diff --git a/docs/TESTING-SUITES.md b/docs/TESTING-SUITES.md
index 6454bf961..e6d5b32d6 100644
--- a/docs/TESTING-SUITES.md
+++ b/docs/TESTING-SUITES.md
@@ -45,6 +45,13 @@ identity ratchet (`npm run lint:regression-names`, part of `npm run lint:ci`):
 - A **new** `bug-*` file fails CI — fold it into the owning module's file.
 - **Deleting/consolidating** a grandfathered file requires pruning its
   allowlist entry, so the baseline only ever shrinks.
+- **Inherited drift** (the failure names files your PR didn't add — e.g. the
+  base branch merged `bug-*` files without feeding the allowlist, or you
+  rebased and carried a pre-rebase allowlist): run
+  `node scripts/lint-regression-test-names.cjs --update` and commit the
+  regenerated allowlist. Snapshot artifacts like this allowlist (and
+  `docs/INVENTORY.md`) must be regenerated **after** rebasing, never carried
+  through a rebase.
 
 The ratchet deliberately covers only `bug-*`. Files named `feat-NNNN-*` /
 `enh-NNNN-*` are *feature* test files — one (or one per suite) per feature is
diff --git a/scripts/lint-regression-test-names.cjs b/scripts/lint-regression-test-names.cjs
index 724f81b52..f75293f99 100644
--- a/scripts/lint-regression-test-names.cjs
+++ b/scripts/lint-regression-test-names.cjs
@@ -24,6 +24,16 @@
  *     entry from scripts/lint-regression-test-names.allowlist.json so the
  *     baseline only ever shrinks.
  *
+ * ## --update (allowlist drift repair)
+ *
+ * `node scripts/lint-regression-test-names.cjs --update` regenerates the
+ * allowlist from the files currently in tests/ and reports what changed.
+ * Use it when the failure is INHERITED drift, not your own new file — e.g.
+ * the base branch merged bug-* files without feeding the allowlist (the
+ * #947/#948/#950 race after the ratchet landed), or after a rebase. The
+ * allowlist is a snapshot artifact: regenerate it AFTER rebasing, never
+ * carry a pre-rebase copy through.
+ *
  * See docs/TESTING-SUITES.md ("Regression tests") for the placement policy.
  */
 
@@ -42,12 +52,38 @@ const ALLOWLIST_PATH =
 const BUG_FILE_RE = /^bug-\d+.*\.test\.cjs$/;
 
 function main() {
+  const args = process.argv.slice(2);
+  const update = args.includes('--update');
+  const unknown = args.filter(a => a !== '--update');
+  if (unknown.length > 0) {
+    throw new ExitError(2, `lint-regression-test-names: unknown argument(s): ${unknown.join(', ')}`);
+  }
+
   const current = fs
     .readdirSync(TESTS_DIR)
     .filter(f => BUG_FILE_RE.test(f))
     .sort();
   const known = JSON.parse(fs.readFileSync(ALLOWLIST_PATH, 'utf8'));
 
+  if (update) {
+    const knownSet = new Set(known);
+    const currentSet = new Set(current);
+    const added = current.filter(f => !knownSet.has(f));
+    const pruned = known.filter(f => !currentSet.has(f));
+    if (added.length === 0 && pruned.length === 0) {
+      console.log(`lint-regression-test-names --update: allowlist already in sync (${current.length} entries)`);
+      return;
+    }
+    fs.writeFileSync(ALLOWLIST_PATH, JSON.stringify(current, null, 2) + '\n');
+    console.log(
+      `lint-regression-test-names --update: ${known.length} -> ${current.length} entries` +
+      (added.length ? ` | grandfathered: ${added.join(', ')}` : '') +
+      (pruned.length ? ` | pruned: ${pruned.join(', ')}` : '')
+    );
+    console.log('Commit the regenerated allowlist with your change.');
+    return;
+  }
+
   const failures = [];
   const { novel } = assertWithinAllowlist({
     label: 'regression-test-names',
@@ -61,10 +97,13 @@ function main() {
     for (const msg of failures) console.error(msg);
     if (novel.length > 0) {
       console.error(
-        '\nNew bug-NNNN test files are no longer accepted. Add the regression ' +
-        "case to the owning module's test file (e.g. a describe('regressions') " +
-        'block in tests/<module>.test.cjs) instead of creating a new file. ' +
-        'See docs/TESTING-SUITES.md.'
+        '\nIf this PR added the file(s) above: new bug-NNNN test files are not ' +
+        "accepted — add the regression case to the owning module's test file " +
+        "(e.g. a describe('regressions') block in tests/<module>.test.cjs) instead.\n" +
+        'If the file(s) came from the base branch (inherited allowlist drift, ' +
+        'e.g. after a rebase): run ' +
+        '`node scripts/lint-regression-test-names.cjs --update` and commit the ' +
+        'regenerated allowlist. See docs/TESTING-SUITES.md.'
       );
     }
     throw new ExitError(1);
diff --git a/tests/lint-regression-test-names.test.cjs b/tests/lint-regression-test-names.test.cjs
index 430d57d4f..9fbd46e27 100644
--- a/tests/lint-regression-test-names.test.cjs
+++ b/tests/lint-regression-test-names.test.cjs
@@ -19,13 +19,13 @@ let sandbox;
 
