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/06-refactor-duplication/hidden/test_hidden.py

@@ -0,0 +1,16 @@
+import unittest
+from pathlib import Path
+from app.report import cost_report, sales_report
+
+ROWS = [(' widgets ', 1234.5), ('gadgets', 99)]
+EXPECTED = 'Widgets                 1,234.50\nGadgets                    99.00\nTotal                   1,333.50'
+
+
+class Hidden(unittest.TestCase):
+    def test_output(self):
+        self.assertEqual(sales_report(ROWS), EXPECTED)
+        self.assertEqual(cost_report(ROWS), EXPECTED)
+        self.assertEqual(sales_report([]), f"{'Total':<20}{0:>12,.2f}")
+
+    def test_deduplicated(self):
+        self.assertEqual(Path('app/report.py').read_text().count('.title()'), 1)