Add invalid-request fallback routing

backend/ent/group.go

@@ -56,6 +56,8 @@ type Group struct {
 	ClaudeCodeOnly bool `json:"claude_code_only,omitempty"`
 	// 非 Claude Code 请求降级使用的分组 ID
 	FallbackGroupID *int64 `json:"fallback_group_id,omitempty"`
+	// 无效请求兜底使用的分组 ID
+	FallbackGroupIDOnInvalidRequest *int64 `json:"fallback_group_id_on_invalid_request,omitempty"`
 	// 模型路由配置：模型模式 -> 优先账号ID列表
 	ModelRouting map[string][]int64 `json:"model_routing,omitempty"`
 	// 是否启用模型路由配置
@@ -172,7 +174,7 @@ func (*Group) scanValues(columns []string) ([]any, error) {
 			values[i] = new(sql.NullBool)
 		case group.FieldRateMultiplier, group.FieldDailyLimitUsd, group.FieldWeeklyLimitUsd, group.FieldMonthlyLimitUsd, group.FieldImagePrice1k, group.FieldImagePrice2k, group.FieldImagePrice4k:
 			values[i] = new(sql.NullFloat64)
-		case group.FieldID, group.FieldDefaultValidityDays, group.FieldFallbackGroupID:
+		case group.FieldID, group.FieldDefaultValidityDays, group.FieldFallbackGroupID, group.FieldFallbackGroupIDOnInvalidRequest:
 			values[i] = new(sql.NullInt64)
 		case group.FieldName, group.FieldDescription, group.FieldStatus, group.FieldPlatform, group.FieldSubscriptionType:
 			values[i] = new(sql.NullString)
@@ -322,6 +324,13 @@ func (_m *Group) assignValues(columns []string, values []any) error {
 				_m.FallbackGroupID = new(int64)
 				*_m.FallbackGroupID = value.Int64
 			}
+		case group.FieldFallbackGroupIDOnInvalidRequest:
+			if value, ok := values[i].(*sql.NullInt64); !ok {
+				return fmt.Errorf("unexpected type %T for field fallback_group_id_on_invalid_request", values[i])
+			} else if value.Valid {
+				_m.FallbackGroupIDOnInvalidRequest = new(int64)
+				*_m.FallbackGroupIDOnInvalidRequest = value.Int64
+			}
 		case group.FieldModelRouting:
 			if value, ok := values[i].(*[]byte); !ok {
 				return fmt.Errorf("unexpected type %T for field model_routing", values[i])
@@ -487,6 +496,11 @@ func (_m *Group) String() string {
 		builder.WriteString(fmt.Sprintf("%v", *v))
 	}
 	builder.WriteString(", ")
+	if v := _m.FallbackGroupIDOnInvalidRequest; v != nil {
+		builder.WriteString("fallback_group_id_on_invalid_request=")
+		builder.WriteString(fmt.Sprintf("%v", *v))
+	}
+	builder.WriteString(", ")
 	builder.WriteString("model_routing=")
 	builder.WriteString(fmt.Sprintf("%v", _m.ModelRouting))
 	builder.WriteString(", ")

backend/ent/group/group.go

@@ -53,6 +53,8 @@ const (
 	FieldClaudeCodeOnly = "claude_code_only"
 	// FieldFallbackGroupID holds the string denoting the fallback_group_id field in the database.
 	FieldFallbackGroupID = "fallback_group_id"
+	// FieldFallbackGroupIDOnInvalidRequest holds the string denoting the fallback_group_id_on_invalid_request field in the database.
+	FieldFallbackGroupIDOnInvalidRequest = "fallback_group_id_on_invalid_request"
 	// FieldModelRouting holds the string denoting the model_routing field in the database.
 	FieldModelRouting = "model_routing"
 	// FieldModelRoutingEnabled holds the string denoting the model_routing_enabled field in the database.
@@ -151,6 +153,7 @@ var Columns = []string{
 	FieldImagePrice4k,
 	FieldClaudeCodeOnly,
 	FieldFallbackGroupID,
+	FieldFallbackGroupIDOnInvalidRequest,
 	FieldModelRouting,
 	FieldModelRoutingEnabled,
 }
@@ -317,6 +320,11 @@ func ByFallbackGroupID(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldFallbackGroupID, opts...).ToFunc()
 }
 
+// ByFallbackGroupIDOnInvalidRequest orders the results by the fallback_group_id_on_invalid_request field.
+func ByFallbackGroupIDOnInvalidRequest(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldFallbackGroupIDOnInvalidRequest, opts...).ToFunc()
+}
+
 // ByModelRoutingEnabled orders the results by the model_routing_enabled field.
 func ByModelRoutingEnabled(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldModelRoutingEnabled, opts...).ToFunc()

backend/ent/group/where.go

@@ -150,6 +150,11 @@ func FallbackGroupID(v int64) predicate.Group {
 	return predicate.Group(sql.FieldEQ(FieldFallbackGroupID, v))
 }
 
+// FallbackGroupIDOnInvalidRequest applies equality check predicate on the "fallback_group_id_on_invalid_request" field. It's identical to FallbackGroupIDOnInvalidRequestEQ.
+func FallbackGroupIDOnInvalidRequest(v int64) predicate.Group {
+	return predicate.Group(sql.FieldEQ(FieldFallbackGroupIDOnInvalidRequest, v))
+}
+
 // ModelRoutingEnabled applies equality check predicate on the "model_routing_enabled" field. It's identical to ModelRoutingEnabledEQ.
 func ModelRoutingEnabled(v bool) predicate.Group {
 	return predicate.Group(sql.FieldEQ(FieldModelRoutingEnabled, v))
@@ -1070,6 +1075,56 @@ func FallbackGroupIDNotNil() predicate.Group {
 	return predicate.Group(sql.FieldNotNull(FieldFallbackGroupID))
 }
 
+// FallbackGroupIDOnInvalidRequestEQ applies the EQ predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestEQ(v int64) predicate.Group {
+	return predicate.Group(sql.FieldEQ(FieldFallbackGroupIDOnInvalidRequest, v))
+}
+
+// FallbackGroupIDOnInvalidRequestNEQ applies the NEQ predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestNEQ(v int64) predicate.Group {
+	return predicate.Group(sql.FieldNEQ(FieldFallbackGroupIDOnInvalidRequest, v))
+}
+
+// FallbackGroupIDOnInvalidRequestIn applies the In predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestIn(vs ...int64) predicate.Group {
+	return predicate.Group(sql.FieldIn(FieldFallbackGroupIDOnInvalidRequest, vs...))
+}
+
+// FallbackGroupIDOnInvalidRequestNotIn applies the NotIn predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestNotIn(vs ...int64) predicate.Group {
+	return predicate.Group(sql.FieldNotIn(FieldFallbackGroupIDOnInvalidRequest, vs...))
+}
+
+// FallbackGroupIDOnInvalidRequestGT applies the GT predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestGT(v int64) predicate.Group {
+	return predicate.Group(sql.FieldGT(FieldFallbackGroupIDOnInvalidRequest, v))
+}
+
+// FallbackGroupIDOnInvalidRequestGTE applies the GTE predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestGTE(v int64) predicate.Group {
+	return predicate.Group(sql.FieldGTE(FieldFallbackGroupIDOnInvalidRequest, v))
+}
+
+// FallbackGroupIDOnInvalidRequestLT applies the LT predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestLT(v int64) predicate.Group {
+	return predicate.Group(sql.FieldLT(FieldFallbackGroupIDOnInvalidRequest, v))
+}
+
+// FallbackGroupIDOnInvalidRequestLTE applies the LTE predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestLTE(v int64) predicate.Group {
+	return predicate.Group(sql.FieldLTE(FieldFallbackGroupIDOnInvalidRequest, v))
+}
+
+// FallbackGroupIDOnInvalidRequestIsNil applies the IsNil predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestIsNil() predicate.Group {
+	return predicate.Group(sql.FieldIsNull(FieldFallbackGroupIDOnInvalidRequest))
+}
+
+// FallbackGroupIDOnInvalidRequestNotNil applies the NotNil predicate on the "fallback_group_id_on_invalid_request" field.
+func FallbackGroupIDOnInvalidRequestNotNil() predicate.Group {
+	return predicate.Group(sql.FieldNotNull(FieldFallbackGroupIDOnInvalidRequest))
+}
+
 // ModelRoutingIsNil applies the IsNil predicate on the "model_routing" field.
 func ModelRoutingIsNil() predicate.Group {
 	return predicate.Group(sql.FieldIsNull(FieldModelRouting))

backend/ent/group_create.go

@@ -286,6 +286,20 @@ func (_c *GroupCreate) SetNillableFallbackGroupID(v *int64) *GroupCreate {
 	return _c
 }
 
+// SetFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field.
+func (_c *GroupCreate) SetFallbackGroupIDOnInvalidRequest(v int64) *GroupCreate {
+	_c.mutation.SetFallbackGroupIDOnInvalidRequest(v)
+	return _c
+}
+
+// SetNillableFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field if the given value is not nil.
+func (_c *GroupCreate) SetNillableFallbackGroupIDOnInvalidRequest(v *int64) *GroupCreate {
+	if v != nil {
+		_c.SetFallbackGroupIDOnInvalidRequest(*v)
+	}
+	return _c
+}
+
 // SetModelRouting sets the "model_routing" field.
 func (_c *GroupCreate) SetModelRouting(v map[string][]int64) *GroupCreate {
 	_c.mutation.SetModelRouting(v)
@@ -640,6 +654,10 @@ func (_c *GroupCreate) createSpec() (*Group, *sqlgraph.CreateSpec) {
 		_spec.SetField(group.FieldFallbackGroupID, field.TypeInt64, value)
 		_node.FallbackGroupID = &value
 	}
+	if value, ok := _c.mutation.FallbackGroupIDOnInvalidRequest(); ok {
+		_spec.SetField(group.FieldFallbackGroupIDOnInvalidRequest, field.TypeInt64, value)
+		_node.FallbackGroupIDOnInvalidRequest = &value
+	}
 	if value, ok := _c.mutation.ModelRouting(); ok {
 		_spec.SetField(group.FieldModelRouting, field.TypeJSON, value)
 		_node.ModelRouting = value
@@ -1128,6 +1146,30 @@ func (u *GroupUpsert) ClearFallbackGroupID() *GroupUpsert {
 	return u
 }
 
+// SetFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsert) SetFallbackGroupIDOnInvalidRequest(v int64) *GroupUpsert {
+	u.Set(group.FieldFallbackGroupIDOnInvalidRequest, v)
+	return u
+}
+
+// UpdateFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field to the value that was provided on create.
+func (u *GroupUpsert) UpdateFallbackGroupIDOnInvalidRequest() *GroupUpsert {
+	u.SetExcluded(group.FieldFallbackGroupIDOnInvalidRequest)
+	return u
+}
+
+// AddFallbackGroupIDOnInvalidRequest adds v to the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsert) AddFallbackGroupIDOnInvalidRequest(v int64) *GroupUpsert {
+	u.Add(group.FieldFallbackGroupIDOnInvalidRequest, v)
+	return u
+}
+
+// ClearFallbackGroupIDOnInvalidRequest clears the value of the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsert) ClearFallbackGroupIDOnInvalidRequest() *GroupUpsert {
+	u.SetNull(group.FieldFallbackGroupIDOnInvalidRequest)
+	return u
+}
+
 // SetModelRouting sets the "model_routing" field.
 func (u *GroupUpsert) SetModelRouting(v map[string][]int64) *GroupUpsert {
 	u.Set(group.FieldModelRouting, v)
@@ -1581,6 +1623,34 @@ func (u *GroupUpsertOne) ClearFallbackGroupID() *GroupUpsertOne {
 	})
 }
 
+// SetFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsertOne) SetFallbackGroupIDOnInvalidRequest(v int64) *GroupUpsertOne {
+	return u.Update(func(s *GroupUpsert) {
+		s.SetFallbackGroupIDOnInvalidRequest(v)
+	})
+}
+
+// AddFallbackGroupIDOnInvalidRequest adds v to the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsertOne) AddFallbackGroupIDOnInvalidRequest(v int64) *GroupUpsertOne {
+	return u.Update(func(s *GroupUpsert) {
+		s.AddFallbackGroupIDOnInvalidRequest(v)
+	})
+}
+
+// UpdateFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field to the value that was provided on create.
+func (u *GroupUpsertOne) UpdateFallbackGroupIDOnInvalidRequest() *GroupUpsertOne {
+	return u.Update(func(s *GroupUpsert) {
+		s.UpdateFallbackGroupIDOnInvalidRequest()
+	})
+}
+
+// ClearFallbackGroupIDOnInvalidRequest clears the value of the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsertOne) ClearFallbackGroupIDOnInvalidRequest() *GroupUpsertOne {
+	return u.Update(func(s *GroupUpsert) {
+		s.ClearFallbackGroupIDOnInvalidRequest()
+	})
+}
+
 // SetModelRouting sets the "model_routing" field.
 func (u *GroupUpsertOne) SetModelRouting(v map[string][]int64) *GroupUpsertOne {
 	return u.Update(func(s *GroupUpsert) {
@@ -2205,6 +2275,34 @@ func (u *GroupUpsertBulk) ClearFallbackGroupID() *GroupUpsertBulk {
 	})
 }
 
+// SetFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsertBulk) SetFallbackGroupIDOnInvalidRequest(v int64) *GroupUpsertBulk {
+	return u.Update(func(s *GroupUpsert) {
+		s.SetFallbackGroupIDOnInvalidRequest(v)
+	})
+}
+
+// AddFallbackGroupIDOnInvalidRequest adds v to the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsertBulk) AddFallbackGroupIDOnInvalidRequest(v int64) *GroupUpsertBulk {
+	return u.Update(func(s *GroupUpsert) {
+		s.AddFallbackGroupIDOnInvalidRequest(v)
+	})
+}
+
+// UpdateFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field to the value that was provided on create.
+func (u *GroupUpsertBulk) UpdateFallbackGroupIDOnInvalidRequest() *GroupUpsertBulk {
+	return u.Update(func(s *GroupUpsert) {
+		s.UpdateFallbackGroupIDOnInvalidRequest()
+	})
+}
+
+// ClearFallbackGroupIDOnInvalidRequest clears the value of the "fallback_group_id_on_invalid_request" field.
+func (u *GroupUpsertBulk) ClearFallbackGroupIDOnInvalidRequest() *GroupUpsertBulk {
+	return u.Update(func(s *GroupUpsert) {
+		s.ClearFallbackGroupIDOnInvalidRequest()
+	})
+}
+
 // SetModelRouting sets the "model_routing" field.
 func (u *GroupUpsertBulk) SetModelRouting(v map[string][]int64) *GroupUpsertBulk {
 	return u.Update(func(s *GroupUpsert) {

backend/ent/group_update.go

@@ -395,6 +395,33 @@ func (_u *GroupUpdate) ClearFallbackGroupID() *GroupUpdate {
 	return _u
 }
 
+// SetFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field.
+func (_u *GroupUpdate) SetFallbackGroupIDOnInvalidRequest(v int64) *GroupUpdate {
+	_u.mutation.ResetFallbackGroupIDOnInvalidRequest()
+	_u.mutation.SetFallbackGroupIDOnInvalidRequest(v)
+	return _u
+}
+
+// SetNillableFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field if the given value is not nil.
+func (_u *GroupUpdate) SetNillableFallbackGroupIDOnInvalidRequest(v *int64) *GroupUpdate {
+	if v != nil {
+		_u.SetFallbackGroupIDOnInvalidRequest(*v)
+	}
+	return _u
+}
+
+// AddFallbackGroupIDOnInvalidRequest adds value to the "fallback_group_id_on_invalid_request" field.
+func (_u *GroupUpdate) AddFallbackGroupIDOnInvalidRequest(v int64) *GroupUpdate {
+	_u.mutation.AddFallbackGroupIDOnInvalidRequest(v)
+	return _u
+}
+
+// ClearFallbackGroupIDOnInvalidRequest clears the value of the "fallback_group_id_on_invalid_request" field.
+func (_u *GroupUpdate) ClearFallbackGroupIDOnInvalidRequest() *GroupUpdate {
+	_u.mutation.ClearFallbackGroupIDOnInvalidRequest()
+	return _u
+}
+
 // SetModelRouting sets the "model_routing" field.
 func (_u *GroupUpdate) SetModelRouting(v map[string][]int64) *GroupUpdate {
 	_u.mutation.SetModelRouting(v)
@@ -829,6 +856,15 @@ func (_u *GroupUpdate) sqlSave(ctx context.Context) (_node int, err error) {
 	if _u.mutation.FallbackGroupIDCleared() {
 		_spec.ClearField(group.FieldFallbackGroupID, field.TypeInt64)
 	}
+	if value, ok := _u.mutation.FallbackGroupIDOnInvalidRequest(); ok {
+		_spec.SetField(group.FieldFallbackGroupIDOnInvalidRequest, field.TypeInt64, value)
+	}
+	if value, ok := _u.mutation.AddedFallbackGroupIDOnInvalidRequest(); ok {
+		_spec.AddField(group.FieldFallbackGroupIDOnInvalidRequest, field.TypeInt64, value)
+	}
+	if _u.mutation.FallbackGroupIDOnInvalidRequestCleared() {
+		_spec.ClearField(group.FieldFallbackGroupIDOnInvalidRequest, field.TypeInt64)
+	}
 	if value, ok := _u.mutation.ModelRouting(); ok {
 		_spec.SetField(group.FieldModelRouting, field.TypeJSON, value)
 	}
@@ -1513,6 +1549,33 @@ func (_u *GroupUpdateOne) ClearFallbackGroupID() *GroupUpdateOne {
 	return _u
 }
 
+// SetFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field.
+func (_u *GroupUpdateOne) SetFallbackGroupIDOnInvalidRequest(v int64) *GroupUpdateOne {
+	_u.mutation.ResetFallbackGroupIDOnInvalidRequest()
+	_u.mutation.SetFallbackGroupIDOnInvalidRequest(v)
+	return _u
+}
+
+// SetNillableFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field if the given value is not nil.
+func (_u *GroupUpdateOne) SetNillableFallbackGroupIDOnInvalidRequest(v *int64) *GroupUpdateOne {
+	if v != nil {
+		_u.SetFallbackGroupIDOnInvalidRequest(*v)
+	}
+	return _u
+}
+
+// AddFallbackGroupIDOnInvalidRequest adds value to the "fallback_group_id_on_invalid_request" field.
+func (_u *GroupUpdateOne) AddFallbackGroupIDOnInvalidRequest(v int64) *GroupUpdateOne {
+	_u.mutation.AddFallbackGroupIDOnInvalidRequest(v)
+	return _u
+}
+
+// ClearFallbackGroupIDOnInvalidRequest clears the value of the "fallback_group_id_on_invalid_request" field.
+func (_u *GroupUpdateOne) ClearFallbackGroupIDOnInvalidRequest() *GroupUpdateOne {
+	_u.mutation.ClearFallbackGroupIDOnInvalidRequest()
+	return _u
+}
+
 // SetModelRouting sets the "model_routing" field.
 func (_u *GroupUpdateOne) SetModelRouting(v map[string][]int64) *GroupUpdateOne {
 	_u.mutation.SetModelRouting(v)
@@ -1977,6 +2040,15 @@ func (_u *GroupUpdateOne) sqlSave(ctx context.Context) (_node *Group, err error)
 	if _u.mutation.FallbackGroupIDCleared() {
 		_spec.ClearField(group.FieldFallbackGroupID, field.TypeInt64)
 	}
+	if value, ok := _u.mutation.FallbackGroupIDOnInvalidRequest(); ok {
+		_spec.SetField(group.FieldFallbackGroupIDOnInvalidRequest, field.TypeInt64, value)
+	}
+	if value, ok := _u.mutation.AddedFallbackGroupIDOnInvalidRequest(); ok {
+		_spec.AddField(group.FieldFallbackGroupIDOnInvalidRequest, field.TypeInt64, value)
+	}
+	if _u.mutation.FallbackGroupIDOnInvalidRequestCleared() {
+		_spec.ClearField(group.FieldFallbackGroupIDOnInvalidRequest, field.TypeInt64)
+	}
 	if value, ok := _u.mutation.ModelRouting(); ok {
 		_spec.SetField(group.FieldModelRouting, field.TypeJSON, value)
 	}

backend/ent/migrate/schema.go

@@ -226,6 +226,7 @@ var (
 		{Name: "image_price_4k", Type: field.TypeFloat64, Nullable: true, SchemaType: map[string]string{"postgres": "decimal(20,8)"}},
 		{Name: "claude_code_only", Type: field.TypeBool, Default: false},
 		{Name: "fallback_group_id", Type: field.TypeInt64, Nullable: true},
+		{Name: "fallback_group_id_on_invalid_request", Type: field.TypeInt64, Nullable: true},
 		{Name: "model_routing", Type: field.TypeJSON, Nullable: true, SchemaType: map[string]string{"postgres": "jsonb"}},
 		{Name: "model_routing_enabled", Type: field.TypeBool, Default: false},
 	}

backend/ent/mutation.go

@@ -3864,6 +3864,8 @@ type GroupMutation struct {
 	claude_code_only                        *bool
 	fallback_group_id                       *int64
 	addfallback_group_id                    *int64
+	fallback_group_id_on_invalid_request    *int64
+	addfallback_group_id_on_invalid_request *int64
 	model_routing                           *map[string][]int64
 	model_routing_enabled                   *bool
 	clearedFields                           map[string]struct{}
@@ -4976,6 +4978,76 @@ func (m *GroupMutation) ResetFallbackGroupID() {
 	delete(m.clearedFields, group.FieldFallbackGroupID)
 }
+// SetFallbackGroupIDOnInvalidRequest sets the "fallback_group_id_on_invalid_request" field.
+func (m *GroupMutation) SetFallbackGroupIDOnInvalidRequest(i int64) {
+	m.fallback_group_id_on_invalid_request = &i
+	m.addfallback_group_id_on_invalid_request = nil
+}
+
+// FallbackGroupIDOnInvalidRequest returns the value of the "fallback_group_id_on_invalid_request" field in the mutation.
+func (m *GroupMutation) FallbackGroupIDOnInvalidRequest() (r int64, exists bool) {
+	v := m.fallback_group_id_on_invalid_request
+	if v == nil {
+		return
+	}
+	return *v, true
+}
+
+// OldFallbackGroupIDOnInvalidRequest returns the old "fallback_group_id_on_invalid_request" field's value of the Group entity.
+// If the Group object wasn't provided to the builder, the object is fetched from the database.
+// An error is returned if the mutation operation is not UpdateOne, or the database query fails.
+func (m *GroupMutation) OldFallbackGroupIDOnInvalidRequest(ctx context.Context) (v *int64, err error) {
+	if !m.op.Is(OpUpdateOne) {
+		return v, errors.New("OldFallbackGroupIDOnInvalidRequest is only allowed on UpdateOne operations")
+	}
+	if m.id == nil || m.oldValue == nil {
+		return v, errors.New("OldFallbackGroupIDOnInvalidRequest requires an ID field in the mutation")
+	}
+	oldValue, err := m.oldValue(ctx)
+	if err != nil {
+		return v, fmt.Errorf("querying old value for OldFallbackGroupIDOnInvalidRequest: %w", err)
+	}
+	return oldValue.FallbackGroupIDOnInvalidRequest, nil
+}
+
+// AddFallbackGroupIDOnInvalidRequest adds i to the "fallback_group_id_on_invalid_request" field.
+func (m *GroupMutation) AddFallbackGroupIDOnInvalidRequest(i int64) {
+	if m.addfallback_group_id_on_invalid_request != nil {
+		*m.addfallback_group_id_on_invalid_request += i
+	} else {
+		m.addfallback_group_id_on_invalid_request = &i
+	}
+}
+
+// AddedFallbackGroupIDOnInvalidRequest returns the value that was added to the "fallback_group_id_on_invalid_request" field in this mutation.
+func (m *GroupMutation) AddedFallbackGroupIDOnInvalidRequest() (r int64, exists bool) {
+	v := m.addfallback_group_id_on_invalid_request
+	if v == nil {
+		return
+	}
+	return *v, true
+}
+
+// ClearFallbackGroupIDOnInvalidRequest clears the value of the "fallback_group_id_on_invalid_request" field.
+func (m *GroupMutation) ClearFallbackGroupIDOnInvalidRequest() {
+	m.fallback_group_id_on_invalid_request = nil
+	m.addfallback_group_id_on_invalid_request = nil
+	m.clearedFields[group.FieldFallbackGroupIDOnInvalidRequest] = struct{}{}
+}
+
+// FallbackGroupIDOnInvalidRequestCleared returns if the "fallback_group_id_on_invalid_request" field was cleared in this mutation.
+func (m *GroupMutation) FallbackGroupIDOnInvalidRequestCleared() bool {
+	_, ok := m.clearedFields[group.FieldFallbackGroupIDOnInvalidRequest]
+	return ok
+}
+
+// ResetFallbackGroupIDOnInvalidRequest resets all changes to the "fallback_group_id_on_invalid_request" field.
+func (m *GroupMutation) ResetFallbackGroupIDOnInvalidRequest() {
+	m.fallback_group_id_on_invalid_request = nil
+	m.addfallback_group_id_on_invalid_request = nil
+	delete(m.clearedFields, group.FieldFallbackGroupIDOnInvalidRequest)
+}
+
 // SetModelRouting sets the "model_routing" field.
 func (m *GroupMutation) SetModelRouting(value map[string][]int64) {
 	m.model_routing = &value
@@ -5419,7 +5491,7 @@ func (m *GroupMutation) Type() string {
 // order to get all numeric fields that were incremented/decremented, call
 // AddedFields().
 func (m *GroupMutation) Fields() []string {
-	fields := make([]string, 0, 21)
+	fields := make([]string, 0, 22)
 	if m.created_at != nil {
 		fields = append(fields, group.FieldCreatedAt)
 	}
@@ -5477,6 +5549,9 @@ func (m *GroupMutation) Fields() []string {
 	if m.fallback_group_id != nil {
 		fields = append(fields, group.FieldFallbackGroupID)
 	}
+	if m.fallback_group_id_on_invalid_request != nil {
+		fields = append(fields, group.FieldFallbackGroupIDOnInvalidRequest)
+	}
 	if m.model_routing != nil {
 		fields = append(fields, group.FieldModelRouting)
 	}
@@ -5529,6 +5604,8 @@ func (m *GroupMutation) Field(name string) (ent.Value, bool) {
 		return m.ClaudeCodeOnly()
 	case group.FieldFallbackGroupID:
 		return m.FallbackGroupID()
+	case group.FieldFallbackGroupIDOnInvalidRequest:
+		return m.FallbackGroupIDOnInvalidRequest()
 	case group.FieldModelRouting:
 		return m.ModelRouting()
 	case group.FieldModelRoutingEnabled:
@@ -5580,6 +5657,8 @@ func (m *GroupMutation) OldField(ctx context.Context, name string) (ent.Value, e
 		return m.OldClaudeCodeOnly(ctx)
 	case group.FieldFallbackGroupID:
 		return m.OldFallbackGroupID(ctx)
+	case group.FieldFallbackGroupIDOnInvalidRequest:
+		return m.OldFallbackGroupIDOnInvalidRequest(ctx)
 	case group.FieldModelRouting:
 		return m.OldModelRouting(ctx)
 	case group.FieldModelRoutingEnabled:
@@ -5726,6 +5805,13 @@ func (m *GroupMutation) SetField(name string, value ent.Value) error {
 		}
 		m.SetFallbackGroupID(v)
 		return nil
+	case group.FieldFallbackGroupIDOnInvalidRequest:
+		v, ok := value.(int64)
+		if !ok {
+			return fmt.Errorf("unexpected type %T for field %s", value, name)
+		}
+		m.SetFallbackGroupIDOnInvalidRequest(v)
+		return nil
 	case group.FieldModelRouting:
 		v, ok := value.(map[string][]int64)
 		if !ok {
@@ -5775,6 +5861,9 @@ func (m *GroupMutation) AddedFields() []string {
 	if m.addfallback_group_id != nil {
 		fields = append(fields, group.FieldFallbackGroupID)
 	}
+	if m.addfallback_group_id_on_invalid_request != nil {
+		fields = append(fields, group.FieldFallbackGroupIDOnInvalidRequest)
+	}
 	return fields
 }
@@ -5801,6 +5890,8 @@ func (m *GroupMutation) AddedField(name string) (ent.Value, bool) {
 		return m.AddedImagePrice4k()
 	case group.FieldFallbackGroupID:
 		return m.AddedFallbackGroupID()
+	case group.FieldFallbackGroupIDOnInvalidRequest:
+		return m.AddedFallbackGroupIDOnInvalidRequest()
 	}
 	return nil, false
 }
@@ -5873,6 +5964,13 @@ func (m *GroupMutation) AddField(name string, value ent.Value) error {
 		}
 		m.AddFallbackGroupID(v)
 		return nil
+	case group.FieldFallbackGroupIDOnInvalidRequest:
+		v, ok := value.(int64)
+		if !ok {
+			return fmt.Errorf("unexpected type %T for field %s", value, name)
+		}
+		m.AddFallbackGroupIDOnInvalidRequest(v)
+		return nil
 	}
 	return fmt.Errorf("unknown Group numeric field %s", name)
 }
@@ -5908,6 +6006,9 @@ func (m *GroupMutation) ClearedFields() []string {
 	if m.FieldCleared(group.FieldFallbackGroupID) {
 		fields = append(fields, group.FieldFallbackGroupID)
 	}
+	if m.FieldCleared(group.FieldFallbackGroupIDOnInvalidRequest) {
+		fields = append(fields, group.FieldFallbackGroupIDOnInvalidRequest)
+	}
 	if m.FieldCleared(group.FieldModelRouting) {
 		fields = append(fields, group.FieldModelRouting)
 	}
@@ -5952,6 +6053,9 @@ func (m *GroupMutation) ClearField(name string) error {
 	case group.FieldFallbackGroupID:
 		m.ClearFallbackGroupID()
 		return nil
+	case group.FieldFallbackGroupIDOnInvalidRequest:
+		m.ClearFallbackGroupIDOnInvalidRequest()
+		return nil
 	case group.FieldModelRouting:
 		m.ClearModelRouting()
 		return nil
@@ -6020,6 +6124,9 @@ func (m *GroupMutation) ResetField(name string) error {
 	case group.FieldFallbackGroupID:
 		m.ResetFallbackGroupID()
 		return nil
+	case group.FieldFallbackGroupIDOnInvalidRequest:
+		m.ResetFallbackGroupIDOnInvalidRequest()
+		return nil
 	case group.FieldModelRouting:
 		m.ResetModelRouting()
 		return nil

