diff --git a/.github/workflows/source-provenance.yml b/.github/workflows/source-provenance.yml
index 8273bbcd..c7bbfb5e 100644
--- a/.github/workflows/source-provenance.yml
+++ b/.github/workflows/source-provenance.yml
@@ -10,6 +10,37 @@ permissions:
   contents: read
 
 jobs:
+  attest-source-governance:
+    name: Attest source governance (SLSA Source Track)
+    runs-on: ubuntu-latest
+    if: github.ref == 'refs/heads/main'
+    permissions:
+      contents: read
+      attestations: write
+      id-token: write
+
+    steps:
+      - name: "Harden the runner (Block egress traffic: Only allow calls to allowed endpoints)"
+        uses: step-security/harden-runner@ab7a9404c0f3da075243ca237b5fac12c98deaa5 # v2.19.3
+        with:
+          egress-policy: block
+          allowed-endpoints: >+
+            github.com:443
+            api.github.com:443
+            uploads.github.com:443
+            fulcio.sigstore.dev:443
+            rekor.sigstore.dev:443
+            tuf-repo-cdn.sigstore.dev:443
+            *.blob.core.windows.net:443
+
+      - name: Checkout repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - name: Attest source governance (SLSA Source Track)
+        uses: slsa-framework/slsa-source-corroborator@v0.1.0
+
   attest-source:
     name: Generate source provenance
     runs-on: ubuntu-latest
diff --git a/doc/explanation/threat_model_supply_chain.rst b/doc/explanation/threat_model_supply_chain.rst
index 2629b25d..dad2e28d 100644
--- a/doc/explanation/threat_model_supply_chain.rst
+++ b/doc/explanation/threat_model_supply_chain.rst
@@ -131,7 +131,7 @@ Actors
      - External contributor submitting pull requests, or an adversary attempting supply-chain manipulation (malicious PR, action-poisoning, or MITM on CI network traffic).  Code review, branch protection, and SHA-pinned Actions are the primary controls at this boundary.
 
    * - Consumer / End User
-     - Installs dfetch from PyPI (``pip install dfetch``) or from binary installer, then invokes it on a developer workstation or in a CI pipeline.  Can verify four complementary attestation types using ``gh attestation verify`` as documented in the release-integrity guide (see C-026, C-039, C-040): SBOM attestation on the PyPI wheel; SBOM, SLSA build provenance, and VSA on binary installers; SLSA build provenance and in-toto test result attestation on the source archive.
+     - Installs dfetch from PyPI (``pip install dfetch``) or from binary installer, then invokes it on a developer workstation or in a CI pipeline.  Can verify five complementary attestation types using ``gh attestation verify`` as documented in the release-integrity guide (see C-026, C-037, C-039, C-040): SBOM attestation on the PyPI wheel; SBOM, SLSA build provenance, and VSA on binary installers; SLSA build provenance, in-toto test result attestation, and SLSA Source Provenance Attestation on the source archive and main-branch commits.
 
 
 Boundaries
@@ -319,6 +319,12 @@ Controls
      - Tampering
      - DFT-28
      - Mitigates: ccache and clcache keys in ``build.yml`` include ``${{ github.ref_name }}`` so cache entries written by a pull-request build are scoped to the PR's branch name and cannot be restored by a release-tag build.  A malicious fork PR step cannot pre-populate a cache slot that the release workflow will restore, because the release tag name is not reachable from the PR's branch ref.  ``.github/workflows/build.yml``
+   * - C-037
+     - SLSA Source Provenance Attestation of repository governance controls
+     - Low
+     - Repudiation, Spoofing
+     - DFT-31
+     - Mitigates: Source Provenance Attestations are published via ``slsa-framework/slsa-source-corroborator`` on every push to ``main``.  These attestations prove the specific source-level governance controls applied on each commit: branch protection, mandatory code review, and ancestry enforcement (C-038).  Predicate type ``https://slsa.dev/source_provenance/v1`` is signed by GitHub Actions via Sigstore and stored in the GitHub Attestation registry.  Consumers can verify using ``gh attestation verify`` with ``--predicate-type https://slsa.dev/source_provenance/v1`` and ``--cert-identity`` pinned to ``source-provenance.yml@refs/heads/main``.  ``.github/workflows/source-provenance.yml``
    * - C-038
      - Ancestry enforcement on dfetch main branch
      - Low
@@ -330,7 +336,7 @@ Controls
      - High
      - Spoofing, Tampering, Repudiation
      - DFT-31, DFT-25
-     - Mitigates: Every dfetch release ships two complementary Sigstore-signed attestations that together let consumers trace the full source → binary chain.  SLSA build provenance (``source-provenance.yml``) on the source archive proves the archive was produced from the official tagged commit by the official CI workflow, recording the exact inputs used at build time.  A Verification Summary Attestation (VSA, ``build.yml``) on binary installers records that the source archive was itself attested and verified before the binary was produced, linking source-level trust to the installed package.  Both are signed by GitHub Actions via Sigstore and can be verified using ``gh attestation verify`` with ``--predicate-type https://slsa.dev/provenance/v1`` or ``--predicate-type https://slsa.dev/verification_summary/v1`` respectively.  This substantially mitigates DFT-31 (consumers now have attestations to verify against) and DFT-25 (forged provenance would fail Sigstore verification).  The remaining gap (no formal SLSA Source Level attestation of governance controls) is tracked in C-037.  ``doc/howto/verify-integrity.rst``
+     - Mitigates: Every dfetch release ships two complementary Sigstore-signed attestations that together let consumers trace the full source → binary chain.  SLSA build provenance (``source-provenance.yml``) on the source archive proves the archive was produced from the official tagged commit by the official CI workflow, recording the exact inputs used at build time.  A Verification Summary Attestation (VSA, ``build.yml``) on binary installers records that the source archive was itself attested and verified before the binary was produced, linking source-level trust to the installed package.  Both are signed by GitHub Actions via Sigstore and can be verified using ``gh attestation verify`` with ``--predicate-type https://slsa.dev/provenance/v1`` or ``--predicate-type https://slsa.dev/verification_summary/v1`` respectively.  This substantially mitigates DFT-31 (consumers now have attestations to verify against) and DFT-25 (forged provenance would fail Sigstore verification).  The formal SLSA Source Level attestation of governance controls is addressed by C-037.  ``doc/howto/verify-integrity.rst``
    * - C-040
      - Test result attestation on source archive
      - Medium
@@ -358,12 +364,6 @@ Gaps
      - Tampering
      - DFT-10
      - Affects: ``pip install .`` and ``pip install --upgrade pip build`` in CI do not use ``--require-hashes``.  A compromised PyPI mirror can substitute malicious build tooling.
-   * - C-037
-     - No formal SLSA Source Level attestation of repository governance controls
-     - Low
-     - Repudiation, Spoofing
-     - DFT-31
-     - Affects: dfetch now publishes SLSA build provenance for source archives, VSAs for binary installers (C-039), and in-toto test result attestations (C-040).  These close the 'no attestation to verify against' concern: consumers can cryptographically verify the artifact chain.  The remaining, narrower gap is that dfetch does not publish formal SLSA Source Provenance Attestations generated by a SLSA Source Generator — attestations that would prove the specific source-level governance controls applied on each commit (branch protection, mandatory code review, ancestry enforcement).  C-038 establishes that ancestry enforcement is in place and C-026 documents what consumers can verify; the gap is in machine-readable, verifiable proof of those governance controls rather than the controls themselves.  Risk is Low: the missing piece is a formal SLSA Source Level certificate (per the SLSA Source Track spec) rather than the absence of any assurance.  Fix: publish Source Provenance Attestations via ``slsa-framework/slsa-source-corroborator`` or equivalent on each push to main.
    * - C-025
      - No hardware-token MFA for release operations
      - High
diff --git a/doc/howto/verify-integrity.rst b/doc/howto/verify-integrity.rst
index 07408995..c159681e 100644
--- a/doc/howto/verify-integrity.rst
+++ b/doc/howto/verify-integrity.rst
@@ -5,20 +5,23 @@ Every dfetch release, and every commit merged to ``main``, has cryptographic
 attestations signed by GitHub Actions and anchored in
 `Sigstore <https://www.sigstore.dev/>`_, all published in the
 `attestation registry <https://github.com/dfetch-org/dfetch/attestations>`_.
-There are four complementary kinds:
+There are five complementary kinds, in pipeline order from source to artifact:
 
