Tracking purchases

Checkout runs on Shopify's domain, so the loader can't see purchases directly. We use two sources, deduplicated by order ID:

1. Proofsplit pixel: switched on automatically after install. It reports page views, cart and checkout steps and completed purchases, respects Shopify's customer-privacy settings, and never sends names, emails or addresses.
2. Orders webhook (automatic): when a shopper adds to cart, the loader writes a hidden cart attribute (_aicro_vid). The orders/create webhook carries it back, so we can attribute the order and its revenue. This needs read_orders.

Cancelled orders (orders/cancelled) are removed from experiment revenue and conversions. If an order can't be matched to a visitor, it stays unattributed — we never guess.