As a preparation to abandon canceled channels, we first extract the
utility method to locate a channel output created in a batch from the
batch verifier into the batch itself.
As a preparation to avoid package import cycles when introducing more
generic terms, we move the FeeSchedule interface and its
LinearFeeSchedule implementation to the terms package.
In this commit, we ensure that if we need to reject a batch for w/e
reason, then we also unregister all funding shims. Otherwise, if we
repeat a modified version of that batch, then we'd fail early as the
attempt to register than same shim would be rejected.
We need this method for further synchronization: once this is sent we
expect the traders to respond with signatures for each of the accounts
involved in the batch. The addition of this message also means that the
responder of the channel funding has time to register their shim (done
before they send their Accept message) as we don't send the
OrderSignBegin message until all traders have accepted the batch. The
initiator can now use receipt of the OrderSignBegin as a signal to
initiate the channel funding.
We also fix an existing oversight in the `OrderMatchSign`: it expected a
fully valid witness, but the only thing the traders can produce by
themselves is a signature for their input.
Previously, if the connection between the trader and auctioneer was torn
down before the trader received a batch's finalize message, then the
trader would lose all context about the batch they participated in.
Committing the batch before providing our signatures to the auctioneer
ensures that this cannot happen. Follow-up work will allow the trader to
obtain the latest information regarding a pending batch upon
reconnections.
