Feature request: Show agent/subagent task progress in terminal UI (parity with third-party tools)

Summary

Love the new desktop UI — but it currently shows significantly less information about agent and subagent activity than third-party wrappers do.

Current behavior

When a subagent is running, the first-party Claude UI only shows:

Running agent  CLAUDE.md compliance review  >

  *  2m 34s · ↓ 2.2k tokens

<img width="1000" height="115" alt="Image" src="https://github.com/user-attachments/assets/05d20760-90c4-490c-8e50-1de6492e6f5b" />

That's it — no task list, no subagent breakdown, no status per agent.

Expected / desired behavior

Third-party tools (e.g. Vibe Island) surface much richer information in their UI:

<img width="844" height="651" alt="Image" src="https://github.com/user-attachments/assets/9521000f-412b-4d64-80a8-a54ed02b62e1" />

• Named tasks with completion status (done / in progress / open)
• A list of subagents with their descriptions, status, and elapsed time
• The current tool/command being run

This creates a situation where users get better observability into Claude's own work from a third-party app than from the official one.

Suggested improvement

The terminal UI should surface at minimum:

• Task list with status indicators (as populated via TaskCreate/TaskUpdate)
• Active subagent names + status
• Current tool invocation (already partially shown via the streaming output, but not in a persistent way during agent runs)

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This is UX feedback, not a bug. The data is clearly available (tasks and subagents are tracked) — it just isn't surfaced in the terminal UI. Closing this visibility gap would make long agentic runs much easier to monitor from the first-party CLI.