refactor(pre-alpha): fail closed on historical preview fallbacks

app/pages/backtests.py

@@ -289,9 +289,9 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
                         row_key="date",
                     ).classes("w-full")
 
-        def validate_current_scenario() -> str | None:
+        def validate_current_scenario(*, entry_spot: float | None = None) -> str | None:
             try:
-                service.run_read_only_scenario(
+                service.validate_preview_inputs(
                     symbol=str(symbol_input.value or ""),
                     start_date=parse_iso_date(start_input.value, "Start date"),
                     end_date=parse_iso_date(end_input.value, "End date"),
@@ -299,6 +299,7 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
                     underlying_units=float(units_input.value or 0.0),
                     loan_amount=float(loan_input.value or 0.0),
                     margin_call_ltv=float(ltv_input.value or 0.0),
+                    entry_spot=entry_spot,
                 )
             except (ValueError, KeyError) as exc:
                 return str(exc)
@@ -320,12 +321,7 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
         def refresh_workspace_seeded_units() -> None:
             validation_label.set_text("")
             entry_spot, entry_error = derive_entry_spot()
-            if (
-                workspace_id
-                and config is not None
-                and config.gold_value is not None
-                and entry_spot is not None
-            ):
+            if workspace_id and config is not None and config.gold_value is not None and entry_spot is not None:
                 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}")
             else:
@@ -335,7 +331,7 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
                 validation_label.set_text(entry_error)
                 render_result_state("Scenario validation failed", entry_error, tone="warning")
                 return
-            validation_error = validate_current_scenario()
+            validation_error = validate_current_scenario(entry_spot=entry_spot)
             if validation_error:
                 validation_label.set_text(validation_error)
                 render_result_state("Scenario validation failed", validation_error, tone="warning")
@@ -351,7 +347,7 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
                 validation_label.set_text(entry_error)
                 render_result_state("Scenario validation failed", entry_error, tone="warning")
                 return
-            validation_error = validate_current_scenario()
+            validation_error = validate_current_scenario(entry_spot=entry_spot)
             if validation_error:
                 validation_label.set_text(validation_error)
                 render_result_state("Scenario validation failed", validation_error, tone="warning")
@@ -371,12 +367,18 @@ def _render_backtests_page(workspace_id: str | None = None) -> None:
                     margin_call_ltv=float(ltv_input.value or 0.0),
                 )
             except (ValueError, KeyError) as exc:
-                render_seeded_summary(entry_spot=None, entry_spot_error=None)
+                entry_spot, entry_error = derive_entry_spot()
+                render_seeded_summary(entry_spot=entry_spot, entry_spot_error=entry_error)
+                if entry_spot is None:
+                    entry_spot_hint.set_text("Entry spot unavailable until the scenario dates are valid.")
                 validation_label.set_text(str(exc))
                 render_result_state("Scenario validation failed", str(exc), tone="warning")
                 return
             except Exception:
-                render_seeded_summary(entry_spot=None, entry_spot_error=None)
+                entry_spot, entry_error = derive_entry_spot()
+                render_seeded_summary(entry_spot=entry_spot, entry_spot_error=entry_error)
+                if entry_spot is None:
+                    entry_spot_hint.set_text("Entry spot unavailable until the scenario dates are valid.")
                 message = "Backtest failed. Please verify the scenario inputs and try again."
                 logger.exception(
                     "Backtest page run failed for workspace=%s symbol=%s start=%s end=%s template=%s units=%s loan=%s margin_call_ltv=%s",

app/pages/event_comparison.py

@@ -203,13 +203,6 @@ def _render_event_comparison_page(workspace_id: str | None = None) -> None:
                     syncing_controls["value"] = False
 
             template_slugs = selected_template_slugs()
-            if not template_slugs:
-                template_slugs = tuple(service.default_template_selection(str(option["slug"])))
-                syncing_controls["value"] = True
-                try:
-                    template_select.value = list(template_slugs)
-                finally:
-                    syncing_controls["value"] = False
 
