Using a reverse swap claim transaction to directly fund a new lightning channel

[Scalena]

In principle, it should be possible to use a reverse swap claim transaction to directly fund a new lightning channel. However, the process is non-trivial, since the steps of reverse swapping and channel negotiation would have to be interleaved. Coarsely outlined:

1. Initiate reverse swap, pay invoice and gather information for constructing the claiming input,
2. initiate channel negotiation to gather the channel lock-in address,
3. construct the claim/fund transaction (and potentially re-negotiate the transaction with the peer node),
4. finish channel negotiation, sign and broadcast the claim/fund transaction.

If the channel negotiation fails, a normal claim transaction has to be created automatically instead.

Apart from the obvious benefit of saving one on-chain transaction, this would also be a privacy benefit for node operators, because the claim/fund transaction would be completely separate from their on-chain wallet and it is not generally visible from the outside who initiated the channel.

[kilrau]

Awesome idea. Love it. We'll have a look how this could work (especially with the dual funding channel establishment protocol gaining traction) after we shipped chain swaps in boltz-client 🙌