## What changed
- Emit started and completed collaboration tool events for multi-agent v2
`spawn_agent` calls, including failed invocations.
- Record execution duration and successful child-agent configuration metadata
without including the spawn prompt.
- Deduplicate collaboration and subagent activity items by call ID when
calculating per-turn subagent tool counts.
## Testing
- Extend the app-server multi-agent v2 integration test to cover successful
and failed spawn telemetry, duration, prompt omission, and turn counts.
GitOrigin-RevId: c1c2fb9cc2a1a9b0f63ef68509ad36d11a92d1e5