feat(db): add upstream_model column to usage_logs

Add nullable VARCHAR(100) column to record the actual model sent to upstream providers when model mapping is applied. NULL means no mapping — the requested model was used as-is.

Includes migration, concurrent index for aggregation queries, Ent schema regeneration, and migration README correction (forward-only runner, not goose).

backend/ent/mutation.go

@@ -18239,6 +18239,7 @@ type UsageLogMutation struct {
 	id                          *int64
 	request_id                  *string
 	model                       *string
+	upstream_model              *string
 	input_tokens                *int
 	addinput_tokens             *int
 	output_tokens               *int
@@ -18576,6 +18577,55 @@ func (m *UsageLogMutation) ResetModel() {
 	m.model = nil
 }
 
+// SetUpstreamModel sets the "upstream_model" field.
+func (m *UsageLogMutation) SetUpstreamModel(s string) {
+	m.upstream_model = &s
+}
+
+// UpstreamModel returns the value of the "upstream_model" field in the mutation.
+func (m *UsageLogMutation) UpstreamModel() (r string, exists bool) {
+	v := m.upstream_model
+	if v == nil {
+		return
+	}
+	return *v, true
+}
+
+// OldUpstreamModel returns the old "upstream_model" field's value of the UsageLog entity.
+// If the UsageLog 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 *UsageLogMutation) OldUpstreamModel(ctx context.Context) (v *string, err error) {
+	if !m.op.Is(OpUpdateOne) {
+		return v, errors.New("OldUpstreamModel is only allowed on UpdateOne operations")
+	}
+	if m.id == nil || m.oldValue == nil {
+		return v, errors.New("OldUpstreamModel requires an ID field in the mutation")
+	}
+	oldValue, err := m.oldValue(ctx)
+	if err != nil {
+		return v, fmt.Errorf("querying old value for OldUpstreamModel: %w", err)
+	}
+	return oldValue.UpstreamModel, nil
+}
+
+// ClearUpstreamModel clears the value of the "upstream_model" field.
+func (m *UsageLogMutation) ClearUpstreamModel() {
+	m.upstream_model = nil
+	m.clearedFields[usagelog.FieldUpstreamModel] = struct{}{}
+}
+
+// UpstreamModelCleared returns if the "upstream_model" field was cleared in this mutation.
+func (m *UsageLogMutation) UpstreamModelCleared() bool {
+	_, ok := m.clearedFields[usagelog.FieldUpstreamModel]
+	return ok
+}
+
+// ResetUpstreamModel resets all changes to the "upstream_model" field.
+func (m *UsageLogMutation) ResetUpstreamModel() {
+	m.upstream_model = nil
+	delete(m.clearedFields, usagelog.FieldUpstreamModel)
+}
+
 // SetGroupID sets the "group_id" field.
 func (m *UsageLogMutation) SetGroupID(i int64) {
 	m.group = &i
@@ -20197,7 +20247,7 @@ func (m *UsageLogMutation) Type() string {
 // order to get all numeric fields that were incremented/decremented, call
 // AddedFields().
 func (m *UsageLogMutation) Fields() []string {
-	fields := make([]string, 0, 32)
+	fields := make([]string, 0, 33)
 	if m.user != nil {
 		fields = append(fields, usagelog.FieldUserID)
 	}
@@ -20213,6 +20263,9 @@ func (m *UsageLogMutation) Fields() []string {
 	if m.model != nil {
 		fields = append(fields, usagelog.FieldModel)
 	}
+	if m.upstream_model != nil {
+		fields = append(fields, usagelog.FieldUpstreamModel)
+	}
 	if m.group != nil {
 		fields = append(fields, usagelog.FieldGroupID)
 	}
@@ -20312,6 +20365,8 @@ func (m *UsageLogMutation) Field(name string) (ent.Value, bool) {
 		return m.RequestID()
 	case usagelog.FieldModel:
 		return m.Model()
+	case usagelog.FieldUpstreamModel:
+		return m.UpstreamModel()
 	case usagelog.FieldGroupID:
 		return m.GroupID()
 	case usagelog.FieldSubscriptionID:
@@ -20385,6 +20440,8 @@ func (m *UsageLogMutation) OldField(ctx context.Context, name string) (ent.Value
 		return m.OldRequestID(ctx)
 	case usagelog.FieldModel:
 		return m.OldModel(ctx)
+	case usagelog.FieldUpstreamModel:
+		return m.OldUpstreamModel(ctx)
 	case usagelog.FieldGroupID:
 		return m.OldGroupID(ctx)
 	case usagelog.FieldSubscriptionID:
@@ -20483,6 +20540,13 @@ func (m *UsageLogMutation) SetField(name string, value ent.Value) error {
 		}
 		m.SetModel(v)
 		return nil
+	case usagelog.FieldUpstreamModel:
+		v, ok := value.(string)
+		if !ok {
+			return fmt.Errorf("unexpected type %T for field %s", value, name)
+		}
+		m.SetUpstreamModel(v)
+		return nil
 	case usagelog.FieldGroupID:
 		v, ok := value.(int64)
 		if !ok {
@@ -20921,6 +20985,9 @@ func (m *UsageLogMutation) AddField(name string, value ent.Value) error {
 // mutation.
 func (m *UsageLogMutation) ClearedFields() []string {
 	var fields []string
+	if m.FieldCleared(usagelog.FieldUpstreamModel) {
+		fields = append(fields, usagelog.FieldUpstreamModel)
+	}
 	if m.FieldCleared(usagelog.FieldGroupID) {
 		fields = append(fields, usagelog.FieldGroupID)
 	}
@@ -20962,6 +21029,9 @@ func (m *UsageLogMutation) FieldCleared(name string) bool {
 // error if the field is not defined in the schema.
 func (m *UsageLogMutation) ClearField(name string) error {
 	switch name {
+	case usagelog.FieldUpstreamModel:
+		m.ClearUpstreamModel()
+		return nil
 	case usagelog.FieldGroupID:
 		m.ClearGroupID()
 		return nil
@@ -21012,6 +21082,9 @@ func (m *UsageLogMutation) ResetField(name string) error {
 	case usagelog.FieldModel:
 		m.ResetModel()
 		return nil
+	case usagelog.FieldUpstreamModel:
+		m.ResetUpstreamModel()
+		return nil
 	case usagelog.FieldGroupID:
 		m.ResetGroupID()
 		return nil