- Add MAX_CONCURRENT_AGENTS configuration (default: 20)
- Check current agent count before spawning
- Reject spawn requests with 429 Too Many Requests when limit reached
- Add comprehensive tests for limit enforcement
Refs #338
- Sandbox now enabled by default for security
- Logs prominent warning when explicitly disabled
- Agents run in containers unless SANDBOX_ENABLED=false
Refs #337
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>