feat: strategy builder

backend/services/strategy_engine.py

@@ -18,6 +18,24 @@ from services.vol_surface import Surface, ScenarioSurface
 DEFAULT_SPREAD_PCT = 0.05  # fallback relative bid/ask spread when no live quote is found
 
 
+def to_native(obj: Any) -> Any:
+    """Recursively converts numpy scalars (bool_, int64, float64, ...) to native Python
+    types. Comparisons/aggregations over numpy-typed inputs (e.g. bid/ask sourced from a
+    DB row that came back as a numpy type, or scipy's norm.cdf) can leave a stray
+    numpy.bool_/numpy.float64 buried in a nested result — FastAPI's default JSON encoder
+    doesn't know those types and fails ('X object is not iterable', then a secondary
+    'vars() argument must have __dict__ attribute' from its own fallback). Applied once
+    at the API boundary (price_combo/payoff_curves/optimizer results) rather than chasing
+    the exact field through the whole pricing pipeline."""
+    if isinstance(obj, dict):
+        return {k: to_native(v) for k, v in obj.items()}
+    if isinstance(obj, (list, tuple)):
+        return [to_native(v) for v in obj]
+    if isinstance(obj, np.generic):
+        return obj.item()
+    return obj
+
+
 def _sign(leg: Dict[str, Any]) -> int:
     return 1 if leg.get("position", "long") == "long" else -1
 
@@ -131,7 +149,7 @@ def price_combo(
     delta_now = greeks_at(legs, spot_now, 0, surface_now, r)["delta"]
     delta_scenario = greeks_at(legs, spot_scenario, horizon_days, surface_scenario, r)["delta"]
 
-    return {
+    return to_native({
         "entry_cost": round(entry_ref, 2),
         "entry_cost_mid": round(entry_ref_mid, 2),
         "scenario_value": round(scenario_exec, 2),
@@ -145,7 +163,7 @@ def price_combo(
         "greeks_scenario": greeks_at(legs, spot_scenario, horizon_days, surface_scenario, r),
         "net_delta_now": delta_now,
         "net_delta_scenario": delta_scenario,
-    }
+    })
 
 
 def check_bounded_risk(legs: List[Dict[str, Any]], entry_ref: float, surface: Any, spot: float) -> Dict[str, Any]: