Function config_for 

pub fn config_for(
    base: &Config,
    models_dir: &Path,
    target: &BenchTarget,
) -> Result<Config, Error>

The config one target runs under: the base with the target’s file in its role’s slot.

The spec carries no URL and no digest - a bench loads what is already on disk and never fetches - and the size is the file’s own, so the engine’s check is against the bytes that are there.