fix(CORE-002C): align historical units with workspace weight

app/domain/backtesting_math.py

@@ -3,8 +3,9 @@ from __future__ import annotations
 from dataclasses import dataclass
 from decimal import Decimal
 
-from app.domain.units import BaseCurrency, Money, _coerce_currency, decimal_from_float, to_decimal
+from app.domain.units import BaseCurrency, Money, Weight, WeightUnit, _coerce_currency, decimal_from_float, to_decimal
 from app.models.backtest import BacktestPortfolioState
+from app.models.portfolio import PortfolioConfig
 
 
 @dataclass(frozen=True, slots=True)
@@ -94,6 +95,23 @@ def asset_quantity_from_floats(portfolio_value: float, entry_spot: float, symbol
     return float(asset_quantity_from_money(notional, spot).amount)
 
 
+def asset_quantity_from_workspace_config(config: PortfolioConfig, *, entry_spot: float, symbol: str) -> float:
+    if config.gold_ounces is not None and config.gold_ounces > 0:
+        try:
+            from app.domain.instruments import asset_quantity_from_weight
+
+            quantity = asset_quantity_from_weight(
+                symbol,
+                Weight(amount=decimal_from_float(float(config.gold_ounces)), unit=WeightUnit.OUNCE_TROY),
+            )
+            return float(quantity.amount)
+        except ValueError:
+            pass
+    if config.gold_value is not None:
+        return asset_quantity_from_floats(float(config.gold_value), entry_spot, symbol)
+    raise ValueError("Workspace config must provide collateral weight or value")
+
+
 def materialize_backtest_portfolio_state(
     *,
     symbol: str,