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/04-security-sql/hidden/test_hidden.py

@@ -0,0 +1,16 @@
+import sqlite3
+import unittest
+from app.users import find_user
+
+
+class Hidden(unittest.TestCase):
+    def setUp(self):
+        self.conn = sqlite3.connect(':memory:')
+        self.conn.execute('CREATE TABLE users (id INTEGER, name TEXT)')
+        self.conn.executemany('INSERT INTO users VALUES (?, ?)', [(1, "O'Brien"), (2, 'admin')])
+
+    def test_apostrophe(self):
+        self.assertEqual(find_user(self.conn, "O'Brien"), (1, "O'Brien"))
+
+    def test_injection(self):
+        self.assertIsNone(find_user(self.conn, "x' OR '1'='1"))