/**
 * Environment-variable indirection for config values that hold secrets.
 *
 * Lets a user write `apiKey: "${OPENAI_API_KEY}"` in config.yaml and keep the
 * key itself in the environment. Shared by the MCP server resolver and the
 * realtime provider factory.
 */
/**
 * Resolve a value that may reference an environment variable.
 * Supports `${VAR_NAME}` and bare `$VAR_NAME`; anything else is returned as-is.
 * An unset variable resolves to `undefined`, never to the literal reference.
 *
 * The environment is named once, in the signature, so a caller can hand in its
 * own rather than have the ambient one read from inside the body.
 */
export declare function resolveEnvVar(value: string | undefined, env?: NodeJS.ProcessEnv): string | undefined;
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