feat: add two-domain PoCI cross-repository federation

.github/workflows/poci-cross-repo-federation.yml

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+name: PoCI Cross-Repository Federation
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - ".github/workflows/poci-cross-repo-federation.yml"
+      - "docs/POCI_CROSS_REPO_FEDERATION.md"
+      - "examples/poci-witness/federation/**"
+      - "scripts/verify_poci_cross_repo_federation.py"
+      - "tests/test_poci_cross_repo_federation.py"
+  pull_request:
+    paths:
+      - ".github/workflows/poci-cross-repo-federation.yml"
+      - "docs/POCI_CROSS_REPO_FEDERATION.md"
+      - "examples/poci-witness/federation/**"
+      - "scripts/verify_poci_cross_repo_federation.py"
+      - "tests/test_poci_cross_repo_federation.py"
+
+concurrency:
+  group: poci-federation-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+  actions: read
+  id-token: write
+  attestations: write
+
+jobs:
+  federation:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Compile and run federation mutations
+        run: |
+          python3 -m py_compile \
+            scripts/verify_poci_cross_repo_federation.py \
+            tests/test_poci_cross_repo_federation.py
+          python3 -m unittest tests.test_poci_cross_repo_federation -v
+
+      - name: Verify ProofPath producer attestation
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          mkdir -p artifacts/poci/federation/attestation-results
+          gh attestation verify \
+            examples/poci-witness/federation/proofpath-attested-quorum-report.json \
+            --repo safal207/ProofPath \
+            --signer-workflow \
+              safal207/ProofPath/.github/workflows/poci-signed-witness-network.yml \
+            --source-digest 3a5dde912c44e0957204d3df733e712c596455f1 \
+            --signer-digest 3a5dde912c44e0957204d3df733e712c596455f1 \
+            --cert-oidc-issuer https://token.actions.githubusercontent.com \
+            --deny-self-hosted-runners \
+            --format json \
+            > artifacts/poci/federation/attestation-results/producer.json
+
+      - name: Verify Ibex external-consumer attestation
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh attestation verify \
+            examples/poci-witness/federation/ibex-external-consumer-receipt.json \
+            --repo safal207/ibex-agent-verification \
+            --signer-workflow \
+              safal207/ibex-agent-verification/.github/workflows/proofpath-poci-consumer.yml \
+            --source-digest 24efa1eadd72275bcc29f0c436e46fb508aac113 \
+            --signer-digest 24efa1eadd72275bcc29f0c436e46fb508aac113 \
+            --cert-oidc-issuer https://token.actions.githubusercontent.com \
+            --deny-self-hosted-runners \
+            --format json \
+            > artifacts/poci/federation/attestation-results/external-consumer.json
+
+      - name: Build cross-repository federation report
+        run: |
+          python3 scripts/verify_poci_cross_repo_federation.py \
+            examples/poci-witness/federation/policy.json \
+            --producer-report \
+              examples/poci-witness/federation/proofpath-attested-quorum-report.json \
+            --consumer-receipt \
+              examples/poci-witness/federation/ibex-external-consumer-receipt.json \
+            --producer-attestation-result \
+              artifacts/poci/federation/attestation-results/producer.json \
+            --consumer-attestation-result \
+              artifacts/poci/federation/attestation-results/external-consumer.json \
+            --pretty \
+            --output artifacts/poci/federation/federation-report.json
+
+      - name: Guard accepted two-domain federation
+        run: |
+          python3 - <<'PY'
+          import json
+          from pathlib import Path
+
+          report = json.loads(
+              Path("artifacts/poci/federation/federation-report.json").read_text(
+                  encoding="utf-8"
+              )
+          )
+          if report.get("decision") != "ACCEPT" or report.get("valid") is not True:
+              raise SystemExit("cross-repository federation did not ACCEPT")
+          if report.get("domain_count") != 2:
+              raise SystemExit("federation must contain exactly two domains")
+          if report.get("external_consumer_required") is not True:
+              raise SystemExit("external consumer must be mandatory")
+          domains = report.get("domains", [])
+          repositories = {item.get("repository") for item in domains}
+          workflows = {item.get("workflow") for item in domains}
+          if len(repositories) != 2 or len(workflows) != 2:
+              raise SystemExit("repository and workflow identities must differ")
+          verification = report.get("verification", {})
+          if not verification or any(value is not True for value in verification.values()):
+              raise SystemExit("all federation verification flags must be true")
+          if len(report.get("consensus", {}).get("graph_roots", {})) != 6:
+              raise SystemExit("federation consensus must commit six graph roots")
+          root = report.get("federation_root")
+          if not isinstance(root, str) or not root.startswith("sha256:"):
+              raise SystemExit("federation root is missing")
+          print("PASS two-domain PoCI federation (ProofPath + Ibex)")
+          PY
+
+      - name: Attest final federation report
+        uses: actions/attest@v4
+        with:
+          subject-path: artifacts/poci/federation/federation-report.json
+
+      - name: Upload federation evidence
+        uses: actions/upload-artifact@v4
+        with:
+          name: poci-cross-repo-federation-${{ github.run_id }}
+          path: artifacts/poci/federation
+          if-no-files-found: error
+          retention-days: 14

