fix(pre-alpha): preserve injected backtest services

app/services/backtesting/ui_service.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass
 from datetime import date
+from math import isclose
 
 from app.domain.backtesting_math import materialize_backtest_portfolio_state
 from app.models.backtest import (
@@ -10,7 +11,7 @@ from app.models.backtest import (
     ProviderRef,
     TemplateRef,
 )
-from app.services.backtesting.historical_provider import DailyClosePoint
+from app.services.backtesting.historical_provider import DailyClosePoint, SyntheticHistoricalProvider
 from app.services.backtesting.service import BacktestService
 from app.services.strategy_templates import StrategyTemplateService
 
@@ -64,12 +65,19 @@ class BacktestPageService:
         template_service: StrategyTemplateService | None = None,
     ) -> None:
         self.template_service = template_service or StrategyTemplateService()
-        self.backtest_service = backtest_service or BacktestService(
+        base_service = backtest_service or BacktestService(
             template_service=self.template_service,
             provider=None,
         )
-        provider = self.backtest_service.provider
-        provider.source = DeterministicBacktestFixtureSource()
+        fixture_provider = SyntheticHistoricalProvider(
+            source=DeterministicBacktestFixtureSource(),
+            implied_volatility=base_service.provider.implied_volatility,
+            risk_free_rate=base_service.provider.risk_free_rate,
+        )
+        self.backtest_service = BacktestService(
+            provider=fixture_provider,
+            template_service=self.template_service,
+        )
 
     def template_options(self, symbol: str = "GLD") -> list[dict[str, str | int]]:
         return [
@@ -122,7 +130,12 @@ class BacktestPageService:
 
         self.template_service.get_template(template_slug)
         derived_entry_spot = self.derive_entry_spot(normalized_symbol, start_date, end_date)
-        if entry_spot is not None and entry_spot != derived_entry_spot:
+        if entry_spot is not None and not isclose(
+            entry_spot,
+            derived_entry_spot,
+            rel_tol=BacktestService.ENTRY_SPOT_REL_TOLERANCE,
+            abs_tol=BacktestService.ENTRY_SPOT_ABS_TOLERANCE,
+        ):
             raise ValueError(
                 f"Supplied entry spot ${entry_spot:,.2f} does not match derived historical entry spot ${derived_entry_spot:,.2f}"
             )

tests/helpers_backtest_sources.py

@@ -0,0 +1,10 @@
+from __future__ import annotations
+
+from datetime import date
+
+from app.services.backtesting.historical_provider import DailyClosePoint
+
+
+class StaticBacktestSource:
+    def load_daily_closes(self, symbol: str, start_date: date, end_date: date) -> list[DailyClosePoint]:
+        return [DailyClosePoint(date=date(2024, 1, 3), close=123.0)]

tests/test_backtest_ui.py

@@ -4,7 +4,10 @@ from datetime import date
 
 import pytest
 
+from app.services.backtesting.historical_provider import SyntheticHistoricalProvider
+from app.services.backtesting.service import BacktestService
 from app.services.backtesting.ui_service import BacktestPageService
+from tests.helpers_backtest_sources import StaticBacktestSource
 
 
 def test_backtest_page_service_uses_fixture_window_for_deterministic_run() -> None:
@@ -186,6 +189,23 @@ def test_backtest_preview_validation_requires_supported_fixture_window_even_with
         )
 
 
+def test_backtest_preview_validation_accepts_close_supplied_entry_spot() -> None:
+    service = BacktestPageService()
+
+    entry_spot = service.validate_preview_inputs(
+        symbol="GLD",
+        start_date=date(2024, 1, 2),
+        end_date=date(2024, 1, 8),
+        template_slug="protective-put-atm-12m",
+        underlying_units=1000.0,
+        loan_amount=68000.0,
+        margin_call_ltv=0.75,
+        entry_spot=100.005,
+    )
+
+    assert entry_spot == 100.0
+
+
 def test_backtest_preview_validation_rejects_mismatched_supplied_entry_spot() -> None:
     service = BacktestPageService()
 
@@ -200,3 +220,17 @@ def test_backtest_preview_validation_rejects_mismatched_supplied_entry_spot() ->
             margin_call_ltv=0.75,
             entry_spot=99.0,
         )
+
+
+def test_backtest_page_service_does_not_mutate_injected_backtest_service() -> None:
+    provider = SyntheticHistoricalProvider(
+        source=StaticBacktestSource(),
+        implied_volatility=0.2,
+        risk_free_rate=0.01,
+    )
+    injected_service = BacktestService(provider=provider)
+
+    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