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

src/strategy/exit_rules.py

@@ -85,6 +85,8 @@ def evaluate_exit(
         reason = "atr_trailing_stop"
     elif be_lock_threat:
         reason = "be_lock_threat"
+    elif model_exit_signal and next_state == PositionState.BE_LOCK:
+        reason = "model_assist_be_lock"
     elif take_profit_hit:
         # Backward-compatible immediate profit-taking path.
         reason = "arm_take_profit"

src/strategy/position_state_machine.py

@@ -62,5 +62,8 @@ def promote_state(current: PositionState, inp: StateTransitionInput) -> Position
         target = PositionState.ARMED
     elif inp.unrealized_pnl_pct >= inp.be_arm_pct:
         target = PositionState.BE_LOCK
+    elif inp.model_exit_signal:
+        # Model signal assists risk posture by tightening to BE_LOCK.
+        target = PositionState.BE_LOCK
 
     return target if _STATE_RANK[target] > _STATE_RANK[current] else current