chore: next build reformats tsconfig.json into a shape prettier rejects, failing the pre-commit check-format hook #4885

Problem

next build / next dev rewrites tsconfig.json — expanding the lib / paths / exclude arrays to multiline and appending a .next/dev/types/**/*.ts include entry. That regenerated shape fails prettier --check (prettier wants the short arrays collapsed onto one line).

Because the pre-commit hook runs check-format (prettier --check .) across the whole repo, committing after a build fails the hook on tsconfig.json, forcing a --no-verify bypass. The file also shows as perpetually "modified" in git status after any build.

Correction: the committed tsconfig.json is already prettier-clean — an earlier note here had it backwards. The failing version is the one Next produces at build time, not the one in git.

Repro

# committed version is clean:
npx prettier --check tsconfig.json    # passes

# after `next build` (arrays expanded to multiline):
npx prettier --check tsconfig.json    # [warn] tsconfig.json  -> check-format / pre-commit fails

Origin

Surfaced during #4877. Introduced by the Next.js 16 upgrade (#4876) — Next rewrites tsconfig.json on build.

Fix (PR #4886)

Add tsconfig.json to .prettierignore. It's a Next-managed file, so prettier shouldn't enforce its format. The committed file is left unchanged (already clean).

Acceptance

• npm run check-format passes even when tsconfig.json is in its build-modified state
• Pre-commit hook no longer requires --no-verify for unrelated commits
• Committed tsconfig.json unchanged