             try:
                 preview_units = float(units_input.value or 0.0)
@@ -243,6 +236,21 @@ def _render_event_comparison_page(workspace_id: str | None = None) -> None:
                 scenario_label.set_text(str(exc))
                 render_selected_summary(entry_spot=None, entry_spot_error=str(exc))
                 return str(exc)
+            except Exception:
+                logger.exception(
+                    "Event comparison preview failed for workspace=%s preset=%s templates=%s units=%s loan=%s margin_call_ltv=%s",
+                    workspace_id,
+                    preset_select.value,
+                    selected_template_slugs(),
+                    units_input.value,
+                    loan_input.value,
+                    ltv_input.value,
+                )
+                message = "Event comparison preview failed. Please verify the seeded inputs and try again."
+                metadata_label.set_text(f"Preset: {option['label']} — {option['description']}")
+                scenario_label.set_text(message)
+                render_selected_summary(entry_spot=None, entry_spot_error=message)
+                return message
             preset = service.event_preset_service.get_preset(str(option["slug"]))
             metadata_label.set_text(f"Preset: {option['label']} — {option['description']}")
             scenario_label.set_text(
@@ -261,15 +269,7 @@ def _render_event_comparison_page(workspace_id: str | None = None) -> None:
         def render_report() -> None:
             validation_label.set_text("")
             result_panel.clear()
-            option = preset_lookup.get(str(preset_select.value or ""))
             template_slugs = selected_template_slugs()
-            if option is not None and not template_slugs:
-                template_slugs = tuple(service.default_template_selection(str(option["slug"])))
-                syncing_controls["value"] = True
-                try:
-                    template_select.value = list(template_slugs)
-                finally:
-                    syncing_controls["value"] = False
             try:
                 report = service.run_read_only_comparison(
                     preset_slug=str(preset_select.value or ""),

app/services/backtesting/ui_service.py

@@ -98,7 +98,7 @@ class BacktestPageService:
             )
         return history[0].close
 
-    def run_read_only_scenario(
+    def validate_preview_inputs(
         self,
         *,
         symbol: str,
@@ -108,7 +108,8 @@ class BacktestPageService:
         underlying_units: float,
         loan_amount: float,
         margin_call_ltv: float,
-    ) -> BacktestPageRunResult:
+        entry_spot: float | None = None,
+    ) -> float:
         normalized_symbol = symbol.strip().upper()
         if not normalized_symbol:
             raise ValueError("Symbol is required")
@@ -125,9 +126,35 @@ class BacktestPageService:
         if not template_slug:
             raise ValueError("Template selection is required")
 
+        self.template_service.get_template(template_slug)
+        resolved_entry_spot = (
+            entry_spot if entry_spot is not None else self.derive_entry_spot(normalized_symbol, start_date, end_date)
+        )
+        _validate_initial_collateral(underlying_units, resolved_entry_spot, loan_amount)
+        return resolved_entry_spot
+
+    def run_read_only_scenario(
+        self,
+        *,
+        symbol: str,
+        start_date: date,
+        end_date: date,
+        template_slug: str,
+        underlying_units: float,
+        loan_amount: float,
+        margin_call_ltv: float,
+    ) -> BacktestPageRunResult:
+        normalized_symbol = symbol.strip().upper()
+        entry_spot = self.validate_preview_inputs(
+            symbol=normalized_symbol,
+            start_date=start_date,
+            end_date=end_date,
+            template_slug=template_slug,
+            underlying_units=underlying_units,
+            loan_amount=loan_amount,
+            margin_call_ltv=margin_call_ltv,
+        )
         template = self.template_service.get_template(template_slug)
-        entry_spot = self.derive_entry_spot(normalized_symbol, start_date, end_date)
-        _validate_initial_collateral(underlying_units, entry_spot, loan_amount)
         initial_portfolio = materialize_backtest_portfolio_state(
             symbol=normalized_symbol,
             underlying_units=underlying_units,

