Syncing Sessions/Carts between Catalyst and Stencil Storefront

[z0n]

Hi again,

This is kinda related to #1138 but that one is more about routing so I'm posting this here.

We're trying to do a gradual migration from a Stencil storefront to a Catalyst storefront. A big roadblock is the session handling. I found the generateSessionSyncJwt mutation which I can add a "fallback" dynamic route in Catalyst which generates a URL based on the path with the session information. That works if I need to go from Catalyst to Stencil.

I'm now struggling with the other direction as I'm not sure what information I need to pass to Catalyst (and how to get it).