diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c6a4df71..5c8ea3c4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -153,3 +153,13 @@ jobs:
 
       - name: run WP5 secret scanner smoke
         run: CARGO_BUILD=0 bash tests/e2e/wp5_secret_scan.sh
+
+      - name: Sprint 2 MCP surface
+        run: bash tests/e2e/sprint_2_mcp_surface.sh
+        env:
+          CARGO_BUILD: "0"
+
+      - name: Phase 3 subsystem clustering determinism
+        run: bash tests/e2e/phase3_subsystems.sh
+        env:
+          CARGO_BUILD: "0"
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index c0c2886e..db4006ef 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -32,6 +32,13 @@ jobs:
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5
 
+      - name: Assert tagged commit is on main
+        if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
+        run: |
+          git fetch --no-tags origin main
+          git merge-base --is-ancestor "$GITHUB_SHA" origin/main || \
+            { echo "::error::tag $GITHUB_REF does not point to a commit on main"; exit 1; }
+
       - uses: dtolnay/rust-toolchain@29eef336d9b2848a0b548edc03f92a220660cdb8
         with:
           toolchain: stable
@@ -117,6 +124,16 @@ jobs:
       - name: WP5 secret scanner smoke
         run: CARGO_BUILD=0 bash tests/e2e/wp5_secret_scan.sh
 
+      - name: Sprint 2 MCP surface
+        run: bash tests/e2e/sprint_2_mcp_surface.sh
+        env:
+          CARGO_BUILD: "0"
+
+      - name: Phase 3 subsystem clustering determinism
+        run: bash tests/e2e/phase3_subsystems.sh
+        env:
+          CARGO_BUILD: "0"
+
   release-governance:
     name: GitHub release governance
     runs-on: ubuntu-latest
@@ -207,22 +224,23 @@ jobs:
       actions: read
       contents: read
     outputs:
-      rust-subjects: ${{ steps.subjects.outputs.rust-subjects }}
+      # CI-03: includes both Rust binaries and Python plugin sdist
+      release-subjects: ${{ steps.subjects.outputs.release-subjects }}
     steps:
       - uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093
         with:
           path: artifacts
 
-      - name: compute Rust archive subjects
+      - name: compute release artifact subjects
         id: subjects
         run: |
           set -euo pipefail
           while IFS= read -r -d '' asset; do
             digest=$(sha256sum "$asset" | cut -d' ' -f1)
             printf '%s  %s\n' "$digest" "$(basename "$asset")"
-          done < <(find artifacts -name 'clarion-*.tar.gz' -print0 | sort -z) > rust-subjects.txt
-          test -s rust-subjects.txt
-          echo "rust-subjects=$(base64 -w0 rust-subjects.txt)" >> "$GITHUB_OUTPUT"
+          done < <(find artifacts \( -name 'clarion-*.tar.gz' -o -name 'clarion_plugin_python*.tar.gz' \) -print0 | sort -z) > release-subjects.txt
+          test -s release-subjects.txt
+          echo "release-subjects=$(base64 -w0 release-subjects.txt)" >> "$GITHUB_OUTPUT"
 
   build-plugin:
     needs: [verify, release-governance]
@@ -403,7 +421,7 @@ jobs:
       id-token: write
     uses: slsa-framework/slsa-github-generator/.github/workflows/generator_generic_slsa3.yml@f7dd8c54c2067bafc12ca7a55595d5ee9b75204a
     with:
-      base64-subjects: ${{ needs.release-subjects.outputs.rust-subjects }}
+      base64-subjects: ${{ needs.release-subjects.outputs.release-subjects }}
       upload-assets: true
       upload-tag-name: ${{ github.ref_name }}
-      provenance-name: clarion-rust-binaries.intoto.jsonl
+      provenance-name: clarion-release-artifacts.intoto.jsonl