP headers, SNS/SQS attributes, EventBridge)
• Falls back to deterministic trace ID from execution ARN when no parent exists
• Creates child spans for each operation (step, wait, invoke, parallel, map)
• Detects replay operations to avoid duplicate spans

Zero user code changes required - existing code with datadog() wrapper works automatically.

Test plan

• Unit tests added (55 new tests)
• All 575 tests pass
• Integration test with deployed durable function
• Verify trace appears correctly in Datadog APM

Example trace output

[api-gateway] POST /workflow
    └─[aws.lambda] my-durable-fn (invocation 1)
          │  trace_id: 123456 (from API Gateway)
          ├─[aws.lambda.durable.step] fetch-user
          └─[aws.lambda.durable.wait] delay-5min (Lambda exits PENDING)

    ... 5 minutes later ...

    └─[aws.lambda] my-durable-fn (invocation 2)
          │  trace_id: 123456 (SAME - preserved)
          │  (fetch-user replayed - no duplicate span)
          ├─[aws.lambda.durable.wait] delay-5min (completes)
          └─[aws.lambda.durable.step] process

🤖 Generated with Claude Code