Receive Chain Swap: claim fails if the user RBF-ed the BTC tx

[ok300]

In the following scenario:

• SDK creates a Receive Chain Swap (receive-payment --method bitcoin --payer-amount-sat 50000)
• user sends the correct amount to the BTC swap address
• user RBFs that tx to bump the fee
• the BTC tx gets confirmed
• SDK fails to claim
  • "Failed to handle Chain Swap ... update: Could not verify user lockup transaction: Transaction was not found in script history"

The reason is that we are looking for the initial tx ID in the swap script history, instead of the new (RBF) tx ID:

breez-sdk-liquid/lib/core/src/chain_swap.rs

Lines 1180 to 1183 in 1389d49

	script_history
	.iter()
	.find(|h| h.txid.to_hex() == user_lockup_tx_id)
	.ok_or(anyhow!("Transaction was not found in script history"))?;

We store the initial tx ID as user_lockup_tx_id as soon as we see it in the mempool, but we don't update it in case it's RBF-ed.

One solution is to update it in our DB on RBF.

Another idea is to skip checking the tx ID here and instead get the 1st tx in the swap script history, since the 1st tx is by definition the lockup tx.

[roeierez]

We should take the first transaction. If there are more transactions they will be refunded.