Flags

When you're working on Next.js internals and need to add or modify feature flags, this walks you through the required wiring across multiple config files. You'll touch config-shared.ts for types, config-schema.ts for validation, and potentially define-env.ts depending on where the flag gets consumed. The skill breaks down the distinction between client-bundled code (where build-time injection works) and pre-compiled runtime bundles (where you need actual process.env variables set). The documentation is thorough on the two approaches for runtime flags, including the tradeoff between simpler runtime env vars versus separate bundle variants that eliminate dead code but add build complexity. This is narrow and deep, aimed squarely at Next.js contributors rather than app developers.