Multi-Channel Card Commerce Engine

The Challenge

The Break Room sells trading cards across eBay, TCGplayer, Whatnot, and the Loupe marketplace—plus its own storefront. Every channel has a different API, or none at all. And the moment a card sells in one place it has to disappear everywhere else, instantly, or you oversell a one-of-one item you no longer have.

The Approach

I built a Next.js + Supabase backend that became the single source of truth for inventory, cost basis, and listing state. A sale on any channel triggers atomic cross-channel delisting; a self-healing reconciliation job enforces one simple, bulletproof rule and recovers on its own when a session dies. Where a channel had no public API—TCGplayer, Loupe—I drove it with headless-browser automation. Claude vision parses order-confirmation emails into cost basis and turns an iPhone photo of a card into a complete eBay listing: player, year, set, grade, title and all.

The Outcome

Thousands of cards stay synced across four channels with effectively zero oversells. Listing a card dropped from minutes of manual data entry to seconds. The same database powers the public storefront, live sealed-box "break" reservations, and accounting sync—a one-person operation running like a team.

Key Details

• Single source of truth in Supabase: holdings, listings, sales, FIFO cost basis
• Atomic cross-channel delist on sale (eBay, TCGplayer, Loupe, storefront)
• Self-healing reconciliation jobs prevent overselling one-of-one cards
• Headless-browser automation (Playwright) for channels with no public API
• Claude vision: receipt → cost basis, and phone photo → finished eBay listing
• Dozens of scheduled jobs for sync, health monitoring, and price refreshes
• Provably-fair randomization for live sealed-box "break" slot sales
• Stripe checkout, QuickBooks accounting sync, and Klaviyo lifecycle automation