fix(clients): derive edit-form flow from per-inbound override

SyncInbound runs once per inbound and unconditionally overwrites the canonical clients.Flow column. A non-flow inbound (Hysteria, WS, gRPC) strips flow to "", so when it syncs after a VLESS Reality inbound the column is wiped, and the hydrate endpoint returned that empty value — the edit form loaded a blank flow for multi-inbound clients (#4792).

Derive the hydrate flow from the first flow-capable client_inbounds.flow_override instead, which is always correct and order-independent. A non-empty guard in SyncInbound was rejected because it would make flow impossible to clear.

Closes #4792

web/service/client.go

@@ -316,6 +316,32 @@ func (s *ClientService) GetRecordByEmail(tx *gorm.DB, email string) (*model.Clie
 	return row, nil
 }
 
+// EffectiveFlow returns the client's flow from the first flow-capable inbound
+// it is attached to (lowest inbound_id with a non-empty flow_override). The
+// canonical clients.Flow column is unreliable for multi-inbound clients: a
+// non-flow inbound (Hysteria, WS, gRPC, …) carries an empty flow and, when its
+// SyncInbound runs last, overwrites the column to "" even though a VLESS Reality
+// inbound stored a real flow. The per-inbound flow_override is always correct,
+// so derive the display flow from it (order-independent). See issue #4792.
+func (s *ClientService) EffectiveFlow(tx *gorm.DB, recordId int) (string, error) {
+	if tx == nil {
+		tx = database.GetDB()
+	}
+	var flows []string
+	err := tx.Model(&model.ClientInbound{}).
+		Where("client_id = ? AND flow_override <> ?", recordId, "").
+		Order("inbound_id ASC").
+		Limit(1).
+		Pluck("flow_override", &flows).Error
+	if err != nil {
+		return "", err
+	}
+	if len(flows) == 0 {
+		return "", nil
+	}
+	return flows[0], nil
+}
+
 func (s *ClientService) GetInboundIdsForEmail(tx *gorm.DB, email string) ([]int, error) {
 	if tx == nil {
 		tx = database.GetDB()