feat: strategy builder

frontend/src/hooks/useApi.ts

@@ -1534,6 +1534,7 @@ export type StrategyScenario = {
   manual_grid?: ManualGridCell[]
   rate?: number
   n_expiries?: number
+  contract_size?: number
 }
 
 export type StrategyLeg = {

frontend/src/pages/StrategyBuilder.tsx

@@ -584,6 +584,7 @@ export default function StrategyBuilder() {
   const [horizonDays, setHorizonDays] = useState(8)
   const [scenario, setScenario] = useState<StrategyScenario>({
     symbol: '', horizon_days: 8, spot_shock_pct: 0, iv_level_shift: 0, skew_tilt: 0, term_shift: 0, manual_grid: [],
+    contract_size: 100_000,
   })
 
   // Chain lookup only commits on blur/Enter/datalist-pick, never mid-keystroke — typing
@@ -662,11 +663,11 @@ export default function StrategyBuilder() {
   const handleLoadScenario = (s: SavedScenario) => {
     setSymbol(s.symbol)
     setHorizonDays(s.horizon_days)
-    setScenario({
+    setScenario(prev => ({
       symbol: s.symbol, horizon_days: s.horizon_days, spot_shock_pct: s.spot_shock_pct,
       iv_level_shift: s.iv_level_shift, skew_tilt: s.skew_tilt, term_shift: s.term_shift,
-      manual_grid: s.manual_grid,
-    })
+      manual_grid: s.manual_grid, contract_size: prev.contract_size,
+    }))
   }
 
   const handleSaveStrategy = () => {
@@ -721,13 +722,24 @@ export default function StrategyBuilder() {
         <div className="card space-y-3">
           <div className="flex items-center justify-between">
             <div className="stat-label">Jambes (1-4) — Spot {chain.spot}</div>
-            <button
-              onClick={addLeg}
-              disabled={legs.length >= 4}
-              className="flex items-center gap-1 text-xs bg-blue-600 hover:bg-blue-500 disabled:opacity-40 text-white px-2.5 py-1 rounded"
-            >
-              <Plus className="w-3.5 h-3.5" /> Ajouter une jambe
-            </button>
+            <div className="flex items-center gap-3">
+              <label className="flex items-center gap-1.5 text-xs text-slate-400" title="Notionnel par contrat (ex. 100 000 = 1 lot standard EURUSD). S'applique à chaque jambe, multiplié par sa quantité.">
+                Nominal (USD)
+                <input
+                  type="number" step={1000} min={1}
+                  value={scenario.contract_size ?? 100_000}
+                  onChange={(e) => setScenario(s => ({ ...s, contract_size: parseFloat(e.target.value) || 100_000 }))}
+                  className="w-28 bg-dark-700 border border-slate-700/50 rounded px-2 py-1 text-slate-200"
+                />
+              </label>
+              <button
+                onClick={addLeg}
+                disabled={legs.length >= 4}
+                className="flex items-center gap-1 text-xs bg-blue-600 hover:bg-blue-500 disabled:opacity-40 text-white px-2.5 py-1 rounded"
+              >
+                <Plus className="w-3.5 h-3.5" /> Ajouter une jambe
+              </button>
+            </div>
           </div>
           <div className="space-y-2">
             {legs.map((leg, i) => (