## What changed
- Record collaboration tool analytics for `send_message`, `followup_task`,
`interrupt_agent`, and `list_agents`, including receiver attribution, duration,
failures, and interrupted calls.
- Include these calls in per-turn subagent tool counts while keeping the existing
`subAgentActivity` output unchanged and omitting additional public collaborator
tool items.
- Extend the collaboration tool schemas with the new tool variants and the
`interrupted` terminal status.
## Testing
- Add an app-server integration test covering successful and failed calls,
receiver attribution, duration, prompt omission, activity items, and turn
counts.
GitOrigin-RevId: e73eaa05c508261e5fc97e7d08d7881a31e04e22
jif
4fa6ad1730