Handle Concurrent Bids and Network Retries in Auction System

Context

You are working on a high-traffic PubNub auction platform where hundreds of users may bid on the same item within seconds. Two problems need to be solved:

1. When two bids arrive nearly simultaneously, both might read the same auction state and both believe their bid is valid, leading to inconsistencies.
2. Network retries can cause the same bid message to be delivered multiple times to the server-side function, potentially processing a single bid attempt more than once.

Task

Write a PubNub Function that ensures safe concurrent bid processing and prevents duplicate bid execution. The function should guarantee that only one bid is processed at a time for a given auction, and that repeated deliveries of the same bid message produce the same result without side effects.

Bids that cannot be processed due to concurrent activity should inform the client that the attempt can be retried shortly.

Expected Outputs

• A PubNub Function that handles concurrent bid processing safely for a single auction
• Logic to detect and handle duplicate message deliveries
• Appropriate response messages for bids that encounter concurrency conflicts
• Use of KV Store for coordination state management