What I Got Wrong Building a RAG Pipeline from Scratch in TypeScript

I'm building a production-grade, multi-tenant AI agent in TypeScript. No Python. No LangChain. Just Node.js, PostgreSQL with pgvector, and a lot of wrong assumptions that taught me than any tutorial. This post covers three things I got wrong while building my RAG (Retrieval-Augmented Generation) pipeline, what I replaced them with, and why the replacements work. If you're building RAG systems, especially in TypeScript, this might save you a few days of debugging. The full codebase is open.