Adversarial Wave 3 pass: the prior 'round-trip locks pb tags' test was a fake lock — symmetric encode/decode via the same proto would not catch a tag swap. Replace with a fixed hex byte-oracle (hand-decoded in the comment) that goes red on any tag change, plus an empty-ocr-body deserialize test. Note in the action that a passed-in URL is used verbatim (not rkey re-signed).