/** Total bytes read thus far. */
  private val byteCount: Long
    get() = countingSource.bytesRead - source.buffer.size

  /** How many bytes to read before [peekHeader] should return false, or -1L for no limit. */
  private var limit = -1L

  /** Type hints scoped to the call stack, manipulated with [withTypeHint]. */
  private val typeHintStack = mutableListOf<Any?>()

  /**