• HTTP endpoint emulating SNS API (POST /?Action=Publish etc.)
- Fan-out to subscribed nodes (SQS queues, HTTP webhooks)
- Topic ARN routing
- MessagePublished events per subscription
- Config: topicArn, subscriptionProtocol (sqs/http)
- Why: Common AWS pattern; SQS already exists so SNS→SQS fan-out is the obvious next step