import type { TapeSnapshot } from './types';
/**
 * Compute a fixed-width window of tape cells centered on the head.
 *
 * The engine's `Tape` class exposes a `viewport` getter that does this for
 * the live tape; `tapeViewport` is the equivalent for the wire-data
 * `TapeSnapshot` carried in `Frame.tape`. Cells outside the snapshot's
 * `symbols` array are padded with `blank`, so the result always has
 * exactly `width` entries.
 *
 * The returned `headIndex` is the head's index within `cells` —
 * deterministic at `Math.floor(width / 2)`, but exposed for callers that
 * want to avoid recomputing it (and to leave room for future non-centered
 * policies without a signature break).
 *
 * Pass the tape's blank symbol from `Snippet.alphabets[i]` (by convention
 * the first entry per tape in the visuals/engine pipeline — verify against
 * how the snippet was recorded).
 */
export declare function tapeViewport(snapshot: TapeSnapshot, width: number, blank: string): {
    cells: string[];
    headIndex: number;
};