The registries are raw substrings and the shortest tokens are four and five bytes
(`Bria`, `Adobe`, `Canva`). Over a megabyte of compressed pixel data such a sequence
turns up by chance: `Bria` matched inside the entropy-coded scan of 4 of 14,707
corpus JPEGs, in none of which the manifest names Bria. The rate is what a four-byte
pattern predicts on that corpus, and the Bria entry asserts AI, so a chance match can
declare an image AI-generated rather than merely mislabel its signer.
`_metadata_region` gives the registry scans the container's metadata: JPEG marker
segments before the coded scan, PNG chunks other than IDAT, both trailers, and
whatever `scan_head` appended past the window. Every other check keeps the full
buffer -- their markers are long and distinctive. A container that does not parse is
returned whole, since dropping real evidence to avoid a chance match is the wrong
trade. `c2pa_marker_in` already refuses a bare `c2pa` substring for this reason;
this is the same defence for the registries.
Verified the way the rules require for a change that MOVES a verdict: over all 48,905
corpus images, exactly one file changed, the one named in advance, from
"C2PA Content Credentials (Bria Artificial Intelligence)" to "(unknown signer)".
Record-path parity is 0 disagreements, down from 75 when this work started.
The audit's own baseline comparison is fixed here too. It compared confidence and
signals only, and so reported "0 changed" for the run whose single intended
correction was a watermark line -- the change it exists to show.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
A full-corpus audit of the record path against the file path found 75 of 48,905
images disagreeing, and 74 were one gap: the SynthID byte scan for containers whose
manifest no parser reaches lived in `get_ai_metadata`, an extractor the record path
does not run. The record silently reported no SynthID for images `identify` flagged.
Moving the scan into `identify_from_evidence` fixes it by construction rather than by
copying the rule into a second extractor -- the same shape `soft_binding` already
uses. Its byte checks mirror `metadata.synthid_source` literally instead of reusing
the broader `has_c2pa` / `c2pa_source_kind` derived above, so the file path's answers
do not move: verdicts over a 4,000-image sample are byte-identical.
`scripts/record_parity_audit.py` is the audit itself, now repeatable. It walks a
dataset, judges every image through both seams with the record round-tripped through
JSON, and reports disagreements by field and by signal. The rule in
`.claude/rules/development.md` says to re-run both sides of this seam after changing
either; this is what to run.
Both timing and audit scripts now put the package's OWN `src` on the path. From a
worktree an editable install resolves to the main checkout, so the audit imported a
different tree than the one under test -- the failure the same rules file warns about,
reproduced within an hour of writing it down.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
