SaaS backend architecture decisions made in week one are the ones you live with at 1,000 users. In 2026, Claude Code makes it dangerously easy to build something that works for 50 users and quietly breaks everything at 500. This episode names the three architectural sins that create six-month rewrites — the microservices complexity trap, the memory and connection limit wall, and the big bang rewrite fallacy — with the math behind each. Then: real compute pricing compared head-to-head (Railway at $160/month vs Fly.io at $42.79 for identical specs, Vercel's hidden 15-cent egress vs Fly.io's 2-cent egress). Database selection with hard limits: Sup ...