export interface PreCompactHookInput {
    readonly projectRoot: string;
    readonly sessionId: string;
    readonly transitionKey: string;
}
export interface PreCompactHookResult {
    readonly triggered: boolean;
    readonly checkpointPath: string | null;
    readonly ratio: number;
    readonly zone: 'none' | 'soft-warn' | 'pre-compact' | 'red-line';
    readonly note: string;
}
/**
 * Check the pre-compact zone and, if active, write a checkpoint.
 * Returns a result envelope the caller can stitch into the
 * transition response. NEVER throws; returns a `triggered: false`
 * result on any error so the transition itself stays the contract
 * surface.
 */
export declare function maybePreCompactCheckpoint(input: PreCompactHookInput): PreCompactHookResult;