Merge pull request 'ci: cosign keyless sigs, SBOM, provenance + fedora digest pin' (#7) from feat/sre-cosign-sbom-attestation into main

.github/workflows/build-iso.yml

@@ -1,3 +1,5 @@
+# TODO: SHA-pin all uses: tags to commit SHAs (Agent 8 audit recommendation).
+# Tracked separately so this PR can land without long web lookups.
 name: Build veilor-os ISO
 
 on:
@@ -20,7 +22,9 @@ on:
     types: [published]
 
 permissions:
-  contents: write   # needed for action-gh-release to create+update ci-latest
+  contents: write       # needed for action-gh-release to create+update ci-latest
+  id-token: write       # cosign keyless OIDC + attest-build-provenance
+  attestations: write   # attest-build-provenance writes the attestation
 
 jobs:
   build:
@@ -46,7 +50,9 @@ jobs:
         # SHA pinning in a follow-up sweep.
         uses: addnab/docker-run-action@v3
         with:
-          image: registry.fedoraproject.org/fedora:43
+          # Pinned to digest from `skopeo inspect --raw` on 2026-05-06.
+          # Refresh by re-running skopeo against fedora:43 and bumping.
+          image: registry.fedoraproject.org/fedora:43@sha256:72e874e771b953c6357c7a5823c6fc1e3e3253b90121e795febe01380e32269b
           options: |
             --privileged
             -v ${{ github.workspace }}:/work
@@ -202,6 +208,34 @@ jobs:
           echo "[OK] split into:"
           ls "${ISO}".part-*
 
+      - name: Install cosign
+        if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
+        uses: sigstore/cosign-installer@v3
+
+      - name: Sign ISO parts (keyless)
+        if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
+        run: |
+          cd build/out
+          for f in *.part-*; do
+            cosign sign-blob --yes "$f" \
+              --output-signature "$f.sig" \
+              --output-certificate "$f.pem"
+          done
+
+      - name: Generate SBOM (SPDX)
+        if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
+        uses: anchore/sbom-action@v0
+        with:
+          path: build/out
+          format: spdx-json
+          output-file: build/out/veilor-os.spdx.json
+
+      - name: Build provenance attestation
+        if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
+        uses: actions/attest-build-provenance@v2
+        with:
+          subject-path: 'build/out/*.iso.part-*'
+
       - name: Publish to ci-latest rolling prerelease
         if: success() && github.ref == 'refs/heads/main'
         # Pinned to last v2 tag confirmed to ship on node20.
@@ -226,6 +260,9 @@ jobs:
           files: |
             build/out/*.iso.part-*
             build/out/*.sha256
+            build/out/*.sig
+            build/out/*.pem
+            build/out/*.spdx.json
 
       # Build log on failure: print inline + skip artifact upload to avoid
       # quota wall. Job log retains everything anyway.