To be clear: while I can describe the problem, I honestly don't have any ideas what the most elegant or clean solution is. I have never found a satisfactory solution. I end up keeping lots of stuff in my head and writing summary emails.
I'm surprised no one has built a better way to do this. We tried syncing with Zapier first (a company I absolutely love), but if I recall correctly it was a one-way sync, and we needed it to go both ways.