Disclosure: LND Excessive Failback Exploit

In the discussion regarding the BOLTs change and its implications on Lightning Network transactions, there seems to be some confusion around the use of terms 'upstream' and 'downstream'. The core of the issue revolves around the process stipulated by the BOLTs change, which mandates that as soon as a preimage is obtained from a downstream node, it must be relayed upstream. This procedure ensures that nodes are required to accurately extract preimages received from downstream counterparts and subsequently send an update_fulfill_htlc message back upstream. However, the conversation also highlights an area of ambiguity, particularly in relation to whether a node is obliged to initiate a force-close if its update_fulfill_htlc message fails to receive an acknowledgment upstream. This point of contention does not seem to directly stem from the new BOLTs requirement but rather from the interpretation of how nodes should manage unacknowledged messages within the context of maintaining network integrity and ensuring transaction veracity.