fix(pre-alpha): preserve injected provider identity

app/services/backtesting/ui_service.py

@@ -1,9 +1,11 @@
 from __future__ import annotations
 
+from copy import copy
 from dataclasses import dataclass
 from datetime import date
 from math import isclose
 
+from app.backtesting.engine import SyntheticBacktestEngine
 from app.domain.backtesting_math import materialize_backtest_portfolio_state
 from app.models.backtest import (
     BacktestRunResult,
@@ -102,10 +104,10 @@ class BacktestPageService:
         )
         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,
-        )
+        self.backtest_service = copy(base_service)
+        self.backtest_service.provider = fixture_provider
+        self.backtest_service.template_service = self.template_service
+        self.backtest_service.engine = SyntheticBacktestEngine(fixture_provider)
 
     def template_options(self, symbol: str = "GLD") -> list[dict[str, str | int]]:
         return [
@@ -209,7 +211,10 @@ class BacktestPageService:
             end_date=end_date,
             initial_portfolio=initial_portfolio,
             template_refs=(TemplateRef(slug=template.slug, version=template.version),),
-            provider_ref=ProviderRef(provider_id="synthetic_v1", pricing_mode="synthetic_bs_mid"),
+            provider_ref=ProviderRef(
+                provider_id=self.backtest_service.provider.provider_id,
+                pricing_mode=self.backtest_service.provider.pricing_mode,
+            ),
         )
         return BacktestPageRunResult(
             scenario=scenario,

tests/test_backtest_ui.py

@@ -235,7 +235,31 @@ def test_backtest_page_service_does_not_mutate_injected_backtest_service() -> No
     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 is not injected_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
+
+
+def test_backtest_page_service_uses_injected_provider_identity_in_provider_ref() -> None:
+    class CustomProvider(SyntheticHistoricalProvider):
+        provider_id = "custom_v1"
+        pricing_mode = "custom_mode"
+
+    provider = CustomProvider(source=StaticBacktestSource(), implied_volatility=0.2, risk_free_rate=0.01)
+    injected_service = BacktestService(provider=provider)
+    page_service = BacktestPageService(backtest_service=injected_service)
+
+    result = page_service.run_read_only_scenario(
+        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,
+    )
+
+    assert result.scenario.provider_ref.provider_id == "custom_v1"
+    assert result.scenario.provider_ref.pricing_mode == "custom_mode"