> This is why, if something is important, I take it out of email and put it into a document people can reference.

This is how things should be done, regardless of which medium is used to discuss the project. Without isolating and aggregating the final decision of each thread, there is no way to determine what everybody has agreed upon as the final product without looking back, which quickly becomes onerous.

Things get messy when you start having different versions of each feature, but that doesn't change the concept of using email/Slack/Discord/text/etc. for discussion and a separate "living" document for formalizing those decisions.

We had this problem in our organization circa 20 years back so I built a ticketing system, now each conversation exists as its own object, and "the same thing being discussed twice" has the opportunity to be merged into one, etc. That seems to have helped a lot with our internal conversations.