Why SSE for AI agents keeps breaking at 2am

Why SSE for AI agents keeps breaking at 2am Every team building AI agent UIs writes their own SSE client. And every team hits the same four bugs. I know because we shipped 36 agent tools at Praxiom before we sat down and wrote a real protocol instead of patching the same streaming code for the fifteenth time. This is a post-mortem on the four bugs. At the end I'll show you what we extracted. The setup You're building a chat-style UI backed by an LLM agent. The agent calls tools, thinks for a few seconds, maybe runs multiple turns. You want the frontend to stream tokens in real-time, show "running web search..." while a tool is active, and display a progress bar for longer operations. SSE seems like the obvious choice. It's simple. You've used it before. You write the server in an afternoon. Then you go to production. Bug #1: The chunk boundary Here's the hand-rolled SSE parser most people write: for await (const chunk of stream) { const text = decoder.decode(chunk); const lines = text.