Clarify appended messages and streamline repair

internal/usecase/repairer.go

@@ -55,19 +55,20 @@ func (r *defaultOutputRepairer) Repair(ctx context.Context, req RepairRequest) (
 		return nil, err
 	}
 
-	messages := domain.ConcatRenderedMessages(req.OriginalMessages, nil)
-	if strings.TrimSpace(req.PreviousOutput) != "" {
-		messages = append(messages, domain.RenderedMessage{
+	hasPreviousOutput := strings.TrimSpace(req.PreviousOutput) != ""
+	suffix := make([]domain.RenderedMessage, 0, 2)
+	if hasPreviousOutput {
+		suffix = append(suffix, domain.RenderedMessage{
 			Role:    domain.RoleAssistant,
 			Content: req.PreviousOutput,
 		})
 	}
 
 	previousResponse := "The previous response was empty."
-	if strings.TrimSpace(req.PreviousOutput) != "" {
+	if hasPreviousOutput {
 		previousResponse = "The previous response is included immediately before this instruction."
 	}
-	messages = append(messages, domain.RenderedMessage{
+	suffix = append(suffix, domain.RenderedMessage{
 		Role: domain.RoleUser,
 		Content: fmt.Sprintf(
 			"Repair attempt %d of %d for validation mode %s.\n"+
@@ -82,6 +83,7 @@ func (r *defaultOutputRepairer) Repair(ctx context.Context, req RepairRequest) (
 			formatRepairDiagnostics(req.ValidationErrors),
 		),
 	})
+	messages := domain.ConcatRenderedMessages(req.OriginalMessages, suffix)
 
 	resp, err := r.llm.Generate(ctx, newGenerationRequest(
 		domain.RenderedPrompt{Messages: messages},