Shopping cart consistency tuning

You operate a Dynamo-style quorum store (replication factor N=3 across 3 regions) backing a globally distributed shopping cart. Most operations tolerate brief staleness, but 'place order from cart' must never undercount or drop an item the user just added. Cross-region round-trips are ~120ms. Design the read/write consistency-level policy per operation, explain how you avoid lost writes and ensure the order path is correct, and describe what conflict resolution and anti-entropy you'd run.