import { Message } from '../../types/messages.js';
/**
 * Check if a message is pinned, including tool-pair partner protection.
 * Returns `true` if the message at `index` is pinned, or if it is the
 * adjacent tool-pair partner (toolUse/toolResult) of a pinned message,
 * matched by toolUseId.
 *
 * @param messages - The full messages array.
 * @param index - The index to check.
 * @returns `true` if the message or its tool-pair partner is pinned.
 */
export declare function isPinned(messages: Message[], index: number): boolean;
/**
 * Pin a message so it is protected from eviction during context reduction.
 * Mutates the message in place by setting `metadata.custom.pinned = true`.
 *
 * @param messages - The messages array containing the message to pin.
 * @param index - The index of the message to pin.
 */
export declare function pinMessage(messages: Message[], index: number): void;
/**
 * Pin the first N messages in the array permanently.
 *
 * @param messages - The messages array.
 * @param count - Number of messages from the start to pin.
 */
export declare function applyPinFirst(messages: Message[], count: number): void;
/**
 * Partition a range of messages into pinned (protected) and unpinned arrays.
 *
 * @param messages - The full messages array.
 * @param start - Start index of the range (inclusive).
 * @param end - End index of the range (exclusive).
 * @returns A tuple of [pinned, unpinned] message arrays.
 */
export declare function partitionPinned(messages: Message[], start: number, end: number): [Message[], Message[]];
/**
 * Unpin a message so it can be evicted during context reduction.
 * Mutates the message in place by removing the `pinned` flag from metadata.
 *
 * @param messages - The messages array containing the message to unpin.
 * @param index - The index of the message to unpin.
 */
export declare function unpinMessage(messages: Message[], index: number): void;
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