Function load_values_for_env 

pub fn load_values_for_env(
    config_dir: &Path,
    resolved: &ResolvedConfig,
) -> Result<Option<ValuesFile>>

Load the per-env values file, tolerating absence.

Missing file → Ok(None). Unresolved placeholders later (against an empty fallback) will surface as ResolutionFailures with a hint to create the file (see format_failures).

Present-but-malformed → propagates Error::YamlParse / Error::InvalidFormat (RFC §5 Edge cases — abort early, before any API call).