A DECISIONS.md file prevented my AI sessions from interfering with each other

I've built with Cursor pretty much every evening lately, and it seems like it was the same story every single time - on Mondays it would pick PostgreSQL while on Thursday it would silently suggest SQLite, replacing half of the data layer in a new chat.

So to solve that, I made a simple text file inside the project folder named DECISIONS.md, where I store each decision on a new line ("Auth uses Supabase magic links, no passwords", "All dates in UTC"). And I copy-paste it into each chat as the very first thing.

Now the model considers that a set of constraints, so my changes were significantly reduced. Also, it makes it easier for me to remember my decisions a week later.

What do you store in your project's memory file? Do you store it somewhere with your code versioning?