/** Secure UUIDs also work on LAN HTTP, where randomUUID is unavailable. */
export function secureUuid(): string {
  const source = globalThis.crypto
  if (typeof source?.randomUUID === 'function') return source.randomUUID()
  if (typeof source?.getRandomValues !== 'function') {
    throw new Error('Secure randomness is unavailable.')
  }
  const bytes = source.getRandomValues(new Uint8Array(16))
  bytes[6] = (bytes[6]! & 0x0f) | 0x40
  bytes[8] = (bytes[8]! & 0x3f) | 0x80
  const hex = Array.from(bytes, byte => byte.toString(16).padStart(2, '0')).join('')
  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20)}`
}