Runtime Debug

Use this skill when reproducing runtime-bundle, module-resolution, or user-bundle inclusion regressions.

Local Repro Discipline

• Mirror CI env vars when reproducing CI failures.
• Key variables: IS_WEBPACK_TEST=1 forces webpack (turbopack is default), NEXT_SKIP_ISOLATE=1 skips packing next.js.
• For module-resolution validation, always rerun without NEXT_SKIP_ISOLATE=1.

Stack Trace Visibility

Set __NEXT_SHOW_IGNORE_LISTED=true to disable the ignore-list filtering in dev server error output. By default, Next.js collapses internal frames to at ignore-listed frames, which hides useful context when debugging framework internals. Defined in packages/next/src/server/patch-error-inspect.ts.

User-Bundle Regression Guardrail

When user next build starts bundling internal Node-only helpers unexpectedly:

1. Inspect route trace artifacts (.next/server/.../page.js.nft.json).