pub fn main_model(&self) -> Result<ModelId> {
        let agent = self.get_agent(&AgentId::default())?;
        agent
            .model
            .clone()
            .ok_or(Error::NoModelDefined(agent.id.clone()))
    }
Returns the model of the main agent

# Errors
- `AgentUndefined` if the main agent doesn't exist
- `NoModelDefined` if the main agent doesn't have a model defined
crates/forge_domain/src/conversation.rs