> I've been digging into a weird bug, deep in Go, that causes FIN_ACK packets to get delayed by hundreds and hundreds of ms.

Just going to put it out there: have you considered the problem might actually be [Nagle’s Algorithm](https://en.wikipedia.org/wiki/Nagle's_algorithm)? This algorithm is the source of 10s of thousands of hours of wasted debugging time of “weird bugs related to latency of networking.” Even the “greats” have wasted time debugging something that ended up being “I forgot about Nagle.”