Add ociremote.WithSubjectDescriptor option#4940
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WriteReferrer unconditionally HEADs the subject reference to build the referrer's subject descriptor, so attaching an attestation fails when the subject manifest is not present in the target repository. The OCI distribution spec explicitly allows manifests whose subject does not exist, and callers that store attestations apart from the image (or before it is pushed) currently have to fork the whole referrer manifest construction just to relax that one HEAD. Let callers supply the subject descriptor directly instead. The descriptor is used verbatim — the caller is responsible for providing a valid descriptor, and a digest that does not match the subject reference is rejected to catch caller bugs. Without the option, behavior is unchanged. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Signed-off-by: Cody Soyland <cody.soyland@chainguard.dev>
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## main #4940 +/- ##
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- Coverage 40.10% 38.86% -1.24%
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Files 155 222 +67
Lines 10044 13620 +3576
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+ Hits 4028 5294 +1266
- Misses 5530 7554 +2024
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codysoyland
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Jun 12, 2026
) Writing a bundle referrer currently requires the subject manifest to exist in the target repository: cosign's `WriteAttestationNewBundleFormat` builds the referrer's subject descriptor by unconditionally HEADing the subject reference, so the write fails when the subject is absent — even though the OCI distribution spec explicitly allows referrer manifests whose subject does not exist. Downstream status tooling hits exactly that case: it attests synthetic digests (layer blobs, pseudo-digests of non-registry entities) into an override repository where the subject manifest never exists. This adds `Statement.SubjectDescriptor`, used verbatim as the referrer's subject when supplied, while nil keeps the strict HEAD behavior. The forked write path mirrors cosign's referrer manifest byte-for-byte (pinned by a parity test) and is temporary until sigstore/cosign#4940, which adds an `ociremote.WithSubjectDescriptor` option upstream, merges. Assisted by Claude Fable 5 --------- Signed-off-by: Cody Soyland <cody.soyland@chainguard.dev> Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
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WriteReferrer unconditionally HEADs the subject reference to build the
referrer's subject descriptor, so attaching an attestation fails when the
subject manifest is not present in the target repository — even though the
OCI distribution spec explicitly allows manifests whose subject does not
exist. This option lets callers that store attestations apart from the
image (or before it is pushed) supply the subject descriptor directly,
instead of forking the referrer manifest construction. The descriptor is
used verbatim, a digest mismatch with the subject reference is rejected,
and behavior without the option is unchanged.
Assisted by Claude Fable 5