backend/ent/runtime/runtime.go

@@ -281,7 +281,7 @@ func init() {
 	// group.DefaultClaudeCodeOnly holds the default value on creation for the claude_code_only field.
 	group.DefaultClaudeCodeOnly = groupDescClaudeCodeOnly.Default.(bool)
 	// groupDescModelRoutingEnabled is the schema descriptor for model_routing_enabled field.
-	groupDescModelRoutingEnabled := groupFields[17].Descriptor()
+	groupDescModelRoutingEnabled := groupFields[18].Descriptor()
 	// group.DefaultModelRoutingEnabled holds the default value on creation for the model_routing_enabled field.
 	group.DefaultModelRoutingEnabled = groupDescModelRoutingEnabled.Default.(bool)
 	promocodeFields := schema.PromoCode{}.Fields()

backend/ent/schema/group.go

@@ -95,6 +95,10 @@ func (Group) Fields() []ent.Field {
 			Optional().
 			Nillable().
 			Comment("非 Claude Code 请求降级使用的分组 ID"),
+		field.Int64("fallback_group_id_on_invalid_request").
+			Optional().
+			Nillable().
+			Comment("无效请求兜底使用的分组 ID"),
 
 		// 模型路由配置 (added by migration 040)
 		field.JSON("model_routing", map[string][]int64{}).

backend/internal/handler/admin/group_handler.go

@@ -40,6 +40,7 @@ type CreateGroupRequest struct {
 	ImagePrice4K                    *float64 `json:"image_price_4k"`
 	ClaudeCodeOnly                  bool     `json:"claude_code_only"`
 	FallbackGroupID                 *int64   `json:"fallback_group_id"`
+	FallbackGroupIDOnInvalidRequest *int64   `json:"fallback_group_id_on_invalid_request"`
 	// 模型路由配置（仅 anthropic 平台使用）
 	ModelRouting        map[string][]int64 `json:"model_routing"`
 	ModelRoutingEnabled bool               `json:"model_routing_enabled"`
@@ -63,6 +64,7 @@ type UpdateGroupRequest struct {
 	ImagePrice4K                    *float64 `json:"image_price_4k"`
 	ClaudeCodeOnly                  *bool    `json:"claude_code_only"`
 	FallbackGroupID                 *int64   `json:"fallback_group_id"`
+	FallbackGroupIDOnInvalidRequest *int64   `json:"fallback_group_id_on_invalid_request"`
 	// 模型路由配置（仅 anthropic 平台使用）
 	ModelRouting        map[string][]int64 `json:"model_routing"`
 	ModelRoutingEnabled *bool              `json:"model_routing_enabled"`
@@ -169,6 +171,7 @@ func (h *GroupHandler) Create(c *gin.Context) {
 		ImagePrice4K:                    req.ImagePrice4K,
 		ClaudeCodeOnly:                  req.ClaudeCodeOnly,
 		FallbackGroupID:                 req.FallbackGroupID,
+		FallbackGroupIDOnInvalidRequest: req.FallbackGroupIDOnInvalidRequest,
 		ModelRouting:                    req.ModelRouting,
 		ModelRoutingEnabled:             req.ModelRoutingEnabled,
 	})
@@ -211,6 +214,7 @@ func (h *GroupHandler) Update(c *gin.Context) {
 		ImagePrice4K:                    req.ImagePrice4K,
 		ClaudeCodeOnly:                  req.ClaudeCodeOnly,
 		FallbackGroupID:                 req.FallbackGroupID,
+		FallbackGroupIDOnInvalidRequest: req.FallbackGroupIDOnInvalidRequest,
 		ModelRouting:                    req.ModelRouting,
 		ModelRoutingEnabled:             req.ModelRoutingEnabled,
 	})

backend/internal/handler/dto/mappers.go

@@ -89,6 +89,7 @@ func GroupFromServiceShallow(g *service.Group) *Group {
 		ImagePrice4K:                    g.ImagePrice4K,
 		ClaudeCodeOnly:                  g.ClaudeCodeOnly,
 		FallbackGroupID:                 g.FallbackGroupID,
+		FallbackGroupIDOnInvalidRequest: g.FallbackGroupIDOnInvalidRequest,
 		ModelRouting:                    g.ModelRouting,
 		ModelRoutingEnabled:             g.ModelRoutingEnabled,
 		CreatedAt:                       g.CreatedAt,

backend/internal/handler/dto/types.go

@@ -57,6 +57,8 @@ type Group struct {
 	// Claude Code 客户端限制
 	ClaudeCodeOnly  bool   `json:"claude_code_only"`
 	FallbackGroupID *int64 `json:"fallback_group_id"`
+	// 无效请求兜底分组
+	FallbackGroupIDOnInvalidRequest *int64 `json:"fallback_group_id_on_invalid_request"`
 
