Label-key consistency invariant

Status

Accepted — enforced from Phase 2.

Context

The family load-bearing invariant: a metric name must carry one label-key set across all of its series. Prometheus rejects inconsistent label sets within a metric family, and this exporter emits some families from more than one code path (e.g. the new vs legacy Redfish resource variants, RefreshSensorsNew/RefreshSensorsOld).

Decision

When a metric family is produced by two paths, emit a union label set in a fixed canonical order, filling empty values for keys that do not apply on a given path. Add an identity label to every series (instance/system) so one exporter process can serve multiple targets. A test enforces the invariant.

Consequences

Mixed-path metric families stay valid. The identity label complements (does not replace) the Prometheus instance relabel, so snapshot/OTLP series are attributable to a target.