Root cause: Next.js 16 defaults to Turbopack for builds, but Payload CMS's
richtext-lexical imports .css files that fail during route collection in
Node ESM context.
Fix: add @payloadcms/richtext-lexical and @payloadcms/next back to
serverExternalPackages so Next.js skips their internal imports during
route collection. Use --webpack explicitly since Turbopack production
builds are incompatible with Payload (payloadcms/payload#14786).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>