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/03-delegation-parsers/hidden/test_hidden.py

@@ -0,0 +1,17 @@
+import unittest
+from app.parsers.csv_parser import parse_csv
+from app.parsers.ini_parser import parse_ini
+from app.parsers.json_parser import parse_json_lines
+
+
+class Hidden(unittest.TestCase):
+    def test_csv(self):
+        self.assertEqual(parse_csv('a, b\n1, "x,y"\n\n2,3\n'), [{'a': '1', 'b': 'x,y'}, {'a': '2', 'b': '3'}])
+
+    def test_json(self):
+        self.assertEqual(parse_json_lines('{"a": 1}\n\n[2]\n'), [{'a': 1}, [2]])
+        with self.assertRaisesRegex(ValueError, '2'):
+            parse_json_lines('{}\n{bad\n')
+
+    def test_ini(self):
+        self.assertEqual(parse_ini('top = 1\n; c\n[s]\n# c\n k = v \n'), {'': {'top': '1'}, 's': {'k': 'v'}})