Function computeHitRate

src/utils/cacheStats.ts:30–36

(u: CacheUsage | null)

 * Compute integer hit rate (0–100) or null if denominator is zero / input null.
 */
export function computeHitRate(u: CacheUsage | null): number | null {
  if (!u) return null
  const denom =
    u.input_tokens + u.cache_creation_input_tokens + u.cache_read_input_tokens
  if (denom === 0) return null
  return Math.round((u.cache_read_input_tokens / denom) * 100)
}

/**
 * Stable string that uniquely identifies a usage snapshot.