fix

internal/server/server.go

@@ -346,9 +346,11 @@ func (s *Server) HandleUploadStream(w http.ResponseWriter, r *http.Request) {
 	ctx := context.Background()
 
 	// Upload to S3
+	// When using chunked transfer (io.Pipe), ContentLength is -1
+	// MinIO requires -1 for unknown size to use streaming upload
 	size := r.ContentLength
 	if size < 0 {
-		size = 0
+		size = -1 // Use streaming upload for unknown size
 	}
 
 	if err := s.s3Backend.Upload(ctx, storageKey, r.Body, size); err != nil {