fix(pre-alpha): preserve injected template services

app/services/backtesting/ui_service.py

@@ -11,7 +11,11 @@ from app.models.backtest import (
     ProviderRef,
     TemplateRef,
 )
-from app.services.backtesting.historical_provider import DailyClosePoint, SyntheticHistoricalProvider
+from app.services.backtesting.historical_provider import (
+    DailyClosePoint,
+    SyntheticHistoricalProvider,
+    SyntheticOptionQuote,
+)
 from app.services.backtesting.service import BacktestService
 from app.services.strategy_templates import StrategyTemplateService
 
@@ -58,22 +62,46 @@ class BacktestPageRunResult:
     entry_spot: float
 
 
+class FixtureBoundHistoricalProvider:
+    def __init__(self, base_provider: SyntheticHistoricalProvider) -> None:
+        self.base_provider = base_provider
+        self.source = DeterministicBacktestFixtureSource()
+        self.provider_id = base_provider.provider_id
+        self.pricing_mode = base_provider.pricing_mode
+        self.implied_volatility = base_provider.implied_volatility
+        self.risk_free_rate = base_provider.risk_free_rate
+
+    def load_history(self, symbol: str, start_date: date, end_date: date) -> list[DailyClosePoint]:
+        rows = self.source.load_daily_closes(symbol, start_date, end_date)
+        filtered = [row for row in rows if start_date <= row.date <= end_date]
+        return sorted(filtered, key=lambda row: row.date)
+
+    def validate_provider_ref(self, provider_ref: ProviderRef) -> None:
+        self.base_provider.validate_provider_ref(provider_ref)
+
+    def resolve_expiry(self, trading_days: list[DailyClosePoint], as_of_date: date, target_expiry_days: int) -> date:
+        return self.base_provider.resolve_expiry(trading_days, as_of_date, target_expiry_days)
+
+    def price_option(self, **kwargs: object) -> SyntheticOptionQuote:
+        return self.base_provider.price_option(**kwargs)
+
+    @staticmethod
+    def intrinsic_value(*, option_type: str, spot: float, strike: float) -> float:
+        return SyntheticHistoricalProvider.intrinsic_value(option_type=option_type, spot=spot, strike=strike)
+
+
 class BacktestPageService:
     def __init__(
         self,
         backtest_service: BacktestService | None = None,
         template_service: StrategyTemplateService | None = None,
     ) -> None:
-        self.template_service = template_service or StrategyTemplateService()
         base_service = backtest_service or BacktestService(
-            template_service=self.template_service,
+            template_service=template_service,
             provider=None,
         )
-        fixture_provider = SyntheticHistoricalProvider(
-            source=DeterministicBacktestFixtureSource(),
-            implied_volatility=base_service.provider.implied_volatility,
-            risk_free_rate=base_service.provider.risk_free_rate,
-        )
+        self.template_service = template_service or base_service.template_service
+        fixture_provider = FixtureBoundHistoricalProvider(base_service.provider)
         self.backtest_service = BacktestService(
             provider=fixture_provider,
             template_service=self.template_service,

tests/test_backtest_ui.py

@@ -230,7 +230,12 @@ def test_backtest_page_service_does_not_mutate_injected_backtest_service() -> No
     )
     injected_service = BacktestService(provider=provider)
 
-    BacktestPageService(backtest_service=injected_service)
+    page_service = BacktestPageService(backtest_service=injected_service)
 
     history = injected_service.provider.load_history("GLD", date(2024, 1, 3), date(2024, 1, 3))
     assert history[0].close == 123.0
+    assert page_service.template_service is injected_service.template_service
+    assert page_service.backtest_service.provider.implied_volatility == 0.2
+    assert page_service.backtest_service.provider.risk_free_rate == 0.01
+    seeded_history = page_service.backtest_service.provider.load_history("GLD", date(2024, 1, 2), date(2024, 1, 8))
+    assert seeded_history[0].close == 100.0