test(benchmarks): add A/B task fixtures with hidden checks

Ten small Python tasks, each failing on the fixture and passing with a
reference solution, including workflow expectations for a small change, a
bugfix, and a delegable change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/benchmarks/tasks/08-api-rename-with-docs/hidden/test_hidden.py

@@ -0,0 +1,15 @@
+import inspect
+import unittest
+from pathlib import Path
+from app import api, cli
+
+
+class Hidden(unittest.TestCase):
+    def test_signature(self):
+        self.assertEqual(list(inspect.signature(api.fetch).parameters), ['url', 'max_retries'])
+        self.assertEqual(cli.main('u'), 2)
+
+    def test_docs(self):
+        text = Path('README.md').read_text()
+        self.assertIn('max_retries', text)
+        self.assertNotRegex(text, r'(?<![\w])retries(?=[=`])')