Function restoreBackup

src/utils/fileHistory.ts:806–839

* Restores a file from its backup path with proper directory creation and permissions. * Lazy mkdir: tries copyFile first, creates the directory on ENOENT.

(
  filePath: string,
  backupFileName: string,
)

 * Lazy mkdir: tries copyFile first, creates the directory on ENOENT.
 */
async function restoreBackup(
  filePath: string,
  backupFileName: string,
): Promise<void> {
  const backupPath = resolveBackupPath(backupFileName)

  // Stat first: if the backup is missing, log and bail before attempting
  // the copy. Separates "backup missing" from "destination dir missing".
  let backupStats: Stats
  try {
    backupStats = await stat(backupPath)
  } catch (e: unknown) {
    if (isENOENT(e)) {
      logEvent('tengu_file_history_rewind_restore_file_failed', {})
      logError(
        new Error(`FileHistory: [Rewind] Backup file not found: ${backupPath}`),
      )
      return
    }
    throw e
  }

  // Lazy mkdir: 99% of calls hit the fast path (destination dir exists).
  try {
    await copyFile(backupPath, filePath)
  } catch (e: unknown) {
    if (!isENOENT(e)) throw e
    await mkdir(dirname(filePath), { recursive: true })
    await copyFile(backupPath, filePath)
  }

  // Restore the file permissions
  await chmod(filePath, backupStats.mode)
}

/**
 * Gets the first (earliest) backup version for a file, used when rewinding