fix(release): sign and attest the image outside the job that builds it - #689
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Twelve signing and attestation operations lived in the docker job, after the push. The build is not byte-reproducible: BuildKit's `provenance: true` attestation carries timestamps of its own whatever the build args say. So one of those twelve failing meant "re-run failed jobs" re-ran the whole job, rebuilt the image and pushed a NEW index under the same 3.0.0 and latest tags, orphaning the index that had already been signed and attested and leaving server.json pinning a digest the tag no longer resolves to. The GitHub release being immutable does not cover that: what moves is a registry tag. They now live in sign-attest, which needs docker and runs no third-party build action. A failed attestation costs a re-run of three minutes of signing against the image that is already published, and no tag moves. The docker job keeps packages: write and loses id-token, so the credential the attestation store trusts is no longer live while code fetched at build time runs. The SBOMs stay in the docker job and cross as an artifact. Moving them would have taken the rehearsal with them: a rehearsal pushes nothing, so there is no registry image to scan, and the only thing there is to scan is the pair of smoke images in that job's own daemon. Generating them there is what keeps syft's install, the scan and the package-count guard rehearsable. mcp-registry and commit-manifests now need sign-attest, so the manifest is never committed to main advertising an image that is not signed. Two smaller corrections while here. BUILD_DATE comes from the commit's own timestamp rather than `date -u`. It does not make the build reproducible on its own, but it removes the one source of churn this workflow controls, and two runs over one commit now agree on the label and the index annotation. winget needs verify-published, the way homebrew already does. It opens a pull request against microsoft/winget-pkgs naming a version, and a version whose published packages do not match the signed checksums must not be announced to a third-party repository. It needed only `release`, so a failed verification still submitted the manifest. Not exercised yet: this restructuring has never run. It needs a rehearsal dispatch before the next tag, which is what rehearsals are for.
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📝 WalkthroughWalkthroughThe release workflow separates Docker image building from signing and attestation. It exports digests and SBOMs, validates and signs published images in ChangesRelease pipeline
Estimated code review effort: 4 (Complex) | ~60 minutes Sequence Diagram(s)sequenceDiagram
participant docker
participant sign_attest
participant registries
participant downstream_jobs
docker->>sign_attest: provide platform digests and SBOM artifacts
sign_attest->>registries: validate digests
sign_attest->>registries: sign indexes and manifests
sign_attest->>registries: publish SBOM attestations and SPDX referrers
sign_attest->>downstream_jobs: enable dependent release jobs
Merge Risk: 🟡 Moderate · up to The workflow can still publish releases and packages without successfully signing and attesting the image, weakening the intended supply-chain guarantee. Documentation also describes outdated attestation behavior. Merge should wait for the publication gate and documentation to be corrected. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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September 10, 2026 11:40
…for one Two defects in what this branch was about to ship, both measured rather than reasoned, and one of them a correction to an argument made here twice. The predicate string made the SBOM invisible to Trivy. `sbom-path` derives the predicate type from spdxVersion and emits https://spdx.dev/Document/v2.3. Trivy matches in_toto.PredicateSPDX, the unversioned https://spdx.dev/Document, by exact equality. Held identical in every other respect, the unversioned form reads as "sigstore-bundle-spdx-json" and the versioned one as "unknown" and is refused. The in-toto specification blesses both spellings, so this is interoperability rather than correctness, but cosign, BuildKit and in-toto-golang all emit the unversioned form and actions/attest is the outlier. predicate-type with predicate-path sets it; the file check sbom-path also performed is already done by the docker job's package-count guard. The index needed the SBOM too. The earlier reasoning here was that an index has no contents of its own, so a document over it would be a document about nothing. That is true of the semantics and false of what consumers do: a client that resolves a tag looks at the index and nowhere else, and with the SBOM on the platform manifests alone `trivy image <tag>` finds nothing, with --platform making no difference. Six attestations, not four. The index carries the amd64 document by convention. Beside them, a bare application/spdx+json referrer published with oras, six attachments in one step. It is not redundant. The attestation is the authenticated answer and needs a Sigstore verifier to unwrap the bundle, the DSSE envelope, the in-toto statement and the predicate; this is the copy a consumer reads with one referrers query and one blob GET, its artifactType is the registered SPDX media type, and it is the shape verifymcp.io's rubric describes. It is also the only one that does not depend on which SPDX predicate string sits in that scanner's accepted set, which is documented nowhere: their own pages carry no occurrence of "predicate", "artifactType" or "in-toto". It runs last because every one of these clients maintains ghcr.io's sha256-<hex> fallback tag by read-modify-write, so they must be sequential, and a failure in the unsigned copy must not cost the signed ones. oras merges into that tag rather than replacing it, and reads the credentials docker/login-action already wrote. oras is fetched by hand and pinned by SHA256, cross-checked against the release's own checksums file. It publishes no cosign signature, only a detached GPG one, so syft's certificate check has no counterpart here and the digest pin is the binding control. Both were verified against the release rather than taken on trust. Not fixed, and not fixable from here: cosign v3 writes its own entry in that fallback tag with a degraded descriptor carrying no artifactType and no annotations, so the image signature on ghcr.io is invisible to any consumer that filters on the descriptor, Trivy included. That is a cosign defect and predates this work.
