Suggestion

Currently, it's hard to write a custom recipe transfer helper because JEI uses a lot of internal information to do so.
The things that I would like exposed to the API to help with this (in IRecipeTransferHandlerHelper, most likely):

a way to create a BasicRecipeTransferHandler without registering it
a way to create a BasicRecipeTransferInfo without registering it
an exposing of ServerInfo.isJeiOnServer() to the API

This would allow me to make a PlayerRecipeTransferHandler for Quark's backpacks without needing to copy large swathes of JEI code and/or harddep on it.

Thanks for the suggestion!
This has been implemented in JEI 11.3.0