Fix cross-session avg_entry_price contamination in positions view

Parking positions now use parking_state.avg_price instead of Alpaca's
blended avg_entry_price, which gets polluted when multiple sessions
share one broker account.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/routers/paper_trading.py

@@ -314,9 +314,15 @@ def get_positions(session_id: str) -> dict[str, Any]:
             is_parking = parking_symbol and p.symbol == parking_symbol
             if ss is None and not is_parking:
                 continue  # Only show positions tracked by this session
-            # Use locally-recorded entry price/qty for strategy positions to avoid
+            # Use locally-recorded entry price/qty to avoid cross-session contamination
-            # orphaned-share contamination of Alpaca's blended avg_entry_price.
+            # of Alpaca's blended avg_entry_price (multiple sessions share one broker account).
             ot = open_trades.get(p.symbol) if not is_parking else None
+            if is_parking and parking_state:
+                qty = float(parking_state.get("qty") or p.qty)
+                entry = float(parking_state["avg_price"]) if parking_state.get("avg_price") else (
+                    float(p.avg_entry_price) if p.avg_entry_price else 0.0
+                )
+            else:
                 qty = float(ot["shares"]) if ot and ot.get("shares") else float(p.qty)
                 entry = float(ot["entry_price"]) if ot and ot.get("entry_price") else (
                     float(p.avg_entry_price) if p.avg_entry_price else 0.0