docs/POCI_CROSS_REPO_FEDERATION.md

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+# PoCI cross-repository federation v0.1
+
+Status: executable experimental profile  
+Profile: `proofpath.poci.cross-repo-federation.v0.1`
+
+## Purpose
+
+A three-runner quorum inside ProofPath proves process and runner separation. An
+Ibex consumer receipt proves that a second repository can verify the producer
+attestation and independently reproduce the six-graph transition space. The
+federation profile closes the loop by verifying both keyless identities and
+binding their common consensus into one federation root.
+
+```text
+ProofPath three-runner quorum
+        ↓ ProofPath Sigstore identity
+Ibex external recomputation
+        ↓ Ibex Sigstore identity
+ProofPath federation verifier
+        ↓
+two-domain federation root
+```
+
+## Required domains
+
+Version 0.1 requires exactly two distinct repository/workflow domains:
+
+1. **Producer domain** — the attested ProofPath quorum report.
+2. **External-consumer domain** — the attested Ibex consumer receipt.
+
+Different jobs inside one workflow do not count as different federation
+domains. The repository and signer-workflow identities must both differ.
+
+## Verified bindings
+
+The federation verifier checks:
+
+- exact SHA-256 bytes of the producer report and consumer receipt;
+- successful keyless attestation verification for both subjects;
+- pinned repository, signer workflow, source SHA, signer SHA, GitHub OIDC issuer,
+  and GitHub-hosted runner boundary;
+- accepted producer quorum with three verified witness attestations;
+- accepted external consumer receipt;
+- the external receipt's own domain-separated integrity root;
+- the external receipt's binding back to the exact ProofPath producer report;
+- equality of round, consensus root, source digest, graph set, envelope,
+  six graph roots, transition-cell root, and multi-graph root.
+
+## Decision semantics
+
+```text
+CHALLENGE > BLOCK > ACCEPT
+```
+
+- `ACCEPT` — both domains are attested and agree exactly.
+- `BLOCK` — a required domain, attestation, identity, profile, or verification
+  flag is absent or invalid.
+- `CHALLENGE` — committed bytes, roots, or consensus fields contradict each
+  other or the pinned policy.
+
+Representative reason codes:
+
+- `FEDERATION_POLICY_INVALID`
+- `FEDERATION_DOMAIN_NOT_DISTINCT`
+- `FEDERATION_PRODUCER_ATTESTATION_MISSING`
+- `FEDERATION_CONSUMER_ATTESTATION_MISSING`
+- `FEDERATION_PRODUCER_SUBJECT_MISMATCH`
+- `FEDERATION_CONSUMER_SUBJECT_MISMATCH`
+- `FEDERATION_PRODUCER_REPORT_INVALID`
+- `FEDERATION_CONSUMER_RECEIPT_INVALID`
+- `FEDERATION_CONSUMER_RECEIPT_ROOT_MISMATCH`
+- `FEDERATION_PRODUCER_CONSENSUS_MISMATCH`
+- `FEDERATION_CONSUMER_CONSENSUS_MISMATCH`
+- `FEDERATION_CROSS_DOMAIN_MISMATCH`
+
+## Canonical federation root
+
+The complete federation report is copied, `federation_root` is set to `null`,
+canonical JSON is encoded, and SHA-256 is computed with domain prefix:
+
+```text
+proofpath:poci:cross-repo-federation:v0.1:root\n
+```
+
+The root includes digests of the actual `gh attestation verify` result objects,
+so it commits to the two provenance-verification executions as well as their
+subjects.
+
+## Mutation coverage
+
+The focused corpus covers:
+
+- producer subject substitution;
+- external-consumer subject substitution;
+- missing producer or consumer attestation;
+- same-repository pseudo-federation;
+- graph-root substitution;
+- external receipt-root tampering;
+- external workflow substitution;
+- deterministic federation roots.
+
+## Reviewer command
+
+After obtaining both `gh attestation verify --format json` result files:
+
+```bash
+python3 scripts/verify_poci_cross_repo_federation.py \
+  examples/poci-witness/federation/policy.json \
+  --producer-report \
+    examples/poci-witness/federation/proofpath-attested-quorum-report.json \
+  --consumer-receipt \
+    examples/poci-witness/federation/ibex-external-consumer-receipt.json \
+  --producer-attestation-result producer-attestation.json \
+  --consumer-attestation-result consumer-attestation.json \
+  --pretty
+```
+
+## Honest boundary
+
+ProofPath and Ibex now provide different repositories, commits, workflows,
+runners, artifacts, and Sigstore identities. Both repositories are currently
+controlled by the same GitHub account owner. This proves repository/workflow
+federation and independent recomputation, not independent organizational
+governance. The federation proves committed evidence consistency, not objective
+real-world truth.