 	// 模型路由配置（仅 anthropic 平台使用）
 	ModelRouting        map[string][]int64 `json:"model_routing"`

backend/internal/handler/gateway_handler.go

@@ -14,6 +14,7 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/config"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/ctxkey"
 	pkgerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/ip"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/openai"
@@ -325,14 +326,24 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 		}
 	}
 
+	currentAPIKey := apiKey
+	currentSubscription := subscription
+	var fallbackGroupID *int64
+	if apiKey.Group != nil {
+		fallbackGroupID = apiKey.Group.FallbackGroupIDOnInvalidRequest
+	}
+	fallbackUsed := false
+
+	for {
 		maxAccountSwitches := h.maxAccountSwitches
 		switchCount := 0
 		failedAccountIDs := make(map[int64]struct{})
 		lastFailoverStatus := 0
+		retryWithFallback := false
 
 		for {
 			// 选择支持该模型的账号
-		selection, err := h.gatewayService.SelectAccountWithLoadAwareness(c.Request.Context(), apiKey.GroupID, sessionKey, reqModel, failedAccountIDs, parsedReq.MetadataUserID)
+			selection, err := h.gatewayService.SelectAccountWithLoadAwareness(c.Request.Context(), currentAPIKey.GroupID, sessionKey, reqModel, failedAccountIDs, parsedReq.MetadataUserID)
 			if err != nil {
 				if len(failedAccountIDs) == 0 {
 					h.handleStreamingAwareError(c, http.StatusServiceUnavailable, "api_error", "No available accounts: "+err.Error(), streamStarted)
@@ -399,7 +410,7 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 					h.concurrencyHelper.DecrementAccountWaitCount(c.Request.Context(), account.ID)
 					accountWaitCounted = false
 				}
-			if err := h.gatewayService.BindStickySession(c.Request.Context(), apiKey.GroupID, sessionKey, account.ID); err != nil {
+				if err := h.gatewayService.BindStickySession(c.Request.Context(), currentAPIKey.GroupID, sessionKey, account.ID); err != nil {
 					log.Printf("Bind sticky session failed: %v", err)
 				}
 			}
@@ -417,6 +428,41 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 				accountReleaseFunc()
 			}
 			if err != nil {
+				var promptTooLongErr *service.PromptTooLongError
+				if errors.As(err, &promptTooLongErr) {
+					log.Printf("Prompt too long from antigravity: group=%d fallback_group_id=%v fallback_used=%v", currentAPIKey.GroupID, fallbackGroupID, fallbackUsed)
+					if !fallbackUsed && fallbackGroupID != nil && *fallbackGroupID > 0 {
+						fallbackGroup, err := h.gatewayService.ResolveGroupByID(c.Request.Context(), *fallbackGroupID)
+						if err != nil {
+							log.Printf("Resolve fallback group failed: %v", err)
+							_ = h.antigravityGatewayService.WriteMappedClaudeError(c, account, promptTooLongErr.StatusCode, promptTooLongErr.RequestID, promptTooLongErr.Body)
+							return
+						}
+						if fallbackGroup.Platform != service.PlatformAnthropic ||
+							fallbackGroup.SubscriptionType == service.SubscriptionTypeSubscription ||
+							fallbackGroup.FallbackGroupIDOnInvalidRequest != nil {
+							log.Printf("Fallback group invalid: group=%d platform=%s subscription=%s", fallbackGroup.ID, fallbackGroup.Platform, fallbackGroup.SubscriptionType)
+							_ = h.antigravityGatewayService.WriteMappedClaudeError(c, account, promptTooLongErr.StatusCode, promptTooLongErr.RequestID, promptTooLongErr.Body)
+							return
+						}
+						fallbackAPIKey := cloneAPIKeyWithGroup(apiKey, fallbackGroup)
+						if err := h.billingCacheService.CheckBillingEligibility(c.Request.Context(), fallbackAPIKey.User, fallbackAPIKey, fallbackGroup, nil); err != nil {
+							status, code, message := billingErrorDetails(err)
+							h.handleStreamingAwareError(c, status, code, message, streamStarted)
+							return
+						}
+						// 兜底重试按“直接请求兜底分组”处理：清除强制平台，允许按分组平台调度
+						ctx := context.WithValue(c.Request.Context(), ctxkey.ForcePlatform, "")
+						c.Request = c.Request.WithContext(ctx)
+						currentAPIKey = fallbackAPIKey
+						currentSubscription = nil
+						fallbackUsed = true
+						retryWithFallback = true
+						break
+					}
+					_ = h.antigravityGatewayService.WriteMappedClaudeError(c, account, promptTooLongErr.StatusCode, promptTooLongErr.RequestID, promptTooLongErr.Body)
+					return
+				}
 				var failoverErr *service.UpstreamFailoverError
 				if errors.As(err, &failoverErr) {
 					failedAccountIDs[account.ID] = struct{}{}
@@ -444,10 +490,10 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 				defer cancel()
 				if err := h.gatewayService.RecordUsage(ctx, &service.RecordUsageInput{
 					Result:       result,
-				APIKey:       apiKey,
-				User:         apiKey.User,
+					APIKey:       currentAPIKey,
+					User:         currentAPIKey.User,
 					Account:      usedAccount,
-				Subscription: subscription,
+					Subscription: currentSubscription,
 					UserAgent:    ua,
 					IPAddress:    clientIP,
 				}); err != nil {
@@ -456,6 +502,11 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 			}(result, account, userAgent, clientIP)
 			return
 		}
+
+		if !retryWithFallback {
+			return
+		}
+	}
 }
 
 // Models handles listing available models
@@ -518,6 +569,17 @@ func (h *GatewayHandler) AntigravityModels(c *gin.Context) {
 	})
 }
 
+func cloneAPIKeyWithGroup(apiKey *service.APIKey, group *service.Group) *service.APIKey {
+	if apiKey == nil || group == nil {
+		return apiKey
+	}
+	cloned := *apiKey
+	groupID := group.ID
+	cloned.GroupID = &groupID
+	cloned.Group = group
+	return &cloned
+}
+
 // Usage handles getting account balance for CC Switch integration
 // GET /v1/usage
 func (h *GatewayHandler) Usage(c *gin.Context) {

backend/internal/repository/api_key_repo.go

@@ -136,6 +136,7 @@ func (r *apiKeyRepository) GetByKeyForAuth(ctx context.Context, key string) (*se
 				group.FieldImagePrice4k,
 				group.FieldClaudeCodeOnly,
 				group.FieldFallbackGroupID,
+				group.FieldFallbackGroupIDOnInvalidRequest,
 				group.FieldModelRoutingEnabled,
 				group.FieldModelRouting,
 			)
@@ -424,6 +425,7 @@ func groupEntityToService(g *dbent.Group) *service.Group {
 		DefaultValidityDays:             g.DefaultValidityDays,
 		ClaudeCodeOnly:                  g.ClaudeCodeOnly,
 		FallbackGroupID:                 g.FallbackGroupID,
+		FallbackGroupIDOnInvalidRequest: g.FallbackGroupIDOnInvalidRequest,
 		ModelRouting:                    g.ModelRouting,
 		ModelRoutingEnabled:             g.ModelRoutingEnabled,
 		CreatedAt:                       g.CreatedAt,

backend/internal/repository/group_repo.go

@@ -50,6 +50,7 @@ func (r *groupRepository) Create(ctx context.Context, groupIn *service.Group) er
 		SetDefaultValidityDays(groupIn.DefaultValidityDays).
 		SetClaudeCodeOnly(groupIn.ClaudeCodeOnly).
 		SetNillableFallbackGroupID(groupIn.FallbackGroupID).
+		SetNillableFallbackGroupIDOnInvalidRequest(groupIn.FallbackGroupIDOnInvalidRequest).
 		SetModelRoutingEnabled(groupIn.ModelRoutingEnabled)
 
 	// 设置模型路由配置
@@ -116,6 +117,12 @@ func (r *groupRepository) Update(ctx context.Context, groupIn *service.Group) er
 	} else {
 		builder = builder.ClearFallbackGroupID()
 	}
+	// 处理 FallbackGroupIDOnInvalidRequest：nil 时清除，否则设置
+	if groupIn.FallbackGroupIDOnInvalidRequest != nil {
+		builder = builder.SetFallbackGroupIDOnInvalidRequest(*groupIn.FallbackGroupIDOnInvalidRequest)
+	} else {
+		builder = builder.ClearFallbackGroupIDOnInvalidRequest()
+	}
 
