Display compact status cards in the chat transcript showing each
sub-agent's name, current activity (Thinking, Using grep, etc.),
and elapsed time. Cards appear while sub-agents are running and
clear when the session goes idle.
- Extend SessionEventRecord with description, error, toolCallId,
and model fields for subagent events
- Forward additional subagent fields in handleTurnScopedEvent
- Add subagentTracker reducer to derive active subagent state from
session events, including agent-activity correlation
- Create SubagentActivityCard component with spinner, status icon,
agent name, activity label, and live elapsed timer
- Wire activeSubagents state in App.tsx and pass to ChatPane
- Add 16 unit tests for the subagent tracker
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