app/services/event_comparison_ui.py

@@ -114,6 +114,8 @@ class EventComparisonPageService:
         loan_amount: float,
         margin_call_ltv: float,
     ) -> BacktestScenario:
+        if not template_slugs:
+            raise ValueError("Select at least one strategy template.")
         try:
             scenario = self.comparison_service.preview_scenario_from_inputs(
                 preset_slug=preset_slug,
@@ -147,6 +149,8 @@ class EventComparisonPageService:
     ) -> EventComparisonReport:
         if not preset_slug:
             raise ValueError("Preset selection is required")
+        if not template_slugs:
+            raise ValueError("Select at least one strategy template.")
         if underlying_units <= 0:
             raise ValueError("Underlying units must be positive")
         if loan_amount < 0:
@@ -162,7 +166,7 @@ class EventComparisonPageService:
         try:
             preview = self.comparison_service.preview_scenario_from_inputs(
                 preset_slug=preset.slug,
-                template_slugs=tuple(template_slugs or preset.scenario_overrides.default_template_slugs),
+                template_slugs=template_slugs,
                 underlying_units=underlying_units,
                 loan_amount=loan_amount,
                 margin_call_ltv=margin_call_ltv,
@@ -180,7 +184,7 @@ class EventComparisonPageService:
         _validate_initial_collateral(underlying_units, preview.initial_portfolio.entry_spot, loan_amount)
         return self.comparison_service.compare_event_from_inputs(
             preset_slug=preset.slug,
-            template_slugs=tuple(template_slugs or preset.scenario_overrides.default_template_slugs),
+            template_slugs=template_slugs,
             underlying_units=underlying_units,
             loan_amount=loan_amount,
             margin_call_ltv=margin_call_ltv,

docs/roadmap/ROADMAP.yaml

@@ -10,6 +10,8 @@ notes:
   - The roadmap source of truth is this index plus the per-task YAML files in the status folders.
   - One task lives in one YAML file and changes state by moving between status folders.
   - Priority ordering is maintained here so agents can parse one short file first.
+  - Pre-alpha policy: we may cut or replace old features without backward compatibility until alpha is declared.
+  - Alpha migration policy: once alpha is declared, compatibility only needs to move forward; backward migrations are not required.
 priority_queue:
   - CORE-001D
   - BT-003B

tests/test_event_comparison_ui.py

@@ -32,23 +32,26 @@ def test_event_comparison_page_service_runs_seeded_gld_preset_deterministically(
     )
 
 
-def test_event_comparison_page_service_uses_preset_default_templates_when_none_selected() -> None:
+def test_event_comparison_page_service_rejects_empty_template_selection() -> None:
     service = EventComparisonPageService()
 
-    report = service.run_read_only_comparison(
-        preset_slug="gld-jan-2024-selloff",
-        template_slugs=(),
-        underlying_units=1000.0,
-        loan_amount=68000.0,
-        margin_call_ltv=0.75,
-    )
+    with pytest.raises(ValueError, match="Select at least one strategy template"):
+        service.run_read_only_comparison(
+            preset_slug="gld-jan-2024-selloff",
+            template_slugs=(),
+            underlying_units=1000.0,
+            loan_amount=68000.0,
+            margin_call_ltv=0.75,
+        )
 
-    assert [item.template_slug for item in report.rankings] == [
-        "protective-put-atm-12m",
-        "ladder-50-50-atm-95pct-12m",
-        "protective-put-95pct-12m",
-        "protective-put-90pct-12m",
-    ]
+    with pytest.raises(ValueError, match="Select at least one strategy template"):
+        service.preview_scenario(
+            preset_slug="gld-jan-2024-selloff",
+            template_slugs=(),
+            underlying_units=1000.0,
+            loan_amount=68000.0,
+            margin_call_ltv=0.75,
+        )
 
 
 def test_event_comparison_page_service_exposes_seeded_preset_options() -> None: