Vercel silently 500'd every API endpoint while the build logs said Ready

TL;DR: Vercel's Node File Trace only bundles files reached through node_modules. Cross-tree relative imports inside /api/ are never packaged into sibling function bundles. The deploy goes green, TypeScript is clean, and every endpoint that imports a shared helper 500s at runtime. Here is how I found it and the only two patterns that work. I am a solo founder building AimVantage (https://aimvantage.uk), an AI job-prep app on Vercel serverless functions. I wanted one obvious thing: shared helper