Timed Auction Service

Model a fictional single-currency auction using exact integer units. Use a fixed closing deadline, no automatic extensions, one highest eligible bid and no payment settlement in this exercise.

• Validate and serialize bids at an authoritative service.
• Bind bid idempotency keys to immutable request contents.
• Enforce deadline during bid admission, not only in a close worker.
• Publish a stable winner and closing event atomically.