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,

app/pages/backtests.py

@@ -5,7 +5,7 @@ from datetime import date, datetime
 from fastapi.responses import RedirectResponse
 from nicegui import ui
 
-from app.domain.backtesting_math import asset_quantity_from_floats
+from app.domain.backtesting_math import asset_quantity_from_workspace_config
 from app.models.workspace import get_workspace_repository
 from app.pages.common import dashboard_page, render_workspace_recovery
 from app.services.backtesting.ui_service import BacktestPageRunResult, BacktestPageService
@@ -66,8 +66,8 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
     config = repo.load_portfolio_config(workspace_id) if workspace_id else None
     default_entry_spot = service.derive_entry_spot("GLD", date(2024, 1, 2), date(2024, 1, 8))
     default_units = (
-        asset_quantity_from_floats(float(config.gold_value or 0.0), default_entry_spot, "GLD")
-        if config and config.gold_value is not None and default_entry_spot > 0
+        asset_quantity_from_workspace_config(config, entry_spot=default_entry_spot, symbol="GLD")
+        if config is not None and default_entry_spot > 0
         else 1000.0
     )
     default_loan = float(config.loan_amount) if config else 68000.0
@@ -217,7 +217,7 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
                 )
             except (ValueError, KeyError):
                 return
-            units_input.value = asset_quantity_from_floats(float(config.gold_value), entry_spot, "GLD")
+            units_input.value = asset_quantity_from_workspace_config(config, entry_spot=entry_spot, symbol="GLD")
             entry_spot_hint.set_text(f"Auto-derived entry spot: ${entry_spot:,.2f}")
 
         def run_backtest() -> None:

app/pages/event_comparison.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 from fastapi.responses import RedirectResponse
 from nicegui import ui
 
-from app.domain.backtesting_math import asset_quantity_from_floats
+from app.domain.backtesting_math import asset_quantity_from_workspace_config
 from app.models.workspace import get_workspace_repository
 from app.pages.common import dashboard_page, render_workspace_recovery
 from app.services.event_comparison_ui import EventComparisonPageService
@@ -54,8 +54,8 @@ def _render_event_comparison_page(workspace_id: str | None = None) -> None:
         )
         default_entry_spot = default_preview.initial_portfolio.entry_spot
     default_units = (
-        asset_quantity_from_floats(float(config.gold_value or 0.0), default_entry_spot, "GLD")
-        if config and config.gold_value is not None and default_entry_spot > 0
+        asset_quantity_from_workspace_config(config, entry_spot=default_entry_spot, symbol="GLD")
+        if config is not None and default_entry_spot > 0
         else 1000.0
     )
 
@@ -129,7 +129,7 @@ def _render_event_comparison_page(workspace_id: str | None = None) -> None:
             template_select.value = list(service.default_template_selection(str(option["slug"])))
             try:
                 preview_units = float(units_input.value or 0.0)
-                if workspace_id and config is not None and config.gold_value is not None:
+                if workspace_id and config is not None:
                     preview_scenario = service.preview_scenario(
                         preset_slug=str(option["slug"]),
                         template_slugs=selected_template_slugs(),
@@ -137,10 +137,10 @@ def _render_event_comparison_page(workspace_id: str | None = None) -> None:
                         loan_amount=float(loan_input.value or 0.0),
                         margin_call_ltv=float(ltv_input.value or 0.0),
                     )
-                    preview_units = asset_quantity_from_floats(
-                        float(config.gold_value),
-                        float(preview_scenario.initial_portfolio.entry_spot),
-                        "GLD",
+                    preview_units = asset_quantity_from_workspace_config(
+                        config,
+                        entry_spot=float(preview_scenario.initial_portfolio.entry_spot),
+                        symbol="GLD",
                     )
                     units_input.value = preview_units
                 scenario = service.preview_scenario(