This commit fixes an instance of a "break" keyword that didn't have the
desired effect (breaking out of the outer for loop).
This didn't lead to an endless loop just because of the break in the
error case a few lines above where we would leave the loop in case of an
invalid state transition.
Without this extra case on restart, the recipient would have an
unhandled state transition that would cause them to not expect the
channel as it should once the batch is finalized.
In this commit we remove the mutation from `RegisterSidecar`. Rather
than modify the sidecar ticket, we instead accept a copy and return a
modified copy. This makes the control flow of future changes easier to
follow.
Whenever we are expecting a sidecar channel with us as the recipient, we
subscribe to the auction server through the special new SubscribeSidecar
RPC that works exactly the same as the SubscribeBatchAuction with the
only difference that we can use our channel funding multisig key as the
authentication key instead of the trader account key.
We have to react to all batch auction messages but our role is somewhat
simplified as we don't have to fully verify or sign the batch itself.
With this commit we add a new sidecar acceptor type that is exclusively
responsible for managing the recipient's tasks of executing a sidecar
channel. The two tasks are:
1. Verify a sidecar ticket and the offer contained within then add the
recipient node information to the ticket so it can be returned to the
sidecar provider. This is step 2/4 of the entire sidecar execution
protocol.
2. Interact with the auction server and connect out to an asker's node in the
right moment then accept the incoming channel. This is step 4/4 of the
entire sidecar execution protocol.
The code for these two tasks are kept separate from the default funding
manager to make it easier to extract a standalone sidecar acceptor
client later on. It also makes it easier to see what code would need to be
re-implemented in another language to integrate just the acceptor part.
