Launch a subagent to handle a complex multi-step task autonomously.

Available subagents:
{agents}

When to use this tool:
- Delegate focused investigation or implementation work to a specialized subagent.
- Run independent work items in parallel by making multiple task tool calls.

Usage notes:
1. Always set `subagent_type` to the target subagent name.
2. Give the subagent a detailed `prompt` that includes expected output.
3. Reuse `task_id` to continue an existing subagent session.
4. After completion, summarize subagent results back to the user in your own response.
