Improve backtest lazy loading and test automation

app/services/backtesting/ui_service.py

@@ -29,6 +29,7 @@ from app.services.backtesting.service import BacktestService
 from app.services.strategy_templates import StrategyTemplateService
 
 SUPPORTED_BACKTEST_PAGE_SYMBOLS = ("GLD", "GC", "XAU")
+SUPPORTED_DATABENTO_BACKTEST_PAGE_SYMBOLS = ("GLD", "XAU")
 
 
 def _validate_initial_collateral(underlying_units: float, entry_spot: float, loan_amount: float) -> None:
@@ -134,6 +135,15 @@ class BacktestPageService:
             self._yfinance_provider = YFinanceHistoricalPriceSource()
         return self._yfinance_provider
 
+    @staticmethod
+    def validate_data_source_support(symbol: str, data_source: str) -> None:
+        normalized_symbol = symbol.strip().upper()
+        if data_source == "databento" and normalized_symbol not in SUPPORTED_DATABENTO_BACKTEST_PAGE_SYMBOLS:
+            raise ValueError(
+                "Databento backtests currently support GLD and XAU only. "
+                "GC futures remain unavailable on the backtest page until contract mapping is wired."
+            )
+
     def get_historical_prices(
         self, symbol: str, start_date: date, end_date: date, data_source: str
     ) -> list[DailyClosePoint]:
@@ -148,6 +158,7 @@ class BacktestPageService:
         Returns:
             List of daily close points sorted by date
         """
+        self.validate_data_source_support(symbol, data_source)
         if data_source == "databento":
             return self._get_databento_provider().load_daily_closes(symbol, start_date, end_date)
         elif data_source == "yfinance":
@@ -171,6 +182,8 @@ class BacktestPageService:
         if data_source != "databento":
             return 0.0
 
+        self.validate_data_source_support(symbol, data_source)
+
         try:
             provider = self._get_databento_provider()
             return provider.get_cost_estimate(symbol, start_date, end_date)
@@ -213,6 +226,8 @@ class BacktestPageService:
         if data_source != "databento":
             return None, None
 
+        self.validate_data_source_support(symbol, data_source)
+
         try:
             provider = self._get_databento_provider()
             return provider.get_available_range(symbol)
@@ -258,6 +273,7 @@ class BacktestPageService:
             raise ValueError("Symbol is required")
         if normalized_symbol not in SUPPORTED_BACKTEST_PAGE_SYMBOLS:
             raise ValueError(f"Backtests support symbols: {', '.join(SUPPORTED_BACKTEST_PAGE_SYMBOLS)}")
+        self.validate_data_source_support(normalized_symbol, data_source)
         if start_date > end_date:
             raise ValueError("Start date must be on or before end date")
         normalized_inputs = normalize_historical_scenario_inputs(