feat: align controlled AI sessions and MVP controls

backend/internal/logic/ai/gateway.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"time"
 
+	"gorm.io/gorm"
 	"gorm.io/gorm/clause"
 	"senlinai-agent/backend/internal/models"
 )
@@ -25,6 +26,11 @@ type SelectedKey struct {
 	KeyType  string
 }
 
+var (
+	ErrAIKeyMissing  = errors.New("no ai key available")
+	ErrAIRateLimited = errors.New("ai rate limit exceeded")
+)
+
 func NewGateway(systemKey string) *Gateway {
 	return NewGatewayWithSecret(systemKey, "development-ai-key-secret-change-me")
 }
@@ -47,15 +53,19 @@ func (g *Gateway) SaveUserKey(userID uint, provider string, apiKey string) error
 
 func (g *Gateway) SelectKey(userID uint) (SelectedKey, error) {
 	var userKey models.SenlinAgentAIKey
-	if err := models.DBService.Where("user_id = ?", userID).First(&userKey).Error; err == nil {
+	err := models.DBService.Where("user_id = ?", userID).First(&userKey).Error
+	if err == nil {
 		apiKey, err := decryptAPIKey(userKey.EncryptedAPIKey, g.encryptionSecret)
 		if err != nil {
 			return SelectedKey{}, err
 		}
 		return SelectedKey{Provider: userKey.Provider, APIKey: apiKey, KeyType: "user"}, nil
 	}
+	if !errors.Is(err, gorm.ErrRecordNotFound) {
+		return SelectedKey{}, err
+	}
 	if g.systemKey == "" {
-		return SelectedKey{}, errors.New("no ai key available")
+		return SelectedKey{}, ErrAIKeyMissing
 	}
 	return SelectedKey{Provider: "openai", APIKey: g.systemKey, KeyType: "system"}, nil
 }
@@ -82,7 +92,7 @@ func (g *Gateway) CheckRateLimit(userID uint, action string, limit int, window t
 		return err
 	}
 	if count >= int64(limit) {
-		return errors.New("ai rate limit exceeded")
+		return ErrAIRateLimited
 	}
 	return nil
 }