/**
 * Layer 3: Emergency Truncation (Failsafe).
 *
 * Last-resort truncation when Layer 2 fails or context is still too large.
 * Drops the oldest conversation turns purely mechanically (no LLM call).
 * Preserves structural integrity: tool_use/tool_result pairs are dropped together.
 *
 * Triggers at 90% of context window (configurable), or reactively when
 * the API returns a context overflow error.
 *
 * This layer also serves as a mid-loop safety valve: it fires inside
 * transformContext during the agentic loop when estimated token count
 * exceeds 90%. Mid-loop truncation does NOT emit onBeforeCompaction
 * (no observational memory processing mid-loop).
 *
 * References:
 *   - compaction-strategy.md (Layer 3: Emergency Truncation)
 *   - phase-5-compaction.md (5.4)
 */
import type { AgentMessage } from '../context-manager.js';
import type { FailsafeConfig } from '../types.js';
export declare const FAILSAFE_DEFAULTS: FailsafeConfig;
/**
 * Result of an emergency truncation operation.
 */
export interface FailsafeTruncationResult {
    /** The truncated conversation history. */
    newHistory: AgentMessage[];
    /** Number of turns removed. */
    turnsRemoved: number;
    /** Estimated tokens after truncation. */
    tokensAfter: number;
}
/**
 * Perform emergency truncation on conversation history.
 *
 * Drops the oldest turns (preserving structural pairs) until the
 * estimated token count drops below the threshold, or until only
 * the preserved tail remains.
 *
 * @param history - Conversation history (post-slot region)
 * @param contextWindow - Total context window size in tokens
 * @param slotTokens - Estimated tokens used by slots
 * @param threshold - Usage ratio threshold (default 0.90)
 * @returns Truncation result with new history and metrics
 */
export declare function emergencyTruncate(history: AgentMessage[], contextWindow: number, slotTokens: number, threshold?: number): FailsafeTruncationResult;
/**
 * Check if emergency truncation should fire based on token count.
 */
export declare function shouldTruncate(currentTokens: number, contextWindow: number, threshold?: number): boolean;
/**
 * Check if an error represents a context overflow.
 * Matches common API error patterns from various providers.
 */
export declare function isContextOverflow(error: Error): boolean;
//# sourceMappingURL=failsafe.d.ts.map