Function write_validate_summary 

pub fn write_validate_summary<W: Write>(
    w: &mut W,
    source: Option<&Path>,
    resolved: &ResolvedConfig,
    notices: &[ConfigNotice],
) -> Result<()>

Render the validation summary. Separated from config_validate so tests can capture the output into a buffer and assert on the printed contract — in particular that rpc_url and otlp_endpoint values never appear.