Function cascade 

pub fn cascade(agents: Vec<AgentBuilder>) -> Composable

Cascade: try agents in sequence, first success wins.

This is an alias for a fallback chain. Each agent is tried in order; the first one that succeeds provides the result.

Example

let robust = cascade(vec![
    AgentBuilder::new("fast").instruction("Quick answer"),
    AgentBuilder::new("thorough").instruction("Detailed answer"),
]);