External vectors written by permissively licensed encoders at pinned
revisions from synthetic pictures (tools/make_external.sh, provenance.json),
generated vectors and negative controls, the facts each encoder was asked
for, the LCEVC streams fetch.sh fetches by digest, and
format_probe_verify.py, written from the two texts.
Co-Authored-By: Claude Opus 5.5 <[email protected]>