@Test void field_skipValue_VARINT() {
    VarintField field = new VarintField(128 << 3 | WIRETYPE_VARINT);
    field.write(buf, 0xffffffffffffffffL);

    ReadBuffer readBuffer = ReadBuffer.wrap(bytes, 1 /* skip the key */, bytes.length - 1);
    skipValue(readBuffer, WIRETYPE_VARINT);
  }
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