Function fetch_tools 

pub async fn fetch_tools(
    transport: &ResolvedTransport,
    timeout: Duration,
) -> Result<Vec<Tool>, String>

List a downstream server’s tools over a pooled session (tools/list). super::pool::acquire guarantees a live session, so the only failure left is a rare mid-flight transport death; because listing is idempotent we evict the suspect session and reopen once. A timeout is surfaced (not retried).