fix: write error messages to stderr rather than stdout

error.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"os"
 )
 
 // ErrorDetailer returns error details for responses & debugging. This enables
@@ -264,7 +265,7 @@ func WriteErr(api API, ctx Context, status int, msg string, errs ...error) error
 	writeErr := writeResponse(api, ctx, status, "", err)
 	if writeErr != nil {
 		// If we can't write the error, log it so we know what happened.
-		fmt.Printf("could not write error: %s\n", writeErr)
+		fmt.Fprintf(os.Stderr, "could not write error: %s\n", writeErr)
 	}
 	return writeErr
 }

transforms.go

@@ -3,6 +3,7 @@ package huma
 import (
 	"bytes"
 	"fmt"
+	"os"
 	"path"
 	"reflect"
 )
@@ -132,7 +133,7 @@ func (t *SchemaLinkTransformer) OnAddOperation(oapi *OpenAPI, op *Operation) {
 						// Catch some scenarios that just aren't supported in Go at the
 						// moment. Logs an error so people know what's going on.
 						// https://github.com/danielgtaylor/huma/issues/371
-						fmt.Println("Warning: unable to create schema link for type", typ, ":", r)
+						fmt.Fprintln(os.Stderr, "Warning: unable to create schema link for type", typ, ":", r)
 					}
 				}()
 				newType := reflect.StructOf(fields)