/**
 * summarizeOldest — fold the oldest foldable turns into one summary message.
 *
 * Pattern: WindowStrategy implementation. Its own module, importing nothing
 *          that registers anything, so a bundle that never mentions it never
 *          carries it (and never carries the summarizer machinery either).
 * Role:    core/ layer.
 * Emits:   N/A — the stage emits, records and costs; this file decides.
 *
 * This is what `.compaction({...})` configures, and the market's familiar
 * move (Claude Code / the Claude Agent SDK call it compaction). What is
 * different here is not the fold — it is that the fold is filed as a claim:
 * a summary is a claim ABOUT the past, and the past itself stays. In the
 * commit log for as long as the process lives, and — since 8.2, under
 * `retain: 'conversation'` — on the conversation checkpoint for as long as
 * the conversation does, which is the half a standing agent actually needs.
 *
 * Everything it decides, it explains. Every engaged path returns a record —
 * including the paths that change nothing, which are the ones a person
 * debugging an over-budget window actually needs.
 */
import type { WindowStrategy } from '../strategy.js';
import type { CompactionOptions } from '../types.js';
/** `WindowRecord.strategy` written by every record this strategy files. */
export declare const SUMMARIZE_OLDEST = "summarize-oldest";
/**
 * Fold the oldest contiguous run of foldable turns into one summary message,
 * keeping the recent turns and stepping over anything unresolved.
 *
 * Triggered by COUNTED tokens: the last call's adapter-reported input tokens
 * against `thresholdTokens`. A provider that reports no usage gets
 * `CompactionUnmeasurableError` rather than an invented number.
 *
 * @example
 * ```ts
 * import { Agent, summarizeOldest } from 'agentfootprint';
 *
 * const agent = Agent.create({ provider: anthropic(), model: 'claude-sonnet-4-5' })
 *   .window(summarizeOldest({
 *     thresholdTokens: 120_000,
 *     summarizer: anthropic(),
 *     model: 'claude-haiku-4-5',
 *   }))
 *   .build();
 * // `.compaction({ ... })` is this exact line, spelled shorter.
 * ```
 */
export declare function summarizeOldest(options: CompactionOptions): WindowStrategy;