refactor(pre-alpha): fail closed on historical fixture bounds

app/services/backtesting/comparison.py

@@ -121,7 +121,9 @@ class EventComparisonService:
         provider_ref: ProviderRef | None = None,
         history: list[DailyClosePoint] | None = None,
     ) -> BacktestScenario:
-        selected_template_slugs = tuple(template_slugs or preset.scenario_overrides.default_template_slugs)
+        selected_template_slugs = (
+            tuple(preset.scenario_overrides.default_template_slugs) if template_slugs is None else tuple(template_slugs)
+        )
         if not selected_template_slugs:
             raise ValueError("Event comparison requires at least one template slug")
 

app/services/backtesting/ui_service.py

@@ -10,11 +10,7 @@ from app.models.backtest import (
     ProviderRef,
     TemplateRef,
 )
-from app.services.backtesting.historical_provider import (
-    DailyClosePoint,
-    HistoricalPriceSource,
-    YFinanceHistoricalPriceSource,
-)
+from app.services.backtesting.historical_provider import DailyClosePoint
 from app.services.backtesting.service import BacktestService
 from app.services.strategy_templates import StrategyTemplateService
 
@@ -40,19 +36,18 @@ DETERMINISTIC_UI_FIXTURE_HISTORY: tuple[DailyClosePoint, ...] = (
 )
 
 
-class FixtureFallbackHistoricalPriceSource:
-    def __init__(self, fallback: HistoricalPriceSource | None = None) -> None:
-        self.fallback = fallback or YFinanceHistoricalPriceSource()
-
+class DeterministicBacktestFixtureSource:
     def load_daily_closes(self, symbol: str, start_date: date, end_date: date) -> list[DailyClosePoint]:
         normalized_symbol = symbol.strip().upper()
         if (
-            normalized_symbol == SUPPORTED_BACKTEST_PAGE_SYMBOL
-            and start_date == date(2024, 1, 2)
-            and end_date == date(2024, 1, 8)
+            normalized_symbol != SUPPORTED_BACKTEST_PAGE_SYMBOL
+            or start_date != date(2024, 1, 2)
+            or end_date != date(2024, 1, 8)
         ):
-            return list(DETERMINISTIC_UI_FIXTURE_HISTORY)
-        return self.fallback.load_daily_closes(normalized_symbol, start_date, end_date)
+            raise ValueError(
+                "BT-001A deterministic fixture data only supports GLD on the seeded 2024-01-02 through 2024-01-08 window"
+            )
+        return list(DETERMINISTIC_UI_FIXTURE_HISTORY)
 
 
 @dataclass(frozen=True)
@@ -75,7 +70,7 @@ class BacktestPageService:
         )
         if backtest_service is None:
             provider = self.backtest_service.provider
-            provider.source = FixtureFallbackHistoricalPriceSource(provider.source)
+            provider.source = DeterministicBacktestFixtureSource()
 
     def template_options(self, symbol: str = "GLD") -> list[dict[str, str | int]]:
         return [