diff --git a/.github/workflows/canonical-governance.yml b/.github/workflows/canonical-governance.yml
index d6a352b4c..fa7b819b0 100644
--- a/.github/workflows/canonical-governance.yml
+++ b/.github/workflows/canonical-governance.yml
@@ -104,15 +104,31 @@ jobs:
             fi
             reason=$(git log -1 --format='%(trailers:key=Contract-Neutral,valueonly,separator=; )' "${commit}" | tr '\n' ' ')
             echo "::group::canonical completion guard @ ${commit}"
+            set +e
+            python3 scripts/release_control/canonical_completion_history.py \
+              --commit "${commit}" --head "${head_sha}"
+            completion_status=$?
+            set -e
+            if [ "${completion_status}" -eq 0 ]; then
+              completion_history=true
+            elif [ "${completion_status}" -eq 3 ]; then
+              completion_history=false
+            else
+              echo "Canonical completion history failed for commit ${commit}."
+              status=1
+              completion_history=true
+            fi
             # Pass the parent as the diff base so the guard compares
             # contract texts parent-vs-commit; the CI index equals HEAD,
             # so the default index comparison would misreport contract
             # updates in earlier commits as insubstantial.
-            if ! git diff-tree --no-commit-id --name-only -r "${commit}" \
-              | PULSE_ALLOW_CONTRACT_NEUTRAL_COMMIT="${reason}" python3 scripts/release_control/canonical_completion_guard.py \
-                  --files-from-stdin --diff-base "${commit}^" --commit "${commit}"; then
-              echo "Canonical completion guard failed for commit ${commit}."
-              status=1
+            if [ "${completion_history}" != true ]; then
+              if ! git diff-tree --no-commit-id --name-only -r "${commit}" \
+                | PULSE_ALLOW_CONTRACT_NEUTRAL_COMMIT="${reason}" python3 scripts/release_control/canonical_completion_guard.py \
+                    --files-from-stdin --diff-base "${commit}^" --commit "${commit}"; then
+                echo "Canonical completion guard failed for commit ${commit}."
+                status=1
+              fi
             fi
             if ! git diff-tree --no-commit-id --name-only -r "${commit}" \
               | python3 scripts/release_control/browser_verification_guard.py \
@@ -146,6 +162,9 @@ jobs:
       - name: Run canonical completion guard unit tests
         run: python3 scripts/release_control/canonical_completion_guard_test.py
 
+      - name: Run canonical completion history unit tests
+        run: python3 scripts/release_control/canonical_completion_history_test.py
+
       - name: Run browser verification guard unit tests
         run: python3 scripts/release_control/browser_verification_guard_test.py
 
diff --git a/.gitignore b/.gitignore
index 002e47b3b..3e4f25351 100644
--- a/.gitignore
+++ b/.gitignore
@@ -224,6 +224,9 @@ scripts/release_control/
 scripts/release_control/*
 !scripts/release_control/canonical_completion_guard.py
 !scripts/release_control/canonical_completion_guard_test.py
+!scripts/release_control/canonical_completion_history.json
+!scripts/release_control/canonical_completion_history.py
+!scripts/release_control/canonical_completion_history_test.py
 !scripts/release_control/commercial_cancellation_reactivation_proof.py
 !scripts/release_control/commercial_cancellation_reactivation_rehearsal.py
 !scripts/release_control/contract_audit.py
diff --git a/scripts/release_control/canonical_completion_history.json b/scripts/release_control/canonical_completion_history.json
new file mode 100644
index 000000000..d55554966
--- /dev/null
+++ b/scripts/release_control/canonical_completion_history.json
@@ -0,0 +1,10 @@
+{
+  "version": 1,
+  "completions": [
+    {
+      "incomplete_commit": "a2dbb27a68463adb02b614e9927174543f5b7799",
+      "completion_commit": "5f99f5c13fcc547e5e34286dfe873415a4876cfa",
+      "reason": "Preserve the reviewed diagnostic-redaction commit while evaluating its separately reviewed contracts and API proof as one historical completion unit."
+    }
+  ]
+}
diff --git a/scripts/release_control/canonical_completion_history.py b/scripts/release_control/canonical_completion_history.py
new file mode 100644
index 000000000..014adfb82
--- /dev/null
+++ b/scripts/release_control/canonical_completion_history.py
@@ -0,0 +1,138 @@
+#!/usr/bin/env python3
+"""Validate exact, reviewed canonical-completion pairs without rewriting history."""
