The SSE Fragmentation Catastrophe That Took Down CareerPilot AI (Smash Stories)

This is a submission for DEV's Summer Bug Smash: Smash Stories powered by Sentry . It was 11:14 PM. My friend DM'd me on Twitter: "Your app just hung for 30 seconds, spun indefinitely, and then completely died." I opened the browser DevTools console pointed at production and saw it — the screen flooded in red: GET https://careerpilot-ai.run.app/api/analyze-career net::ERR_INCOMPLETE_CHUNKED_ENCODING 200 (OK) The Server-Sent Events stream powering CareerPilot AI was systematically collapsing on Google Cloud Run. And I had no idea why. Locally on localhost:3000 , the agentic pipeline was a masterpiece. The multi-stage reasoning logs streamed gracefully — Step 1 flowed into Step 6, the final structured JSON payload arrived within seconds, the UI lit up with a complete personalized career roadmap. Beautiful. But once deployed behind Google's Front End (GFE) proxy, the pipeline was a graveyard of broken sockets. The Architecture Under Fire CareerPilot AI runs a six-stage agentic pipeline on every career analysis request. Instead of firing a single long-running prompt to Gemini and making the user stare at a blank screen for 20+ seconds, we designed a Server-Sent Events logging stream to broadcast real-time reasoning steps directly to the browser — giving the interface the feel of a live, active mentor thinking out loud. Once the final stage (Self-Evaluation & Constraint Validation) completed, the backend constructed a massive, nested 15KB JSON payload containing the personalized roadmap: skill weightings, role benchmarks, resource links, and a 30-day milestone calendar. Here was the delivery mechanism — and the landmine hiding inside it: // server.ts — The vulnerable streaming channel app . get ( " /api/analyze-career " , async ( req , res ) => { res . setHeader ( " Content-Type " , " text/event-stream " ); res . setHeader ( " Cache-Control " , " no-cache " ); res . setHeader ( " Connection " , " keep-alive " ); // Stream intermediate reasoning logs per step for ( let st