feat: add two-domain PoCI cross-repository federation

[safal207]

What changed

Adds the ninth PoCI slice: a two-domain federation between ProofPath and an external Ibex consumer.

The implementation adds:

• an exact-byte ProofPath producer quorum subject;
• an exact-byte Ibex external-consumer receipt subject;
• a pinned federation policy for both repositories, workflows, PR provenance SHAs, subject digests, receipt root, and six-graph consensus;
• a dependency-free federation verifier;
• mandatory distinct repository and workflow identities;
• verification of both keyless Sigstore/SLSA attestations;
• binding from the Ibex receipt back to the exact ProofPath producer report;
• exact equality checks for round, consensus root, source digest, graph set, envelope, six graph roots, transition-cell root, and multi-graph root;
• a domain-separated federation root that includes both attestation-verification result digests;
• 10 mutation and determinism tests;
• a dedicated CI workflow that attests and uploads the final federation report.

Federation chain

ProofPath three-runner quorum
        ↓ ProofPath keyless identity
Ibex external recomputation (PR #74)
        ↓ Ibex keyless identity
ProofPath federation verifier
        ↓
two-domain federation root

Reviewer expectation

decision: ACCEPT
domain_count: 2
external_consumer_required: true
repository identities: 2 distinct
workflow identities: 2 distinct
graph roots: 6 exact matches

Exact-byte boundary

Sigstore signs subject bytes rather than semantic JSON. The committed producer report and Ibex receipt therefore preserve the exact formatting and SHA-256 bytes that were attested in their source workflows.

Trust boundary

ProofPath and Ibex now have separate repositories, commits, workflows, runners, artifacts, independent graph recomputation, and different Sigstore identities. Both repositories are currently controlled by the same GitHub account owner, so this demonstrates repository/workflow federation rather than independent organizational governance.

Stacked PR

Base: agent/poci-signed-multirunner-witness-v0.1 / #200

Consumes Ibex external-consumer PR #74 at head 1426154d18f646f37c9d281ba4d9b5d45d808c92 and its successful keyless receipt attestation.

No merge is performed by this PR.

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 6d6c0216-848a-4a4b-a88d-9c65d5c4d46e

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[safal207]

Validation complete

Final head: 0a821562a7336c918ab76006dd47d8dc8f8a6fa6

Passed:

• PoCI Cross-Repository Federation run Write ProofPath HTTP Profile v0.1 #1 (30619564355)
  • 10 mutation/determinism tests;
  • exact ProofPath producer subject verification;
  • exact Ibex external-consumer subject verification;
  • two keyless Sigstore/SLSA provenance checks;
  • distinct repository and workflow identities;
  • exact agreement on round, consensus root, source digest, graph set, envelope, six graph roots, transition-cell root, and multi-graph root;
  • final federation report attestation and artifact upload.
• PoCI run Community experiment L0: README and philosophy feedback #14 — success.
• Rust run #281 — formatting, clippy, workspace tests, Compute Witness, metrics, reusable action, Personal Agent Guard, and Agent Payment Guard all succeeded.

Federation result:

• decision: ACCEPT
• domains: 2
• external consumer required: true
• federation root: sha256:f045abce1526680b818e2630ac3100217add46b7be060bd56ad106148a4e857a

Evidence artifact:

• name: poci-cross-repo-federation-30619564355
• artifact id: 8788773864
• size: 17493 bytes
• SHA-256: e036a8622219fd4a036922bedcf46a2a41d8d33c18cc94699fe372d10a579461
• expires: 2026-08-14T09:20:33Z

Honest boundary: ProofPath and Ibex use separate repositories, commits, workflows, runners, artifacts, recomputation paths, and Sigstore identities; both repositories are still controlled by the same GitHub account owner.