test(cp1): pin EASY pre-roll length so the diagnostic gate can't pass vacuously

tests/grid/test_predator_evade_behavior.py

@@ -27,7 +27,11 @@ def test_cut_handover_positions_are_deterministic():
 
 
 def test_diagnostic_invariant_optimal_differs_from_habit_at_handover():
-    scenario, game, _ = _build_at_handover()
+    scenario, game, cut = _build_at_handover()
+    # Pin the pre-roll length: habit_action reads _last_focal_move, which
+    # defaults to "left" in __init__, so habit=="left" could pass vacuously
+    # if the Cut never ran. Asserting cut makes "the pre-roll ran" explicit.
+    assert cut == 2, "EASY pre-roll length changed — re-verify layout"
     optimal = scenario.optimal_action(game)
     habit = scenario.habit_action(game)
     assert habit == "left"          # the inertia: keep walking west into the dead-end