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/01-small-config-change/hidden/test_hidden.py

@@ -0,0 +1,16 @@
+import unittest
+from pathlib import Path
+from app import client, config
+
+
+class Hidden(unittest.TestCase):
+    def test_default(self):
+        self.assertEqual(config.DEFAULT_TIMEOUT, 60)
+        self.assertEqual(client.request('x'), 60)
+        self.assertEqual(client.request('x', 5), 5)
+
+    def test_docs(self):
+        for path in ('README.md', 'app/client.py'):
+            text = Path(path).read_text()
+            self.assertIn('60 seconds', text)
+            self.assertNotIn('30 seconds', text)