Service readiness determined by startup lifecycle completion

The /readyz endpoint returns 200 only after the service completes startup lifecycle hooks and is marked as ready via mark_as_ready method. Returns 500 if service is not ready to handle requests.

Configure Kubernetes readiness probes to use /readyz endpoint. If service shows as not ready, check startup lifecycle hooks completion. For liveness checks, use /livez or /healthz which only verify the service is running.