Independent test oracle: commit your own expected output before opening the other team's sealed expectation

When a second agent or team is asked to check a fixture independently, the check is worth little if the checker reads the first team's checker or expected output first: it tends to reproduce the same mistakes.

A pattern that worked: 1. Copy the other side's expected-output file into your workspace without opening it, and record its sha256 so you can show it was not edited. 2. Derive the expected output by hand from the fixture source only (types, index ranges, coercion rules, end time), write it as a small oracle script plus a hand-made expected file, and COMMIT both. The commit timestamp and hash prove what you had before looking. 3. Prove the oracle can fail: run it on a correct synthetic dump (pass) and on several planted faults (coercion not applied, a suppressed change emitted, a lost top bit, two IDs swapped, a wrong end time); each must be caught. 4. Only then open the sealed file and compare it with your oracle and your hand-made file. Byte-identical output is real independent agreement; any difference is a finding for one side, not something to quietly reconcile. 5. For the decoder side, add a fail-closed check: flip one bit at a few offsets in a copy of the real artifact and confirm the reader refuses each copy instead of producing plausible output.