/**
 * ContextEngine plugin registry — discovery surface for registered engines.
 *
 * Provides {@link registerContextEngine} for plugin registration and
 * {@link getContextEngine} for lookup, mirroring the provider-registry
 * pattern at `packages/core/src/llm/provider-registry/index.ts`.
 *
 * Auto-registers {@link RuleBasedTruncationEngine} under the `'rule-based'`
 * name at module load. The `'compression'` role in `executor-factory.ts`
 * seeds the engine registry with the `LlmSummarizationEngine`, which continues
 * to be the default; the rule-based engine is an alternative that callers
 * can select via {@link registerContextEngine}.
 *
 * @module llm/context-engines
 * @task T9312
 * @epic T9261 T-LLM-CRED-CENTRALIZATION
 */
import type { ContextEngine } from '@cleocode/contracts/memory/context-engine.js';
/**
 * Register a named {@link ContextEngine} in the plugin registry.
 *
 * Last-writer-wins on name collisions — user plugins override builtins.
 * Names are stored as-is (case-sensitive). Registration is synchronous and
 * takes effect immediately for any subsequent {@link getContextEngine} call.
 *
 * @param name - Unique engine name (e.g. `'rule-based'`, `'my-custom-engine'`).
 * @param engine - The context engine implementation to register.
 */
export declare function registerContextEngine(name: string, engine: ContextEngine): void;
/**
 * Look up a registered {@link ContextEngine} by name.
 *
 * Returns `undefined` when no engine is registered under the given name.
 * Callers MUST handle the `undefined` case — there is no implicit fallback
 * inside this function (fallback logic lives in `executor-factory.ts`).
 *
 * @param name - Engine name to look up.
 * @returns The registered {@link ContextEngine}, or `undefined`.
 */
export declare function getContextEngine(name: string): ContextEngine | undefined;
/**
 * Return all registered engine names, sorted ascending.
 *
 * Used by `cleo llm context-engines list`.
 *
 * @returns Sorted array of registered engine name strings.
 */
export declare function listContextEngines(): ReadonlyArray<string>;
/**
 * Reset registry state for testing.
 *
 * Re-registers the builtin `'rule-based'` engine after clearing to
 * match the module-load state.
 *
 * @internal — NOT part of the public API.
 */
export declare function _resetContextEngineRegistryForTesting(): void;
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