How does multi-warehouse / state-by-state inventory routing work?

Magento 2.3+ ships with MSI (Multi-Source Inventory), which lets you define multiple warehouses (sources) and ship orders from the closest one. We layer on ShipperHQ for rules-based routing (e.g. “ship from CA warehouse for ZIPs west of 100, NJ warehouse for east”), dimensional-weight pricing, and rural-route fallbacks (USPS for ZIPs UPS won’t deliver to). For B2B with reserved stock, we add custom code to lock inventory per quote until expiry. ShipStation integration handles label printing + tracking back to Magento.