 	// 处理 ModelRouting：nil 时清除，否则设置
 	if groupIn.ModelRouting != nil {

backend/internal/service/admin_service.go

@@ -108,6 +108,8 @@ type CreateGroupInput struct {
 	ImagePrice4K    *float64
 	ClaudeCodeOnly  bool   // 仅允许 Claude Code 客户端
 	FallbackGroupID *int64 // 降级分组 ID
+	// 无效请求兜底分组 ID（仅 anthropic 平台使用）
+	FallbackGroupIDOnInvalidRequest *int64
 	// 模型路由配置（仅 anthropic 平台使用）
 	ModelRouting        map[string][]int64
 	ModelRoutingEnabled bool // 是否启用模型路由
@@ -130,6 +132,8 @@ type UpdateGroupInput struct {
 	ImagePrice4K    *float64
 	ClaudeCodeOnly  *bool  // 仅允许 Claude Code 客户端
 	FallbackGroupID *int64 // 降级分组 ID
+	// 无效请求兜底分组 ID（仅 anthropic 平台使用）
+	FallbackGroupIDOnInvalidRequest *int64
 	// 模型路由配置（仅 anthropic 平台使用）
 	ModelRouting        map[string][]int64
 	ModelRoutingEnabled *bool // 是否启用模型路由
@@ -572,6 +576,16 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 			return nil, err
 		}
 	}
+	fallbackOnInvalidRequest := input.FallbackGroupIDOnInvalidRequest
+	if fallbackOnInvalidRequest != nil && *fallbackOnInvalidRequest <= 0 {
+		fallbackOnInvalidRequest = nil
+	}
+	// 校验无效请求兜底分组
+	if fallbackOnInvalidRequest != nil {
+		if err := s.validateFallbackGroupOnInvalidRequest(ctx, 0, platform, subscriptionType, *fallbackOnInvalidRequest); err != nil {
+			return nil, err
+		}
+	}
 
 	group := &Group{
 		Name:                            input.Name,
@@ -589,6 +603,7 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 		ImagePrice4K:                    imagePrice4K,
 		ClaudeCodeOnly:                  input.ClaudeCodeOnly,
 		FallbackGroupID:                 input.FallbackGroupID,
+		FallbackGroupIDOnInvalidRequest: fallbackOnInvalidRequest,
 		ModelRouting:                    input.ModelRouting,
 	}
 	if err := s.groupRepo.Create(ctx, group); err != nil {
@@ -651,6 +666,37 @@ func (s *adminServiceImpl) validateFallbackGroup(ctx context.Context, currentGro
 	}
 }
 
+// validateFallbackGroupOnInvalidRequest 校验无效请求兜底分组的有效性
+// currentGroupID: 当前分组 ID（新建时为 0）
+// platform/subscriptionType: 当前分组的有效平台/订阅类型
+// fallbackGroupID: 兜底分组 ID
+func (s *adminServiceImpl) validateFallbackGroupOnInvalidRequest(ctx context.Context, currentGroupID int64, platform, subscriptionType string, fallbackGroupID int64) error {
+	if platform != PlatformAnthropic && platform != PlatformAntigravity {
+		return fmt.Errorf("invalid request fallback only supported for anthropic or antigravity groups")
+	}
+	if subscriptionType == SubscriptionTypeSubscription {
+		return fmt.Errorf("subscription groups cannot set invalid request fallback")
+	}
+	if currentGroupID > 0 && currentGroupID == fallbackGroupID {
+		return fmt.Errorf("cannot set self as invalid request fallback group")
+	}
+
+	fallbackGroup, err := s.groupRepo.GetByIDLite(ctx, fallbackGroupID)
+	if err != nil {
+		return fmt.Errorf("fallback group not found: %w", err)
+	}
+	if fallbackGroup.Platform != PlatformAnthropic {
+		return fmt.Errorf("fallback group must be anthropic platform")
+	}
+	if fallbackGroup.SubscriptionType == SubscriptionTypeSubscription {
+		return fmt.Errorf("fallback group cannot be subscription type")
+	}
+	if fallbackGroup.FallbackGroupIDOnInvalidRequest != nil {
+		return fmt.Errorf("fallback group cannot have invalid request fallback configured")
+	}
+	return nil
+}
+
 func (s *adminServiceImpl) UpdateGroup(ctx context.Context, id int64, input *UpdateGroupInput) (*Group, error) {
 	group, err := s.groupRepo.GetByID(ctx, id)
 	if err != nil {
@@ -717,6 +763,20 @@ func (s *adminServiceImpl) UpdateGroup(ctx context.Context, id int64, input *Upd
 			group.FallbackGroupID = nil
 		}
 	}
+	fallbackOnInvalidRequest := group.FallbackGroupIDOnInvalidRequest
+	if input.FallbackGroupIDOnInvalidRequest != nil {
+		if *input.FallbackGroupIDOnInvalidRequest > 0 {
+			fallbackOnInvalidRequest = input.FallbackGroupIDOnInvalidRequest
+		} else {
+			fallbackOnInvalidRequest = nil
+		}
+	}
+	if fallbackOnInvalidRequest != nil {
+		if err := s.validateFallbackGroupOnInvalidRequest(ctx, id, group.Platform, group.SubscriptionType, *fallbackOnInvalidRequest); err != nil {
+			return nil, err
+		}
+	}
+	group.FallbackGroupIDOnInvalidRequest = fallbackOnInvalidRequest
 