+
+from __future__ import annotations
+
+import argparse
+import json
+from pathlib import Path
+import re
+import subprocess
+import sys
+import tempfile
+
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+REGISTRY = Path(__file__).with_name("canonical_completion_history.json")
+SHA_PATTERN = re.compile(r"[0-9a-f]{40}")
+
+
+def git(*args: str, cwd: Path = REPO_ROOT) -> str:
+    return subprocess.run(
+        ["git", *args],
+        cwd=cwd,
+        check=True,
+        capture_output=True,
+        text=True,
+    ).stdout.rstrip("\n")
+
+
+def load_completions(path: Path = REGISTRY) -> dict[str, dict[str, str]]:
+    document = json.loads(path.read_text(encoding="utf-8"))
+    if not isinstance(document, dict) or set(document) != {"version", "completions"}:
+        raise ValueError("completion registry must contain only version and completions")
+    if document["version"] != 1 or isinstance(document["version"], bool):
+        raise ValueError("unsupported completion registry version")
+    if not isinstance(document["completions"], list):
+        raise ValueError("completion registry entries must be a list")
+
+    result: dict[str, dict[str, str]] = {}
+    required = {"incomplete_commit", "completion_commit", "reason"}
+    for entry in document["completions"]:
+        if not isinstance(entry, dict) or set(entry) != required:
+            raise ValueError("completion entry has unexpected fields")
+        if not all(isinstance(entry[field], str) and entry[field].strip() for field in required):
+            raise ValueError("completion entry fields must be non-empty strings")
+        incomplete = entry["incomplete_commit"]
+        completion = entry["completion_commit"]
+        if not SHA_PATTERN.fullmatch(incomplete) or not SHA_PATTERN.fullmatch(completion):
+            raise ValueError("completion entry revisions must be full lowercase commit IDs")
+        if incomplete == completion or incomplete in result:
+            raise ValueError("completion entries must identify distinct, unique commits")
+        result[incomplete] = entry
+    return result
+
+
+def changed_files(commit: str) -> list[str]:
+    return [
+        line
+        for line in git("diff-tree", "--no-commit-id", "--name-only", "-r", commit).splitlines()
+        if line
+    ]
+
+
+def validate_completion(incomplete: str, head: str) -> bool:
+    """Return False for an ordinary commit; validate and return True for a registered pair."""
+    entry = load_completions().get(incomplete)
+    if entry is None:
+        return False
+    if not SHA_PATTERN.fullmatch(head):
+        raise ValueError("head must be a full lowercase commit ID")
+
+    completion = entry["completion_commit"]
+    git("cat-file", "-e", f"{incomplete}^{{commit}}")
+    git("cat-file", "-e", f"{completion}^{{commit}}")
+    git("cat-file", "-e", f"{head}^{{commit}}")
+    subprocess.run(
+        ["git", "merge-base", "--is-ancestor", incomplete, completion],
+        cwd=REPO_ROOT,
+        check=True,
+    )
+    subprocess.run(
+        ["git", "merge-base", "--is-ancestor", completion, head],
+        cwd=REPO_ROOT,
+        check=True,
+    )
+
+    files = sorted(set(changed_files(incomplete) + changed_files(completion)))
+    with tempfile.TemporaryDirectory(prefix="pulse-canonical-completion-") as temp:
+        worktree = Path(temp) / "pulse"
+        git("worktree", "add", "--detach", str(worktree), completion)
+        try:
+            guard = worktree / "scripts/release_control/canonical_completion_guard.py"
+            result = subprocess.run(
+                [
+                    sys.executable,
+                    str(guard),
+                    "--files-from-stdin",
+                    "--diff-base",
+                    f"{incomplete}^",
+                    "--commit",
+                    completion,
+                ],
+                cwd=worktree,
+                input="".join(f"{path}\n" for path in files),
+                text=True,
+            )
+            if result.returncode != 0:
+                raise ValueError(
+                    f"registered completion {completion} does not complete {incomplete}"
+                )
+        finally:
+            git("worktree", "remove", "--force", str(worktree))
+
+    print(
+        "Canonical completion history passed "
+        f"({incomplete} completed by {completion}: {entry['reason']})"
+    )
+    return True
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--commit", required=True)
+    parser.add_argument("--head", required=True)
+    return parser.parse_args()
+
+
+def main() -> int:
+    args = parse_args()
+    try:
+        return 0 if validate_completion(args.commit, args.head) else 3
+    except (OSError, ValueError, subprocess.CalledProcessError, json.JSONDecodeError) as error:
+        print(f"Canonical completion history failed: {error}", file=sys.stderr)
+        return 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/scripts/release_control/canonical_completion_history_test.py b/scripts/release_control/canonical_completion_history_test.py
new file mode 100644
index 000000000..c63e6e645
--- /dev/null
+++ b/scripts/release_control/canonical_completion_history_test.py
@@ -0,0 +1,32 @@
+import json
+import tempfile
+import unittest
+from pathlib import Path
+
+from canonical_completion_history import load_completions, validate_completion
+
+
+class CanonicalCompletionHistoryTest(unittest.TestCase):
+    def test_registry_names_the_exact_reviewed_completion_pair(self):
+        entries = load_completions()
+        self.assertEqual(
+            entries["a2dbb27a68463adb02b614e9927174543f5b7799"]["completion_commit"],
+            "5f99f5c13fcc547e5e34286dfe873415a4876cfa",
+        )
+
+    def test_registry_rejects_unknown_fields(self):
+        with tempfile.TemporaryDirectory() as temp:
+            path = Path(temp) / "history.json"
+            path.write_text(
+                json.dumps({"version": 1, "completions": [], "unexpected": True}),
+                encoding="utf-8",
+            )
+            with self.assertRaisesRegex(ValueError, "only version and completions"):
+                load_completions(path)
+
+    def test_unregistered_commit_uses_the_normal_guard(self):
+        self.assertFalse(validate_completion("0" * 40, "1" * 40))
+
+
+if __name__ == "__main__":
+    unittest.main()