Background subagents continue after stop, unclear what's running

Problem

When pressing the stop button during a session that has spawned background subagents:

1. The main conversation stops, but subagents continue running and keep prompting for permissions
2. The spinner continues with no indication of what's still active
3. From the iOS remote control, this is especially confusing — you see permission prompts appearing for work you thought you stopped

Expected behavior

• Stop should cancel all active subagents, or
• The UI should clearly show which subagents are still running with individual stop controls
• Permission prompts from subagents should identify which agent is requesting

Suggested approach

Show an active agent list when subagents are running:

Main session: stopped
├─ Explore agent (a8bf...): still running [Stop]
└─ Research agent (a5b8...): still running [Stop]

On mobile, each running agent could be a dismissible card with its own stop button.

Environment

• Claude Code 2.1.56
• iOS Claude app via remote control