Framework semantic default

Next.js cookies headers async request APIs synchronous usage runtime error Next 15 official docs

Auth middleware/page fails at runtime after request APIs become async.

Next.jsWeb frameworkFramework semantic defaultnext16

Agent Quick Fix

Repair against the current Next.js contract, then keep the change narrow and source-backed.

Product: Next.js
Current-contract area: Next.js cookies()/headers() old synchronous usage
Likely root cause: Auth middleware/page fails at runtime after request APIs become async.
Repair direction: Verifier checks behavior across multiple requests/build modes, not merely compilation. Check request count, response freshness, and render behavior over multiple calls.

Symptom

Auth middleware/page fails at runtime after request APIs become async.

Why This Happens

Local code often type-checks under both old and new framework semantics; the failure depends on the installed framework version and current runtime defaults.

Common Wrong Fixes

Changing local code without checking the current external contract.
Retrying the same install, build, or API call with no version/source change.
Applying a broad unsafe bypass when a narrow compatibility fix is available.

Codex Search Keywords

These are the search terms observed in a neutral Codex validation run for this failure shape.

Next.js cookies headers async request APIs synchronous usage runtime error Next 15 official docs
site:nextjs.org/docs/messages/sync-dynamic-apis cookies headers async
https://nextjs.org/docs/messages/sync-dynamic-apis
'Async Request APIs' in https://nextjs.org/docs/app/guides/upgrading/version-15