feat: strategy builder

backend/routers/strategy_builder.py

@@ -5,7 +5,7 @@ from pydantic import BaseModel
 
 from services.option_chain import get_chain_slice
 from services.vol_surface import build_surface, apply_scenario
-from services.strategy_engine import payoff_curves
+from services.strategy_engine import payoff_curves, DEFAULT_CONTRACT_SIZE
 from services.strategy_optimizer import optimize as run_optimizer
 from services.database import (
     save_scenario, get_scenarios, delete_scenario,
@@ -34,6 +34,7 @@ class ScenarioIn(BaseModel):
     manual_grid: Optional[List[Dict[str, Any]]] = None
     rate: float = 0.05
     n_expiries: int = 3
+    contract_size: float = DEFAULT_CONTRACT_SIZE
 
 
 class PriceRequest(BaseModel):
@@ -121,6 +122,7 @@ def price(req: PriceRequest):
     result = payoff_curves(
         legs, chain_slice, surface_now, surface_scenario,
         req.scenario.horizon_days, req.scenario.rate,
+        contract_size=req.scenario.contract_size,
     )
     result["spot"] = chain_slice["spot"]
     result["scenario_spot"] = surface_scenario.spot
@@ -146,6 +148,7 @@ def optimize(req: OptimizeRequest):
             constraints=req.constraints.model_dump(),
             objective=req.constraints.objective,
             top_n=req.constraints.top_n,
+            contract_size=req.scenario.contract_size,
         )
     except Exception as e:
         import traceback