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/usagelog_create.go

@@ -57,6 +57,20 @@ func (_c *UsageLogCreate) SetModel(v string) *UsageLogCreate {
 	return _c
 }
 
+// SetUpstreamModel sets the "upstream_model" field.
+func (_c *UsageLogCreate) SetUpstreamModel(v string) *UsageLogCreate {
+	_c.mutation.SetUpstreamModel(v)
+	return _c
+}
+
+// SetNillableUpstreamModel sets the "upstream_model" field if the given value is not nil.
+func (_c *UsageLogCreate) SetNillableUpstreamModel(v *string) *UsageLogCreate {
+	if v != nil {
+		_c.SetUpstreamModel(*v)
+	}
+	return _c
+}
+
 // SetGroupID sets the "group_id" field.
 func (_c *UsageLogCreate) SetGroupID(v int64) *UsageLogCreate {
 	_c.mutation.SetGroupID(v)
@@ -596,6 +610,11 @@ func (_c *UsageLogCreate) check() error {
 			return &ValidationError{Name: "model", err: fmt.Errorf(`ent: validator failed for field "UsageLog.model": %w`, err)}
 		}
 	}
+	if v, ok := _c.mutation.UpstreamModel(); ok {
+		if err := usagelog.UpstreamModelValidator(v); err != nil {
+			return &ValidationError{Name: "upstream_model", err: fmt.Errorf(`ent: validator failed for field "UsageLog.upstream_model": %w`, err)}
+		}
+	}
 	if _, ok := _c.mutation.InputTokens(); !ok {
 		return &ValidationError{Name: "input_tokens", err: errors.New(`ent: missing required field "UsageLog.input_tokens"`)}
 	}
@@ -714,6 +733,10 @@ func (_c *UsageLogCreate) createSpec() (*UsageLog, *sqlgraph.CreateSpec) {
 		_spec.SetField(usagelog.FieldModel, field.TypeString, value)
 		_node.Model = value
 	}
+	if value, ok := _c.mutation.UpstreamModel(); ok {
+		_spec.SetField(usagelog.FieldUpstreamModel, field.TypeString, value)
+		_node.UpstreamModel = &value
+	}
 	if value, ok := _c.mutation.InputTokens(); ok {
 		_spec.SetField(usagelog.FieldInputTokens, field.TypeInt, value)
 		_node.InputTokens = value
@@ -1011,6 +1034,24 @@ func (u *UsageLogUpsert) UpdateModel() *UsageLogUpsert {
 	return u
 }
 
+// SetUpstreamModel sets the "upstream_model" field.
+func (u *UsageLogUpsert) SetUpstreamModel(v string) *UsageLogUpsert {
+	u.Set(usagelog.FieldUpstreamModel, v)
+	return u
+}
+
+// UpdateUpstreamModel sets the "upstream_model" field to the value that was provided on create.
+func (u *UsageLogUpsert) UpdateUpstreamModel() *UsageLogUpsert {
+	u.SetExcluded(usagelog.FieldUpstreamModel)
+	return u
+}
+
+// ClearUpstreamModel clears the value of the "upstream_model" field.
+func (u *UsageLogUpsert) ClearUpstreamModel() *UsageLogUpsert {
+	u.SetNull(usagelog.FieldUpstreamModel)
+	return u
+}
+
 // SetGroupID sets the "group_id" field.
 func (u *UsageLogUpsert) SetGroupID(v int64) *UsageLogUpsert {
 	u.Set(usagelog.FieldGroupID, v)
@@ -1600,6 +1641,27 @@ func (u *UsageLogUpsertOne) UpdateModel() *UsageLogUpsertOne {
 	})
 }
 
+// SetUpstreamModel sets the "upstream_model" field.
+func (u *UsageLogUpsertOne) SetUpstreamModel(v string) *UsageLogUpsertOne {
+	return u.Update(func(s *UsageLogUpsert) {
+		s.SetUpstreamModel(v)
+	})
+}
+
+// UpdateUpstreamModel sets the "upstream_model" field to the value that was provided on create.
+func (u *UsageLogUpsertOne) UpdateUpstreamModel() *UsageLogUpsertOne {
+	return u.Update(func(s *UsageLogUpsert) {
+		s.UpdateUpstreamModel()
+	})
+}
+
+// ClearUpstreamModel clears the value of the "upstream_model" field.
+func (u *UsageLogUpsertOne) ClearUpstreamModel() *UsageLogUpsertOne {
+	return u.Update(func(s *UsageLogUpsert) {
+		s.ClearUpstreamModel()
+	})
+}
+
 // SetGroupID sets the "group_id" field.
 func (u *UsageLogUpsertOne) SetGroupID(v int64) *UsageLogUpsertOne {
 	return u.Update(func(s *UsageLogUpsert) {
@@ -2434,6 +2496,27 @@ func (u *UsageLogUpsertBulk) UpdateModel() *UsageLogUpsertBulk {
 	})
 }
 
+// SetUpstreamModel sets the "upstream_model" field.
+func (u *UsageLogUpsertBulk) SetUpstreamModel(v string) *UsageLogUpsertBulk {
+	return u.Update(func(s *UsageLogUpsert) {
+		s.SetUpstreamModel(v)
+	})
+}
+
+// UpdateUpstreamModel sets the "upstream_model" field to the value that was provided on create.
+func (u *UsageLogUpsertBulk) UpdateUpstreamModel() *UsageLogUpsertBulk {
+	return u.Update(func(s *UsageLogUpsert) {
+		s.UpdateUpstreamModel()
+	})
+}
+
+// ClearUpstreamModel clears the value of the "upstream_model" field.
+func (u *UsageLogUpsertBulk) ClearUpstreamModel() *UsageLogUpsertBulk {
+	return u.Update(func(s *UsageLogUpsert) {
+		s.ClearUpstreamModel()
+	})
+}
+
 // SetGroupID sets the "group_id" field.
 func (u *UsageLogUpsertBulk) SetGroupID(v int64) *UsageLogUpsertBulk {
 	return u.Update(func(s *UsageLogUpsert) {