Regex-based on purpose: converts simple top-level CJS patterns to ESM, remaps package specifiers to their @choojs homes, points retired nano* packages at built-in replacements (choo-lazy-route → lazy()), and reports everything it refuses to guess at instead of guessing. Validated against choo's own v7 example app: migrated output runs on v8 unmodified. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_014NgfSjHE11oFpoSnLVKLXd