Why do I only find out I tagged a metric wrong when the invoice arrives?

Tagging a metric with a high-cardinality attribute like a user ID, session ID, or request path multiplies a single time-series into hundreds of millions, and the bill follows a week later rather than a CI failure follows a minute later. By 2026, observability spend has reached 15 to 25 percent of total cloud spend at affected SaaS companies, with documented single-service incidents generating $90,000 in charges over a weekend. Every major backend, including Datadog, Grafana Cloud, and Prometheus, detects cardinality explosions only after ingestion, meaning the only signal is a budget alert or an invoice line item, not a pull request annotation. The OpenTelemetry SDK added optional cardinality caps in early 2026, but these are runtime circuit-breakers that silently drop data rather than upstream gates that catch the problem before it ships. There is no widely adopted CI primitive that ana