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In @.github/workflows/release.yml:
- Line 570: Update the release job’s needs declaration to include sign-attest
alongside preflight and docker, ensuring release publication waits for
successful image signing and attestation.
In `@CLAUDE.md`:
- Line 398: Update CLAUDE.md lines 398-398 to say “twelve attestations” and
revise the SBOM description to use predicate-type/predicate-path and include
index attestation, removing the outdated sbom-path and “never over the index”
wording. Update .github/workflows/release.yml lines 51-53 and 546 to say
fourteen signing and attestation operations, reflecting two signatures plus
twelve attestations.
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While signing and attestation lived in the docker job, one of those steps failing failed that job, and every publisher downstream of it stopped. Moving them into sign-attest took that gate with it: release named preflight, e2e and docker, so the GitHub release could publish, and npm, PyPI, NuGet, Homebrew and winget with it, beside an image that was never signed. npm, PyPI and NuGet versions are permanent, so that is not a state a re-run can walk back. release now names sign-attest. mcp-registry and commit-manifests already did; this covers the five that did not. The cost is the signing's three minutes on the critical path. A rehearsal is unaffected. sign-attest carries no job-level condition: it runs and succeeds with its steps skipped, rather than being skipped itself, which a needs edge would have propagated to everything below.
Three counts and one policy statement were left behind by the two commits before this one. The job holds fourteen operations, not twelve: two cosign signatures and twelve attestations, six of provenance and six of SBOM. The two comments in release.yml that say twelve now say fourteen; the one that says "twelve attestations" is about the twelve that reach one actions/attest version and stays as it is. CLAUDE.md said sign-attest holds ten attestations, and described the SBOM half as it was before the predicate fix: attested through sbom-path and published per platform and never over the index. Both halves of that are now wrong. sbom-path derives the predicate type from spdxVersion and emits https://spdx.dev/Document/v2.3, which Trivy will not match; the steps pass the unversioned type explicitly. And the index does carry one, because a scanner given a tag resolves it to the index and looks nowhere else, so an index with no SBOM reads as a server that publishes none. The paragraph also records the bare application/spdx+json referrers, which nothing outside the workflow mentioned. The security page told a reader to verify the SBOM by a platform digest because the tag would find nothing. It finds one now, so the page shows both forms with the predicate type that matches, and points at oras discover for the bare referrers. English and Spanish alike.
…list On ghcr.io, which serves no referrers API, the referrers list is the client-maintained sha256-<hex> tag, and cosign writes it through go-containerregistry, whose releases before v0.22.1 wrote a descriptor short of what the distribution spec requires: the config's media type as the artifactType until v0.21.6 and no annotations until v0.22.1. The 3.0.0 signature is listed there as application/vnd.oci.empty.v1+json with no annotations (cosign v3.0.6, go-containerregistry v0.21.3), and v3.1.3 still drops the annotations. gh attestation verify --bundle-from-oci, Kyverno's ClusterPolicy SigstoreBundle type and Trivy's referrer discovery filter that list on the descriptor and report the image unsigned on ghcr.io while finding the same signature on Docker Hub, whose registry builds the descriptors itself. cosign verify opens every listed manifest and was never affected. cosign main carries go-containerregistry v0.22.1 since 2026-09-05 and no release ships it yet, and it repairs nothing already written. A script that reads each listed manifest and rewrites the tag only when an entry says less than its manifest does runs last in sign-attest, on ghcr.io only, and warns rather than fails: this job gates every publisher, and a list entry is not a signature. Measured against a registry:2 holding the 3.0.0 index: the rewrite is idempotent, oras discover filtered on the bundle type finds the signature afterwards, and cosign verify passes before and after on the index and on a platform manifest.
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Description
Fourteen signing and attestation operations lived in the
dockerjob, after the push: two cosign signatures and twelve attestations. That job's build is not byte-reproducible: BuildKit's ownprovenance: trueattestation carries timestamps whatever the build args say.So one of those fourteen failing meant "re-run failed jobs" re-ran the whole job, rebuilt the image, and pushed a new index under the same
3.0.0andlatesttags, orphaning the index that had already been signed and attested and leavingserver.jsonpinning a digest the tag no longer resolves to.The GitHub release being immutable does not cover this. What moves is a registry tag.
