Book: System Design Pocket Guide: Interviews Also by me: Event-Driven Architecture Pocket Guide My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub Picture a growth team that ships a "weekly digest" on a Wednesday. The cron job enqueues a couple million emails in minutes, the email provider throttles the account for exceeding its contracted send rate, and the incident channel turns into a wall of red. Every notification produced after the throttle goes into a tight retry loop, which produces more 429s, which produces more retries. The canonical failure mode is not volume. It is the shape of the volume: synchronous, undeduplicated, retry-greedy, and bottlenecked behind a third-party rate limit you do not control. The second-pass design is what you build after you have lost a Wednesday to a digest job and you want the next launch to absorb 10x without paging anyone.…