build(deps): upgrade to Next.js 16 - #12
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Next.js 15.5.20 -> 16.3.4, with React 19.2.8 and the matching @types and eslint-config-next majors. Turbopack is the default bundler in 16, so `next dev --turbopack` loses the flag. The build already ran through Turbopack and there is no webpack config here, so nothing needs `--webpack`. The one real break was ESLint. @next/eslint-plugin-next now ships flat config only, and the old `FlatCompat.extends('next/core-web-vitals', 'next/typescript')` call throws a circular-structure error against it. The two configs are imported directly as flat arrays instead, which drops the last consumer of @eslint/eslintrc. Verified the Next rules still fire (no-img-element) and that the same 20 files are linted as before. tsconfig changes are the ones `next build` writes itself: `jsx` must be `react-jsx` in 16, and `.next/dev/types` joins `include` now that dev and build write to separate output directories. The nextjs-agent-rules block in AGENTS.md is generated and re-added by `next dev`; committing it keeps the tree clean. None of the other version 16 breaking changes apply — no middleware, no images.domains, no AMP, no serverRuntimeConfig/publicRuntimeConfig, no sync params or searchParams, no parallel routes, and `next lint` was never used. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Upgrades the template from Next.js 15.5.20 to 16.3.4.
Changes
next15.5.20 → 16.3.4,react/react-dom→ 19.2.8,@types/react,@types/react-dom,eslint-config-next→ 16.3.4--turbopackfrom thedevscriptdevandbuildin 16. There is no webpack config here, so nothing needs the--webpackescape hatch.eslint.config.mjsto importeslint-config-next/core-web-vitalsandeslint-config-next/typescriptdirectly@next/eslint-plugin-nextnow ships flat config only, and the oldFlatCompat.extends('next/core-web-vitals', 'next/typescript')call throwsTypeError: Converting circular structure to JSONagainst it.@eslint/eslintrcFlatCompatwas its last consumer.tsconfig.json:jsx→react-jsx,.next/dev/types/**/*.tsadded toincludenext builditself.devandbuilduse separate output directories in 16.AGENTS.mdgained anextjs-agent-rulesblocknext dev. Committing it keeps the tree clean; deleting it just re-creates an uncommitted change.README.md,AGENTS.md,src/app/page.tsx,e2e/example.spec.tsBreaking changes that did not apply
Checked each item in the version 16 upgrade guide against the tree. None of these are present:
middleware(→proxy),images.domains, AMP,serverRuntimeConfig/publicRuntimeConfig, synchronousparams/searchParams/cookies()/headers()/draftMode(), parallel routes needingdefault.js,next/legacy/image,unstable_cache imports, single-argumentrevalidateTag,experimental_ppr,experimental.dynamicIO/useCache, removeddevIndicatorsoptions.next lintwas never used — thelintscript already calledeslintdirectly.next.config.tsalready used the stable top-levelturbopackkey.Node is already on 24 via
.nvmrc, above the new 20.9 floor.Verification
All run in the worktree against 16.3.4:
pnpm type-check— cleanpnpm lint— cleanpnpm format:check— cleanpnpm test— 2/2pnpm build— succeeds, both routes prerendered staticpnpm test:e2e --project=chromium— 4/4, including the@elirobinson/ai-patternscontract checks (touch targets, visible focus, WCAG AA contrast) in light and darkpnpm dev— Next 16.3.4 boots, home page renders, no browser console errors and no dev-indicator errorsAfter the ESLint rewrite I confirmed the Next rules still fire by linting a throwaway file with a bare
<img>;@next/next/no-img-elementcaught it. The same 20 files are linted before and after.Visual diff
The only rendered change is one card label: "Next.js 15" → "Next.js 16". Layout, spacing, type, and color are untouched, and the design system contract E2E specs pass unchanged. Skipping a before/after screenshot pair for a one-word text delta.
🤖 Generated with Claude Code