On-chain RGB Swap PSBTs

[cryptoquick]

A swap PSBT will set a price for the buyer input and include the RGB21 transfer output. This then can be provided to the buyer to be paid with one of their sats inputs.

• create_swap_psbt - Create Swap PSBT
  • Seller specifies recipients in the format, Vec<(Address, i64)>>
  • These are then totaled
  • A new dust output is added to the the seller_uda_address, so they can transfer again
  • A transaction fee is also added
  • Returns struct including: total, psbt, and seal.
• pay_swap_psbt - Pays the Swap PSBT

[cryptoquick]

I imagine this to work similarly to how OpenOrdex works. Try listing this for sale:

https://openordex.org/inscription?number=d209f2e45bba4da70496b4e3108ef4ca06a1232d4dec43669709b2a95059c4bfi0

Except it would have an RGB transfer PSBT as one input, which signs a PSBT template for the payment input (with fixed price, so buyer cannot set zero, or dust amount) + market fee, with the sighash flag SINGLE|ANYONECANPAY

We can then swap the output to the seller, the RGB transfer goes to the buyer's UTXO from the invoice, and a second output is added for the market fee.