The best small-SaaS observability stack is the smallest system that can distinguish customer-visible notification delivery failure from an unhealthy process, while retaining enough logs, metrics, and error detail to explain the difference across Europe and the US. TL;DR: probe the public path from outside each serving region, measure delivery outcomes inside the application, correlate both with structured events, and page only on sustained SLO risk. A green /health response is useful evidence,...