feat: strategy builder

backend/routers/strategy_builder.py

@@ -41,6 +41,12 @@ class ScenarioIn(BaseModel):
     # options (e.g. dte_min=20, dte_max=60) instead of horizon_days doing double duty.
     dte_min: Optional[int] = None
     dte_max: Optional[int] = None
+    # "Dériver d'un historique" mode: reconstruct the chain (and every leg strike drawn
+    # from it, including in /optimize) as it stood at/before this date instead of live —
+    # e.g. so the optimizer searches over what was ACTUALLY quoted on the day a realized
+    # scenario's window starts, not today's chain. None (default) = live, unchanged
+    # behavior for the normal Construire flow.
+    as_of: Optional[str] = None
 
     @property
     def shocked_rate(self) -> float:
@@ -118,7 +124,7 @@ class StrategySaveRequest(BaseModel):
 def _build_surfaces(scenario: ScenarioIn):
     chain_slice = get_chain_slice(
         scenario.symbol, scenario.horizon_days, scenario.n_expiries,
-        dte_min=scenario.dte_min, dte_max=scenario.dte_max,
+        dte_min=scenario.dte_min, dte_max=scenario.dte_max, as_of=scenario.as_of,
     )
     surface_now = build_surface(chain_slice)
     surface_scenario = apply_scenario(
@@ -206,6 +212,20 @@ def price(req: PriceRequest):
     return result
 
 
+@router.get("/realized-scenario")
+def realized_scenario(symbol: str = Query(...), start_date: str = Query(...), end_date: str = Query(...)):
+    """"Dériver d'un historique" mode: turns a real Du→Au window into scenario inputs
+    (spot_shock_pct/iv_level_shift/horizon_days) computed from what actually happened —
+    see services.realized_scenario. The frontend copies these into the normal scenario
+    state (same one Construire/optimize use) rather than this being a separate pricing
+    path of its own."""
+    from services.realized_scenario import compute_realized_scenario
+    try:
+        return compute_realized_scenario(symbol, start_date, end_date)
+    except ValueError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+
+
 @router.post("/suggested-profile")
 def suggested_profile(scenario: ScenarioIn):
     """Mode 1 of the scenario/profile/constraints split: what Greek behavior this scenario