/**
 * history-payload.ts — shrink + window the WebSocket `history` frame.
 *
 * Agent prompts still read the full on-disk `.log`. This module only shapes
 * what the SPA receives so a large transcript does not stall first paint:
 *   1. Cap `activity.steps[].preview` (tool dumps dwarf the reply).
 *   2. Send the newest messages first (count + byte budget).
 *   3. Follow with `history-prepend` chunks of older turns.
 */
import type { ChatMessage } from '../core/types.js';
/** Tool-step previews in history / active-run replay. Disk `.log` is unchanged. */
export declare const HISTORY_PREVIEW_MAX_CHARS = 500;
/** Prefer at most this many messages in the first `history` frame. */
export declare const HISTORY_TAIL_MAX_MESSAGES = 40;
/**
 * Soft cap on estimated UTF-16 units in the first frame. One huge latest
 * reply still goes out in full (the user is looking at it); older bulky
 * turns wait for prepend chunks.
 */
export declare const HISTORY_TAIL_MAX_BYTES: number;
/** Older messages per `history-prepend` frame (nearest-to-tail first). */
export declare const HISTORY_PREPEND_CHUNK = 40;
export declare function capHistoryPreview(preview: string | undefined): string | undefined;
export declare function slimActivitySteps<T extends {
    preview?: string;
}>(steps: T[]): T[];
export declare function slimHistoryMessage(message: ChatMessage): ChatMessage;
export declare function slimHistoryMessages(messages: ChatMessage[]): ChatMessage[];
export declare function estimateHistoryMessageBytes(message: ChatMessage): number;
/** Index where the first-paint tail begins (0 = send everything). */
export declare function historyTailStart(messages: ChatMessage[]): number;
export interface HistoryPrependChunk {
    messages: ChatMessage[];
    startIndex: number;
    remaining: number;
}
export interface HistoryDelivery {
    tail: ChatMessage[];
    tailStart: number;
    olderCount: number;
    prepend: HistoryPrependChunk[];
}
/**
 * Slim previews, then split into a first-paint tail + prepend chunks.
 * Chunks are ordered nearest-to-tail first so each prepend attaches
 * without leaving a gap in the SPA transcript.
 */
export declare function splitHistoryDelivery(messages: ChatMessage[]): HistoryDelivery;
/** First non-empty user line in the full log — session rail title. */
export declare function historySessionTitle(messages: ChatMessage[]): string | undefined;
/**
 * Cloud transcript revision for the SPA rail + cache stamp.
 *
 * Prefer the newest message timestamp when the transcript has turns —
 * `lastActivity` is also bumped by metadata patches (set-workspace) and
 * getOrCreate touches, which must not rewrite the rail age to "Just now"
 * when the user merely switches sessions.
 *
 * Empty threads still fall back to lastActivity.
 */
export declare function historyUpdatedAt(input: {
    lastActivity?: Date | number | string;
    messages: Array<{
        timestamp?: Date | number | string;
    }>;
}): number;
export declare function buildHistoryWireFrames(messages: ChatMessage[], meta: Record<string, unknown>, decorate: (m: ChatMessage, absIndex: number) => Record<string, unknown>): Array<Record<string, unknown>>;
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