import { type LanguageModel, type ModelMessage } from 'ai';
/**
 * Automatic conversation-history compaction.
 *
 * Long-running sessions (weeks-long WhatsApp threads) grow unbounded; budget
 * truncation silently loses the early relationship. Compaction summarizes the
 * older history into one system note and keeps the recent tail verbatim, so
 * the model retains facts/decisions without paying the full token cost.
 *
 * Runs post-turn (off the user's latency path) when the estimated history
 * tokens exceed `triggerTokens`, and force-runs as the recovery step after a
 * provider context-overflow error (see `contextOverflow.ts`).
 */
export interface CompactionConfig {
    /** Summarizer model. Defaults to the active agent's controlModel/model. */
    model?: LanguageModel;
    /** Estimated history tokens that trigger compaction. Default: 8000. */
    triggerTokens?: number;
    /** Number of recent messages kept verbatim. Default: 12. */
    keepRecentMessages?: number;
    /** Override the summarizer system prompt. */
    summaryPrompt?: string;
}
export declare const DEFAULT_COMPACTION_TRIGGER_TOKENS = 8000;
export declare const DEFAULT_COMPACTION_KEEP_RECENT = 12;
export type CompactionResult = {
    compacted: true;
    /** Verbatim retained tail — never includes a compaction summary message. */
    messages: ModelMessage[];
    /** Summary text for the system-note channel (`addSystemNote`, lifetime `run`). */
    summary: string;
    beforeTokens: number;
    afterTokens: number;
    summarizedCount: number;
} | {
    compacted: false;
    reason: 'under-threshold' | 'too-few-messages' | 'summarizer-error';
    beforeTokens: number;
};
export declare function estimateMessagesTokens(messages: ModelMessage[]): number;
export interface CompactMessagesOptions {
    messages: ModelMessage[];
    model: LanguageModel;
    config: CompactionConfig;
    /** Skip the threshold check (overflow recovery). */
    force?: boolean;
    abortSignal?: AbortSignal;
    /** Real last-turn prompt tokens when available (replaces chars/4 for threshold). */
    lastPromptTokens?: number;
    /** Prior compaction summary — folded into the summarizer input so facts chain across rounds. */
    priorSummary?: string;
}
/**
 * Pure compaction step: returns a new message list when compaction applied.
 * The kept tail always starts at a `user` message so assistant/tool-call
 * pairs are never split across the summary boundary.
 */
export declare function compactMessages(options: CompactMessagesOptions): Promise<CompactionResult>;