Not sure if we need to complicate it by adding the message to the TextLayout struct. Maybe just check if params.node().id is null instead of layout.stop_message.empty()?

I meant that there might be other error messaging in get_text_layout, but if you think so, then this is not required.

Thanks for the patch. I think this can be cleaned up slightly so we don't have to retrieve the font in multiple places.
Since we don't usually use exceptions, I would recommend returning std::optional<TextLayout> from get_text_layout.
The get_text_layout function can add the error message itself after the existing retrieval of the font, and return std::nullopt.
node_geo_exec could check if the optional is empty and return early.