/**
 * Plugin contract for extending string utilities.
 */
export type StringExtnPlugin = {
    /** The unique plugin name used for registration and lookup. */
    name: string;
    /** The function invoked when the plugin runs. */
    fn: (input: string, ...args: any[]) => string;
};
/**
 * Register a plugin for later execution.
 * @param plugin The plugin to register.
 * @throws If a plugin with the same name is already registered.
 */
export declare function registerPlugin(plugin: StringExtnPlugin): void;
/**
 * Execute a registered plugin by name.
 * @param name The plugin name to execute.
 * @param input The input string passed to the plugin.
 * @param args Additional arguments forwarded to the plugin function.
 * @returns The plugin's result string.
 * @throws If the plugin does not exist.
 */
export declare function runPlugin(name: string, input: string, ...args: any[]): string;
/**
 * List all registered plugin names in registration order.
 * @returns An array of plugin names.
 */
export declare function listPlugins(): string[];
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