The six provenance attestations #684 added, and the six SBOM attestations added here, are what made that failure surface large enough to notice.
Related Issue
Follows the review of #684. No separate issue: the defect was found reviewing that branch and is fixed here rather than growing it.
Type of Change
Changes Made
sign-attestjob,needs: [preflight, docker], holding the two cosign signatures and all twelve attestations. It runs no third-party build action: no QEMU image, no BuildKit, no GoReleaser.dockerkeepspackages: writeand losesid-token, so the credential the attestation store trusts is no longer live while code fetched at build time runs. It publishes the index digest and both platform digests as job outputs.mcp-registryandcommit-manifestsnow needsign-attest, so the manifest is never committed tomainadvertising an image that is not signed.releaseneedssign-attesttoo. While the signing lived indocker, a failed signature failed that job andreleasenamed it, so nothing published. Moving the steps out took that gate with it, and npm, PyPI and NuGet versions are permanent, so a release beside an unsigned image could not be withdrawn. This restores it for the GitHub release and the five publishers below it. Safe for rehearsals becausesign-attestcarries no job-levelif: it succeeds with its steps skipped rather than being skipped, which aneedsedge would propagate.predicate-type: https://spdx.dev/Documentrather thansbom-path.sbom-pathderives the type fromspdxVersionand emits the/v2.3spelling, which Trivy compares by exact equality and misses. The index is attested because a scanner handed a tag resolves it to the index and reads nowhere else. The same documents are attached again as bareapplication/spdx+jsonreferrers withoras, for a reader that looks for the media type rather than a sigstore bundle.sha256-<hex>tag, and go-containerregistry inside cosign wrote a descriptor short of what the distribution spec asks for: the config's media type as theartifactTypeuntil ggcr v0.21.6 and no annotations until v0.22.1, which no cosign release ships yet.gh attestation verify --bundle-from-oci, Kyverno'sSigstoreBundlepolicy type and Trivy's SBOM discovery all filter that list, so on ghcr.io they report 3.0.0 unsigned while Docker Hub, which serves the referrers API and builds the descriptors itself, reports it signed.cosign verifyopens every entry and never read the descriptor, so it is unaffected either way. The step warns rather than failing: a list entry is not a signature and should not hold the publishers this job now gates.BUILD_DATEcomes from the commit's own timestamp instead ofdate -u.wingetneedsverify-published, the wayhomebrewalready does.Why the SBOMs stay in the
dockerjobMoving them would have taken the rehearsal with them, which is the opposite of what #684 just fixed.
A rehearsal pushes nothing, so there is no registry image to scan. The only thing there is to scan is the pair of smoke images in the
dockerjob's own daemon. Generating the documents there is what keeps syft's install, the scan and the package-count guard rehearsable; they cross tosign-attestas an artifact, and only the attesting moves.On
BUILD_DATEThis does not make the build reproducible on its own, and the commit says so. BuildKit's provenance attestation carries timestamps of its own. What it removes is the one source of churn this workflow controls: two runs over one commit now agree on the label and the index annotation, where before every run produced a different one.
How to Test
python3 -c "import yaml; yaml.safe_load(open('.github/workflows/release.yml'))"parses.go run ./cmd/audit_supply_chain/passes.sign-attest needs [preflight, docker];mcp-registryandcommit-manifestsboth list it;dockerhas no attestation step left and its permissions arecontents: read, packages: writeonly.What has not been exercised
This restructuring has never run. It needs a rehearsal dispatch before the next tag, which is exactly what rehearsals are for: the rehearsal path is the one that exercises the syft install, the scan, the guard and the artifact upload, and it will show whether
sign-atteststarts and skips cleanly with nothing pushed. The dispatch is run againstmainonce this lands, rather than against the branch, so the tree it exercises is the tree a tag would build.Two things a rehearsal cannot show, both unchanged in kind from before this branch: the attestation steps themselves, skipped when nothing was pushed, and the ghcr.io referrers repair, skipped for the same reason. Only a real tag exercises either.
Breaking Changes / Migration Notes
N/A for consumers. For the release itself, the job graph gains a node, so a maintainer watching a release will see one more job between
dockerand the publishers.Checklist
Code Quality
go run ./cmd/audit_supply_chain/passesCLAUDE.mdTesting
Documentation
CLAUDE.mdrecords why signing is not in the build jobSecurity
uses:here already appears in this workflow