Verify and document that all exit paths are covered:
- Orphan cleanup on startup via cleanup_orphans()
- RAII CleanupGuard ensures cleanup on drop
- Global cleanup_temp_dir() before process::exit()
- Atexit handler registration for external signals
- Signal handling for SIGINT/SIGTERM
- HookInstaller cleanup with idempotent flag
- Panic safety with catch_unwind
All 90 library tests + 28 integration tests pass.
Exit path matrix shows all scenarios covered with defense in depth.
Co-Authored-By: Claude <noreply@anthropic.com>
