Under the hood
Subagent progress events now include the specific API error kind, not just a yes/no flag
What
When a subagent (a secondary Claude instance handling part of a task) reports a tool-use event that involved an API error, the event now carries an apiErrorKind field with the specific error value, in addition to the existing plain yes/no isApiError flag.
Why
This gives the interface and telemetry more detail about what specifically went wrong with a subagent's API call, rather than only knowing that some error occurred.