code: func encodeInvCursor(cur *internal.InvocationsCursor) (string, error) {
  	if cur.LastScanned == 0 {
  		return "", nil
  	}
  
  	blob, err := proto.Marshal(cur)
  	if err != nil {
  		return "", err // must never actually happen
  	}
  
  	return base64.RawURLEncoding.EncodeToString(blob), nil
  }
docs: // encodeInvCursor serializes the cursor to base64-encoded string.