Function build_check_failed 

pub fn build_check_failed(
    hint: &CheckHint,
    exit_code: i32,
    stderr: &str,
) -> Check

Build the Check for a check: job that exited non-zero. The script crashed before it could report a status, so we surface Unknown with the exit code + a stderr snippet rather than leaving a stale Ok on the Health tab (a persistently-crashing check must not read as healthy).