Hello, the following MWE produces an error, which looks like it might be a bug:

```
\localrightbox{xyz}%
\hfill\break
\localleftbox{abc}%
\bye
```

Output:

```
This is LuaTeX, Version 1.21.0 (TeX Live 2025/Homebrew)
 restricted system commands enabled.
(./free.tex
warning  (nodes): attempt to copy free hlist node 399, ignored

warning  (nodes): attempt to copy free hlist node 369, ignored

Underfull \hbox (badness 10000) in paragraph at lines 2--4