/**
 * rill install: Install an extension from npm registry or local path.
 *
 * Constraints (FR-EXT-2/3/4, UXI-EXT-2/3/4):
 * - assertBootstrapped pre-check before any npm subprocess
 * - Collision pre-check before spawning npm (EC-8)
 * - npm subprocess uses --prefix so project-root package.json is never modified (NFR-EXT-6)
 * - Config edit + validation < 1s (NFR-EXT-2)
 */
/**
 * Install an extension into the current project.
 *
 * Implements UXI-EXT-2 (registry) and UXI-EXT-3 (local path) order of operations.
 */
export declare function run(argv: string[]): Promise<number>;