Amazon blocked Meta's Muse shopping agent yesterday. This morning, Shopify opened every one of its stores to the same agent. The split makes perfect sense once you follow where each company's money actually comes from. Amazon made $68.6 billion selling ads last year. Roughly 90% of that is Sponsored Listings, per The Trade Desk's Jeff Green. Those are the paid placements woven into search results, the digital version of brands paying for eye-level shelf space. An agent never sees the…