Function validate_topic 

pub fn validate_topic(
    plugin_id: &str,
    name: &str,
    summary: &str,
    body: &str,
    related_commands: Vec<String>,
) -> Result<HelpTopicSpec, String>

Validate a guest’s topic declaration, or reject it.

Guest output is untrusted. The two rejections are the ones a buggy guest actually produces: a body that is empty or blank (a page that opens to nothing looks like a broken editor, not a broken plugin), and a name the host cannot namespace. Both are Err, which the seam turns into the WIT err — the plugin’s OTHER topics still register.