See https://gist.github.com/kanzure/2fa531afaf03fddd6568eb0212ac8c4c

See fig.yml for where these environment variables are defined.

Last known serialized unspent transaction output

When a deposit transaction is detected even with zero-confirms, make a transaction that spends the deposited unspents with a transaction that also spends the previous serialized unspent transaction output (SUTXO). This new transaction is now the latest serialized unspent transaction output. When creating the next withdrawal transaction, reference the latest serialized unspent transaction output in the same transaction.

Implementation details

• When a deposit is received, create a new transaction to move the deposit to a change address while also including the SUTXO.
• When the network mutates that last transaction, generate another transaction that spends the same outputs. This should be generally true for any type of transaction that is created.
• When a deposit goes missing (not mutated, just gone) (like because of a reorg), either halt the system or generate a plan for which other transactions to continue to make or exclude from the signing process....