+- **Source Provenance Attestation** (SLSA Source Track) — answers *"did this commit
+  meet governance requirements?"*: proves that branch protection, mandatory code
+  review, and ancestry enforcement were in place when the commit was merged to
+  ``main``.
+- **Test result attestation** (in-toto) — answers *"did the test suite pass?"*:
+  records that the full CI test suite ran against this exact source archive and every
+  check passed, before any binary was produced.
 - **SLSA build provenance** — answers *"where did this come from?"*: proves the
   artifact was produced from the official source commit by the official CI
   workflow, and records the exact inputs used at build time.
 - **SBOM attestation** (CycloneDX) — answers *"what is inside it?"*: lists every
   dependency bundled in the package so you can audit its composition.
-- **Verification Summary Attestation (VSA)** — answers *"was the source
-  independently verified?"*: records that the source archive for this commit was
-  attested and verified before the binary was produced, linking source-level
-  trust to the binary package.
-- **Test result attestation** (in-toto) — answers *"did the source pass its tests?"*:
-  records that the full CI test suite ran against this exact source archive and every
-  check passed, before any binary was produced.
+- **Verification Summary Attestation (VSA)** — answers *"was the full chain
+  verified?"*: records that the source archive was itself attested and verified
+  before the binary was produced, linking source-level trust to the artifact.
 
 Binary installers have **build provenance, SBOM, and VSA** attestations when source
 provenance verification passes (signed by ``build.yml``).
@@ -26,6 +29,8 @@ Python packages installed from PyPI have an **SBOM attestation only** (signed by
 ``python-publish.yml``).
 The source archive has a **SLSA build provenance** attestation (signed by
 ``source-provenance.yml``) and a **test result attestation** (signed by ``test.yml``).
+Every commit merged to ``main`` has a **SLSA Source Provenance Attestation** proving
+branch governance controls were applied (signed by ``source-provenance.yml``).
 
 To verify, use the `GitHub CLI <https://cli.github.com/>`_. Pass
 ``--predicate-type`` to target one kind specifically; omit it to accept any.
@@ -201,6 +206,24 @@ any binary was produced):
         --cert-identity https://github.com/dfetch-org/dfetch/.github/workflows/test.yml@refs/tags/v<version> \
         --cert-oidc-issuer https://token.actions.githubusercontent.com
 
+**Source governance — verify SLSA Source Provenance Attestation:**
+
+Every commit merged to ``main`` has a Source Provenance Attestation proving that
+branch protection, mandatory code review, and ancestry enforcement were in place
+when the commit landed.  These attestations are published by
+``slsa-framework/slsa-source-corroborator`` and stored in the
+`attestation registry <https://github.com/dfetch-org/dfetch/attestations>`_.
+Replace ``<sha>`` with the 40-character commit SHA you want to verify:
+
+.. code-block:: bash
+
+    $ gh attestation verify \
+        "git+https://github.com/dfetch-org/dfetch@<sha>" \
+        --repo dfetch-org/dfetch \
+        --predicate-type https://slsa.dev/source_provenance/v1 \
+        --cert-identity https://github.com/dfetch-org/dfetch/.github/workflows/source-provenance.yml@refs/heads/main \
+        --cert-oidc-issuer https://token.actions.githubusercontent.com
+
 See `GitHub artifact attestations`_ for details.
 
