Under the hood
Server-side tool-use tracking now records which agent made the call
What
The metadata Claude Code builds for each turn where it tracks model and effort level now also includes an optional agentId field, alongside the existing model, effort, and message-count fields.
Why
Since a spawned subagent (a separate Claude instance handling a subtask) can now be identified by its agentId, this lets per-turn tracking data be tied back to the specific agent that made a given tool call, rather than only to the overall session.