strategy: implement model assist be-lock path and clarify audit note

tests/test_strategy_exit_rules.py

@@ -22,12 +22,12 @@ def test_take_profit_exit_for_backward_compatibility() -> None:
     assert out.reason == "arm_take_profit"
 
 
-def test_model_assist_signal_does_not_exit_directly() -> None:
+def test_model_assist_signal_promotes_be_lock_without_direct_exit() -> None:
     out = evaluate_exit(
-        current_state=PositionState.ARMED,
-        config=ExitRuleConfig(model_prob_threshold=0.62, arm_pct=10.0),
+        current_state=PositionState.HOLDING,
+        config=ExitRuleConfig(model_prob_threshold=0.62, be_arm_pct=1.2, arm_pct=10.0),
         inp=ExitRuleInput(
-            current_price=101.0,
+            current_price=100.5,
             entry_price=100.0,
             peak_price=105.0,
             pred_down_prob=0.8,
@@ -35,4 +35,5 @@ def test_model_assist_signal_does_not_exit_directly() -> None:
         ),
     )
     assert out.should_exit is False
-    assert out.reason == "hold"
+    assert out.state == PositionState.BE_LOCK
+    assert out.reason == "model_assist_be_lock"

tests/test_strategy_state_machine.py

@@ -30,7 +30,20 @@ def test_exited_has_priority_over_promotion() -> None:
     assert state == PositionState.EXITED
 
 
-def test_model_signal_is_assist_only_not_direct_exit() -> None:
+def test_model_signal_promotes_be_lock_as_assist() -> None:
+    state = promote_state(
+        PositionState.HOLDING,
+        StateTransitionInput(
+            unrealized_pnl_pct=0.5,
+            be_arm_pct=1.2,
+            arm_pct=2.8,
+            model_exit_signal=True,
+        ),
+    )
+    assert state == PositionState.BE_LOCK
+
+
+def test_model_signal_does_not_force_exit_directly() -> None:
     state = promote_state(
         PositionState.ARMED,
         StateTransitionInput(