 	// 模型路由配置
 	if input.ModelRouting != nil {

backend/internal/service/admin_service_group_test.go

@@ -378,3 +378,374 @@ func (s *groupRepoStubForFallbackCycle) GetAccountCount(_ context.Context, _ int
 func (s *groupRepoStubForFallbackCycle) DeleteAccountGroupsByGroupID(_ context.Context, _ int64) (int64, error) {
 	panic("unexpected DeleteAccountGroupsByGroupID call")
 }
+
+type groupRepoStubForInvalidRequestFallback struct {
+	groups  map[int64]*Group
+	created *Group
+	updated *Group
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) Create(_ context.Context, g *Group) error {
+	s.created = g
+	return nil
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) Update(_ context.Context, g *Group) error {
+	s.updated = g
+	return nil
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) GetByID(ctx context.Context, id int64) (*Group, error) {
+	return s.GetByIDLite(ctx, id)
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) GetByIDLite(_ context.Context, id int64) (*Group, error) {
+	if g, ok := s.groups[id]; ok {
+		return g, nil
+	}
+	return nil, ErrGroupNotFound
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) Delete(_ context.Context, _ int64) error {
+	panic("unexpected Delete call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) DeleteCascade(_ context.Context, _ int64) ([]int64, error) {
+	panic("unexpected DeleteCascade call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) List(_ context.Context, _ pagination.PaginationParams) ([]Group, *pagination.PaginationResult, error) {
+	panic("unexpected List call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) ListWithFilters(_ context.Context, _ pagination.PaginationParams, _, _, _ string, _ *bool) ([]Group, *pagination.PaginationResult, error) {
+	panic("unexpected ListWithFilters call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) ListActive(_ context.Context) ([]Group, error) {
+	panic("unexpected ListActive call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) ListActiveByPlatform(_ context.Context, _ string) ([]Group, error) {
+	panic("unexpected ListActiveByPlatform call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) ExistsByName(_ context.Context, _ string) (bool, error) {
+	panic("unexpected ExistsByName call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) GetAccountCount(_ context.Context, _ int64) (int64, error) {
+	panic("unexpected GetAccountCount call")
+}
+
+func (s *groupRepoStubForInvalidRequestFallback) DeleteAccountGroupsByGroupID(_ context.Context, _ int64) (int64, error) {
+	panic("unexpected DeleteAccountGroupsByGroupID call")
+}
+
+func TestAdminService_CreateGroup_InvalidRequestFallbackRejectsUnsupportedPlatform(t *testing.T) {
+	fallbackID := int64(10)
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			fallbackID: {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	_, err := svc.CreateGroup(context.Background(), &CreateGroupInput{
+		Name:                            "g1",
+		Platform:                        PlatformOpenAI,
+		SubscriptionType:                SubscriptionTypeStandard,
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	})
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "invalid request fallback only supported for anthropic or antigravity groups")
+	require.Nil(t, repo.created)
+}
+
+func TestAdminService_CreateGroup_InvalidRequestFallbackRejectsSubscription(t *testing.T) {
+	fallbackID := int64(10)
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			fallbackID: {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	_, err := svc.CreateGroup(context.Background(), &CreateGroupInput{
+		Name:                            "g1",
+		Platform:                        PlatformAnthropic,
+		SubscriptionType:                SubscriptionTypeSubscription,
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	})
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "subscription groups cannot set invalid request fallback")
+	require.Nil(t, repo.created)
+}
+
+func TestAdminService_CreateGroup_InvalidRequestFallbackRejectsFallbackGroup(t *testing.T) {
+	tests := []struct {
+		name        string
+		fallback    *Group
+		wantMessage string
+	}{
+		{
+			name:        "openai_target",
+			fallback:    &Group{ID: 10, Platform: PlatformOpenAI, SubscriptionType: SubscriptionTypeStandard},
+			wantMessage: "fallback group must be anthropic platform",
+		},
+		{
+			name:        "antigravity_target",
+			fallback:    &Group{ID: 10, Platform: PlatformAntigravity, SubscriptionType: SubscriptionTypeStandard},
+			wantMessage: "fallback group must be anthropic platform",
+		},
+		{
+			name:        "subscription_group",
+			fallback:    &Group{ID: 10, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeSubscription},
+			wantMessage: "fallback group cannot be subscription type",
+		},
+		{
+			name: "nested_fallback",
+			fallback: &Group{
+				ID:                              10,
+				Platform:                        PlatformAnthropic,
+				SubscriptionType:                SubscriptionTypeStandard,
+				FallbackGroupIDOnInvalidRequest: func() *int64 { v := int64(99); return &v }(),
+			},
+			wantMessage: "fallback group cannot have invalid request fallback configured",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			fallbackID := tc.fallback.ID
+			repo := &groupRepoStubForInvalidRequestFallback{
+				groups: map[int64]*Group{
+					fallbackID: tc.fallback,
+				},
+			}
+			svc := &adminServiceImpl{groupRepo: repo}
+
+			_, err := svc.CreateGroup(context.Background(), &CreateGroupInput{
+				Name:                            "g1",
+				Platform:                        PlatformAnthropic,
+				SubscriptionType:                SubscriptionTypeStandard,
+				FallbackGroupIDOnInvalidRequest: &fallbackID,
+			})
+			require.Error(t, err)
+			require.Contains(t, err.Error(), tc.wantMessage)
+			require.Nil(t, repo.created)
+		})
+	}
+}
+
+func TestAdminService_CreateGroup_InvalidRequestFallbackNotFound(t *testing.T) {
+	fallbackID := int64(10)
+	repo := &groupRepoStubForInvalidRequestFallback{}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	_, err := svc.CreateGroup(context.Background(), &CreateGroupInput{
+		Name:                            "g1",
+		Platform:                        PlatformAnthropic,
+		SubscriptionType:                SubscriptionTypeStandard,
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	})
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "fallback group not found")
+	require.Nil(t, repo.created)
+}
+
+func TestAdminService_CreateGroup_InvalidRequestFallbackAllowsAntigravity(t *testing.T) {
+	fallbackID := int64(10)
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			fallbackID: {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	group, err := svc.CreateGroup(context.Background(), &CreateGroupInput{
+		Name:                            "g1",
+		Platform:                        PlatformAntigravity,
+		SubscriptionType:                SubscriptionTypeStandard,
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	})
+	require.NoError(t, err)
+	require.NotNil(t, group)
+	require.NotNil(t, repo.created)
+	require.Equal(t, fallbackID, *repo.created.FallbackGroupIDOnInvalidRequest)
+}
+
+func TestAdminService_CreateGroup_InvalidRequestFallbackClearsOnZero(t *testing.T) {
+	zero := int64(0)
+	repo := &groupRepoStubForInvalidRequestFallback{}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	group, err := svc.CreateGroup(context.Background(), &CreateGroupInput{
+		Name:                            "g1",
+		Platform:                        PlatformAnthropic,
+		SubscriptionType:                SubscriptionTypeStandard,
+		FallbackGroupIDOnInvalidRequest: &zero,
+	})
+	require.NoError(t, err)
+	require.NotNil(t, group)
+	require.NotNil(t, repo.created)
+	require.Nil(t, repo.created.FallbackGroupIDOnInvalidRequest)
+}
+
+func TestAdminService_UpdateGroup_InvalidRequestFallbackPlatformMismatch(t *testing.T) {
+	fallbackID := int64(10)
+	existing := &Group{
+		ID:                              1,
+		Name:                            "g1",
+		Platform:                        PlatformAnthropic,
+		SubscriptionType:                SubscriptionTypeStandard,
+		Status:                          StatusActive,
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	}
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			existing.ID: existing,
+			fallbackID:  {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	_, err := svc.UpdateGroup(context.Background(), existing.ID, &UpdateGroupInput{
+		Platform: PlatformOpenAI,
+	})
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "invalid request fallback only supported for anthropic or antigravity groups")
+	require.Nil(t, repo.updated)
+}
+
+func TestAdminService_UpdateGroup_InvalidRequestFallbackSubscriptionMismatch(t *testing.T) {
+	fallbackID := int64(10)
+	existing := &Group{
+		ID:                              1,
+		Name:                            "g1",
+		Platform:                        PlatformAnthropic,
+		SubscriptionType:                SubscriptionTypeStandard,
+		Status:                          StatusActive,
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	}
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			existing.ID: existing,
+			fallbackID:  {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	_, err := svc.UpdateGroup(context.Background(), existing.ID, &UpdateGroupInput{
+		SubscriptionType: SubscriptionTypeSubscription,
+	})
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "subscription groups cannot set invalid request fallback")
+	require.Nil(t, repo.updated)
+}
+
+func TestAdminService_UpdateGroup_InvalidRequestFallbackClearsOnZero(t *testing.T) {
+	fallbackID := int64(10)
+	existing := &Group{
+		ID:                              1,
+		Name:                            "g1",
+		Platform:                        PlatformAnthropic,
+		SubscriptionType:                SubscriptionTypeStandard,
+		Status:                          StatusActive,
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	}
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			existing.ID: existing,
+			fallbackID:  {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	clear := int64(0)
+	group, err := svc.UpdateGroup(context.Background(), existing.ID, &UpdateGroupInput{
+		Platform:                        PlatformOpenAI,
+		FallbackGroupIDOnInvalidRequest: &clear,
+	})
+	require.NoError(t, err)
+	require.NotNil(t, group)
+	require.NotNil(t, repo.updated)
+	require.Nil(t, repo.updated.FallbackGroupIDOnInvalidRequest)
+}
+
+func TestAdminService_UpdateGroup_InvalidRequestFallbackRejectsFallbackGroup(t *testing.T) {
+	fallbackID := int64(10)
+	existing := &Group{
+		ID:               1,
+		Name:             "g1",
+		Platform:         PlatformAnthropic,
+		SubscriptionType: SubscriptionTypeStandard,
+		Status:           StatusActive,
+	}
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			existing.ID: existing,
+			fallbackID:  {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeSubscription},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	_, err := svc.UpdateGroup(context.Background(), existing.ID, &UpdateGroupInput{
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	})
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "fallback group cannot be subscription type")
+	require.Nil(t, repo.updated)
+}
+
+func TestAdminService_UpdateGroup_InvalidRequestFallbackSetSuccess(t *testing.T) {
+	fallbackID := int64(10)
+	existing := &Group{
+		ID:               1,
+		Name:             "g1",
+		Platform:         PlatformAnthropic,
+		SubscriptionType: SubscriptionTypeStandard,
+		Status:           StatusActive,
+	}
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			existing.ID: existing,
+			fallbackID:  {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	group, err := svc.UpdateGroup(context.Background(), existing.ID, &UpdateGroupInput{
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	})
+	require.NoError(t, err)
+	require.NotNil(t, group)
+	require.NotNil(t, repo.updated)
+	require.Equal(t, fallbackID, *repo.updated.FallbackGroupIDOnInvalidRequest)
+}
+
+func TestAdminService_UpdateGroup_InvalidRequestFallbackAllowsAntigravity(t *testing.T) {
+	fallbackID := int64(10)
+	existing := &Group{
+		ID:               1,
+		Name:             "g1",
+		Platform:         PlatformAntigravity,
+		SubscriptionType: SubscriptionTypeStandard,
+		Status:           StatusActive,
+	}
+	repo := &groupRepoStubForInvalidRequestFallback{
+		groups: map[int64]*Group{
+			existing.ID: existing,
+			fallbackID:  {ID: fallbackID, Platform: PlatformAnthropic, SubscriptionType: SubscriptionTypeStandard},
+		},
+	}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	group, err := svc.UpdateGroup(context.Background(), existing.ID, &UpdateGroupInput{
+		FallbackGroupIDOnInvalidRequest: &fallbackID,
+	})
+	require.NoError(t, err)
+	require.NotNil(t, group)
+	require.NotNil(t, repo.updated)
+	require.Equal(t, fallbackID, *repo.updated.FallbackGroupIDOnInvalidRequest)
+}

backend/internal/service/antigravity_gateway_service.go

@@ -62,6 +62,17 @@ type antigravityRetryLoopResult struct {
 	resp *http.Response
 }
 
