Subagent details can also be sent to a session's event stream

A subagent is a helper agent Claude starts to work on part of a task. Claude Code saves details about each subagent in a small file next to the session (agent-<id>.meta.json). It now records which session the file belongs to and, when a setting allows it, also sends those details as an event on the session's event stream (the live feed of what the session is doing). Claude Code records whether each send succeeded, was held back, or failed.

Before, the details were only written to the file.