Architectural Foundation: Understanding the Cart-to-Order Lifecycle Diagnosing checkout failures requires tracing how WooCommerce converts temporary runtime cart data into permanent database records. The process begins with session initialization managed by WC_Session_Handler . Dynamic cart state relies on browser cookies, including wp_woocommerce_session_ to track session tokens, alongside woocommerce_cart_hash and woocommerce_items_in_cart to manage cache invalidation and cart detection. If aggressive server caching intercepts or strips these cookies, checkout sessions drop unexpectedly. Refer to guidelines on configuring caching plugins to ensure checkout and cart endpoints bypass static caches. Frontend checkout submissions follow two architectural pathways: Classic Checkout: Dispatches a form payload to the endpoint ?wc-ajax=checkout , running standard validation hooks such as woocommerce_check_cart_items and woocommerce_checkout_process . Cart & Checkout Blocks: Submit...