/**
 * quality-score.ts
 *
 * Compaction quality scoring, evaluates the output of a compaction strategy
 * by combining compression ratio and semantic retention signals.
 *
 * Score range: 0.0 (worst) → 1.0 (best)
 * Auto-switch threshold: scores below LOW_QUALITY_THRESHOLD trigger a strategy
 * escalation to the next more-aggressive strategy.
 */
import type { StrategyInput, StrategyOutput, CompactionStrategy } from './types.js';
/**
 * Compaction runs scoring below this value are considered low-quality and
 * trigger an automatic strategy switch.
 */
export declare const LOW_QUALITY_THRESHOLD = 0.4;
/** Letter grade derived from the composite quality score. */
export type CompactionQualityGrade = 'A' | 'B' | 'C' | 'D' | 'F';
/** Semantic retention signals evaluated during scoring. */
export interface SemanticRetentionSignals {
    /** At least one handoff/summary message is present in the output. */
    hasHandoff: boolean;
    /** Output contains non-trivial content (not just a blank handoff note). */
    hasNonTrivialContent: boolean;
    /** The output message count is a reasonable fraction of the input. */
    messageCountSane: boolean;
    /** The output token count is positive. */
    positiveTokenCount: boolean;
}
/** Full quality score breakdown for a compaction run. */
export interface CompactionQualityScore {
    /** Fraction of tokens removed: (tokensBefore - tokensAfter) / tokensBefore. */
    compressionRatio: number;
    /** Normalised compression dimension score (0–1). */
    compressionScore: number;
    /** Semantic retention dimension score (0–1). */
    retentionScore: number;
    /** Composite quality score: weighted sum of compression + retention (0–1). */
    score: number;
    /** Letter grade derived from score. */
    grade: CompactionQualityGrade;
    /** Individual semantic retention signals. */
    signals: SemanticRetentionSignals;
    /** True when score < LOW_QUALITY_THRESHOLD and strategy escalation should occur. */
    isLowQuality: boolean;
    /** Human-readable description of the score for diagnostics. */
    description: string;
}
/**
 * Produces a human-readable diagnostic description for a quality score.
 */
export declare function describeScore(score: CompactionQualityScore): string;
/**
 * Computes the quality score with description filled in.
 *
 * Prefer this over `scoreCompactionOutput` for all public use.
 */
export declare function computeQualityScore(input: StrategyInput, output: StrategyOutput): CompactionQualityScore;
/**
 * Returns the next more-aggressive strategy for escalation when quality is low.
 *
 * Escalation path:
 *   microcompact → autocompact → collapse → collapse (ceiling)
 *   reactive     → reactive (already maximum)
 *
 * @param current - The strategy that produced the low-quality result.
 * @returns The escalated strategy to re-run with.
 */
export declare function escalateStrategy(current: CompactionStrategy): CompactionStrategy;
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