Function agent_swarm_batch_violation 

pub fn agent_swarm_batch_violation<'a>(
    tool_names: impl Iterator<Item = &'a str>,
) -> Option<AgentSwarmBatchViolation>

Detect whether a batch of tool-call names violates the agent_swarm exclusivity rule. Returns None when the batch is valid: no agent_swarm call, or exactly one agent_swarm call by itself.