feat(PRICING-001): add GLD expense ratio decay correction

tests/test_backtesting_units.py

@@ -50,6 +50,11 @@ def test_asset_quantity_from_floats_matches_workspace_backtest_conversion() -> N
 
 
 def test_asset_quantity_from_workspace_config_uses_instrument_weight_conversion_for_gld() -> None:
+    """GLD shares are calculated using expense-adjusted backing (~0.0916 oz/share in 2026)."""
+    from datetime import date
+
+    from app.domain.instruments import gld_ounces_per_share
+
     config = PortfolioConfig(
         gold_ounces=220.0,
         entry_price=4400.0,
@@ -60,7 +65,12 @@ def test_asset_quantity_from_workspace_config_uses_instrument_weight_conversion_
 
     quantity = asset_quantity_from_workspace_config(config, entry_spot=100.0, symbol="GLD")
 
-    assert quantity == 2200.0
+    # 220 oz / 0.091576... oz/share ≈ 2402.37 shares (NOT 2200 with old 0.1 ratio)
+    current_backing = float(gld_ounces_per_share(date.today()))
+    expected_shares = 220.0 / current_backing
+    assert abs(quantity - expected_shares) < 0.0001
+    # Verify it's more than the old 2200 shares
+    assert quantity > 2200.0
 
 
 def test_materialize_backtest_portfolio_state_uses_typed_asset_boundary() -> None: