The curated subset of stack-level metrics exported to the Prometheus /metrics endpoint.

These are emitted by the periodic measurements above (and, for receive_lag, by the replication client) and are already exported to OTel/StatsD/Call-Home via ElectricTelemetry.StackTelemetry. They are passed to ApplicationTelemetry as additional_prometheus_metrics so they reach the single shared Prometheus aggregator without being double-reported through the other reporters.

Note: these definitions carry no stack_id tag, so they assume a single stack per instance. With multiple stacks the series would collide in the shared aggregator.