[Bug] Sub-agent spawning ignores user constraints and exhausts token quota

**Bug Description**
I have specifically asked not to spawn multiple sub agents and still it exhausted all my tokens by spawning so many subagents. Also, on checking the usage, the usage always showed lower number after recent update. to get correct usage stats, I need to restart claude everytime.
**Environment Info**
- Platform: darwin
- Terminal: iTerm.app
- Version: 2.1.270
- Feedback ID: 9d73191d-0210-4b79-b373-6f836d93d662

**Errors**
```json
[]
```

Reproduce on darwin with iTerm.app and version 2.1.270, checking both sub-agent behavior after a no-multiple-agents instruction and usage immediately after activity. Trace the relevant sub-agent spawning and usage-stat paths; done means user constraints prevent excess spawning and usage remains accurate without restarting Claude.

Written by the indexing model from the issue text.