feat(BT-002): add historical snapshot provider

tests/test_event_comparison_ui.py

@@ -148,6 +148,21 @@ def test_event_comparison_page_service_preview_uses_same_materialization_path()
     assert [ref.slug for ref in scenario.template_refs] == ["protective-put-atm-12m"]
 
 
+def test_event_comparison_page_service_derives_entry_spot_without_caller_collateral_validation() -> None:
+    service = EventComparisonPageService()
+
+    entry_spot = service.derive_entry_spot(
+        preset_slug="gld-jan-2024-drawdown",
+        template_slugs=(
+            "protective-put-atm-12m",
+            "ladder-50-50-atm-95pct-12m",
+            "ladder-33-33-33-atm-95pct-90pct-12m",
+        ),
+    )
+
+    assert entry_spot == 100.0
+
+
 def test_event_comparison_page_service_rejects_undercollateralized_historical_start() -> None:
     service = EventComparisonPageService()