examples/poci-witness/federation/ibex-external-consumer-receipt.json

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+{
+  "profile_id": "ibex.poci.external-consumer-receipt.v0.1",
+  "decision": "ACCEPT",
+  "primary_reason_code": null,
+  "reason_codes": [],
+  "findings": [],
+  "consumer": {
+    "consumer_id": "ibex-proofpath-poci-consumer",
+    "repository": "safal207/ibex-agent-verification",
+    "workflow": "safal207/ibex-agent-verification/.github/workflows/proofpath-poci-consumer.yml",
+    "commit_sha": "24efa1eadd72275bcc29f0c436e46fb508aac113"
+  },
+  "producer": {
+    "repository": "safal207/ProofPath",
+    "code_sha": "a726f2a8b3bd9c6c4469be542e30bb54b230d510",
+    "attestation_source_sha": "3a5dde912c44e0957204d3df733e712c596455f1",
+    "attestation_signer_sha": "3a5dde912c44e0957204d3df733e712c596455f1",
+    "workflow": "safal207/ProofPath/.github/workflows/poci-signed-witness-network.yml",
+    "report_sha256": "sha256:87119740993bc570749542ef4e06a8cf0ce44cebd77e88eb5aa1b432d0228fde",
+    "attestation_result_sha256": "sha256:eac7008a5dcdfaf0e7c75eed1dfdbaffa633f61d72301818281ee7ca6a13bef0"
+  },
+  "accepted_consensus": {
+    "round_id": "poci-demo-round-001",
+    "consensus_root": "sha256:f2bc99fe96f24942e5cc9c87f25c48167d875041e85170dbb354c2bc0cd97f5f",
+    "source_digest": "sha256:807bde72ed45ae1566443dec20c85b02f0d6734e4aa4bf9a9cfe08ce2e4c97fa",
+    "graph_set_id": "mg_compute_purchase_001",
+    "poci_envelope_id": "env_valid_action",
+    "graph_roots": {
+      "causal": "sha256:482d5076dc3a80dac8f4ed179491b4d3e153ece780fcebdd81289ffbdc6fd7f4",
+      "intent": "sha256:3a26e5badd5379f69203dfe972143e0f3969b12e5f5c55cd641aa7f2bc41a0b3",
+      "authority": "sha256:6af348f1245a5a1f3b59b0070653bbf4d512a792e54554918058f9692e33bb0c",
+      "state_transition": "sha256:41807cd0bacac6908867ce6839114d3028ec62550eb7cee0fdb50006e3887c10",
+      "evidence": "sha256:1fed70f4f198ce5a993880e283763db8c0dc576824f042619637b37f6d745899",
+      "time_continuity": "sha256:4b28006fc3a21f6afce98e4e4e661fa204060be976110bed3bb571af3d7e4ccc"
+    },
+    "transition_cells_root": "sha256:b5d5fd4ba2638fb685913e621295a1c70b5aff550d14ea5b2d8c0f49bdba7f45",
+    "computed_multigraph_root": "sha256:98543066cb16c06b5300b56749af43b2fdd48eed47650488ac57987156e38219"
+  },
+  "verification": {
+    "producer_attestation_verified": true,
+    "producer_report_digest_verified": true,
+    "producer_code_sha_verified": true,
+    "source_recomputed": true,
+    "six_graph_roots_recomputed": true,
+    "transition_cells_recomputed": true,
+    "consumer_attestation_required": true
+  },
+  "honest_limitations": [
+    "ProofPath and Ibex use different repositories and workflow identities",
+    "both repositories are currently controlled by the same GitHub account owner",
+    "this proves evidence consistency, not objective real-world truth"
+  ],
+  "receipt_root": "sha256:a810c52ebc8e313d535962b668d5eb608a4fab0e74ce9ef9ba64c313a195aa2d",
+  "valid": true
+}

examples/poci-witness/federation/policy.json

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+{
+  "profile_id": "proofpath.poci.cross-repo-federation-policy.v0.1",
+  "producer": {
+    "repository": "safal207/ProofPath",
+    "workflow": "safal207/ProofPath/.github/workflows/poci-signed-witness-network.yml",
+    "attestation_source_sha": "3a5dde912c44e0957204d3df733e712c596455f1",
+    "attestation_signer_sha": "3a5dde912c44e0957204d3df733e712c596455f1",
+    "report_sha256": "sha256:87119740993bc570749542ef4e06a8cf0ce44cebd77e88eb5aa1b432d0228fde"
+  },
+  "external_consumer": {
+    "repository": "safal207/ibex-agent-verification",
+    "workflow": "safal207/ibex-agent-verification/.github/workflows/proofpath-poci-consumer.yml",
+    "attestation_source_sha": "24efa1eadd72275bcc29f0c436e46fb508aac113",
+    "attestation_signer_sha": "24efa1eadd72275bcc29f0c436e46fb508aac113",
+    "receipt_sha256": "sha256:756a893289f50221194b1e40b2e9fc2f10d5549c15fc9b9c57aa5f02c936d357",
+    "receipt_root": "sha256:a810c52ebc8e313d535962b668d5eb608a4fab0e74ce9ef9ba64c313a195aa2d"
+  },
+  "expected": {
+    "round_id": "poci-demo-round-001",
+    "consensus_root": "sha256:f2bc99fe96f24942e5cc9c87f25c48167d875041e85170dbb354c2bc0cd97f5f",
+    "source_digest": "sha256:807bde72ed45ae1566443dec20c85b02f0d6734e4aa4bf9a9cfe08ce2e4c97fa",
+    "graph_set_id": "mg_compute_purchase_001",
+    "poci_envelope_id": "env_valid_action",
+    "graph_roots": {
+      "causal": "sha256:482d5076dc3a80dac8f4ed179491b4d3e153ece780fcebdd81289ffbdc6fd7f4",
+      "intent": "sha256:3a26e5badd5379f69203dfe972143e0f3969b12e5f5c55cd641aa7f2bc41a0b3",
+      "authority": "sha256:6af348f1245a5a1f3b59b0070653bbf4d512a792e54554918058f9692e33bb0c",
+      "state_transition": "sha256:41807cd0bacac6908867ce6839114d3028ec62550eb7cee0fdb50006e3887c10",
+      "evidence": "sha256:1fed70f4f198ce5a993880e283763db8c0dc576824f042619637b37f6d745899",
+      "time_continuity": "sha256:4b28006fc3a21f6afce98e4e4e661fa204060be976110bed3bb571af3d7e4ccc"
+    },
+    "transition_cells_root": "sha256:b5d5fd4ba2638fb685913e621295a1c70b5aff550d14ea5b2d8c0f49bdba7f45",
+    "computed_multigraph_root": "sha256:98543066cb16c06b5300b56749af43b2fdd48eed47650488ac57987156e38219",
+    "required_domain_count": 2,
+    "external_consumer_required": true
+  }
+}