Woocommerce caching. This is Pantheon host specific.
Woocommerce Universal behavior (all hosts):
- Sets DONOTCACHEPAGE / no-cache headers on cart, checkout, and my-account pages. This is standard and expected — those pages should never be cached.
On Pantheon:
- WooCommerce also sets woocommerce_items_in_cart and woocommerce_cart_hash as HTTP cookies whenever someone has items in their cart. On most hosts this is harmless — those cookies are just used by JS for cart fragments.
- But Pantheon's Varnish treats any unrecognized cookie as a signal to bypass cache entirely. So once a visitor adds something to their cart, every single page they visit becomes uncacheable — not just cart/checkout.
- You also can't edit VCL on Pantheon, so you can't strip those cookies at the Varnish layer like you would on a self-managed Varnish setup.
What this plugin does:
- Blocks woocommerce_items_in_cart and woocommerce_cart_hash from being set server-side.
- Moves that data to sessionStorage via the JS patch so cart fragments still work.
- Renames the session cookie with STYXKEY_ prefix so Pantheon treats it as cache-varying (separate buckets) instead of cache-busting.