Is it possible to generate a lightning network invoice without the encumbrance of a full lightning node (lightning node defined as: fully synced channel graph, knowledge of channel outpoints, and current channel state)?
A great definition of a not-full lightning node. The answer is yes you can with some trick. Phoenix is implemented in that way and I think the lightning implementation lightning-kmp is packing all the logic to do exactly this https://github.com/ACINQ/lightning-kmp
There are a couple of feature that you need to use in order to do this, and they are static-channels backups, trampoline payments and some constraint on how you generate invoice and offers
