Implement Payjoin for Batch Transactions

[ConorOkus]

https://payjoin.org/docs/why-payjoin/lightning

https://payjoindevkit.org/2025/03/18/the-evolution-of-payjoin/

[aftermath2]

Thanks for opening this!

Payjoins would definitely improve the privacy and costs of the channel transactions. I'll be reviewing the proposal, the documentation and the Oblivious HTTP RFC to see how to implement a client when I find some time.