/**
 * Oldest-first planner-input trimming for context overflow.
 *
 * Port of codex's `history.remove_first_item()` retry on
 * `ContextWindowExceeded` (`compact.rs:309-343`). Codex can discard trimmed
 * history because it writes a summary; Atomic promises validated deletion
 * boundaries over the original numbered lines, so trimming here is a *view*
 * over the same region:
 *
 * - the planner is shown only lines `offset+1..N`, renumbered `1..N-offset`;
 * - protected spans and prior filtered markers are rebased into that view;
 * - the returned ranges are rebased back onto the original numbering;
 * - the withheld head becomes a deterministic deletion range, because the
 *   planner cannot rank what it was not shown and the oldest lines carry the
 *   lowest continuation value. Protected lines inside the head still survive:
 *   `validateDeletedRanges` splits every range around protected lines.
 */
import type { LineRange, NumberedRegion, RawLineRange } from "./compaction-types.js";
/**
 * Return the region as seen after withholding its oldest `offset` lines, or
 * `undefined` when that offset leaves nothing rankable.
 */
export declare function trimRegionHead(region: NumberedRegion, offset: number): NumberedRegion | undefined;
/**
 * Next withheld-head size after an overflow, halving what remains each time, or
 * `undefined` when no further trimming is possible.
 */
export declare function nextTrimOffset(region: NumberedRegion, currentOffset: number): number | undefined;
/**
 * Map ranges validated against a trimmed view back onto the original region,
 * adding the withheld head as a deterministic deletion.
 */
export declare function rebaseTrimmedRanges(validated: readonly LineRange[], offset: number): RawLineRange[];
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