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

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(