/**
 * Returns an ISO-8601 timestamp with millisecond precision that is
 * STRICTLY GREATER than any previous timestamp returned for the same
 * `orderingKey` within this process.
 *
 * Formula: `Math.max(baseMs, lastMs + 1, floorMs)` where `floorMs` is
 * `notBeforeMs + 1` when a finite `notBeforeMs` is supplied (else 0), and:
 *   - baseMs = parsed agentClock if provided (and valid), else Date.now()
 *   - lastMs = previously-emitted ms for this orderingKey (or 0 if first)
 *
 * `agentClock` ANCHORS the timestamp when provided. This is the load-bearing
 * behavior for agy's transcript replay: agy emits events with their original
 * `created_at` even during a backfill (so subscription clients see them in
 * logical order, not in replay-arrival order). For hook-driven plugins
 * (claude/codex/gemini), `agentClock` is left undefined and baseMs = wallMs.
 *
 * Memory: bounded LRU with cap=MAX_LRU_KEYS. Eviction order is least-
 * recently-touched, so active orderingKeys are never evicted. Resets on
 * process restart (correct: restart is a new lifecycle).
 */
export declare function prepareEventTimestamp(opts: {
    orderingKey: string;
    agentClock?: string;
    notBeforeMs?: number;
}): string;
/**
 * Test-only: clear the per-key map. Used by jest/vitest to reset state
 * between tests. Not exported from the package root.
 */
export declare function _resetPrepareEventTimestampForTesting(): void;