Function validate_launch_values 

pub fn validate_launch_values(
    directory: &Path,
    session_id: Option<&str>,
    pair_id: &str,
    controller_args: &[String],
    windows: bool,
) -> Result<(), ToolError>

“Values that reach a shell” (spec Launcher): ids match their patterns, a newline is refused everywhere, ; in the directory on Windows (wt splits its command line on it), and on Windows a controller argument with a cmd.exe metacharacter. Nothing is written before this passes.