Shutdown behavior

Gestalt uses a graceful shutdown sequence on SIGINT/SIGTERM. The first Ctrl+C starts the shutdown. Additional Ctrl+C presses are logged and ignored so the graceful sequence can finish.

Shutdown has an overall 5s deadline with a 1s budget per phase. Phases are ordered to keep dependencies alive while dependents stop (for example, the OTel SDK stops before the collector, and event bridges stop before the event bus).

Acceptance checklist

• Run 10 start/stop cycles; after each stop there are no defunct (zombie) processes left behind by the backend.
• A normal Ctrl+C shutdown logs info-level shutdown entries and avoids error-level logs when possible. Any remaining errors should indicate unavoidable failures rather than ordering issues.