Function render_response 

pub fn render_response(
    status: u16,
    meta: &str,
    body: Option<&str>,
) -> Result<(String, bool), ResponseError>

Render a complete response: header, and the body only for a 2x.

The meta becomes one line (control characters → spaces, trimmed), an empty meta takes the status’s default, and a body given with any status other than 2x is dropped — Gemini defines no body for them, and a client reading one would take it for the next response’s garbage. The caller learns whether that happened from the second return value.