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>
Three gaps found while measuring the record path against the file path, each one
a signal the library could not see:
WebP stores `XMP ` after the pixels, so on any WebP above the scan window a fixed
read stops short of the label. `_riff_late_metadata` steps over the coded image to
reach it, the RIFF analogue of the existing PNG and ISOBMFF readers. Three corpus
files hid an IPTC "Made with AI" tag and a C2PA `trainedAlgorithmicMedia` there.
The decoder-backed fallback now covers only what it is actually for -- metadata the
raw bytes do not spell, such as a compressed PNG `zTXt` packet.
A C2PA reader failure returned the same `None` as a file with no manifest, so a
verdict could fall back to the raw byte scan with no trace anywhere. Failures now
log at warning and only genuine ones do: a file without credentials never reaches
that branch, and an unsupported container is demoted to debug through the reader's
own `C2paError.NotSupported`. The first corpus run with it found a truncated PNG.
`scan_dataset.py` never registered the pillow-heif opener it declares as a
dependency, so every HEIC was scanned as unreadable -- no EXIF, and a pixel layer
that was 397 of 406 features NaN instead of 136.
`_riff_late_metadata` caps its total like `isobmff.scan_c2pa_region` does. Clamping
each chunk to the bytes remaining is not enough on its own: one chunk can declare a
length spanning most of the file, and this runs on the memoized verdict path over
images from arbitrary sources.
Also lands `identify_metadata_record` and `ProvenanceReport.to_dict()`, the
one-call entry point and the versioned JSON contract for the record path.
Record-vs-file equality holds over 3,478 corpus images, and the eight files these
fixes recovered still report AI.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
`collect_metadata_record` returns a JSON-safe record carrying an image's
provenance metadata regions -- never its pixels -- and the existing
`evidence_from_metadata_record` + `identify_from_evidence` build the verdict
from it without opening the file. The contract is equality with
`identify(path, metadata only)`, verified over the tracked fixtures and over a
local corpus of 3,478 images (every file carrying a rare signal, plus a random
slice): zero differences.
Three placements defeated earlier drafts and each is now a rule with a test:
the `scan_head` buffer is the head CONCATENATED with late metadata, so a
structural walk must read the raw head instead; Samsung splits its evidence
between a post-EOI trailer and the coded scan; and PIL's info keys must be
emitted in the file path's candidate order, since the first token match wins.
Also fix a real detection gap found while establishing that equality: a label
the decoder can read but a raw byte scan cannot -- a compressed PNG `zTXt`
packet, or a WebP XMP chunk past the scan window -- was invisible to
`identify`. Eight corpus files carrying a China TC260 AIGC label or an IPTC
"Made with AI" tag were reported as no signal at all.
`scripts/detection_timing.py` and its report script measure the metadata path
per method; they write outside the repository and are read-only over a dataset.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
