nextjs-modernizer

@devexpgbb

Use this skill when the user asks to migrate, upgrade, or modernize a Next.js codebase from Next 14 to Next 15 — including phrasings like "bump next to 15", "upgrade next.js", "migrate to next 15", "next 15 upgrade", "we're stuck on next 14", or when preparing a major-version dependency PR involving next ^14.x. Also fires when the user mentions Next 15 indirect symptoms: async cookies/headers errors, sync params/searchParams warnings, fetch no longer cached by default, removed experimental.bundlePagesExternals or experimental.serverComponentsExternalPackages, react 19 peer warnings, GET route handlers losing default caching, NextRequest geo/ip removed, or asks for a migration plan / breaking changes audit on a Next 14 repo. This skill audits, classifies (SAFE / AUTOFIX / MANUAL), applies safe autofixes, and emits a phased migration plan grounded in the official Next.js 15 upgrade guide. It does NOT run the consumer's tests; it does NOT bump package.json; it emits a plan the team executes under review.