Next.js 16 Turbopack Bug Turns require.resolve Into Integer, Breaking Runtime File Paths

A developer at a private company discovered a critical runtime bug after deploying a Next.js 16 service, where a tool designed to convert PDF pages into JPEG images returned no output. The root cause was Next.js 16's default bundler, Turbopack, which resolves require.resolve calls at build time and replaces them with integer module IDs instead of file path strings. When this integer was passed to path.dirname, a TypeError crashed the feature — an issue undetectable by type checks, unit tests, or direct script calls, since none of those go through the Turbopack build step. The fix involved resolving the package location relative to the process's working directory, though this solution works only with Turbopack and not with webpack. Following the incident, the team added a pre-deployment checklist item requiring a production-equivalent build to be started and tested externally, and documented the procedure ten days later.