diff --git a/.github/workflows/pr-validation.yml b/.github/workflows/pr-validation.yml
index 9bb869d1..a42e488f 100644
--- a/.github/workflows/pr-validation.yml
+++ b/.github/workflows/pr-validation.yml
@@ -47,6 +47,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
 
+      - name: Check testsuite workflow contract
+        run: python3 scripts/check-testsuite-workflow-ref.py
+
       - name: Check for undeclared gitlinks
         shell: bash
         env:
@@ -228,7 +231,7 @@ jobs:
     permissions:
       contents: read
       packages: write  # testsuite pushes screenshot OCI artifacts to GHCR
-    # Keep the testsuite SHA centralized in run-testsuite.yml.
+    # Keep the testsuite workflow ref centralized in run-testsuite.yml.
     uses: ./.github/workflows/run-testsuite.yml
     with:
       image: ghcr.io/projectbluefin/bluefin:testing
diff --git a/docs/skills/ci/SKILL.md b/docs/skills/ci/SKILL.md
index 067f575d..55d150d0 100644
--- a/docs/skills/ci/SKILL.md
+++ b/docs/skills/ci/SKILL.md
@@ -127,12 +127,12 @@ collects coverage but does not own pass/fail.
 - Preserve action pinning and workflow permissions.
 - Do not add PAT-based authentication.
 - Keep end-to-end suites on their configured event.
-- Reference `projectbluefin/testsuite`'s reusable E2E workflow through its
-  managed `@v1` tag, never an immutable digest; testsuite advances `v1` after
-  each successful main-branch merge. `config:best-practices` pins action refs
-  to digests, so `projectbluefin/testsuite` is disabled for the
-  `github-actions` manager in `.github/renovate.json5`; without that rule
-  Renovate re-pins the ref and freezes the gate on a stale test tree.
+- Reference `projectbluefin/testsuite`'s reusable E2E workflow by its managed
+  `@v1` tag, never a digest; testsuite advances `v1` after each successful main
+  merge. It is disabled for the `github-actions` Renovate manager in
+  `.github/renovate.json5`, or re-pinning freezes the gate on a stale test tree.
+- Route testsuite calls through `.github/workflows/run-testsuite.yml`;
+  `scripts/check-testsuite-workflow-ref.py` enforces that and `test_ref: v1`.
 - Update this skill when workflow behavior changes.
 
 ## Verification
diff --git a/docs/skills/ci/references/workflow-map.md b/docs/skills/ci/references/workflow-map.md
index eace9c5f..b8e2f2a9 100644
--- a/docs/skills/ci/references/workflow-map.md
+++ b/docs/skills/ci/references/workflow-map.md
@@ -9,3 +9,27 @@ For current workflows:
 find .github/workflows -maxdepth 1 -type f -name '*.yml' -o -name '*.yaml' | sort
 git grep -n '^name:\|^on:' .github/workflows
 ```
+
+## The testsuite reference contract
+
+`.github/workflows/run-testsuite.yml` is the only workflow that may reference
+`projectbluefin/testsuite/.github/workflows/e2e.yml` directly. Every other
+caller goes through that wrapper, so the ref and `test_ref` are set in exactly
+one place.
+
+Two invariants, both enforced by `scripts/check-testsuite-workflow-ref.py` in
+the `validate` job:
+
+- the reference is `@v1` — testsuite advances that tag after each successful
+  main-branch merge, so a digest pin silently freezes the gate on a stale test
+  tree (this is the #929 regression);
+- the wrapper passes `test_ref: v1`.
+
+Renovate would otherwise undo the first one: `config:best-practices` pins
+action refs to digests, so `projectbluefin/testsuite` is excluded from the
+`github-actions` manager in `.github/renovate.json5`. Removing that exclusion
+re-pins the ref and reintroduces the same freeze.
+
+```bash
+python3 scripts/check-testsuite-workflow-ref.py
+```
diff --git a/scripts/check-testsuite-workflow-ref.py b/scripts/check-testsuite-workflow-ref.py
new file mode 100644
index 00000000..1bc0ba6d
--- /dev/null
+++ b/scripts/check-testsuite-workflow-ref.py
@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+"""Enforce the Bluefin-to-testsuite reusable-workflow contract."""
+
+from pathlib import Path
+import re
+import sys
+
+
+ROOT = Path(__file__).resolve().parents[1]
+WORKFLOW_DIR = ROOT / ".github" / "workflows"
+WRAPPER = WORKFLOW_DIR / "run-testsuite.yml"
+WORKFLOW_REF = re.compile(
+    r"^\s+uses:\s+projectbluefin/testsuite/\.github/workflows/e2e\.yml@([^\s#]+)",
+    re.MULTILINE,
+)
+TEST_REF = re.compile(r"^\s+test_ref:\s+([^\s#]+)", re.MULTILINE)
+
+
+def main() -> int:
+    errors: list[str] = []
+    wrapper_refs = WORKFLOW_REF.findall(WRAPPER.read_text(encoding="utf-8"))
+
+    if wrapper_refs != ["v1"]:
+        errors.append(
+            f"{WRAPPER.relative_to(ROOT)} must contain exactly one direct testsuite "
+            f"workflow reference at @v1; found {wrapper_refs!r}"
+        )
+
+    wrapper_test_refs = TEST_REF.findall(WRAPPER.read_text(encoding="utf-8"))
+    if wrapper_test_refs != ["v1"]:
+        errors.append(
+            f"{WRAPPER.relative_to(ROOT)} must pass exactly one test_ref: v1; "
+            f"found {wrapper_test_refs!r}"
+        )
+
+    for workflow in sorted(WORKFLOW_DIR.glob("*.y*ml")):
+        if workflow == WRAPPER:
+            continue
+        refs = WORKFLOW_REF.findall(workflow.read_text(encoding="utf-8"))
+        if refs:
+            errors.append(
+                f"{workflow.relative_to(ROOT)} calls testsuite e2e directly; "
+                "call the local run-testsuite wrapper instead"
+            )
+
+    if errors:
+        print("Testsuite workflow contract failed:", file=sys.stderr)
+        for error in errors:
+            print(f"- {error}", file=sys.stderr)
+        return 1
+
+    print("Testsuite workflow contract passed: canonical wrapper uses @v1 with test_ref: v1")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())