/**
 * Plugin host: manages plugin registration and capability widening.
 * - Ensures idempotency: same plugin applied twice is a no-op
 * - Tracks capabilities: merges { validation, pubsub, ... } from applied plugins
 * - Returns the widened router type (same instance, type-level only)
 *
 * Internal; called by router.plugin().
 */
import type { ConnectionData } from "../context/base-context.js";
import type { Router } from "../core/router.js";
import type { Capabilities, Plugin } from "./types.js";
export declare class PluginHost<TContext extends ConnectionData = ConnectionData> {
    private readonly router;
    private readonly applied;
    private capabilities;
    constructor(router: Router<TContext, any>);
    /**
     * Apply a plugin with idempotency check.
     * - If the plugin was already applied, return the router as-is (type-widened).
     * - Otherwise, call the plugin, merge capabilities, and return the result.
     * @param plugin Pure function: (router) => Router<TContext, TCaps>
     */
    apply<P extends Plugin<TContext, any>>(plugin: P): ReturnType<P>;
    /**
     * Get readonly view of merged capabilities.
     */
    getCapabilities(): Readonly<Capabilities>;
}
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