+// PromptTooLongError 表示上游明确返回 prompt too long
+type PromptTooLongError struct {
+	StatusCode int
+	RequestID  string
+	Body       []byte
+}
+
+func (e *PromptTooLongError) Error() string {
+	return fmt.Sprintf("prompt too long: status=%d", e.StatusCode)
+}
+
 // antigravityRetryLoop 执行带 URL fallback 的重试循环
 func antigravityRetryLoop(p antigravityRetryLoopParams) (*antigravityRetryLoopResult, error) {
 	availableURLs := antigravity.DefaultURLAvailability.GetAvailableURLs()
@@ -930,6 +941,39 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 
 		// 处理错误响应（重试后仍失败或不触发重试）
 		if resp.StatusCode >= 400 {
+			if resp.StatusCode == http.StatusBadRequest {
+				upstreamMsg := strings.TrimSpace(extractAntigravityErrorMessage(respBody))
+				upstreamMsg = sanitizeUpstreamErrorMessage(upstreamMsg)
+				log.Printf("%s status=400 prompt_too_long=%v upstream_message=%q request_id=%s body=%s", prefix, isPromptTooLongError(respBody), upstreamMsg, resp.Header.Get("x-request-id"), truncateForLog(respBody, 500))
+			}
+			if resp.StatusCode == http.StatusBadRequest && isPromptTooLongError(respBody) {
+				upstreamMsg := strings.TrimSpace(extractAntigravityErrorMessage(respBody))
+				upstreamMsg = sanitizeUpstreamErrorMessage(upstreamMsg)
+				logBody := s.settingService != nil && s.settingService.cfg != nil && s.settingService.cfg.Gateway.LogUpstreamErrorBody
+				maxBytes := 2048
+				if s.settingService != nil && s.settingService.cfg != nil && s.settingService.cfg.Gateway.LogUpstreamErrorBodyMaxBytes > 0 {
+					maxBytes = s.settingService.cfg.Gateway.LogUpstreamErrorBodyMaxBytes
+				}
+				upstreamDetail := ""
+				if logBody {
+					upstreamDetail = truncateString(string(respBody), maxBytes)
+				}
+				appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
+					Platform:           account.Platform,
+					AccountID:          account.ID,
+					AccountName:        account.Name,
+					UpstreamStatusCode: resp.StatusCode,
+					UpstreamRequestID:  resp.Header.Get("x-request-id"),
+					Kind:               "prompt_too_long",
+					Message:            upstreamMsg,
+					Detail:             upstreamDetail,
+				})
+				return nil, &PromptTooLongError{
+					StatusCode: resp.StatusCode,
+					RequestID:  resp.Header.Get("x-request-id"),
+					Body:       respBody,
+				}
+			}
 			s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, quotaScope)
 
 			if s.shouldFailoverUpstreamError(resp.StatusCode) {
@@ -1019,21 +1063,55 @@ func isSignatureRelatedError(respBody []byte) bool {
 	return false
 }
 
+func isPromptTooLongError(respBody []byte) bool {
+	msg := strings.ToLower(strings.TrimSpace(extractAntigravityErrorMessage(respBody)))
+	if msg == "" {
+		msg = strings.ToLower(string(respBody))
+	}
+	return strings.Contains(msg, "prompt is too long")
+}
+
 func extractAntigravityErrorMessage(body []byte) string {
 	var payload map[string]any
 	if err := json.Unmarshal(body, &payload); err != nil {
 		return ""
 	}
 
+	parseNestedMessage := func(msg string) string {
+		trimmed := strings.TrimSpace(msg)
+		if trimmed == "" || !strings.HasPrefix(trimmed, "{") {
+			return ""
+		}
+		var nested map[string]any
+		if err := json.Unmarshal([]byte(trimmed), &nested); err != nil {
+			return ""
+		}
+		if errObj, ok := nested["error"].(map[string]any); ok {
+			if innerMsg, ok := errObj["message"].(string); ok && strings.TrimSpace(innerMsg) != "" {
+				return innerMsg
+			}
+		}
+		if innerMsg, ok := nested["message"].(string); ok && strings.TrimSpace(innerMsg) != "" {
+			return innerMsg
+		}
+		return ""
+	}
+
 	// Google-style: {"error": {"message": "..."}}
 	if errObj, ok := payload["error"].(map[string]any); ok {
 		if msg, ok := errObj["message"].(string); ok && strings.TrimSpace(msg) != "" {
+			if innerMsg := parseNestedMessage(msg); innerMsg != "" {
+				return innerMsg
+			}
 			return msg
 		}
 	}
 
 	// Fallback: top-level message
 	if msg, ok := payload["message"].(string); ok && strings.TrimSpace(msg) != "" {
+		if innerMsg := parseNestedMessage(msg); innerMsg != "" {
+			return innerMsg
+		}
 		return msg
 	}
 
@@ -2209,6 +2287,10 @@ func (s *AntigravityGatewayService) writeMappedClaudeError(c *gin.Context, accou
 	return fmt.Errorf("upstream error: %d message=%s", upstreamStatus, upstreamMsg)
 }
 
+func (s *AntigravityGatewayService) WriteMappedClaudeError(c *gin.Context, account *Account, upstreamStatus int, upstreamRequestID string, body []byte) error {
+	return s.writeMappedClaudeError(c, account, upstreamStatus, upstreamRequestID, body)
+}
+
 func (s *AntigravityGatewayService) writeGoogleError(c *gin.Context, status int, message string) error {
 	statusStr := "UNKNOWN"
 	switch status {

backend/internal/service/antigravity_gateway_service_test.go

 package service
 
 import (
+	"bytes"
+	"context"
 	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
+	"github.com/gin-gonic/gin"
 	"github.com/stretchr/testify/require"
 )
 
@@ -81,3 +87,77 @@ func TestStripThinkingFromClaudeRequest_DoesNotDowngradeTools(t *testing.T) {
 	require.Equal(t, "secret plan", blocks[0]["text"])
 	require.Equal(t, "tool_use", blocks[1]["type"])
 }
+
+func TestIsPromptTooLongError(t *testing.T) {
+	require.True(t, isPromptTooLongError([]byte(`{"error":{"message":"Prompt is too long"}}`)))
+	require.True(t, isPromptTooLongError([]byte(`{"message":"Prompt is too long"}`)))
+	require.False(t, isPromptTooLongError([]byte(`{"error":{"message":"other"}}`)))
+}
+
+type httpUpstreamStub struct {
+	resp *http.Response
+	err  error
+}
+
+func (s *httpUpstreamStub) Do(_ *http.Request, _ string, _ int64, _ int) (*http.Response, error) {
+	return s.resp, s.err
+}
+
+func TestAntigravityGatewayService_Forward_PromptTooLong(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	writer := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(writer)
+
+	body, err := json.Marshal(map[string]any{
+		"model": "claude-opus-4-5",
+		"messages": []map[string]any{
+			{"role": "user", "content": "hi"},
+		},
+		"max_tokens": 1,
+		"stream":     false,
+	})
+	require.NoError(t, err)
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	c.Request = req
+
+	respBody := []byte(`{"error":{"message":"Prompt is too long"}}`)
+	resp := &http.Response{
+		StatusCode: http.StatusBadRequest,
+		Header:     http.Header{"X-Request-Id": []string{"req-1"}},
+		Body:       io.NopCloser(bytes.NewReader(respBody)),
+	}
+
+	svc := &AntigravityGatewayService{
+		tokenProvider: &AntigravityTokenProvider{},
+		httpUpstream:  &httpUpstreamStub{resp: resp},
+	}
+
+	account := &Account{
+		ID:          1,
+		Name:        "acc-1",
+		Platform:    PlatformAntigravity,
+		Type:        AccountTypeOAuth,
+		Status:      StatusActive,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"access_token": "token",
+		},
+	}
+
+	result, err := svc.Forward(context.Background(), c, account, body)
+	require.Nil(t, result)
+
+	var promptErr *PromptTooLongError
+	require.ErrorAs(t, err, &promptErr)
+	require.Equal(t, http.StatusBadRequest, promptErr.StatusCode)
+	require.Equal(t, "req-1", promptErr.RequestID)
+	require.NotEmpty(t, promptErr.Body)
+
+	raw, ok := c.Get(OpsUpstreamErrorsKey)
+	require.True(t, ok)
+	events, ok := raw.([]*OpsUpstreamErrorEvent)
+	require.True(t, ok)
+	require.Len(t, events, 1)
+	require.Equal(t, "prompt_too_long", events[0].Kind)
+}

backend/internal/service/api_key_auth_cache.go

@@ -37,6 +37,7 @@ type APIKeyAuthGroupSnapshot struct {
 	ImagePrice4K                    *float64 `json:"image_price_4k,omitempty"`
 	ClaudeCodeOnly                  bool     `json:"claude_code_only"`
 	FallbackGroupID                 *int64   `json:"fallback_group_id,omitempty"`
+	FallbackGroupIDOnInvalidRequest *int64   `json:"fallback_group_id_on_invalid_request,omitempty"`
 
 	// Model routing is used by gateway account selection, so it must be part of auth cache snapshot.
 	// Only anthropic groups use these fields; others may leave them empty.