NIP-XX: Marketplace Auctions

[pats2sats]

Summary

Adds auction events for marketplace listings. The proposal keeps listings as the canonical description of what is being sold, while a separate auction event describes the sale mechanism, timing, bidding rules, and auction arbiter.

What this defines

• kind:30421 marketplace auction events attached to NIP-99 listings.
• kind:1023 bid events and kind:1024 auction completion events.
• Reuse of the marketplace payment lifecycle for bid collateral, acknowledgments, rejection, settlement, and refunds.
• The one-arbiter rule for preventing split-brain auction state.
• Auction timing, anti-sniping, reserve, bid amount, bid chain, and completion behavior.

Scope

This defines auction coordination on top of marketplace listings and payment lifecycle events. It does not replace fixed-price listings or require a listing to be auction-only.