You ask Claude to "store the user and their last 10 orders," and 30 seconds later you ship something that looks fine in review:

Orders embedded in the user document — until a power user has 9,000 of them and you hit the 16 MB document limit at 3 a.m.

A find({ email }) query with no index — COLLSCAN over 50 million docs every login.

new MongoClient(uri) inside the request handler — your Atlas dashboard shows 4,000 connections and the cluster starts dropping new ones.

db.users.find({ role: req.query.role }) — and someone passes { "$ne": null } to dump every user in the database.

The model didn't fail. It pattern-matched on tutorials where MongoDB is a toy with twelve documents and zero ops concerns. Production makes each one a real incident.

A CLAUDE.md at the root of your repo fixes this. Claude Code reads it on every task. Cursor, Aider, and Copilot do the same.…