I’m not sure about hidden dependency if the metrics break immediately. Important metrics should have alerts when absent or change unexpectedly.

Communication and the decision to depend on the logs as a source of metrics would be key to keeping these systems connected and functioning.

Taking a dependence on logs based metrics without communicating that is the failing here.

The same breakage could happen by depending on the event being emitted and a developer changing the event structure.

Communication and understanding helps both scenarios, not duplicating the effort by emitting logging for debugging, events for auditing and metrics for business.