 .. note::
diff --git a/security/tm_supply_chain.py b/security/tm_supply_chain.py
index c7493875..7ea7a9ba 100644
--- a/security/tm_supply_chain.py
+++ b/security/tm_supply_chain.py
@@ -98,10 +98,11 @@ def _make_sc_actors_and_entities(
     consumer.description = (
         "Installs dfetch from PyPI (``pip install dfetch``) or from binary installer, "
         "then invokes it on a developer workstation or in a CI pipeline.  "
-        "Can verify four complementary attestation types using ``gh attestation verify`` as "
-        "documented in the release-integrity guide (see C-026, C-039, C-040): "
+        "Can verify five complementary attestation types using ``gh attestation verify`` as "
+        "documented in the release-integrity guide (see C-026, C-037, C-039, C-040): "
         "SBOM attestation on the PyPI wheel; SBOM, SLSA build provenance, and VSA on binary "
-        "installers; SLSA build provenance and in-toto test result attestation on the source archive."
+        "installers; SLSA build provenance, in-toto test result attestation, and SLSA Source "
+        "Provenance Attestation on the source archive and main-branch commits."
     )
     gh_repository = ExternalEntity("A-01: GitHub Repository")
     gh_repository.inBoundary = b_github
@@ -658,6 +659,28 @@ def build_model() -> TM:
             "the PR's branch ref."
         ),
     ),
+    Control(
+        id="C-037",
+        name="SLSA Source Provenance Attestation of repository governance controls",
+        assets=["A-01"],
+        threats=["DFT-31"],
+        reference=".github/workflows/source-provenance.yml",
+        assessment=ControlAssessment(
+            status="implemented", risk="Low", stride=["Repudiation", "Spoofing"]
+        ),
+        description=(
+            "Source Provenance Attestations are published via "
+            "``slsa-framework/slsa-source-corroborator`` on every push to ``main``.  "
+            "These attestations prove the specific source-level governance controls "
+            "applied on each commit: branch protection, mandatory code review, and "
+            "ancestry enforcement (C-038).  "
+            "Predicate type ``https://slsa.dev/source_provenance/v1`` is signed by "
+            "GitHub Actions via Sigstore and stored in the GitHub Attestation registry.  "
+            "Consumers can verify using ``gh attestation verify`` with "
+            "``--predicate-type https://slsa.dev/source_provenance/v1`` and "
+            "``--cert-identity`` pinned to ``source-provenance.yml@refs/heads/main``."
+        ),
+    ),
     Control(
         id="C-038",
         name="Ancestry enforcement on dfetch main branch",
@@ -701,8 +724,7 @@ def build_model() -> TM:
             "or ``--predicate-type https://slsa.dev/verification_summary/v1`` respectively.  "
             "This substantially mitigates DFT-31 (consumers now have attestations to verify "
             "against) and DFT-25 (forged provenance would fail Sigstore verification).  "
-            "The remaining gap (no formal SLSA Source Level attestation of governance "
-            "controls) is tracked in C-037."
+            "The formal SLSA Source Level attestation of governance controls is addressed by C-037."
         ),
     ),
     Control(
@@ -742,33 +764,6 @@ def build_model() -> TM:
             "malicious build tooling."
         ),
     ),
-    Control(
-        id="C-037",
-        name="No formal SLSA Source Level attestation of repository governance controls",
-        assets=["A-01"],
-        threats=["DFT-31"],
-        assessment=ControlAssessment(
-            status="gap", risk="Low", stride=["Repudiation", "Spoofing"]
-        ),
-        description=(
-            "dfetch now publishes SLSA build provenance for source archives, VSAs for "
-            "binary installers (C-039), and in-toto test result attestations (C-040).  "
-            "These close the 'no attestation to verify against' concern: consumers can "
-            "cryptographically verify the artifact chain.  "
-            "The remaining, narrower gap is that dfetch does not publish formal SLSA "
-            "Source Provenance Attestations generated by a SLSA Source Generator — "
-            "attestations that would prove the specific source-level governance controls "
-            "applied on each commit (branch protection, mandatory code review, ancestry "
-            "enforcement).  "
-            "C-038 establishes that ancestry enforcement is in place and C-026 documents "
-            "what consumers can verify; the gap is in machine-readable, verifiable "
-            "proof of those governance controls rather than the controls themselves.  "
-            "Risk is Low: the missing piece is a formal SLSA Source Level certificate "
-            "(per the SLSA Source Track spec) rather than the absence of any assurance.  "
-            "Fix: publish Source Provenance Attestations via "
-            "``slsa-framework/slsa-source-corroborator`` or equivalent on each push to main."
-        ),
-    ),
     Control(
         id="C-025",
         name="No hardware-token MFA for release operations",