Function describeCacheReuse

src/llm/cache-layout.ts:75–87

(prev: Message[] | null, next: Message[])

/** Compare this turn's prompt against the previous turn's to estimate KV-cache reuse. */
export function describeCacheReuse(prev: Message[] | null, next: Message[]): CacheReuse {
  if (!prev || prev.length === 0) {
    return { reusedMessages: 0, totalMessages: next.length, changedAt: 0, reuseRatio: 0, reusedChars: 0 };
  }
  const reused = commonPrefixLength(prev, next);
  return {
    reusedMessages: reused,
    totalMessages: next.length,
    changedAt: reused < next.length ? reused : -1,
    reuseRatio: next.length === 0 ? 0 : reused / next.length,
    reusedChars: prefixChars(next, reused),
  };
}

/** Output tokens per second. Returns 0 for non-positive latency to avoid Infinity. */
export function computeThroughput(outputTokens: number, latencyMs: number): number {