tenth version

internal/position/manager.go

@@ -2,6 +2,8 @@ package position
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"time"
 
 	"github.com/shopspring/decimal"
@@ -11,6 +13,8 @@ import (
 	"overnight-trading-bot/internal/repository"
 )
 
+var ErrExitFillExceedsPositionLots = errors.New("exit fill exceeds local position lots")
+
 type Manager struct {
 	repo repository.Repository
 }
@@ -109,7 +113,21 @@ func (m Manager) OnExitFill(ctx context.Context, pos domain.Position, exitOrder
 	if lot <= 0 {
 		lot = 1
 	}
-	executedLots := min(exitOrder.FilledLots, pos.Lots)
+	if exitOrder.FilledLots > pos.Lots {
+		err := fmt.Errorf("%w: filled_lots=%d position_lots=%d instrument_uid=%s", ErrExitFillExceedsPositionLots, exitOrder.FilledLots, pos.Lots, pos.InstrumentUID)
+		if m.repo != nil {
+			_ = m.repo.InsertRiskEvent(ctx, domain.RiskEvent{
+				TS:            now,
+				Severity:      domain.SeverityCritical,
+				EventType:     "exit_overfill",
+				InstrumentUID: pos.InstrumentUID,
+				Message:       err.Error(),
+				ContextJSON:   fmt.Sprintf(`{"filled_lots":%d,"position_lots":%d}`, exitOrder.FilledLots, pos.Lots),
+			})
+		}
+		return pos, err
+	}
+	executedLots := exitOrder.FilledLots
 	if executedLots < 0 {
 		executedLots = 0
 	}

internal/position/manager_test.go

@@ -2,6 +2,7 @@ package position
 
 import (
 	"context"
+	"errors"
 	"testing"
 	"time"
 
@@ -183,3 +184,34 @@ func TestOnExitFillUsesLotInRealizedEdgeCommissionBase(t *testing.T) {
 		t.Fatalf("realized edge=%s, want -10 bps", updated.RealizedEdgeBps)
 	}
 }
+
+func TestOnExitFillRejectsOverfillWithCriticalRiskEvent(t *testing.T) {
+	ctx := context.Background()
+	repo := testutil.NewMemoryRepository()
+	manager := NewManager(repo)
+	openAt := time.Now().UTC()
+	pos := domain.Position{
+		AccountIDHash: "hash",
+		InstrumentUID: "uid",
+		OpenTradeDate: openAt,
+		Lots:          3,
+		Lot:           1,
+		AvgBuyPrice:   decimal.NewFromInt(100),
+		Status:        domain.PositionHoldingOvernight,
+		OpenedAt:      &openAt,
+	}
+	updated, err := manager.OnExitFill(ctx, pos, domain.Order{
+		InstrumentUID: "uid",
+		FilledLots:    5,
+		AvgFillPrice:  decimal.NewFromInt(110),
+	})
+	if !errors.Is(err, ErrExitFillExceedsPositionLots) {
+		t.Fatalf("err=%v, want ErrExitFillExceedsPositionLots", err)
+	}
+	if updated.Lots != 3 || updated.Status != domain.PositionHoldingOvernight {
+		t.Fatalf("position was mutated despite overfill: %+v", updated)
+	}
+	if len(repo.RiskEvents) != 1 || repo.RiskEvents[0].Severity != domain.SeverityCritical || repo.RiskEvents[0].EventType != "exit_overfill" {
+		t.Fatalf("risk events=%+v, want one critical exit_overfill", repo.RiskEvents)
+	}
+}