/**
 * Classify an install spec as a marketplace plugin reference or a plain npm package.
 *
 * Rules (applied in order):
 *  1. Starts with `@` (scoped npm) -> always npm.
 *  2. Contains `@` after the first character -> split on the LAST `@`.
 *     If the right-hand side is a known marketplace name, it's a marketplace ref.
 *     Otherwise it's an npm spec (e.g. `pkg@1.2.3`).
 *  3. No `@` -> npm.
 */
export declare function classifyInstallTarget(spec: string, knownMarketplaces: Set<string>): {
    type: "marketplace";
    name: string;
    marketplace: string;
} | {
    type: "npm";
    spec: string;
};