/**
 * before_compaction hook — transcript backfill before context window compaction.
 *
 * Serializes the recent conversation messages and submits them to engram's
 * /api/backfill/session endpoint for server-side observation extraction.
 * This is fire-and-forget: the hook must never block compaction.
 */
import type { EngramRestClient } from '../client.js';
import type { PluginConfig } from '../config.js';
import type { BeforeCompactionEvent, PluginHookContext, PluginLogger } from '../types/openclaw.js';
/**
 * Handle the before_compaction hook.
 *
 * @param event  - The before_compaction event from OpenClaw.
 * @param ctx    - The hook context containing agent identity fields.
 * @param client - Shared engram REST client.
 * @param config - Resolved plugin config.
 */
export declare function handleBeforeCompaction(event: BeforeCompactionEvent, ctx: PluginHookContext, client: EngramRestClient, config: PluginConfig, logger?: PluginLogger): void;
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