EPIC: Shopping, bidding and post-purchase

Programme: #1

Own normalized commerce data, comparison/ranking UI, checkout/payment handoff, auctions, global commitments, receipts, tracking, returns and recurring purchase rules.

## Child issues
- [ ] #80 SHOP-01 — Product, variant and offer graph
- [ ] #81 SHOP-02 — Custom shopping UI, comparison and monitors
- [ ] #82 SHOP-03 — Checkout and payment integration
- [ ] #83 SHOP-04 — Auctions and maximum commitments
- [ ] #84 SHOP-05 — Receipts, orders, returns and recurring purchases

## Cross-cutting gates
Product/variant/offer/order are distinct, missing price components remain unknown, affiliate/conflict signals are disclosed, live write support requires provider approval, totals/bids are authority-bound, and ambiguous writes never repeat automatically.

Start with the parent programme #1 and review child issues #80–#84 to understand the separate product, UI, checkout, auction, and post-purchase scopes. No files or tests are named. Done means the child work addresses the listed commerce areas and respects the cross-cutting gates for data, disclosures, provider approval, authority-bound totals, and non-repeating ambiguous writes.

Written by the indexing model from the issue text.