Invoke a specialist agent to handle a delegated task.

Use this when the task is better handled by a domain specialist (for example, complex multi-step work or tasks tied to a known specialist capability).

If you are not certain which specialist to use, call list_agents first.

Provide:
- agent_name: exact name from list_agents.
- task: clear, concrete objective.
- context: optional supporting details that improve execution quality.

After invoking, wait for the delegated result, then continue with your own final response to the user.
