ISS metric broken for catastrophic ISS

The `issCount` metric works properly when a few nodes experienced localized ISSes. But when the network has a catastrophic ISS, the `issCount` metric does not register that event.

No source files, tests, or entry points are named. Locate the issCount metric handling and trace how localized versus catastrophic ISS events are recorded, then add coverage for the catastrophic case. Done means the metric registers a catastrophic ISS as well as localized ISS events.

Written by the indexing model from the issue text.