import type { EnvUsage, FrameworkWarning } from '../../config/types.js';
/**
 * Nuxt environment variable validation rules.
 *
 * Background (Nuxt 3):
 *  - Runtime configuration lives in `runtimeConfig` (private, server-only) and
 *    `runtimeConfig.public` (exposed to the client) and is read via
 *    `useRuntimeConfig()`.
 *  - In production, `.env` files are NOT read at runtime, and `process.env` is
 *    not populated in the browser. Direct `process.env` access in
 *    client/universal code is therefore unreliable — `useRuntimeConfig()`
 *    should be used instead.
 *  - Environment variables only override runtime config when prefixed with
 *    `NUXT_` (private) or `NUXT_PUBLIC_` (public).
 *
 * @param u - The environment variable usage information
 * @param warnings - The array to push warnings into
 */
export declare function applyNuxtRules(u: EnvUsage, warnings: FrameworkWarning[]): void;
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