// Minimal UUIDv7 generator for Codex session/thread/turn identity parity.
export function uuidV7(): string {
  const bytes = crypto.getRandomValues(new Uint8Array(16))
  const ms = Date.now()
  // 48-bit big-endian millisecond timestamp.
  bytes[0] = (ms / 2 ** 40) & 0xff
  bytes[1] = (ms / 2 ** 32) & 0xff
  bytes[2] = (ms / 2 ** 24) & 0xff
  bytes[3] = (ms / 2 ** 16) & 0xff
  bytes[4] = (ms / 2 ** 8) & 0xff
  bytes[5] = ms & 0xff
  // Version 7 in the high nibble of byte 6.
  bytes[6] = ((bytes[6] ?? 0) & 0x0f) | 0x70
  // RFC 4122 variant (10xx) in the high bits of byte 8.
  bytes[8] = ((bytes[8] ?? 0) & 0x3f) | 0x80
  const hex = Array.from(bytes, (b) => b.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)}`
}