Bitcoin Fragment Sweep

Sequence Diagram for SweepTx and RefundTx

Intuitively, this sweep process works like commitmentTx in lightning, where the client always have an exit transaction available in case the counterparty refuses to respond.

In Boomerang, before a Fragment signs on the SweepTx, the new Fragment Judge proposes a Refund Transaction on the previous state of the reserve. Once all the new Fragment signatories sign on the refund transaction, the Sweep signing begins on the unlocked Fragment address.