Book: TypeScript in Production Also by me: The TypeScript Library — the 5-book collection My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub You take a tiny TypeScript library. Call it string-tools . A few hundred lines counting tests. You publish to both registries: npm because Node lives there, and JSR because by early 2026 it has crossed 40,000 packages and the Deno team keeps adding features the npm side has been asking for since 2018. The npm publish goes through. npm publish returns happy output. You install it from a fresh project. It works. The JSR publish does not. The CLI prints four categories of warnings, refuses to upload, and points you at a documentation page titled "slow types." You look at your exports map, which npm accepted without comment, and discover three things wrong with it that npm never mentioned. Then you run attw against the npm version you already shipped, and attw agrees.…