import type { Message } from '../types/message/index.js';
/**
 * Indices of every message protected by a `retain` marker, expanded across
 * provider-valid turns.
 *
 * Transitive by necessity, not politeness. A `tool_result` whose
 * `tool_use` was dropped is rejected by the provider outright, and a
 * compacted conversation whose first non-system message is an assistant
 * turn is rejected before the pair is even considered. Pinning half a pair
 * — or the pair without its user turn boundary — would therefore turn a
 * retention request into a broken next turn. A pinned tool result pulls in
 * the assistant turn that issued the call; a pinned assistant turn pulls in
 * the user message that opened its turn and EVERY result answering it. The
 * second result hop matters, because an assistant turn with three calls and
 * one surviving result is the same dangling error in the other direction.
 */
export declare function findRetainedIndices(messages: readonly Message[]): Set<number>;
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