Function render_placeholders 

pub fn render_placeholders(
    template: String,
    values: &[(&'static str, String)],
) -> String

Replaces {{key}} placeholders with provided values.

Replacement is a single left-to-right pass: substituted values are never re-scanned, so a user-controlled value containing {{another_key}} cannot trigger a second expansion. Unknown or unterminated tokens stay literal.