runtime-debug

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: Inspect route trace artifacts ( .next/server/.../page.js.nft.json ). Inspect traced server chunks for forbidden internals (e.g. next/dist/server/stream-utils/node-stream-helpers.js , node:stream/promises ). Add a test-start-webpack assertion that reads the route trace and traced server chunks, and fails on forbidden internals. This validates user-project bundling (not publish-time runtime bundling). Bundle Tracing / Inclusion Proof To prove what user bundling includes, emit webpack stats from the app's next.config.js : // next.config.js module . exports = { webpack ( config ) { config . profile = true return config } , } Then use stats.toJson({ modules: true, chunks: true, reasons: true }) and diff webpack-stats-server.json between modes. This gives concrete inclusion reasons (e.g. which module required node:stream/promises ) and is more reliable than analyzer HTML alone.