It is useful for accounting and informational reasons for users to
be informed when a payment has been successfully forwarded. Thus,
when an HTLC which represents a forwarded leg is claimed, we
generate a new `PaymentForwarded` event.
This requires some additional plumbing to return HTLC values from
`OnchainEvent`s. Further, when we have to go on-chain to claim the
inbound side of the payment, we do not inform the user of the fee
reward, as we cannot calculate it until we see what is confirmed
on-chain.
Substantial code structure rewrites by:
Valentine Wallace <vwallace@protonmail.com>
`Event::PaymentSent` serialization has a bug where we
double-serialize the payment_preimage field but do not attempt to
read it twice. This results in a failure to read `ChannelManager`s
from disk if we have a pending `Event::PaymentSent` pending
awaiting handling when we serialize.
Instead of attempting to read both versions, we opt to simply fix
the serialization, assuming it is exceedingly rare for such a
scenario to appear (and if it does, we can assist in manual
recovery).
The release notes have been updated to note this inconsistency.
Found by the chanmon_consistency fuzz target.
