@Test void field_readLengthPrefix_LENGTH_DELIMITED() {
    BytesField field = new BytesField(128 << 3 | WIRETYPE_LENGTH_DELIMITED);
    field.write(buf, new byte[10]);

    ReadBuffer readBuffer = ReadBuffer.wrap(bytes, 1 /* skip the key */, bytes.length - 1);
    assertThat(readBuffer.readVarint32())
      .isEqualTo(10);
  }
Shows we can reliably look at a byte zero to tell if we are decoding proto3 repeated fields.
zipkin/src/test/java/zipkin2/internal/Proto3FieldsTest.java