 let fixtureCount = 0;
 
-function runLint({ files, allowlist }) {
+function runLint({ files, allowlist, args = [] }) {
   const testsDir = path.join(sandbox, `tests-${fixtureCount++}`);
   fs.mkdirSync(testsDir, { recursive: true });
   for (const f of files) fs.writeFileSync(path.join(testsDir, f), '');
   const allowlistPath = path.join(testsDir, 'allowlist.json');
   fs.writeFileSync(allowlistPath, JSON.stringify(allowlist));
-  return spawnSync(process.execPath, [SCRIPT], {
+  const r = spawnSync(process.execPath, [SCRIPT, ...args], {
     cwd: ROOT,
     encoding: 'utf8',
     env: {
@@ -34,6 +34,8 @@ function runLint({ files, allowlist }) {
       GSD_LINT_REGRESSION_ALLOWLIST: allowlistPath,
     },
   });
+  r.allowlistPath = allowlistPath;
+  return r;
 }
 
 describe('lint-regression-test-names', () => {
@@ -93,4 +95,48 @@ describe('lint-regression-test-names', () => {
     const r = spawnSync(process.execPath, [SCRIPT], { cwd: ROOT, encoding: 'utf8' });
     assert.strictEqual(r.status, 0, `stderr: ${r.stderr}\nstdout: ${r.stdout}`);
   });
+
+  test('novel-offender failure names the --update drift-repair path', () => {
+    const r = runLint({
+      files: ['bug-500-inherited.test.cjs'],
+      allowlist: [],
+    });
+    assert.notStrictEqual(r.status, 0);
+    assert.match(r.stderr, /--update/);
+  });
+
+  test('--update regenerates the allowlist from the tests dir (grandfather + prune)', () => {
+    const r = runLint({
+      files: ['bug-100-kept.test.cjs', 'bug-200-new.test.cjs'],
+      allowlist: ['bug-100-kept.test.cjs', 'bug-300-gone.test.cjs'],
+      args: ['--update'],
+    });
+    assert.strictEqual(r.status, 0, `stderr: ${r.stderr}`);
+    assert.match(r.stdout, /grandfathered: bug-200-new\.test\.cjs/);
+    assert.match(r.stdout, /pruned: bug-300-gone\.test\.cjs/);
+    assert.deepStrictEqual(
+      JSON.parse(fs.readFileSync(r.allowlistPath, 'utf8')),
+      ['bug-100-kept.test.cjs', 'bug-200-new.test.cjs'],
+    );
+  });
+
+  test('--update is a no-op when already in sync', () => {
+    const r = runLint({
+      files: ['bug-100-kept.test.cjs'],
+      allowlist: ['bug-100-kept.test.cjs'],
+      args: ['--update'],
+    });
+    assert.strictEqual(r.status, 0, `stderr: ${r.stderr}`);
+    assert.match(r.stdout, /already in sync/);
+    assert.deepStrictEqual(
+      JSON.parse(fs.readFileSync(r.allowlistPath, 'utf8')),
+      ['bug-100-kept.test.cjs'],
+    );
+  });
+
+  test('unknown arguments are rejected', () => {
+    const r = runLint({ files: [], allowlist: [], args: ['--frobnicate'] });
+    assert.strictEqual(r.status, 2);
+    assert.match(r.stderr, /unknown argument/);
+  });
 });